Title: Age differences in attention
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Permanent Link: http://ufdc.ufl.edu/UF00102856/00001
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Title: Age differences in attention
Physical Description: Book
Language: English
Creator: Harbin, Thomas J., 1954-
Copyright Date: 1981
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Bibliographic ID: UF00102856
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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Full Text







Dedicated, with love and gratitude, to

Mlarian E. Saffer


I would initially like to thank myself for the

perseverance which has culminated in this dissertation.

However, as with most achievements, this project resulted

104 from creativity and 90% from collaboration. I would like

to take this opportunity to thank my collaborators.

I am grateful to my doctoral committee, Drs. Walter R.

Cunninghamt (~chair), ZI. Keith Berg (cochair), James J.

Algina, Nathan W. Perry, and Ira S. Fischler, for their

assistance throughout my graduate training; to Dr.

Cunninghas for introducing me to the ropes of academic

survival; to Dr. Berg for infecting me with his enthusiasm

for research and teaching; and to Dr. Algina for reminding

me of the difference between a statistical hypothesis and a

fervent wish.

I wish to thank the director of the Alachua County

Older Americans Council, Ann Cuddyback, for assistance with

subject recruitment; the steering committee of the

University of Florida Center for Gerontological Studies, for

support throughout my graduate training; and Mr. william

Tucker, my once and future role-model.


Finally, I gratefully and wholeheartedly acknowledge my

pare nts, Helen `I. Harbin and Robert J7. Harbin, for

encouraging me to climb the tall trees, and for my innate

cynicism; and my a associate, M imi Saff er, pour le feu.


















1 INTBODUCTIO..........~~~,.....~.~.........

The Startle Reflex............................
Reflex Inhibition.......~......~.............
Re fle x P aci lita tion .................. ..~....
Seflex Latency Modification...................
Cognitive Contributions .....~....~......... ~,
The Aging of Attentional Processes,.~......... ~

2 GENERAL METHODOLOGY...........................

Subjects ...I ........ ~.. .. ........... ... .. .. .
Apparatus .....1........ ..... ......... ... ..
Procedure. 1..~.~.~~....~.................
Data Analysis.......,....~..........~.........

3 EXPERTHENT 1.,...............................

Method.............~ ~~..............,,....
Results..~....C.~...... .. .. .. .. .. ....I.. ..

4 EXPERIMENT 2..,....~..1.......~........~.......

Method..l1~~... ~~...~.....~............ ...


5 EXPERIMENT 3...,................,....~~.......

reth od .... ....... ...... .................... .


6 EXPERIMENT 4.................,...............

seth odl ..... ...~..~......l. .......... .~... .


7 DISCUSSIO N...,... .... ~ ...................... 82


RE ERENCES................................~~... 107

BIOGRAPHICAL SKETCH.............~......~~......... 115

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy




JUNE, 1981

Chairman: Walter R. Cunningham
Cochairman: w. Keith Berg
najor department: Psychology

It is possible to inhibit elicited re-flexes by

preceding the eliciting stimulus (ES) by a prestimsulus (PS).

This project tested the hypothesis that the PS engages the

attentive faculties so that an ES following thereafter does

not have complete access to these processes. The ES is

therefore rendered functionally less intense, resulting in a

smaller reflex.

It was predicted that in young subjects, manipulations

designed to facilitate either automatic or effortful

attention toward the PS would increase the amount of reflex

inhibition. It was further hypothesized that only attempts

to man ipulia te automatic attention would suc cess full y

increase the amount of inhibition in elderly subjects.


These issues were investigated in a series of four

experiments. Tn each experiment, eyeblink and heart rate

(HR) responses were measured subsequent to a periorbital

airpuff. In the first three experiments, a 70 decibel tone

PS preceded the ES in a variety of temporal formats. In the

fourth experiment, gaps in a continuous tone served as

pre stimuli.

Experiment 1 was designed to manipulate automatic

attention. Twenty-seven young and 27 elderly subjects

received 54 trials. On nine trials, the ES vas presented

alone, on 48 trials, the ES was preceded by a tone of 20 or

200 milliseconds (msees), at interstimulus intervals of 60,

120, 240, or 420 asecs. Results revealed greater eyeblink

inhibition with the longer PS in both age groups. The effect

of ?S duration did not interact with age. The HR response in

both age groups was biphasic, with a deceleration followed

by an acceleration. In the young subjects, the PS augmented

the size of the deceleration, and to a lesser extent, the

acceleration, moreso for the longer PS. The elderly HR vas

not affected by the PS.

Experiment 2 attempted to ma ni pulate ef fort ful

a tte nation. On 25 trials, the BS was preceded by a PS of one

of two frequencies, either 500 Hertz or 1000 Hertz (the

"common" PS). On five trials, the other PS was presented

(the "rare" PS). The ES was presented alone on 15 trials.

One half of the 40 young and 410 elderly subjects were


instructed to count the number of rare pre sti muli. This

manipulation had no effect upon eyeblink inhibition or HR

modification in either age group.

Experiment 3 was also designed to manipulate effortful

attention. In three conditions, 24 young and 24 elderly

subjects received six ES-alone trials and six in which the

ES was preceded by a 1000 Hertz, 70 decibel PS, at an

interstimulus interval of 120 asecs. In Conditions 2 and 3,

a reaction time task was included in the procedure. In

Condition 2, a reaction time response was required at random

intervals. In Condition 3, the response was required five

seconds after FS. The reaction time task increased the

amount of eyeblinkr inhibition and the size of the HR

deceleration in young but not in elderly subjects.

Experiment 4 investigated the effects of a gap in a

continuous tone of 10, 20, 40, 80, and 120 asecs preceding

the es by 120 asecs, in 16 young and 16 elderly subjects.

The amount of eyeblink inhibition increased with increasing

gap duration. Neither age group evidenced effects of the PS

on the HR response.

The results of these experiments support four

con clusrions: 1) the amount of eyeblink inhibition is

affected by manipulations of attention, 2) automatic

attention is more completely preserved into old age than is

effortful a tte nti o n, 3) prestimulati on augments the

decelerative component of a biphasic HR response in young

subjects, and 4) heart. rate responses are obtainable in the

eld e rl y; h owev er, they are less plastic than those of

younger subjects.


Basic reflexes have intrigued psychologists for many

years. Perhaps due to the reliability of reflexive behavior

or possibly to the status of physiological reflexes as

predictors of neurophysiological functioning and integrity,

reflexes have played a central role in mlany historically

prominent psychological theories.

various reflexes such as kneejerks elicited by taps to

the patellar tendon and eyeblinks elicited by airpuffs or

sudden sounds can be modified by changes in the sensory

environment. Depending upon stimulus parameters, the

magnitude and latency of an elicited reflex can be increased

or decreased by prior stimulation.

It will be my purpose in this dissertation to

investigate the extent to which attention contributes to the

reflex modification process. In addition, the phenomenon

will be investigated in young and old adults with the hope

of shedding light upon possible mechanisms underlying

reported decreases in attentional capacity in old age.

The Startle Reflex

The startle reflex vas studied in detail by Landis and

Hunt (1939). Using extremely rapid photographic equipment,

these investigators thoroughly described the topography of

the human startle reflex. As they described it, the startle

consists of a generalized and largely syametrical

contraction of the flexor musculature. This pattern includes

an eyeblink, forward head movemrent, abduction of the upper

arms, flexion of the elbows, fingers, and knees, pronation

of the lover armps, forward sovemrent of the trunk, hunching

of the shoulders, and abdominal contraction.

The eyeblink is the first component of the reflex to

appear, having an onset latency of about 40 milliseconds

(asecs). The other muscular components appear about 160

asecs after onset of the eliciting stimulus (ES). According

to Landis and Hunt (1939), reflexive behavior is

distinguishable froma voluntary responses to the ES by the

greater latency of voluntary responses (about 150 asecs).

The temrporal order of the reflex was described as beginning

with an eyeblink and then passing down over the rest of the


Landis and Hunt (1939) also described autonomic nervous

system components of startle. In particular, they reported a

decrease in skin resistance and a heart ra te (HR)

acceleration occurring at a latency of 500 asecs to 1000

asecs. In addition, they reported an initial respiratory

inspiration followed by an elevated rate of respiration and

a rise in systolic blood pressure. In a review of the HR

li te rature Gra ha m ( 19 79) concluded that Landis and Hunt

(1939) were correct in their report of an acceleration as a

component of startle.

In ascribing a brief HR acceleration to the startle,

Graham (1979) depended heavily upon Pleshler's work

(7 le shler, 1965) in order to specify stimulus configurations

likely to produce a startle response. Fle sh ler (1965)

concluded that the critical stimulus parameters for startle

elicitation in rats were stimulus intensity and suddenness

or rise time. He found that as ES rise time increased (i~e.

the ES became "less sudden"), the threshold intensity for

startle elicitation also increased. He concluded that rise

time per se was not as critical as the requirement that the

ES reach a certain intensity within the first 10 to 15

asecs. This work was a follow-up of studies by Hoffaan and

Fleshier (1963) and Hoffaan,, Fleshler, and Alplanalp (1964)

demonstrating increasing response magnitude with increasing

Es intensity.

K. H.Berg (1973) investigated effective ES parameters

in humans and found that the reflex was affected by both ES

rise time and duration. Berg's findings indicated that,

contrary to Pleshler's (1965) conclusion, the latency and

amplitude of startle eyeblinks were affected by variations

in ES duration and rise tiae well beyond this 10 to 15 asec

range. Berg suggested that the startle reflex is controlled

by 2 neural systems. A system of short time-constant neurons

which summate spatially but not temporally was hypothesized

to produce a primary component of startle, including the

eyeblink in humans and muscular flexion in rats. The longer

latency HR response was attributed to a secondary component

of startle. This component was hypothesized by Berg to be

controlled by a system of long time-constant neurons which

are able to summate temporally but not spa tially.~ The se

neural systems have been described by Gersoni (1965,1971).

In support of Berg's (1973) dual-component hypothesis,

Pinckney and Ison (1979) found very little correlation

between lead stimulus effects upon the flexion and cardiac

startle responses in rats. At this point, it seems

reasonable to conclude that startle elicitation is primarily

responsive to BS rise time, although the 10 to 15 asec

interval is probably not as critical as hypothesized by

Pleshler (1965).

Finally, there is disagreement upon the exact form of

the HR response to startle-eliciting stimuli. In agreement

with Landis and Hunt (1939) and Graham (1979), Fleshler

(1965) and Chalmaers and Soffsan (1973) found a HR

acceleration. In contrast, Berg (1973) and Pinckney and Ison

(1979) found a bip ha sic response with an initial

deceleration followed by an acceleration.

Re~fl~ex Inhibition

Since the late nineteenth century it has been known

that various aspects of elicited reflexes can be modified by

changes in the sensory environment. Boyditch and Oarren

(1890) investigated the effects of stimuli in various

modalities upon the magnitude of kneejerks elicited by taps

to the patellar tendon. The basic stimulus configuration

consisted of a prestimulus (PS) followed by an interstimulus

interval (ISI) followed by the ES. The effect of the PS upon

reflex magnitude was either inhibitory or facilitative,

depending upon the ISI.

After this early demonstration of reflex modification

with sensory stimuli, the effect was not investigated for

the next 35 years. 'In 1926, Dodge and Louttit published a

report of investigations into reflex magnitude as a function

of the ISI between successive presentations of the ES.

Measuring the effects of ISIs ranging from approximately 180

to 500 asecs, they found that the response to the second

stimulus was uniformly smaller than that to the first. They

attributed this effect to refractoriness in the startle

mechanisms. In addition to any refractoriness, it is

probable that the first stimulus was serving as an
inhibitory PS. Shortly after the Dodge and Louttit (1926)

study, several investigations of reflex modification were

reported from Yale University. H~ilgard (1933) reported that

the ISI between the PS and the ES was critical for the

effect of the PS. Cohen, Bilgard, and Pendt (1933) used the

inhibitory effects of visual PS to demonstrate that the

peripheral blindness reported by a patient was not of

organic etiology. Though the patient could not report

seeing stimuli in his peripheral fields, these stimuli did

effectively inhibit his response to sudden noise.

Subsequent to these and several other studies in the 1930's,

the paradigar was again ignored until 1963. IZn 1963, soffman

and Fleshler noticed that the magnitude of elicited startle

was increased in the presence of background noise. However,

when the noise pulsed on and off with a 500 apsec du-ty cycle,

the reflex was greatly inhibited.. This paper initiated an

area of research which has continued to the present.

Probably the mpost crucial parameter determining the

effects of a PS upon an elicited startle is the ISI between

the PS and the ES. Hoffaan and Searle (1965) found that a

10 asec noise burst presented shortly before the ES (ISI =

20 to 160 ansecs) served to inhibit the elicited reflex. This

demonstration replicated the findings of Hilgard (19 33).,

However, Hilgard (1933) found that the reflex was inhibited

at ISIs equal to 100 to 425 assecs and facilitated at ISIs of

20 to 50 ase cs. Hoffaan and Searle (1965) found only

inhibition at ISIs of 20 to 160 asecs. The fact that

inhibition can be seen at very short ISIs is important for

ruling out the possibility that the inhibition is due to

protective reflexes of the middle ear, since these

protective reflexes occur much more slowly than the

inhibition process. ALlso, inhibition can be seen with

stimuli auch too weak to elicit such protective reflexes

(e.g. Harsh, Hoffaan and Stitt, 1978). This possibility is
also ruled out by the fact that reflex inhibition can be

seen with prestimuli of a different modality from the ES

(e.g. Bowditch and Warren, 1890; Harsh, Hoffaan, and Stitt,

1976; Pinckney, 1976; Schwartz, Hofflaan, Stitt, and Marsh,

1976; Reiter and Ison, 1977; and Sanes, Ison, and Adelson,

1978). It is also unlikely that the effect is due to

auditory masking of the ES by the PS, since inhibition is

relatively insensitive to the frequency characteristics of

the stimuli (Marsh, Hoffaan, Stitt, and Schwartz, 1975)

whereas masking is frequency-dependent.

