Group Title: Problem-solving by mature rats as conditioned by the length, and age at imposition, of earlier free-environmental experience ..
Title: Problem-solving by mature rats as conditioned by the length, and age at imposition, of earlier free-environmental experience
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Title: Problem-solving by mature rats as conditioned by the length, and age at imposition, of earlier free-environmental experience
Physical Description: 60 leaves : ; 28 cm.
Language: English
Creator: Eingold, Bernard, 1927-
Publication Date: 1956
Copyright Date: 1956
Subject: Learning, Psychology of   ( lcsh )
Psychology thesis Ph. D   ( lcsh )
Dissertations, Academic -- Psychology -- UF   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: leaves 57-59.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Dissertation (Ph. D.) - University of Florida, 1956.
General Note: Biography.
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Bibliographic ID: UF00098027
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000549684
oclc - 13275241
notis - ACX3980


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JUNE, 1956

Shew writer whah64 to express his app~reeleto to

Dr., Relland~ H. Wsters, obakrma of k~ie gapdorio

**melttee, for his he~lp to hte seelme of this sturdy.

We el~se wishe to thankl CIhe the~r membes of his eemelittee,

Drs. R. J. AndrrSern, A. R. &Ferrtt, E. D. Minekley,

W. W. Eheeany, and 0. 8. Tam..., for their williag


~and to his wif6, De~rethJ, for her leg hours of

workr, her )apiratteln, activation, sad emeouragement goes
his deepest thaks.~r

i OllEA48WS5thfWHM



AQYKNOWLEDBOMENT . .. .. .. . ... .. .. .

LIST OF TABPLES ... .. ... . . .. iv

LIST OF FIOURES .. . ... ... .. ,


I. Int~redwtion . . t . . . . 1

II. Batiews of th Literature . .. . . 4

III. Experbeenta Design~ ae4 Metthod . . . 18

IV. Ikesult .... ....... ...... 32

V. Discasin . . .. .. .. 37

VI. Summar . . . . . . . . 48

APPENSIX * ..... *. ****** ****

RP~EFERINGBS******************** 57



LAstI at SaghWS

1. FreeS~l,-anvtivemtl Plassa'mt . ... . t3

2. a **y lup ***9~ eaete t ones ***-

Thkani96e ...... ........ 34

3. Ceggariseas Mae en Mlaen Dtre of Lg* *$
wl~h~e Qreswere Supeset' to Pree-
Staistee 'Seh Ve). .. . . .


Figure~ Pat*

1. Phetegraph of the Free-Envireronetal
Strature.................. 19

2. Pieetegraph of Test App~warata .. .. .. 24

3.Floor Plan of Prac~tice and Test Predbles . 24



The problem of childhood experience and its ~ffect
on adult behavior is one which has been of constant inter-

est to man. Philosophical, religious, and political

figures, and students of behavior have all elaborated
relevant principles many of which were considered final
and definitive.

Reasons for the lasting interest in this problem

are not difficult to uncover. Casting science and its

constant thirst for knowledge aside for the moment, the

problem appears to have implications in many areas of

life. Religious and philosophical leaders are concerned

with moral issues and ethical values. Political figures

attempt to instill in their subjects a way of life which

will preserve the nation's culture and heritage. In short

all are concerned with the developmea~t and maintenance of

certain ideas, values, goals, and purposes. In many, if

not in most, instances the young child has been the target

of this training. The leaders hate long Cbaused that

knowledge obtained in childhood or the effects of early

experience are fairly permanent and long lasting.

The proposition that early experience has an

effect on later behavior implies that child rearing

practices are of extreme importance and that some or many
of their effects will be seen in subsequent years. Freud

was one of the first to emphasize and treat this impli-

cation in a systematic fashion. Watson, too, although his

theoretical approach to the subject was completely differ-

ent, emphasized this period of life. He is credited with
the statement that were he permitted to rear a child and

to determine the experiences it would have, the child

would later become whatever he, Watson, had previously

decided upon, be it doctor, lawyer, merchant, chief or


Although this assertion may be viewed as opti-
mistic, nalve, or one-sided, it does indicate the

importance attached to environmental influences by some

psychologists. However, it cannot be dismissed glibly
with a comment about its naivetee, It may be true that

the range indicated may not be open to the individual,
but that which is availabletnder normal conditions is

indeed wide. The problem requires the imposition of

certain environmental variables during the developmental

stages and testing their effects on behavior at maturity.
A task of this sort is a practical impossibility if

children were to be used as experimental subjects.

Equating them genetically and controlling the environment

in such a way as to meet experimental standards would be

impossible. Finally, the time repaired would make such
a study impracticable.

The rat appears to be a subject excellently suited

for research of this type. Praetically pure, in-bred

strains are available; control of the environment is not

difficult; and they are mature at the age of ninety dayt.

For these reasons rats were selected for the present

study, an investigation aimed at providing a single

experimental variable and determining its effect on

subsequent behavior. Rats were selected with the

knowledge that generalizations to human development and

behavior must be guarded, however, it was felt that strict

experimental control was of major lapportance.
The specific purpose of the present study is to

test the following hypothesis: The effect of free-

environmetntal experience on problea-solving ability of

as~iture rats is a function of the length of this experience

and the age at which it is permitted.



Comprehensive reviews of investigations covering
early experience and its effect on subsequent behavior in
both