In several parametric studies of the effects of ISI, it

has been found that the PS has little effect upon reflex

amplitude for ISIs less than about 20 asec s. Simila rl y,
inhibition is usually not seen at ISIs greater than 500 to

1000 rasecs. In rats, maxiana inhibition is seen at ISIs of

about 50 asecs (Ison and Hassond, 1971; Schwartz, Hoffaan,

Stitt, and Marsh, 1976; Fechter and Ison, 1972), al tho ugh

some have reported maximum inhibition at longer ISIs (e~g.

Ash, Parisi, and Ison, 1978; Stitt, Ho ff ma n, and Marsh,

1973). Beyond 100 asecs, the inhibitory effect diminishes to

zero by about 1000 asecs (Ison and Rammond, 1971). In

humans, the pattern is similar except that maximum

inhibition is seen at somewhat longer ISIs, usually 100 to

150 asees (Graham and Murray, 1977; Sanes, Ison, and

Adelson, 1978) although mazians inhibition at shorter ISIs

has been seen (Kranter, Leonard, and Ison, 1973).

In addition to ISI, PS intensity determines its

inhibitory effect. Hoffmaan and Wible (1970) used auditory

prestimuli ranging in intensity from 3S to 95 dB to inhibit

acoustic startle in rats. They found that as PS intensity

increased, reflex amaplitude decreased. This effect was

replicated by Krauter, Leonard, and Ison (1973). Sirailarly,

B~arsh, Hoffaan, and Stitt (1978) found that as the auditory

PS increased in intensity, airpuff-elicited eyeblinks

decreased in amplitude in humans. Also using a puff-

elicited eyeblink, Reiter and Ison (1977) found that

increases in the intensity of a visual PS had the same

effect as reported above for auditory prestimuli. Finally,

Pinckney (1976) used several intensities of shock as the PS

and found that whole-body acoustic startle in rats was a

decreasing function of increasing shock intensity.

In summrary, reflex inhibition is a robust phenomenon

which has been demonstrated for a number of reflexes (e~g.

eyeblink and kneejerk in heaans, whole-body startle in rats,

pigeonus, and guinea pigs) and for a number of eliciting

stimuli (acoustic, visual, tactile) as well as prestimuli

(acoustic, visual, tactilee. The effect is evident primarily
at ISIs between 20 and 500 asecs and increases with PS

i nte nsi ty. It should be emphasized that an effective

prestimulus need not consist of a discrete tone or light or

any other addition of energy to the sensory environment.

Stimulus offset (Stitt, Hoffaan, and Harsh, 1973) as well as

a change in the frequency characteristics of continuous

noise (Stitt, Hoffaan, Harsh, and Boskoff, 1974; Harsh,

Hoffaan, Stitt, and Schwartz, 1975) has been used as

inhibitory stimuli. Indeed, it seems that virtually any

change in the sensory environment can serve as an inhibitory

PS, given the appropriate temporal configuration.

Reflex fagilitation

Quite early in the literature, it was discovered that

the same PS can inhibit or facilitate the magnitude of

elicited reflexes depending upon the ISI. As mentioned

above, Hilgard (1933) found reflex inhibition when the PS

preceded the ES by 25 to 50 asecs. Bowditch and ffarren

(1890) also noted opposite effects of a PS depending upon

the ISI. More recently, it has generally been shown that

short intervals (e.g. 20 to 500 asecs) produce inhibition,

whereas ISIs greater than 1000 asecs are usually necessary

in order to see amplitude facilitation.

Hoffman and Fleshler (1963) found that with rats a

continuous background noise level of 85 dB facilitated the

amplitude of elicited reflexes whereas turning the noise on

and off every 500 asecs inhibited the reflex. In this case,

the inhibitory effects of the pulsed background were

probably due to the changes in stimulation occurring within

500 asecs of the ES. The effects of continuous noise are

often ascribed (e~g. Grahas, 1975) to activation of an

arousal system (see nalsro (1959) for a discussion of

arousal). Hoffiaan and Searle (1965) found that as background

noise intensity increased from 50 to 90 dB, reflex

facilitation also i ncrea se d. Hoffman and aible (1970)

compared the effects of a 75 db noise stimulus initiated at

intervals ranging from 100 to 6400 asecs before ES onset. In

addition, the PS was either present until ES onset or turned

off after 20 asec. With the continuous PS, the reflex was

facilitated for stimulus onset asynchronies ( SO s) greater

than or equal to 400 asecs. However, with the discrete PS,

all intervals less than 3200 asecs produced inhibition and

facilitation was not evident at any of the intervals. The

authors concluded that facilitation and inhibition were

independent processes and that facilitation was a function

of stimulation present at the time of ES initiation.

Ison, McAdamt, and Hammond (1973) produced a situation

in which the Ps was initiated at various intervals before

the ES and terminated only after BS presentation. The SOA

varied from 0 to 2000 asecs. In agreement with Hilgard

(1 9 33) f aci lit at ion was seen at short SOAs (5 and 10

asecs), while inhibition was seen at SO~s of 20 to 170

asecs. The apparent contradiction of these results with


those finding facilitation only at long ISls can possibly to

resolved by reference to two recent papers. Hoffaan and

Stitt (1980) and Hoffmaan, Cohen, and Stitt (In press) found

that stimuli presented simultaneously with an effective ES

will augment the elicited reflex even when the stimuli are

of insufficient intensity to elicit the reflex themselves.

The short time-constant system, hypothesized by Berg (19'73)

to control the initial skeletal components of startle, is

able to summate stimuli presented within 15 asees of one

another. Thus stimuli vith SO~s less than 15 asecs may both

contribute to startle elicitation. Therefore, short SOA

facilitation is probably a function of the total amount of

stimulation present at or near ES initiation. The

facilitation seen in experiments on rats differs in some

respects from that found in the next group of studies to be

reviewed, which used human subjects.

Grahamr, Putnam, and Leavitt (1975) investigated the

effects of either continuous or 14 asec prestimuli presented

at SOl~s ranging from 200 to 2000 asecs before ES initiation.

As expected, both the continuous and the discrete prestimtuli

inhibited the reflex at the 200 asec SOA. At 800 asecs,

neither PS affected the reflex. However at 1400 and 2000

asecs, both the discrete and the continuous prestimuli

facilitated the reflex. These results replicated the data

from rats in all respects except one. In rats, no

facilitation had been seen with discrete prestimuli. Graham


(1975) accounted for the disparity between rats and humans

by referring to two distinct facilitative processes. She

proposed that facilitation due to background stimulation and

to continuous prestimuli say be due to general arousal. She

further speculated that facilitation produced by discrete

prestiaali vas due to physiological rebound triggered by ES

presentation. Since Graham, Putnam, and Leavitt (1975) found

a HR deceleration during the interval between PS and ES, it

was hypothesized that the PS produced an orienting response

(RR deceleration is a component of the orienting response)

because the PS signalled the beginning of an uncertain

interval which ends at ES presentation. Initiation of the ES

eliminates this uncertainty, terminates orienting, and

produces a physiological rebound. Presumably, this

orienting-related uncertainty does not occur in rats and

thus, neither does facilitation due to discrete prestimuli.

Bloch and Toukatly (1976) directly tested the

hypothesis of reflex facilitation due to stimulus

uncertainty. They presented a discrete PS at a long ISI

(2000 asecs) before the ES. The PS vas one of three

different visual stimuli. One indicated that the ES would

follow vith 100% certainty, one indicated a 50X probability

of ES presentation, and the third indicated 100%b certainty

of no ES. In support of Grahas's (1975) hypothesis, they

found facilitation in the 50% but not in the 100% certainty


Bohlin and Grahama (1977) speculated that if

facilitation is due to a termination of orienting, any

manipulation which caused orienting to persist through the

ES should prevent facilitation. One half of their subjects

were required to discriminate the duration of a soft tone

presented within the 2000 iasec PS to ES intervral. The other

half vere required to estimate the duration of the ES. It

was hypothesized that the latter subjects would show no

facilitation since orienting would hopefully be maintained

through the entire ES. The results were negative. Both

groups of subjects evidenced equal amounts of facilitation.

However, since both groups showed a HIR acceleration

following the BS, there was no evidence that the second

group continued to produce an orienting reaction through the


In a second experiment from the same paper, Bohlin and

Grahama (1977) chose a subsample of subjects who did show HR

deceleration through the ES and evaluated the effects of the

PS. Even in this group, the PS produced facilitation. These

results therefore argue against the notion that facilitation

is due to termination of orienting. Since HR deceleration is

thought to enhance sensory input (e~g. Sokolov, 1960, 1963;

Lacey, 1967; Lacey, Kagan, Lacey, and Moss, 1963), Bohlin

and Grahama (1977) speculated that the PS initiates orienting

which enhances ES input and thus facilitates startle.


Silverstein and Grahama (1978) tested this possibility

by requiring subjects to judge the duration of an

electrotactile stimulus presented simultaneously with the

ES. It was hypothesized that by directing attention away

from the acoustic ES facilitation would be prevented. In

fact, when this procedure was employed, the PS produced no

facilitation. Considered in conjunction with the Boblin and

Grahamr (1977 ) paper, these findings suggested to the

authors that discrete PS facilitation is due to the

direction of attention to the ES by the PS.

In summrtary, there seem to be two distinct processes

which can produce reflex ampitude facilitation. The

facilitation evident at short ~IS~s as well as that produced

by background noise seems to be a function of the total

stimulus energy present at ES initiation. This maay be a

result of stimulus-produced arousal (Grahamp, 19 75) or due

to the total effect of several sources of stimulation, each

having independent access to neural sites responsible for

reflex initiation (Hoffman, Cohen, and Stitt, In press). In

contrast, reflex facilitation produced by discrete

prestimuli at long ISIs seems to be a process unique to

humans, since it is not reliably observed in other species,

and say involve relatively sophisticated cognitive

processes. If the PS serves to direct the respondent's

attention toward the ES (possibly also producing a HR

deceleration during the PS-ES interval), the reflex will be


Reflex Zatency godification

The discussion has thus far focused upon modification

of reflex amplitude. various stimulus parameters also have

reliable effects up reflex latency. Hoffman, Fleshler, and

Alplanalp (1964) discovered that reflex latency in rats

decreased with increasing ES intensity, an effect replicated

by Berg (1973) in humans. Fleshier (1965) found no effect of
ES rise time or duration upon latency, a finding

incompatible with those of Berg (1973) who found decreasing

reflex latency with increasing ES duration. In terias of ES

parameters, it can be said generally that in humaans the same

ma nipulations which increase reflex amplitude serve to
decrease reflex latency.

The presentation of a ES before the ES has effects upon
reflex latency in addition to those upon reflex amplitude.

Hilgard (1933) found that the samae IS~s which resulted in

amplitude inhibition (75 to 450 asecs) also decreased the

latency of elicited eyeblinkrs in humaans. MIore recently,

Ho~ffan and Searle (1968) reported that 50As of S to 15

~asecs reduced latency in rats even though there were no

effects upon amaplitude at the 5 asec SOA. This effect was

replicated by Ison, ScAdamn, and Hiammond (1973) who found

latency reduction at SOhs of 5 and 10 rasecs but (contrary to

Hilgard, 1933) latency increase for SO~Ls at or beyond 40
asecs. Stiaulus onset asynchronies greater than 170 rasecs


had no effect upon reflex latency. The authors also found

that increasing the intensity of background noise produced

increases in reflex latency. Hoffaan and Rible (1970) also

found increased latency with increasing PS intensity, but

only at an ISI of 150 asecs. At an ISI of 5 lasecs, increases

in PS intensity produced decreases in response latency.

Schwartz, Hoffaan, Stitt, and IMarsh (1976) found latency

reduction at SO~s of 2, 4, and 8 asecs (but not at 1 and 64

asecs) as well as larger amounts of latency reduction with

increasing PS intensity. P inck ne y (1976) found latency

increases at 40 and 250 asec IS~s, but no effect at 10 or

1000 asecs. Stitt, Hoffaan, and Mlarsh (1976) similarly found

that an SOA of 4 asecs reduced latency whereas an SOA of 64

asecs increased it.

In humans, PS effects upon latency have not been as

extensively investigated as in the studies reviewed above

using rats, rabbits, and pigeons. Reiter and Ison (1977)

found increased latency with increasing PS intensity, a

finding at variance with those of Schwartz, Boffman, Stitt,

and Marsh (1976). However, the 100 asec ISI employed by

Reiter and Ison corresponds closely to the 150 asec ISI used

by Heffean and Wible (1970) who also found increasing

Latency with increasing PS intensity. The 5 asec SII

condition of Hoffaan and Pible (1970) produced decreasing

latency for increasing PS intensity, a finding replicated bry

Schwartz, Hoffman, Stitt, and Clarsh (1976) with a 4 asec


SOA. Graham and 8urray (1977) found reduced reflex latency

for TS~Is of 30 and 60 asecs, increased latency at 120 apsecs,

and no difference at 240 asecs.

The studies of response latency reviewed thus far have

used IS~s within the range which normally produces amplitude

inhibition. Bloch and Toukatly (1976) presented the PS at an

ISI of 2000 asecs (thereby producing amplitude facilitation)

and found a decrease in latency, a finding replicated by

Bohlin and GrahamI (1977) and Silverstein and Graham (1978).

The latency reduction was relatively unaffected by the

various manipulations of attention in these last three


In summary, the latency of elicited reflexes is

affected by variations in PS and BS parameters as is reflex

amplitude. Increases in Es intensity produce decreases in

reflex latency. In rats, ES duration and rise time have so

far shown no effect upon latency. However, in humans the

latency of elicited reflexes has been shown to decrease with

increasing ES duration. The addition of a PS produces

independent effects upon latency., At ISIs between 5 and 60

asecs, reflex latency is reduced. Interstimulus intervals

between 60 and 200 asecs produce increases in reflex

latency. Increasing the ISI: to 2000 asecs again reduces

latency. The effects of PS intensity are complex. At short

ISIs (e~g. 5 asecs), increases in PS intensity produced

decreases in reflex latency. A~t longer ISIs (elg. 150


asecs), increases in PS intensity produce increases in

reflex latency. Finally, as with amplitude inhibition,

latency can be reduced by changes in the bandwidth of a

noise PS (Marsh, Hoffman, Stitt, and Schwartz, 1975) and by

stimulus offset (Stitt, Hoffnan, and Marsh, 1973).

In concluding the review of the literature concerning

the effects of various stimulus parameters upon reflex

modification, it should be mentioned that the amlplitude

inhibition and latency reduction effects seem to be

independent of variables affecting reflex elicitation. For

exasyle, Stitt, Hoffman, and Mlarsh (1976) found that ISI

effects did not differ for ES intensities ranging from 90 to

120 dB. Hoffiaan, Marsh, and Stitt (1980) found that not only

is amount of inhibition independent of ES intensity, but so

is the amount of latency reduction.

Cognitive Contributions

Until very recently, reflex modification was

investigated largely from a physiological or stimulus-

paranetric standpoint. If any attempt was mlade to relate the

phenomena to psychological processes, it was usually by

calling upon rather global terms such as arousal. However,

it has been known for some time that various cognitive

processes can affect elicited reflexes. Lombard (1887)

investigated the effects of various psychological "states"

upon the maagnitude of elicited kneejerks. Bamong other

interesting relationships, Lombard (1887) found that he

could reduce the apparent intensity of the ES (Loabard

served as his own subject) as well as the magnitude of the

response by ". directing the thoughts to somae
indifferent subject, for instance, by quietly concentrating

the attention on the varath of the skin of the hand" (p.


Explici t attempts to cast the effects of reflex

facilitation in a psychological framework have been made by

Grahas and her colleagues. For example, Bohlin and Graham

(1977), Bloch and Toukatly (1976), and Silverstein and

Graham (1978) demonstrated that the phenomenon of reflex

facilitation depends not only upon the parameters of

stimulation, but also upon the meaning ascribed to the

stimuli., Bohlin and Graham (1977) suggested that reflex

facilitation may occur because the PS signals the approach

of the ES and thus directs attention toward it. Bloch and

Toukatly (1976) found that if the PS signalled the approach

of the ES only uncertainly, the facilitative effect was

enhanced. Finally, Silverstein and Graham (1978) reported

that a manipulation designed to focus attention away from

the ES prevented the facilitative effects of an

appropriately placed PS, which instead inhibited the reflex.

The attempt to account for reflex inhibition in

cognitive teras is more recent and tentative. Grahas (1975)

speculated that reflex inhibition may be a method of


protecting preattentive processing. Drawing upon Neisser's

(1967) concept of preattentive processing, Graham
characterized startle as an interrupt system, designed to

halt ongoing cognitive activity and free the organism to

deal with incoming stimulation. The effect of the inhibitory!

PS is to minimize the distracting effects of a full-blown

startle. Hofffaan and Ison (1980), in a review of the reflex

modification literature, proposed their own model to account

for the effects of facilitative and inhibitory prestimuli.

This largely neurophysiological model postulates independent

excitatoryl and inhibitory systems acting upon a startle

A brief review of the characteristics of a potent

inhibitory PS indicates a relatively simple principle: given

the appropriate temporal relationships, the "bigger" or more

salient the PS, the greater is its inhibitory potency.~ For

example, inhibition increases as PS intensity increases. In

addition, when using a fregnency shift in a continuous tone

or band of noise as a PS, the larger the shift the greater

is the amount of inhibition. The same manipulations which

tend to increase the inhibitory effect of a PS are the same

as those which tend to decrease psychophysical thresholds

(Weber, 1834, cited in Gescheider, 1976).

If it is assumed that the organism has a facility for

detecting discrete stimulation, and if it is further assumed

that various stimulus parameters determine to what extent


this facility is engaged, it is possible to propose a model

of reflex modification based upon this facility. Neisser

(1967) describes such a process and refers to it as

"preattentive processing." when coining the term, Neisser

(1967, p. 89) described preattentive processing as a

preliminary analytical operation which serves to separate

objects from ground W. which later mechanisms are to

flesh out and interpret." The process serves to separate an

object from others ". . as a potential framework for the

subsequent and more detailed analyses of attention." In

short, preattentive processes serve to locate and identify

figures from ground, or signal frost noise, and to render

these unities as material for subsequent cognitive analyses.

If it is further assumed that this process takes a finite

amount of time, it is possible to conceive of. reflex

inhibition as due, in part, to the "capture" or engagement

of the attentive and preattentive processes. If the ES

arrives very shortly after the PS, it is rendered

functionally less intense by the fact that the PS has

engaged the preattentive processes. This model can also

account for the effects of ISI upon inhibition. At very

short ISIs, the PS has not yet fully engaged the processes

by the time the ES arrives sos there is little inhibition.

At long ISIs, there is ample time for the PS to be detected

and for the processes to be disengaged and then re-engaged

by the ES, again producing little inhibition.


Although the proposed model is couched in terms usually

a ssocia ted with a n i nforma tion-p rocessin g approach, it is

quite com pa tibl e with other a ppr oa che s to cog n iti ve

psychology. For example, Gibson (1966) speaks of a process

of resonance wherein the person extracts information from

the energy available at the sensory receptors. Gibson

further posits that some structures in the environment are

more attractive than others. "Certain loci in the array

contain more information than others. The peripheral retina

registers such a locus, the brain resonates vaguely, and the

eye is turned. Subjectively we say that something 'catches

our attention'" (1966, p. 260).

In support of the proposed model, it has been found

that equal intensity eliciting stimuli are judged less

intense if they are preceded by a PS (Cohen, Soffaran, and

stitt, In press). The effect was independent of the

magnitude of the response to the ES. DelPezzo and Hoffman

(1980) found that if their subjects were instructed to

attend to the PS there was greater inhibition than if the

subjects were instructed to .ignore it. They proposed a model

very similar to the attentional model that I have outlined.
The authors referred to a characterization of attention

proposed by Posner, Snyder, and Davidson (1980); "Attention

can be likened to a spotlight that enhances the efficiency

of detection of events within its beaan (p. 172). In support

of this conceptualization, Posner, Snyder, and Davidson

(1980) found that reaction times to a stimulus were

decreased if the stimulus appeared in an expected position

and increased if it appeared in an unexpected position.

Viewed in this way, results of older studies are

consistent. For example, Lombard's (1887) finding that he

could reduce the apparent intensity of taps to the patellar

tendon as well as the magnitude of the elicited kneejerks by

concentrating on unrelated matters supports the proposed

c onc ept ualza ti on. In addition, Peak (1931) found that

elicited eyeblink reflexes were facilitated if the subject

was required to react rapidly to the ES by moving a finger

or making a voluntary lid movement. In teras of the

attentional model, Lomabard (1887) was directing attention

away froa, and Peak (1931) was directing attention toward
the IS. More recently, Boelhouver (1979) found that the R2

component of the eyeblink (that component which accounts for
the majority of actual lid movement) was smaller during the

period between the warning stimulus and the imperative
stimulus in a reaction time task. If it is assumed that

attention in this case was being directed toward the

imminent imperative stimulus and away from the ES, these

results can be construed as support for the attentional

model proposed.

This model can be extended to account for facilitation

of reflex amplitude seen with discrete prestimull at long

ISIs. It is possible that the PS is presented at a lead


interval long enough in this case to allow voluntary aspects

of attention to be directed toward the upcoming ES. In

agreement with Bohlin and Graham (1977), the HR deceleration
often seen between PS and ES in these long ISI situations

may be an index of this sort of attentional preparation.

Tht Aqingat oftteqtional Processes

The literature on the adult development of attention

reveals marked differences in attentional and perceptual

processes in old age (see Hoyer and Plude, 1980 for a

review). The changes in attentional behavior can be

summarized by two general Isaxims: 1) performaance on tasks

designed to measure attentional and perceptual processes (as
is true for virtually any behavior) tend to slow vith age;

2) as task demands increase, age differences in performance

also increase.

The evidence for the slowing of perceptual behavior

with age comes from a variety of sources. For example, older

people need longer exposures in order to identify briefly

presen-ted forms (Salthouse, 1976), have lower flicker fusion

thresholds (Uealle, 1965) and click fusion thresholds (WJeiss,

1963), and require longer .ISIs in order to avoid visual

masking effects (Walsh, Williams, and Hertzog, 1979).

At least two attempts to account for this behavioral

slowing have been made by prominent gero-psychologists.

Botvinick (1978, p. 157 ) has postulated that the central


nervous system of the older person needs a greater time to

clearn a stimulus out, in effect producing a greater

stimulus persistence." This idea was originally formulated

to account for the phenomena mentioned above as well as

other age-related behavioral changes (e.g. less precise

judgements of sequentially lifted weights and greater

susceptibility to visual illusions). There have Leen

subsequent studies supporting increased stimulus persistence

in the aged, including investigations of the ability to

integrate sequentially presented word halves (Kline and

Orae-Rogers, 1978) as well as other, mostly tachistoscopic,

studies. The stimulus persistence model is very similar to

"integration" models of visual masking (see Turvey, 1973,

for a review), and it is therefore not surprising that it

relies heavily upon studies of visual perception for its

support. The general idea is that humans do not have perfect

temporal resolution abilities so that if one stimulus

follcus another in close temporal proximity, the person is

left with a "double exposure" out of which he attempts to

make sense. Botwinick proposes that this persistence

increases with age.

Bitren (1965, 1974) has also proposed a model to

account for behavioral slowing in the elderly. He likens the

behavior of the elderly to a calculator or electric sotor

operating on less than optimal voltage. According to
Birren, an insufficient operating voltage causes a

calculator to perform more slowly. However, since a

calculator loses no information, it will perform its

functions correctly. In contrast, human cognitive processes

are subject to information loss due to decaying stimulus or

memory traces. So unlike a calculator, the slower old person

say have more difficulty on some tasks, because during the

greater timre required to carry out certain functions, more
information is lost than by quicker young persons. The

implications of this model are subtle but noteworthy. Birren

proposes that speed of processing is important for the

accuracy of such diverse behaviors as visual perception,

learning, motor skills, and intelligence. Indeed, Birre n

(1974) suggests that ". . one may regard the changes with

age in central processing time as the major independent

variable in explaining andh of the behavioral changes with

age" (p. 813).
The second w~axis can be construed to predict age by

task complexity interactions for miost tasks. That is, as the

attentional demands of the task increase, so do the age

differences in performance. Perhaps a fruitful avenue of

approach to this issue is one adopted by Hoyer and Plude

(1980). These investigators drew upon various models of

attention (e~g. Hasher and Zacks, 1979) which distinguish

between automatic attention (e.g. tasks which tap highly

practiced skills) and effortful attention (e.g. tasks in
which new strategies or conscious efforts to maintain


vigilance are required). Generally, it has been found that

tasks which require effortful attention show much greater

age differences than those which largely require automatic

attention (se.g. Plude and Boyer, 1980).

The experiments undertaken here will involve various

manijulations designed to increase the salience (and thus,

hopefully the "attention-getting" valIue) of the PS in a

reflex inhibition situation. This will be attempted by

strategies designed to direct either automatic or effortful

attention to the PS. On the basis of the literature reviewed

above, it was hypothesized that increasing either automatic

or effortful attention to the PS would enhance its

inhibitory effect upon the elicited reflex, but that smaller

age differences would occur with manipulations of automatic
than of effortful attention.

Stated briefly, the purposes of the research to follow

are threefold; 1) to test an attentional model of reflex

inhibition, 2) to investigate age differences in reflex

inhibition produced by manipulations of attention, and 3) to

juxtapose the models of age-related slowing proposed by

Birren and Botwinick. The investigation will be informative

for at least two reasons. First, these models were

formulated based largely upon data from reaction time and

visual perception research. Subsequent tests of Botwinick's

model have typically employed similar methods. It would be

informative to test the models not only with a radically

different methodology, but with an involuntary response.

Kline and Scheiber (1981) have indicated the need for such a

departure from traditional investigative methodology in this

regard. The use of an elicited reflex will hopefully

minimize probleas of interpretation due to age differences

in activation or experimental anxiety. Secondly, a direct

test of these two models has not yet been attempted. Such a

test would be heuristically valuable in the sense of more

precisely channelling future progging for the processes

underlying the observed behavioral slowing in old age.


Sub -ects

The young subjects in these studies ranged in age from

17 to 30 and were recruited from the Department of

Psychology subject pool. Subjects participated in

experiments in order to fulfill requirements of the

Introductory Psychology class. Old subjects were recruited

through the Alachua County Older Americans Council of

Gainesville, Florida. Subjects received no remuneration for

their participation. Subjects were not screened on the bases

of health, sensory acuity, or socioeconomic status with the

exception of several elderly subjects whose data were

eliminated from the analyses due to obvious severe hearing

loss or use of a cardiac pacemaker.


Stimulus timing and presentation as well as eyeblink

response measurement were controlled on-line by a PDP 8/E

laboratory computer. Airpuff stimuli were produced by

electronically opening a solenoid valve fitted on a

pressure-regulated scuba tank. The air was directed through


plastic tubing to an adjustable fitting mounted on the

headset used to deliver tone stimruli. This fitting allowed

presentation of the airpuff stimuli virtually anywhere on

the right side of the face. For all experiments to be

reported here, the opening of the airhose was positioned

about one centimeter posterior to the outer canthus of the

right eye at a distance of one centimeter from the skin

surface. The intensity of the airpuff was measured by

connecting a manometer from a blood pressure

sphygaosanometer (A8bco H18810401-390102) to the end of the

althose. The relationship between the steady-state pressure

and the momentary pressure of the airpuff stianui was

established by using a Harco Bio-Systems Physiograph (Model

DHP 4)8), Strain Gage Coupler (Type 7172) and pressure

transducer (1700-1010). Puff intensities were controlled by

an Airco,Inc. regulator (1806-9106).

Tone stimuli vere produced by a Bewlett-Packard vide

range oscillator (Model 200CD) or a Krohn-Hiite function

generator (Model 5300). Sine wave tones were gated through
Iconix electronic switches (tSR37). Tone intensities were

controlled with a Bewlett-Packrard attenuator (1350D) and

tones were presented through TD)H-49 earphones fitted with

nI-41/AB cushions. Rise/decay times for all tone stimuli

vere set at 5 asecs. Tone frequencies were visually checked

with a Textronixt dual-channel storage oscilloscope (Model

R5648). Tone intensities were checked with a Hewlett-


Packard volt meter (Model 400E), which was calibrated with a

Bruel and Kjaer sound level seter (lType 2203), fitted with a

six cubic centimeter coupler, and calibrated with a Type

4132 microphone.

Responses were recorded on a B~eckman polygraph (Mlodel

S411B) using Type 9806A A-C couplers. Time constants and

high frequency filtering vere as follows; for

elect rocardio gra m (ECG), high fregoncy filters were set at

22 Bz and time constant at .004 Hz, for electrooculogras

(EOG), high frequency filters were set at 22 Hz and time

constant at 1 Hz.

Electroocologram was sampled on-line at the rate of

1/asec and stored on floppy disk for subsequent off-line

analysis. Electrocardiogram, BOG, and a pulse coincident

with airpuff delivery were also stored on channels 1, 2, and

4, respectively of a Hewlett-Packard 3960 Instrumentation PM

tape recorder. The tape was replayed for heart rate


All testing was done in an IAC 10983 sound-attenuating

chamber which was located in a room separate from all

equipment. With the door to the rooms closed and the door to

the chamber open, ambient sound level was approximately 35

dB(A1). Electrocardiogram and EOG were recorded using Beckman

ALg/AgCl 11 as cup electrodes (8650437), adhesive collars,

and Synapse electrode cream (Med-Tek Corporation). For

recording BOG, small areas above the left eyebrow and above


the left cheekbone were lightly abraided with Redox Paste

and wiped clean before application of the electrodes. For

ECG, electrodes were attached to the volar surface of the

left and right forearms or below the aidline of the right

clavicle and to the left ankle. A ground electrode was

attached to the left forearm (or left ankle). No ungrounded

devices operating on line voltage were within reach of the

grounded subjects. Subjects were continuously monitored over
closed-circuit television and two-vay communication was

available via intercom.


Subjects were brought into the laboratory and first

read and signed an informed consent agreement. Upon

completion of the informed consent form, subjects were

seated in the IAC chamber and any experimental instructions

were given in an informal manner as the electrodes were

attached and the headset placed in position. Considerable

effort was undertaken to make the situation as non-

threatening as possible, as there is evidence that

physiological responses are subject to variation due to the

measurement setting (Harbin and Cunningham, 1978). After all

electrodes were in place, subjects were asked to relax while

the recording equipment was turned on and gain settings

adjusted. This took about five minutes. Then, the

instructions were repeated, questions answered, and the door

to the roomt was closed. The door to the IAC chamber was


always left open to maintain good air circulation. At the

conclusion of -the session, the purposes of the experiment

and the polygraph records were discussed with the subjects.

Voltage changes associated with the elicited eyeblinks

were sampled once per asec for 250 asecs following

initiation of the airpuff stimuli. Off line analysis later

measured onset latency, onset voltage level, peak voltage

level, and blink amplitude (equal to peak voltage minus

voltage at onset). A graphic depiction of the response was

displayed on a Tektronix Type 602 cathode ray tube and

measured from this display with a coaputer-guided cursor and

readcat of voltage levels at each asec.

The BR data vere analyzed by replaying the recorded

ECG. Channel 1 of the tape was played through an Iconix

Schiaitt Trigger (X6804) with the reference voltage level set

to give a pulse coincident with each R-wave. The computer

was prograssed to measure the R-R intervals to the nearest

asec for two seconds before and 12 seconds after the airpuff

initiation. These intervals were later transformed into

average HR/second in accordance with Grahaa's (1978)

rec ommenda ti ons. The data analyses to be reported were

carried out using the last second before and the first five

seconds following the airpuff.

Onless otherwise noted, data vere statistically

analyzed using the P2V routine of the BnDP 1979 statistics


package. In order to correct for violations of sphericity

(Hunyph and Feldt, 197 0) the Hugyh and Feldt (1976)

estimator of the Box (1954)) corrective adjustment for

degrees of freedom was calculated for all significant

within-subject contrasts. The observed F statistic was

tested a critical F with reduced degrees of freedom (see

Aunyh and Feldt, 1976 for a discussion of this procedure).

Contrasts which were significant with full, but not with

reduced degrees of freedom, will be noted in the text. Since

the P statistic is not seriously biased by departures from

normality, conformity with this assumption was not



The discussion in Chapter 1 emphasized that those

manipulations which serve to lower sensory thresholds (or

increase stimulus salience) are also those which tend to

increase the inhibitory potency of a particular PS (e~g.

increased PS intensity). In terats of the dual-process model

of attention, these manipulations are likely affecting

automatic attention to a greater extent than effortful

attention. An obvious PS manipulation which has not yet been

discussed in teras of reflex inhibition is that of varying

PS duration. Increasing stimulus duration produces decreases

in its intensity threshold (vithin limits;) and should

therefore produce increasing amounts of inhibition if the

attentional model is accurate.

Grahaas Putnasa, and Leavitt (1975) investigated the

effects of discrete (duration = 14 aasecs) and continuous

prestimuli presented at various SOls. The continuous PS was

terminated at ES presentation. At the shortest SOA employed

(200 asecs), equal amounts of inhibition were produced by
the two PS durations. Similarly, Graham and Hurray (1977)

found no difference between 20 asec and continuous PS

durations at 50As ranging fromr 30 to 240 asecs. Thus there

was apparently no effect of ES duration upon the amount of

inhibition, contrary to the prediction of the attentional


One possible explanation for the negative findings in

this regard lies in the use of a continuous PS as opposed to

one whose duration varies, but is always terminated well

before ES initiation. Since the magnitude of an elicited

reflex is not only a function of the ES but of other

stimulation present at ES initiation (Cohen, Hoffaran, and

Stitt, In press), the continuous PS may have both inhibited

the reflex (due to PS onset within the inhibitory range) and

facilitated the reflex by increasing the total amount of

stimulation present at ES initiation. Thus any additional

inhibition engendered by the longer PS may have been

nullified by its facilitative effects.

Dykaan and Ison (1979) presented prestimruli of three

durations (;2, 20, and 200 asecs) and two intensities (55 and

8S dB) at 150 apsecs ISI. They used both rats and humans as

subjects. For the rats, the ES was a 120 dB tone and the

measured response was whole body startle. For the humans,

the ES was a small shock delivered to the skin over the

supraorbital branch of the trigeminal nerve and the measured

response was eyeblink.


Both rats and humans demonstrated more inhibition with

the more intense PS, as expected. In addition, the rats

showed increasing amounts of inhibition with increasing PS

duration at both PS intensities. This was true for the

humans for the 55 dB PS. With the 85 dB PS, the humans

evidenced greater inhibition for the 20 asec PS than for the

2 asec PS, but the 200 asec PS produced slightly less

inhibition than the 20 asec PS.

These results apparently support the attentional

model's prediction of increasing inhibition with increasing

PS duration. Unfortunately, interpretation of these data is

difficult due to the authors' method of controlling ISI.

Dykaan and Ison (1979) set the interval between PS and ES at

150 asecs, measured from the aidp~oint of the PS to the onset

of the ES. This resulted in a situation in which PS duration

coraried with onset-to-onset as well as offset-to-onset

times. Since both PS onset and offset can serve as

inhibitory stimuli, it is not possible in the Dykaan and

Ison study to separate effects due to PS duration from those

due to onset-to-onset and offset-to-onset times.

In this experiment, the effects of two PS durations

were observed at four ISIs in two age groups. In accordance

with the attentional model, it was expected that the longer

PS vould produce more inhibition. Since it was hypothesized

that varying PS duration would affect automatic attention,

age differences in the amount of inhibition were expected to


be minimal. However, since most perceptual processes seem

to be slower in the elderly, the usual U-shaped ISI function

was expected to be shifted toward greater IS~s in the

elderly group.

Prestimulus durations and ~ISIs were chosen so as to

provide a means of assessing the effects of PS duration

independent of SOA and ISI. The duration of the PS was
either 20 or 200 asecs, and ~ISIs were equal to 60, 120, 240,

or 420 asecs measuredd from PS offset to ES onset). Thus

offset-to-onset times did not corary with PS duration. In

addition, four of the conditions served as a control for

onset-to-onset times. The 20 asec PS, 240 asec ISI and the

200 asec PS, 60 iasec ISI both resulted in SOAs of 260 a~secs.

Similarly, the 20 asec PS, 420 asec ISI and the 200 asec PS,

240 asec ISI resulted in an 30A of 440 asec.


There were SQ participants in this study, 27 young and

27 old. The young group was comprised of 13 females and 14

males ranging in age from 17 to 27 years (mean = 20.0). The

old group was coaprised of 13 females and 14 males ranging

in age fros 57 to 77 years (mean = 68.4). Twelve additional

young subjects were eliminated from the analyses, 11 for

producing fever than three scoreable blink responses per

condition and one due to the qualitatively abnormal


appearance of the eyeblink responses. Nine elderly subjects

were eliminated, five for insufficient data, two for

procedural error, one for obvious severe hearing impairment,

and one for past traumatic injury to the left eye.


The experiment included nine treatment conditions,

eight of which consisted of a PS followed after a variable

ISI by the ES. The ninth condition was a presentation of the

ES alone with no preceding PS. The PS was a 1000 Hz sine

wave presented at 70 dB(fA) for either 20 or 200 asecs.

Rise/fall time for the PS was set at 5 aisecs. The ISI was

set at one of four values: 60, 120, 240, 420 asecs (offset-

to-onset). The ISI was terminated by a 50 rasec airpuff set

at an intensity of 80 mm alg. (80 as ag=10,665 N/(a**2)=1.55

psi.) The two PS durations were combined factorially with

the four ISIs to produce eight conditions. These eight plus

the ES-alone control condition were randomly combined into a

9 I 9 latin square. Subjects proceeded through six rows of

the latin square for a total of 54 trials, six in each

condition. For the purpose of counterbalancing order of

treatment presentation, subjects started at different rows

of the latin square. Preliminary analyses indicated that

neither the effect of row not any of its interactions were

significant. Randomly occurring intertrial intervals

equaled 15, 20, 25, 30, or 35 secs, with a mean of 25 secs

over the experiment.


Eyeblink maagnitude for each subject was averaged within

each of the nine conditions. The mean amplitude of the

control response for each subject was then subtracted from

the other eight condition neans. These difference scores

were then corrected for the gain setting and comprised the

data for the analyses to be reported. The use of absolute

difference scores rather than percent difference has been

supported by data reviewed by Hoffsran and Ison (1980).

The data (depicted in Figure 1) were submitted to a 2

AGE I 2 PS durations (DUR) I 4 ISI analysis of variance. The

results of this analysis revealed, first of all, that the

200 asec PS produced more inhibition than the 20 asec PS

(F(1,52)=39. 41, p<.0001). Secondly, the effects of ISI and

DUR I ISI were also significant (F(3,156)=3.54. p=.0162, and

g(3, 156) =4.31, p=.00 59). A Neviaan-keuls follovap test

indicated that the 200 asec PS produced more inhibition than

the 20 asec PS at all ISIs except 420 asecs. There was

neither an effect of AGE on the maount of inhibitics, nor

did AGE interact with DUR. However, the AGE I DUR I( ISI was

significant (F(3, 156) =2.93, p=.0354).,
Due to the significance of the AGE I DUR I ISI

interaction, the data vere analyzed separately for the young

and old subjects. For both groups the data vere analyzed

with a 2 DUR I 4 ISI analysis of variance. In the young

group, all contrasts were significant, including DUR

F(1,26)=17.19, p=.0003) ISI (F_(3,78)=4.84, p=.0039) and

nDR I ISI (_F(3,7 8)=6. 53, p=.000S). The pattern was quite

different for the old subjects. The effect of DUR was still

highly significant ( (1,26) =22. 45, p=. 000 1)., But neither the

ISI nor the DUE I ISI contrasts were significant.

The results of the analysis thus far implied several

co nclu sion s. First increasing the duration of the PS

produced increases in the amount of inhibition in both age

groups. Second, the effect of ISI was such stronger in the

young than in the old. Third, the effect of ISI interacted

with PS duration strongly in the young group (p=. 000 5) and

marginally in the old (p=.089).
As a result of these interactions, orthogonal trends

over ISI were evaluated within each group at each PS

duration. In the young subjects, the amount of inhibition

for the 20 asec PS increased with increasing ISI. This was

confirmed by a significant linear trend (P(1,26)=11.95,

p=.0019) and nonsignificant quadratic and cubic trends. For

the 200 asec PS the ISI effect was U-shaped, as expected

from the literature. The gnadratic trend was significant

('P(1,26)=8.71, p=.0066), while the linear and cubic

components were not.

In the old group, there was no significant IST effect

for the 20 asec PJS. The ISI maain effect, as well as all

coapanent trends, produced P values less than 1.00. For the


200 asec PS however, the ISI effect approached significance

(F(3,78)=2.56, p=.0613) and the expected U-shaped function

was evident. This was supported by a significant quadratic

trend (FP(1,26)=8.73, p=.0066) and nonsignificant linear and

cubic trends.

In order to address the possibility that the

significant PS duration effects were due to different onset-

to-onset times (SO~s), a final analysis of variance was

undertaken with four of the eight conditions. The 20 asec

PS, 240 asec IST. and the 200 apsec PS, 60 ~asec ISI each

resulted in SO~s of 260 asecs. Siailarly, the 20 ~asEc Ps,

420 asec ISI and the 200 asec PS, 240 asec IST produced SOAs

of 440 asecs. These four conditions were submitted to a 2

AGE I 2 SOA I 2 DUR analysis of variance. The results

indicated a strong effect of DUR (F (1,52) =12.5 8, p=.000 8) .

In addition, the greater SOA produced more inhibition than

the shorter (F(1,52)=8.49, p=.0053).~ The AGE effect and all

interactions were not significant.

ReSLft Rate
Beart rate responses were measured for one second

before and five seconds following the airpuff. The responses

were averaged second by second yielding nine responses per

subject, one for each condition. heart rate responses from
trials which did not produce scoreable eyeblinks were not

included in these averages. The responses, averaged within

condition and age group, are depicted in Figure 2.

The initial step in the analysis was undertaken in

order to determine if there was a reliable HR response and

whether this response vas affected in any wayl by the

stimulus conditions or age. Data vere analyzed with a 2 AGE

I 9 conditions (COND) I 6 seconds (SEC) analysis of

variance. Results first indicated no effect for AGE or

COND, implying that there were no differences in overall BR

level between age groups or among the stimulus conditions.

This will facilitate unambiguous interpretation of results

since the law of initial values (Wilder, 1950) is not likely

to cceplica~te further analyses. ( subsequent analysis

provided additional support for this conclusion by finding
no effect of stimulus condition on the prestimulos point.)

The COND X SEC I AGE contrast was significant when tested

with full (F(40,1920)=1.65, p=.0068) but not with reduced

degrees of freedon (.10>p>.05). This can be taken as weak
evidence that the stimulus conditions affect the shape of

the response differently for young and old subjects.

Significant COND I SEC ~(0(0,1920)=2.52, p<.0001) and AGE X

SEC (_P(5,240)=S.49, p=.0001) effects implied that the shape

of the response was affected by the conditions and was

different for the two age groups. The significant COiND I AGE

effect (F{(8,384)=2.33, p=.019) indicated that the overall HR

level was affected differently by the conditions in the two

age groups. Finally, the highly significant SEC effect

1(5(,240)=24.72, p<.0001) confirmed the robust BR response
to the airpuff.

Perusal of Figure 2 reveals that the maain component of

the HR response seems to be an initial BR deceleration

peaking at 1 to 2 sees and a return to prestimulus level.

The addition of a PS produces a secondary acceleration

peaking at 4 to 5 secs. The size of the deceleration as well

as the acceleration appears to be a function of stimulus

condition. Due to the significant AGE interactions, analyses

of variance for 9 COND H 6 SEC vere undertaken within the

two age groups.

The complexity of these analyses preclude presentation

here. A detailed description is provided in the Appendix.

The results of the analyses indicated that stimulus

condition had no effect upon the elicited HR response of the

elderly. The young subjects however, revealed a robust

effect of condition. The next step in the analysis dealt

with specifically with the effects of PS duration and ISI.

The elderly evidenced no effect of PS duration, ISI, or

their interaction upon the shape of the HR and strongest at

the middle ISIs. The PS tended to accentuate the

decelerative component of the response, and to a lesser

extent, the accelerative component. The effect was greater

with the 200 lasec PS than with the 20 asec PS.

The next step in the analysis dealt specifically with

the accelerative and decelerative components of the

response. Separate DUR I ISI analyses of variance were

conducted for the first postatimrulus second (the point of

maximuma deceleration) and the fourth poststimulus second

(the point of maximuma acceleration) within the two age

groups. The elderly revealed no effects upon either the

deceleration or the acceleration. The young subjects also

evidenced no effect upon the acceleration. Ho we've r, the

decelerative component showed significant effects due to DUR

(f1(1,49)=12.27, p=.0010) and ISI (P(3,1417)=3.03, p=.0314).

The final analysis conducted served as a control for PS

onset to ES onset time effects. As with the eyeblink

responses, the 20 asec PS, 240 asec ISI and the 200 asec PS,

60 asec ISI produced SOAs of 260 asec. Similarly, the 20

asec PS, 420 asec ISI and the 200 asec PS, 240 asec ISI~

produced SOAs of 440 asecs. These four conditions were

submitted to a 2 DUR X 2 SOA I 6 SEC analysis of variance in

the young and old groups separately. For the old subjects,
neither DUR or SOA or their interaction interacted with SEC,

indicating again no effect of DUR upon the elicited

response. For the young subjects, DUR interacted with cutic

SEC ~P( 1, 25) =6. 06, p=. 02 11 ), in dica ting that even

controlling for onset-to-onset times, the 200 asec Ps

affects the elicited HR response more than the 20 asec PS.

In addition, the DUR I SOA I SEC effect (P (S,125)=2.33,

p=.0467) was marginally significant.


The results from analyses performed upon the eyeblink

data demonstrated a robust effect of DUR upon the amount of

inhibition. This finding replicated those of Dykaan and

Ison (1979) and did so while controlling for onset-to-onset

and offset-to-onset times. The fact that greater duration

prestimuli produce more inhibition is also in line with

predictions of the attentional model of reflex inhibition

proposed here.

It is also apparent that it is possible to inhibit the

eyeblink in elderly subjects and that the effect is every

bit as robust as in younger subjects. One of the hypotheses

of this study was not supported, however. It was predicted

that, since most responses slow with age, the ISI function

of the elderly should be shifted toward greater values

compared to the young. This was obviously not the case. If

anything, the point of maaximaum inhibition occurred earlier

in the old, as is evident in Figure 1.

Perusal of Figure 1 also reveals that these data are at

variance with the literature in some respects. For example,

with the 200 asec PS the young subjects exhibited maximon

inhibition at an ISI of 240 asec. This is such later than

the 100 to 150 asec nadir usually seen (e~g. Graham and

Murray, 1977). The pattern is even more anomnalous with the

20 asec PS. At this PS duration, the young subjects

demonstrated increasing inhibition with increasing ISI


whereas the old subjects failed to demonstrate any effect of

ISI whatsoever. This finding could be due to the use of an

airpuff ES. Most studies investigating the effect of ISI

have used acoustic eliciting stimuli. It is possible that

the airpuff elicited some combination of the startle and

corneal reflexes and that these combined reflexes respond

somewhat differently to changes in ISI, especially at short

PS durations.

The HR response seen in this experiment was primarily

decelerative. This finding is at variance with the

conclusion of Graham (1979) that the HR component of startle

is a small, brief acceleration. In support of Grahas

(1979), Chalaers and Hoffaan (1973) found a monophasic

acceleration in rats on control trials which was reduced in

magnitude by the addition of a PS at an SOA of 100 asecs.
Pinckney and Ison (1979) however, found a pattern somewhat

similar to that reported here. Their rats evidenced a

triphasic (accel era tion-dece lera tio n-accelera ti on) re sponse .

They presented a PS at an SOA of 60 asec vbich reduced the

magnitude of the initial acceleration and the deceleration.

The re spon se in humans seems to be primarily

dece ler ative. Berg (1973) reported a deceleration and

indicated that there was no evidence of an acceleration even

on early tri als. Clarkson (1 979) found a deceleration

(peaking at 1 to 2 sees poststimulus) which was modified by

the PS into an acceleration (peaking at 4 to 5 secs). The

present results are similar to Clarkson's in finding a
deceleration on control tr~ials. The addition of the PS added

a later accelerative component peaking at about the same


It seems inappropriate to speak of the effects of the

PS on the elicited HR response as inhibitory. Unlike the

eyeblink, the decelerative and (to a lesser extent) the

accelerative components of the HR response were magnified by

the PS. This result contradicts the finding by Chalmers and

Hoffman (1973) of PS-inhibited HR acceleration. However, the

effects reported here were larger for the 200 asec than for

the 20 asec PS and the magnitude of the effects generally

exhibited a U-shaped ISI function. In this regard, the

results are clearly consistent with the eyeblink data.

The age comparisons were not consistent across the two

response systems. The eyeblink data demonstrated very few

age differences. The DUR and ISI effects as well as response

magnitudes were quite similar. This supported the prediction

of few age differences proposed under the assumption that

maniFulating PS duration would affect automatic attention.

The IST function, however, did not conform to prediction.

Based upon tise-dependent studies of perceptual behavior

(e~g. visual masking), it was predicted that the elderly
would show a similar ISI function but that it would be

shifted toward later times. If anything, the elderly

function was shifted toward earlier times. This discrepancy

may to due to the use here of an involuntary response as

opposed to the usual practice of employing voluntary


The heart rate data evidenced marked age differences.

Essentially, the elderly HR response was unaffected by any

of the experimental maanipu lations. I~t was not the case

however, that the elderly heart was not responsive. The

response was robust, unlike previous studies showing little

or no BR responsivity in the elderly (e~g. Ilorris and

Thoapson, 1969; Shaavonian, Miller, and Cohen, 1970;

Botwinick and Thompson, 1971). This fact tends to discount

the possibility that decreased arterial elasticity (Hallock

and Benson, 19 37) decreased baroreceptor sensitivity

(Nelson and Gellhorn, 1958), decreased cardiac muscle

responsivity (Frolkis, Shertchuk, Verkhratsky, Stupina,

Karpora and Lakiza, 1979), or other physiological changes

known to reduce HR responsivity in old age can account for

the lack of effects demonstrated here.

In summary, the eyeblink data generally conformed to

the predictions of the attentional sodel. There was greater

inhibition for longer prestimuli and this effect was

consistent across age groups. The HR data did not conform to

a pattern of reflex inhibition, though the DUR and ISI

manipulations were effective in the young subjects. The

elderly subjects demonstrated an absence of HR modifiability

though the ES produced a robust HR response. The

inconsistency of results between the eyeblink and the HR

response systems seems to support Berg's (1973) conclusion

that these represent two distinct neural systems, a

conclusion also supported by the data of Pinckney and Ison

(1979) who found very small correlations between cardiac and

whole-body startle in rats.


It has been demonstrated that manipulations designed to

"automatically" increase PS salience tend to increase its

inhibitory effect upon elicited reflexes. There is evidence

that instructions designed to purposefully direct attention

to the PS have similar effects. DelPezzo and Hoffaan (1980)

presented subjects with a semicircle of lights, any one of

which served as a PS on any given trial. Instructions to

at tend to a particular li ght increased that li ght 's

inhibitory effect relative to the others, while instructions

to ignore a particular light produced the opposite effect.

This effect was evident even though the subjects did not

move their eyes.

The following experiment was undertaken in order to

test this effect with a different manipulation and to

investigate age differences in the effectiveness of the

experimental conditions. In order to cause subjects to

"effortfullyA direct attention to the PS, an experimental

strategy was adopted from evoked cortical potential

research. Two tones of different frequencies served as

pr estimuli. One (labelled the "comaon" PS) occurred more

often than the other (labelled the "rare" PS). Subjects

were assigned to two groups, one of which was instructed to

count the rare tone and the other of which was not. If it is

assumed that instructions to count the rare PS would direct

attention toward the PS, it could be predicted that the

counting groups would evidence more inhibition.

Based upon the adult development literature on

attention (see Boyer and Plude, 1980, for a review), it

could be predicted that this manipulation would he more

effective in the young than in the old subjects, since the

elderly sees to be less able to allocate attention



Snb sc

There were 20 young sales and 20 young females in this

experiment, ranging in age from 17 to 26 years (maean=19.4

years). The old group consisted of 20 males and 20 females

ranging in age from 57 to 86 years (aean=69.2 years). Four

additional young subjects were eliminated froma the analyses,

three for failing to produce at least three scoreable

eyeblink responses per condition and one due to equipment
failure. Six old subjects were eliminated, two for too few

responses, three for use of a hearing aid, and one for past
transatic injury to the left eye.


Stimuli in this experiment again consisted of a tone FS

folleved after an ISI of 120 asecs by a 50 ansec airpuff ES.

The PS had an intensity of 70 dB(A), a duration of 50 asecs,

and rise/fall times of 5 asecs. The ES was delivered at an

intensity of 80 as Hg. The PS was set at one of two

frequencies, 500 Hz or 1000 Hz.

Subjects received three stiankus configurations. The

first consisted of an airpuff-alone control condition. The

other two conditions consisted of the PS followed by the

airpuff. One of the tone prestimuli was designated the rare
PS and occurred on 11% of the trials. The common PS occurred

on 66% of the trials. The remaining 33%C of the trials were

control trials. These trial types were randomly arranged

into nine rows of nine conditions with the restriction that

each rov contained one rare prestimulus, six canmon

prestimuli, and three control trials. Subjects started at

different rows of the 9 I 9 stimulus table and proceeded

through five rows for a total of 45 trials. This resulted in

the presentation of five rare tones, 25 common tones, and 15
control trials.

After being connected to the recording equipment, all

subjects were told that they would hear high and low tones

and were given examples of each. One half of the subjects in

each of the four age by sex groups were then instructed to

count the number of rare tones presented, while the other

half vere not so instructed. The pitch of the rare tone

(either high or low) was counterbalanced within each of the

eight age by sex by experimental groups. Following the

session, all subjects were asked the number of rare tones



In order to have an index of the success of the

instructions in directing attention toward the PS, the

number of rare tones counted was analyzed with a 2 AGE I 2

e xperiment al groups (GRP) analysis of variance. The

significant GRP effect (P(1,76)=13.03, p=.0005) indicated

(not surprisingly y) that the group instructed to count the
care tones was more accurate in estimating the number

actually presented (5.9 vs. 1.) The significant AGE

effect (P ( 1,76) =4. 12, p=. 045 8) indicated that the old

counted the tones more accurately than the young subjects

(7.1 os. 10.3). The interaction was not significant.


The mean responses froa the trials with a PS vere

subtracted from the mean response on the control trials and

corrected for the gain. These two gain-corrected differences

comprised the data for each subject. Overall means are

depicted in Figure 3.

The data vere first analyzed with a 2 AGE X 2 stimulus

configuration (STIM) I 2 GRP analysis of variance. None of


the effects reached significance, though the AGE effect was

close (q(1,76)=3.92, p=.0514). For exploratory purposes, the

data vere also analyzed separately in the two age groups.

For the old subjects, there was a marginally

significant effect for STIIN ( (1, 36) =4. 3, p=.0443). No

other effects were significant. For the young subjects,

none of the effects reached significance. Therefore the

attempt to affect inhibition by having subjects count one of

the two prestimuli was unsuccessful. Overall, there was

significant inhibition 9(1,76)=128.97, p<.0001), but the
stimulus conditions did not affect the amount of response

reduction. The within-subject factor of PS frequencyl was

effective in the old subjects, but the effect was small and

opposite the direction predicted (i. e. the common PS

produced greater inhibition).

Rgart rate
As in the first experiment, the BR data vere analyzed

over the last second before and the first five seconds

following ES presentation. These data are depicted in Figure

4, and were first analyzed with a 2 AGE It 3 STIn X 2 GRP X 6

SEC analysis of variance. This analysis revealed a

significant SEC effect 2(S~(,38B0) =1 3 00, p< 0 0 01) implying
that there was a reliable response to the ES. The

significant AGE X SEC ef fect F (5, 38 0)=-3.07, p=.~0099)

indicated that the shape of the response was different in

the two age groups. There were no other significant effects.

Due to the AGE X SEC interaction, the data vere analyzed

separately within the young and old groups and analyzed for
trends with STIN I GRP X SEC analyses of variance.

In the old subjects, there was a significant SEC effect

(F(5,190)=10.43, p<.0001). This effect was composed of a

large cubic component (E(1,38)=39.69, p<.0001), substantial

qu adr at ic component (II(1,3 8) =15. 6 1, p=. 0003) and a

aarginally significant quintic component (e(1,38)=4.22,

p=.0470). These findings corroborate those from Experiment 1

in finding a biphasic response composed of an initial

deceleration followed by an acceleration.

The young subjects revealed an almost identical

pattern. Again, the SEC contrast was highly significant

(P(5, 190)=7.4 7, p<. 0001) This contrast was composed of a

strong cubic component (F_(1,38)=37.28, p<.0001), and a

smaller linear trend (E (1,38) =6. 93, p=.I0 12 2). None of the

other contrasts were significant in either group. These

results are consistent with those from the eyeblink data in

finding no effect for experimental instructions and little

or no effect of PS frequency.

Due to the very strong cubic trends evident in both age

groups, analysis of the points of saziana deceleration and
acceleration way be informative. If these analyses also

revealed no significant effects, it would be very difficult

to argue against the conclusion that the experimental

manipulations had no effect. Therefore, the first and fourth


poststimulus seconds were submitted to a 2 AGE X 3 STIN X 2

GRP analysis of variance. Besults of the analysis for the

deceleration revealed a sig nif ica nt STI N effect

(F (2,152) =3.48, p=.0 334), as well as a STIN X AGE

interaction ( (2, 152) =4.26, p=. 015 9) implying that the

stimulus configuration did affect the decelerative component

of the response, but differently for the young and old

subjects. In addition, the AGE I GRP interaction was

significant (F(1,76)=4.09, p=.0466), implying that the

dece lerativre com ponent was affected differently by the

experimental instructions in the two age groups.

Du e to the significant AGE i ntera ct ion s, the

decelerative component was analyzed separately with STIN X

GRP analyses of variance in the young and old groups. For

the c14 subjects, none of the effects reached significance.

For the young subjects, the STIn effect was significant

(F (2,76)=S.20, p=.0076), indicating that the stimulus

configuration al tered the decelera tive component of the

elicited HR response. This effect was the result of a larger

deceleration with the race ES.

The results of the analysis of the fourth poststimulus

second (the point of maxiana acceleration) revealed only a

significant AGE effect (P{1,76)=S.76, p=.0189), in dic ating

that this component of the elicited HR response was more

prominent in the young than in the old subjects.


It can be seen in Figure 4) that the control treads for

the young and old appear topographically dissimilar, whereas

the response of the elderly subjects appears to be a

deceleration and return to baseline, the young response was

apparently a late acceleration and return. This difference

was analyzed with a 2 AGE I 2 GRP X 6 SEC analysis of

variance on the control responses. The analysis revealed a

significant SEC effect (g(Sr380)=-5.81, p<.0001), which was

composed primarily of a cubic component (E(1,76)=27.03,

p<.0001), and a much smaller linear component (9(1,76)=4.35,

p=.0404). None of the other effects reached significance.
This confirmed the biphasic nature of the responses and

indicated that it was not affected by age or experimental



In teras of the attentional model of reflex inhibition,

the results of this experiment imply one of two conclusions.

It is possible that reflex inhibition is a function only of

automatic attention and that direction of effortful

attention has no effect upon the process. This seems

unlikely in light of the findings of DelPezzo and Boffaan

(1980). These researchers found that the instruction to

ignore or attend to a particular PS significantly affected
the amount of inhibition it engendered. In addition, it has

been found that acoustical thresholds for eyeblink


elicitation are elevated when subjects are allowed to read

(K.n. Berg, personal communication, 1981).

The second, and more likely conclusion, is that the

procedure utilized in this experiment was not powerful

enough in terms of directing attention. The difference

between a 500 Hz tone and a 1000 Hz tone presented for 50

asecs at 70 dB is quite salient and possibly required very

little attentional effort. Under the assumption that this

was the case, Experiment 3 was designed with the purpose of

more forcefully engaging effortful attentional processes.


This experiment was designed for the purpose of

manipulating effortful attention by incorporating a reaction

time (RT) task into the reflex modification procedure. Since
it has been demonstrated that there is a reliable HR

deceleration during the foreperiod of a earned reaction time

task (e~g. Lacey, 1967) and since HRB deceleration is thought

to be a component of orienting (Grahas and Clifton, 1966),

it is conceivable tha-t the procedure could be utilized for

the purpose of directing attention toward or away from
selected stisoli.

Ison and ~Ashkenazie (1980) instructed their: subjects to

respond to an airpuff ES by pressing a button as rapidly as

possible. The ES was preceded by either a "warning stimulus"
at an ISI of 120 aisecs secs, a ndiscriminative stimulus" at

an IST of 100 asecs, or both of these stimuli. The warning

stimulus alone produced a saall facilitative effect upon the

eyeblink and in addition, seemed to slightly increase the
inhibitory effect of the discriminative stimulus when they

were presented together. If it is assumed that the warning

stimulus directed attention toward the next stimulus

(whether the discrim~inative stimulus or the ES), both the

facilitation and the augmented inhibition are consonant with

predictions of the attentional model which I have proposed.

The next experiment attempted to determine the

contribution of attention to reflex amplitude by the use of

an RT task. In the first of two conditions, subjects

received high and low frequency tone prestimuli, followed by

an airpuff ES, which was in turn followed by a light which

served as an imperative stimulus (IS). They were instructed

to respond as quickly as poss ible to the IS by

simultaneouslyp pressing switches held in the left and right

hands. In the second condition, subjects were instructed to

respond wi-th one hand when the PS was high and with the
other when the PS was low. This was intended to provide the

PS with task-relevant information in the latter condition,

thus directing attention to the PS and increasing its

inhibitory potency. Since the sti mulus configuration was

identical in the two conditions, any difference in the

amount of inhibition could be ascribed more confidently to

attention, or at least to the experimental instructions.

Pilot testing with young subjects revealed no

difference in the amount of inhibition between the two

conditions. However, the overall amount of inhibition was

much greater than in the previous two e xpe rimaents. In

Experiments 1 and 2, the PS produced a reduction of

approximately 10% to 30%h, depending upon stimulus

configuration. This pilot project resulted in inhibition of

roughly 65%C, or double the previous inhibition.

This work was followed by three additional pilot

studies in order to define the stimulus conditions necessary

to produce this effect. In the first of these, the effect of

the BT task itself was compared to a no-RT task condition.

In one of two counterbalanced, within-subject conditions,

subjects were required to respond to an IS, which followed

the ES by five seconds, by pressing a button. In the other

condition, no IS was presented and no response was required.

In both conditions, subjects received ES-alone trials and

trials in which the PS preceded the ES. When the no-

response condition preceded the response condition, there

was almost three times greater inhibition in the response

condition. Howverer, if the response condition was

experienced first, there was no difference between the
conditions. A comparison between the order groups on the

first condition experienced (RT vs. no-RT) rere aled

approximately five ties greater inhibition in the BT group.

These results suggested a residual effect from the response

condition. This pattern could be explained by either a

slowly subsiding arousal produced by the RT task or by the

inability of the subjects to suppress the direction of

attention toward the PS.


In an attempt to more evenly distribute the residual

effect of response condition, the next pilot project used

six alternating blocks of nine trials instead of two blocks

of 27 trials, as in the previous investigation. with this

manipulation, slightly mnore inhibition occurred in the

response condition (26%g vs. 31X).

In both of these pilot studies, the PS and/or the ES

could serve as an adequate warning stimulus for the required

response since the temporal interval between them vas always

fixed. The final pilot project was an attempt to remove any

warning or signal value from the PS and the ES by

eliminating any predictive relationship between these

stimuli and the IS. The investigation was comprised of two

c ond iti ons, presented in two blocks of 18 trials. In the

first condition, the IS was not presented and no response

was required. In the second condition, an Is was presented

every 23 secs, while the intertrial interval varied from 20

to 40 secs. Thus the PS and ES provided no information

regarding the time until the next required response. The

difference in the amount of inhibition between the two

conditions was negligible (255 vs. 28%). This seemed to

imply that the BT task per se was not sufficient to augment

the inhibitory process.

These pilot projects suggested that the inclusion of an

aT task within the reflex modification procedure greatly

increased the amount of inhibition produced by the PS. The


reason for this effect is not at all apparent. As indicated

by Ison and Ashkrenazie (1980), it could be due either to

generalized arousal or to a manipulation of attention due to

the signal value of the PS and ES in predicting the imminent


The third experiment in this dissertation was

accordingly designed in an attempt to separate these

possibilities. All subjects received three conditions

presented in three homogeneous trial blocks. The first

condition consisted of ES-alone control trials and trials

with a preceding PS. The second condition included an IS,

which was temporarll independent of the ES and PS. The third

condition was arranged so that the IS followed the ES by a

constant interval. If the ES or the PS-ES pair serves as an

attended signal for the imminent IS, inhibition should be

greatest in the third condition. On prepulse trials, the

attentional model would predict augmented inhibition due to

increased attention directed toward the PS by virtue of its

value in predicting the IS. On ES-alone trials, the ES

fulfills this function and therefore, these responses should

be augaented. Both of these phenomena vould contribute to

greater inhibition. If the effect is due to arousal,

conditions 2 and 3 should produce equally greater inhibition

than Condition 1. It both arousal and attention are

co ntrib uting Conditions 1, 2, and 3 should produce

increasing amounts of inhibition. Finally, due to the

decline with age in the efficiency of effortful attention,

any effects due to this variable should be more pronounced

in young than in elderly subjects.

There were 24 young and 24 old subjects in this

experiment. Due to difficulty in locating elderly sales,

both the old and young groups were comprised of six wales

and 18 females. The young subjects ranged in age from 17 to

2~3 years (nean=19.4). The old subjects ranged in age from 57

to 82 years (aean=69.4). Two additional young subjects were

eliminated from the analyses, one for procedural error and

one for drowsiness. One elderly subject was eliminated for

producing fewer than three scoreable eyeblink responses per
co ndi tion.


Stimuli in this experiment consisted of a tone PS, an

airpuff ES, and a red LED vbich served as the IS. The PS was

presented for 50 asecs at a frequency of 1000 Hz and an

intensity of 70 dB. Rise/fall times were set at 5 asecs. The

ES was delivered at an intensity of 80 am ag for 50 asecs.

The ISI between PS and ES was set at 120 asecs, measured

from offset to onset.

There were three conditions in this experiment. In

Condition 1, subjects received only the PS-ES combination

and ES-alone control trials. In Condition 2, subjects

received the PS and ES, but in addition, the IS was

presented and subjects responded to it by pressing a thuit
switch held in the left hand. Three randoaly occurring IS-

to-IS intervals were employed, 17, 30, and 43 sees (iaean=30

secs). In Condition 3, the ES was followed by the IS after a
constant interval of 5 secs. In each condition, subjects

received six control trials and six prepulsed trials

arranged in random order. The intertrial interval ranged

from 20 to 40 sees with a mean of 30 secs. These intervals

resulted in the presentation of 12 imperative stimunli to

which responses were required in both Conditions 2 and 3.

Condition order was counterbalanced within sex and age.

After being connected to the recording equipment,

subjects received five airpuff stimuli for the purpose of

adjusting gain settings and to famiiliarize the subjects with
the stimulus. Instructions were then given at the beginning

of each condition. For Condition 1, subjects were instructed

to simply sit quietly and stay awake. For Condition 2,

subjects were told that the red light would occur at "randomp

times" throughout the condition and that they were to

respond as quickly as possible by pressing the switch. It
was stressed that the occurrence of the IS was unrelated to

ES presentation. For Condition 3, subjects were told that

the IS would "follow predictably" after the ES. All other

instructions were identical to Condition 2. In Conditions 2


and 3, subjects were provided with a Lafayette Model 54417

clock/counter which displayed their reaction times and were

encouraged to continually better their times. Reaction times

were also measured outside the experimental roca with an

Iconix Hodel 6225 clock/counter and recorded to the nearest



Reacfiqg time

Median reaction times for each subject from Conditions

2 and 3 vere analyzed with a 2 AGE I 2 Condition analysis of

variance. Results indicated a significant age difference

(P(1,46)=11. 41, p=.0015) and a strong effect of Condition

(E(1,93)=73.42, p<.0001). The AGE I Condition interaction

was not significant. Neither of these effects is

particularly surprising. The elderly were slower in their

responses and the responses of both groups were faster in

Condition 3. This imp]lies that the ES and the PS-ES

combination were indeed functioning as warning stimpuli in

Condition 3.


For each of the three conditions, each subject's mean

control response was subtracted from the response on the

prepulsed trials and corrected for gain. These gain-

difference scores were first analyzed with a 2 AGE I 3

Condition I 6 Order analysis of variance. (Mean responses


are depicted in Figure 5.) The only significant contrast was

a main effect of Condition (P (2, 72) =4.53, p=.0141t).

For exploratory purposes, the data vere next analyzed

within each age group with one-way analyses of variance

testing the three conditions. This contrast was not

significant in the old subjects, but did reach significance

in the young subjects (F(2,46)=5.09, p=.0101). A followup

Nevaan-keuls analysis revealed that Conditions 2 and 3 were

reliably different from Condition 1 but not from each other.

Thus the incorporation of an RT task into the reflex

modification procedure greatly increased the amount of

inhibition in young but not in old subjects.

Hea~rf rate

As in the previous experiments, HR vas measured for one

second before and for five seconds after the airpuff ES.

These responses are depicted in Figure 6 for the young

subjects and in Figure 7 for the elderly subjects.

Data were initially analyzed with a 2 AGE I 2 prepulse

versus control (PC) I 3 RT condition (COND) I 6 SEC analysis

of variance. This analysis revealed several significant

effects. The significant SEC effect (P(5,220)=8.35, p<.0001)

indicated that there was a reliable response. The CORD I SEC

(II.(10,440) =4.52, p<.0001) and PC I SEC (F(5,220)=2.40,

p=.0383) effects indicated that the shape of the response
was a function of both the RT task conditions and the

presence of a PS. Finally, AGE interacted significantly with


PC (I(1,44)=5.27, p=.0265) and SEC (P (5, 22 0) = 5.33, p=. 00 01) ,

indicating that the PS affected HR differently in the two

age groups and that the response shape was also different

for young and old subjects. (Previous analyses indicated
that treatment order was not an important factor in either


Based upon the AGE interactions, the data were analyzed

separately for young and old subjects with 2 PC X 3 CONSD X 6

SEC analyses of variance with orthogonal trend

decomposition. The elderly subjects revealed a significant

SEC effect (F(5,110)=2.71, p=.0237) which was composed of

significant quadratic ({E(1,22)= 5.29, p=.0313) and cubic

(F(1,22)=9.93, p=.0046) components. In addition, the COID

effect was significant (f(2,44)=6.53, p=.0033), as was the

COND X quadratic SEC effect (f(2, 44)=4. 33s p<.05). The

latter effect provided weak evidence that the HR response

was affected by the BT task condition. Notably, none of the

effects involving the PS reached significance. The young

subjects also evidenced a significant SEC effect

( (5, 110)=7.99, p<.0001). This was coarposed of a strong

cubic trend (g(1,22)=98.77, p<.0001) and smaller quadratic

( (1,22)=8.24, p=.0089) and guintic (E(1,22)=8.11, p=.0094)

components. The significant COND I SEC effect

(E(10,220)=3.SS, p=.0002) was composed of a significant COND

X quadratic SEC effect (11(2,44)= 5.69, p<.01) indicating an
effect of RT condition on the BR response. The significant

PC It SEC effect (P(5,110)=2.65, p=.0264) was composed of

significant PC I quadratic SEC (F(1,22)=10.11, p=.0043) and

PC It cubic SEC: (f(1,22)=4.91, p=.0373) effects, implying

that the HR response was affected by the PS.

There are several points to be made on the basis of

these analyses: 1) the HR response of the young subjects

was again modified by the PS while that of the elderly was

not, 2) the HR response of the young was robustly affected

by the RT task conditions, while that of the elderly was

affected weakly, if at all, 3) the overall HR level was

affected by the inclusion of the RT task in the elderly but

not in the young subjects, and 4) the lack of significant PC

It COND I SEC effects in either group implies that the effect

of the PS upon the HR response was not a function of the BT

task conditions.

In order to explore the effects upon the decelerative

and accelerative components of the elicited HR response in

maore detail, the points of maaxiana dece le ration (first

postatimulus second) and acceleration (third poststimulus

second) vere analyzed by 3 Condition I 2 PC analyses of

variance within the two age groups. The Desults confirmed

earlier conclusions in that the old subjects produced an

effect of Condition for both the decelerative (F(2,44)=6.52,

p=.00 33) and the accelerative (H (2, 44) =5. 89, p=.0054)

components of the response, whereas the PS had no effect

upon responding in this group. In contrast, the young

subjects showed no effect of Condition (indicating no

differences across condition in HR level), but reliable

effects due to the PS on the magnitude of the deceleration

(P(1,22)=17.24, p=.0004) and, to a lesser extent, upon the

acceleration (P(1,22)=5.77, p=. 0252). However, unlike

previous finding gs, the effect of the PS upon the

accelerative component was to produce a diminution rather

than an augmentation of this portion of the elicited HR



The results of this experiment support the conclusion

that reflex modification is profoundly affected by the

inclusion of a reaction time task in young subjects but not

in the elderly. As predicted, the effect upon the eyeblink

was to increase the inhibitory effect of the PS. Although

for the HR response the effect of Condition did not interact

with the presence or absence of the PS, perusal of Figure 6

suggests that the effect is one of augmenting the

decelerative component of the BR response, moreso in the two

RT conditions.

The RT conditions produced effects upon the responses

which were greater than the no-RT condition and not

different from each other. This clearly supports the

configuration advanced in the introduction to this

experiment as support for some type of arousal operating


upon the reflex modification process. It is conceivable that

an elevated state of central nervous system activity was

produced by the challenging RT task and that this state

augmented the inhibition of elicited eyeblinks and the

modification of the elicited hB responses.

There are at least two reasons to question this

conclusion. As Lacey (Lacey, 1967; Lacey, Ktagan, Lacey, and

noss, 1963) has indicated, arousal is not an unidimrensional

process. Various autonomic and central responses do not

covary across experimental conditions. In addition, the

effect of a PS has been found to be independent of various

manipulations (e.g. changes in ES intensity) which result in
increases or decreases in the amplitude of the elicited

response (see Hoffaan and Ison, 1980 for a discussion). It
seems reasonable to suppose that one effect of arousal would

be to determine, at leas-t in part, the amplitude of the

elicited response. Therefore, if the amount of inhibition is

independent of the amplitude of the response, it is unlikely
that arousal would affect the inhibition process. Secondly,

in this experiment the elderly subjects demonstrated a

significantly elevated HR level in the two RT conditions,

suggesting an increased arousal, yet the eyeblink

modification process was unaffected. In contrast, the young

subjects, who did yield the predicted effects upon the

eyeblink and HR responses, showed no effects of Condition

upon HR level. The mean HR levels for the young subjects in

Conditions 1, 2, and 3 were 75.9 beats per minute (bpmt)

76.6 bpm, and 76.6 bpa respectively, while corresponding

values for the old subjects were 74.9 bps, 76.2 hps, and

76.8 bps. Thus the old subjects had a range of 1.9 bpa

across conditions compared to .7 bpa for the young subjects.

If HR level is a valid index of arousal, this finding argues

against the possibility that these results are due to

arousal produced by the RT task.

Boelbouvrer (1980) elicited eyeblinks at various times

during a three second foreperiod of a reaction time

procedure. He found effects upon both the mronosynaptic and

polysynaptic components of the neural activity responsible

for the eyeblink. These components varied in amplitude as a

function of the time intervening between the warning

stimulus and the presentation of the ES. Unless it is

hypothesized that arousal can fluctuate several times during

a three second foreperiod, another process is required tc

explain these results.

To reiterate, DelPezzo and Hoffaan (1980) were able to

increase or decrease the inhibitory effect of a particular

PS by simply instructing subjects to attend or ignore the

stimulus. The findings reported here suggest that a similar

process say be operating. It is conceivable that when

subjects await an imperative stimulus to which a response is

required, theyr become more attentive to 111 stianlation.

That the young subjects are more able to direct this


effortful attention is further supported by the HR responses

depicted in Figures 6 and 7. The young subjects exhibited a

large HR deceleration between seconds three and five in the

contingent RT condition (Condition 3). This deceleration is

commonly found in constant-foreperiod BT tasks. (In this

case, the IS was presented at the fifth second.) The

deceleration was not nearly as evident in the elderly

subjects, a finding consistent with Thompson and Nowlin

(1973) and NIorris and Thosrpson (1969). If it is true, as

suggested by Lacey (Lacey, 1967; Lacey, Kagan, Lacey, and

Moss, 1963; Lacey and Lacey, 1974)), that HR deceleration

facilitates attention toward the sensory environment, these

data suggest that the elderly are less able to accomplish

this effortful direction of attention.


As previously indica-ted, virtually any change in the

sensory environment will function as an inhibitory PS, given

the appropriate temporal relationships. Stimuli which have

been employed to date include tones (e1g. Grahas and Murray,

1977), lights (e~g. Reiter and Ison, 1977), shock s (e~ g.

Pinckney, 1976), noise offset (e~g. Stitt, Boffaan, and

Ma rsh, 1973) and a shift in the frequency spectrum of

broad-band noise (e~g. harsh, Hoffaan, Stitt, and Schwartz,

1975). In addition to these stimuli, I son (personal

c oasunication, 1980) has found that a discrete gap in a

continuous noise background will also serve to inhibit

whole-body startle in rats.

The experiment to follow was designed to test

Botwinick's (1978) stimulus persistence hypothesis by using

a gap in a continuous tone as a PS. Botvinick has proposed

that the older central nervous system needs a greater amount

of time in order to "clear" a stimulus, and that this

increased stimulus persistence results in differential

performance on a number of perceptual ta sk s, including


reduced flicker fusion thresholds (rWeale, 1965) and click

fusion thresholds (neiss, 1963), and greater exposure

durations when identifying tachistoscopicly presented forms

(S althouse, 1976). In an elegant test of this hypothesis,

Kline and Orae-Rogers (1978) found that elderly subjects

were better able to identify words when halves of the word

forms were presented sequentially. The elderly were able to

identify the words at greater ISIs than were the young.

In the following experiment, gaps ranging in duration

from 10 to 120 asecs were used as prestiaali and three

hypotheses were tested. (Psychophysical research has

indicated that gaps as small as 5 asecs can be reliably

detected in tones of similar frequency and intensity to

those employed here. See for example Ploap, 1964 and Perrott

and W~illiaas, 1971.) First, it was hypothesized that the

ga ps would effectively inhibit the elicited ref lexes.

Secondly, drawing upon the proposed attentional model, it

was predicted that the amount of inhibition would increase

with PS duration, as in Experiment 1. Finally, based upon

Botwinick's stimulus persistence hypothesis, it was expected

that young subjects would demonstrate significant inhibition

at smaller gap durations than elderly subjects.


Poung subjects in this experimaent consisted of 12

females and four sales, ranging in age from 18 to 24 years

[aean=19.4). There were also 12 elderly females and four

elderly males, ranging in age from 61 to 78 years

(maean=70.0). One young subject and two elderly subjects were

eliminated fromt the analyses for procedural error and one

additional elderly subject was eliminated for producing

fewer than three scoreable eyeblink responses per condition.


After the subject was connected to the recording

equipment and the door to the experimental chamber was

closed, a 70 dB, 1000 Bz tone was turned on and remained on

until the end of the session. None of the subjects reported

this tone to be uncomfortable when queried subsequent to

testing. As in previous experiments, the ES was a 50 asec

airpuff presented at an intensity of 80 as Hg. On prepulsed

trials, a gap in the continuous tone was presented at an ISI

of 120 asecs (measured from gap offset to ES onset). Gap

durations were 10, 20, 40, 80, and 120 asecs. Rise/fall

times were set at 1 asec instead of the usual 5 asecs so as

not to obscure the shorter duration gaps. No switching

transients were easily perceptible. The five PS durations

plus the ES-alone control condition were arranged into a 6 X


6 latin square. For the purpose of counterbalancing orders

of conditions, subjects started at different rows of the

latin square and preceded through the entire square for a

total of 36 trials, six in each condition. Intertrial

intervals ranged from 20 to 40 secs with a mean of 30 secs.



Data vere averaged within each condition and subject

and corrected for the gain setting. The mean control

response was then subtrac-ted from each of the prepulsed

responses. These gain-corrected difference scores comprised

the data for the analyses and are depicted in Fiqure 8.

Data vere first analyzed with a 2 AGE I 5 PS duration

analysis of variance with orthogonal trend decomposition.

There was a significant effect of PS duration

(P(4,12 0)= 5.09, p=.0008) which was comprised of significant

quadratic ( (1,30)=8.24, p=.0074) and linear (P(1,30)=7.52,

p=.0102) components. In addition, the linear trend

interacted significantly with iAGE (f(1,30)=4.63, p=. 0397).

These results implied that the gap served as an effective PS

and that the amount of inhibiton varied as a function of TS

duration. The AGE I linear PS duration contrast indicated

that the shape of the function was different for the two age

groups. Consequently, the data vere analyzed separately

within the age groups with a 5 PS duration analysis of


variance with orthogonal trend decomposition. As implied ty

Figure 8, the young subjects evidenced a significant

quadratic function ( (1,15)=4.56, p=.0496) whereas the

elderly curve was linear across PS duration (Pi(1,15)-=13.22,


In order to specifically test the hypothesis that the

younger subjects would show inhibition at smaller PS

durations than the elderly, Dunnett's follosop test (K~irk,

1968) was used to test for differences between the control

response and each of the prepulsed responses. This test

indicated that all of the prepulsed responses were

significantly smaller than the control response in the young

subjects. In the elderly subjects, all were different except
the 10 asec PS.

Heart rate was measured for 1 sec before and for 5 secs

after the airpuff ES. The responses were averaged within

each condition and subject. The mean responses are depicted

in Figure 9 for the young subjects and in Figure 10 for the

elderly subjects. Data vere initially analyzed with a 2 AGE

I 6 Condition I 6 Second (SEC) analysis of variance. The

only effects to reach significance were the SEC effect

(F([5,150)=7.0U, p<. 000 1) and the AGE I SEC interaction

(p(5,150)=S.93, p<.0001), indicating a significance respoDSe

which differed in shape across the age groups.

Orthogonal trend analyses within the two age groups

indicated significant quadratic (P(1,15)=13.29, p=.0024) and

cubic (P(1,15)=10.44, p=.0056) coiaponents of the SEC effect

in the old group, as well as a significant quintic component

(F(1,15)=10. 02, p=.0064), though this component accounted

for spuch less variance than the other two. The young

subjects also evidenced quadratic (X= 8.77, p=.00 97) and

cubic (P=11.48, p=.0041) SEC trends.

Notably, there was an absence of effects involving

stisolus condition upon the shape of the HR response, though

it appears in Figures 9 and 10 that the PS tended to

accentuate the initial decelerative component, as in

previous experiments. Perusal of Figure 9 also indicates

that the PS seemed to reduce the magnitude of the

accelerative component of the response in the young

subjects. In a post-hoc attempt to assess these effects, the

first and third poststimaulus seconds were analyzed within

the age groups with one-way analyses of variance over the

six stimulus conditions. The results were consistent with

the preceding analyses in showing no effect of condition

upon either the deceleration or acceleration in either age



These results are consistent with Berg's (1973)

conclusion that the eyeblink and HR responses represent

different components of the startle reflex. This was

indicated by the significant effects of the PS upon the

eyeblink and the absence of effects upon the elicited HR

re sponse.

The attentional model again finds support in these

data. The amount of inhibition increased with increasing PS

duration with the exception of the longest PS in the young

group. The absence of age differences in the amount of

inhibiton supports the notion that the direction of

automatic attentional processes is preserved well into old


Final ly, Botwinick' s (1978) stimulus persistence

hypothesis received tentative support from these results.

Although the AGE I PS duration contrast was not significant,

the followap tests did indicate that the young subjects

showed reflex inhibition with smaller duration gaps than the



The re sults reported here strong ly support the

conclusion, proposed by Berg (1973), that the eyeblink and

HR components of the elicited startle reflex represent less

than perfectly correlated responses. The primary aspect of

my results which favors such a conceptualization is the

ontogenetic dissociation of the two responses which occurred

repeatedly in these experiaents. In none of the four

experiments did the elderly reveal large effects of a PS

upon the elicited HR response, despite consistent eyeblink
inhibition. As previously emphasized, this was not due to a

lack of HR responsivity in the elderly. Both age groups

revealed robust phasic changes in HR subsequent to the

eliciting airpuff. It seems evident therefore, that the

eyeblink and HR responses reflect semi-independent

components of the startle and that the modification of these

responses pursue dissimilar developmental courses.
The eyeblink and HR responses were also differentially

influenced by the experimental manipulations in this

investigation. Restricting attention for the moment to the

young subjects, it is evident that inhibition of the

eyeblink by a suitably arranged PS is no guarantee that this

prestimulus will affect HR. For example, in Experiment 1,

both eyeblink and HR modification were evident. For both

responses, the effects were greater for longer duration

prestimsuli and evidenced a U-shaped function over the range

of ISIs investigated. In the third experiment, the inclusion

of a reaction time task in the procedure greatly increased

the amount of eyeblink modification while affecting the HR

response only mparginally. Finally, in Experiment 4, the PS

had virtually no effect upon the BR response while

inhibiting the eyeblink significantly. It remains for future

research to elucidate the critical stimulus parameters for

differentiation of these startle components.

The literature is inconsistent regarding the exact

shape of the elicited HR response. In a review of the HR

literature, Graham (1979) concluded that the response was

composed of a small, brief acceleration followed by a return

to prestimulus HR level. Grahaa's (1979) conclusions were

hampered, however, by the paucity of studies specifically

investigating the startle reflex. It was necessary for her

to carefully evaluate the stimulus parameters of the studies

reviewed and make a decision as to whether or not the

stimuli vere likely to elicit eyeblink in humans or whole-

body startle in laboratory animals. In agreement with Graham

(1979), Chalaers and Hoffaan (1973) found a HR acceleration

accompanying whole-body startle in rats. Berg (1973),

however, found a decelerative response as did Clarkson

(1979). In the four experiments reported here, the control

response in both age groups was biphasic (and this
conclusion was consistently supported by significant cubic

trends). The decelerative component reached a nadir at 1 to

2 secs poststimulus and was more variable in magnitude than

the acceleration, which peaked at 3 to 4 secs.

Developmentally, the accelerative coaponent was less

prominent in the elderly subjects, though it was always
statistically reliable.

The results of this research have indicated that the

effect of a PS upon the elicited HR response is primarily

upon the decelerative component of the response. The effect
is one of accentuating the magnitude of this deceleration.

In some cases, the accelerative component was also altered,

but these changes were smaller and less reliable. It is

inappropriate to refer to these effects as inhibitory.
Unlike the effect upon eyeblink, the PS served to augment

various aspects of the HR response. This conclusion is at
variance with Chalmers and Hoffaan (1973), who found that a

PS functioned to reduce the size of a primarily accelerative

response. This finding again underscores the conclusion that
the eyeblink and HtR components of the startle complex are

somewhat independent of one another.


The results of the analyses of the eyeblink responses

suggest that reflex inhibition can be profitably discussed

in terms of the amplifyingg" effects of attention.

Consistent with predictions of the attentional model which I

have proposed, manipulations which rendered the PS sore

salient, or attention-getting, also served to increase its

inhibitory potency. This was true whether the manipulation

was to increase the duration of a tone PS or a gap in a

continuous tone. The latter finding is important in that it

indicates that the results of Experiment 1 vere not simply

due to increasing the total energy of the PS. This

strengthens the argument that these effects are due, at

least in part, to attentional as opposed to basic, energy-

related neurophysiological processes.

The failure to affect the amount of inhibition in

Experiment 2 by instructing subjects to count a rare PS is

puzzling. DelPezzo and Hoffaan (1980) vere able to produce

changes in the amount of inhibition with a manipulation

which seems at least as subtle as the one used in Experiment

2. They were able to increase or decrease the amount of

inhibition simply by instructing their subjects to attend or

ignore a particular PS. I can only speculate that the
difference between the 1000 Hz and the 500 Hzt was so

salient, and the number of tones to be counted so small

(five), that the task was too easy to sufficiently engage

effortful attentional processes to anyl degree in Experiment


The developmental perspective taken in this

investigation was useful not only in describing age

differences in reflex modification (indeed, in demonstrating

that the elderly will produce the phenomenon at all), but

also in elucidating the contribution of attention to the

reflex inhibition process. In drawing upon a literature

independent of the history of reflex modification (i~e. age
differences in effortful versus automatic attention), it was

possible to add to existing knoviedge regarding both reflex

modification and the adult development of attention. This

investigation supported the position advanced by Hoyer and

Plude (1980) that the elderly maintain their automatic

attentional abilities to a greater extent than their

effortful attentional processes. The distinction between

automatic and effortful processing is not clear-cut and is

usually made at the empirical level. For example, Plude and

Hoyler (1980) utilized a card-sorting task in which a target
letter was imbedded in zero to eight distractor letters.

when the letters to be searched for were unchanging, no age

differences in performance were found. However, wben the

target letters changed over trials, consistent age

decrements were found. According to the authors, the

unchanging set allowed for the development of automatic

search strategies whereas the changing set required active

retrieval and comparison.


One criterion for deciding whether or not a skill is

automatic was proposed by LaBerge and Samuels (1974).

ALccording to these researchers, if a task can be

accomplished while attention is directed elsewhere, it

involves automatic processes. In their analysis of reading

skills, they emphasized repetition as necessary for the

development of automaticity. For example, with practice a

reader is able to recognize words and their meanings with

very little effort. However, the beginning reader must make

a conscious effort to identify individual letters and their

associated sounds, combine those letters into words, and

remember the meaning ascribed to that particular

constellation of letters and sounds. Hasher and Zacks

(1979) defined automatic processes as not requiring

awareness of their use and as not benefitting from practice

or feedback. The utilization of these processes was seen as

outside the bounds of voluntary control. Effortful processes

were described as requiring voluntary use and as benefitting

from practice. Finally, effortful, but not automatic,

processes Limit one's ability to carry out other tasks. It

seems reasonable to suppose that the PS duration effects

evident in Experimaents 1 and 4 would obtain when attention

was directed elsewhere, though it remains for future

research to confirm this speculation. It seems unlikely

that the reaction timpe task in Experim~ent 3 could be

performed as successfn11y if attention was allocated to

another task. The absence of age differences in those

experiments purporting to manipulate automatic (Experiments
1 and 4) coupled with the significant age differences when

effortful attention was supposedly varied (Experiment 3)

lends greater credence to the contention that attention was

in fact being manipulated. Extensive training of the

reaction time skills required in Experiment 3 would

presumably lead to automraticity and it could be predicted
that this training vould decrease the age differences in

reflex inhibition seen in this experiment. In addition,

since involuntary responses were measured, age differences

in response criteria, cautiousness, or task-specific

abilities are implausible explanations for these results.

The fourth experiment demonstrated that the reflex

inhibition procedure can be used to investigate

a tte nti onal/ perceptual1 p he no mpena., Bo twi nic k 's (1978)

stimulus persistence hypothesis received tentative support

in that the young subjects revealed significant inhibition

with a smaller gap PS than the elderly. Evaluations of the

stisolus persistence model with other than visual,

tach istoscopi c methods fills a void which has teen

previously indicated (K~line and Scheiber, 1980). As stated
in Chapter 6, however, the AGE I DURATION interaction was

not significant. Follosop tests provided weak evidence in

favor of the hypothesis, though additional research is

certainly warranted.


Birren's (1974) calculator model was not supported by1

the results of Experiment 1. If indeed, the elderly nervous

system is running more slowly, the reflex inhibition process

should also occur more slowly. This would cause a shift in

the elderly toward greater effective ISIs between PS and ES

(similar to the results of visual masking studies). This

was not found. The ISIs employed were chosen from a wide

range, however, and it will be necessary to more precisely
define the ISI functions within age groups before strong

conclusions regarding t~he speed of the inhibition can be

made. A~lso, Birren's (1974) model has emphasized that this

slowing primarily involves voluntary decision-making rather

than sensory or motor processes. The involuntary responses

investigated in the present research may not be directly

analogous to those supporting Birren's model.

This project finally indicates some considerations

which should be addressed by future research in reflex

modification. First, it is important to consider the

attentional state of the subject when assessing the effects

of various stimulus condition upon the inhibition process.

This includes instructions to the subjects and any tasks to

be performed. Second, it is evident that the startle reflex

is not a unitary process, that at least two components of

the reflex, HE and eyeblink, do not covary perfectly in

response to changes in stimulus configuration. Thirdly, the

investigation of reflex modification and other


psychophysiological response systems can benefit both

substantively and theoretically from a developmental

approach to investigation.

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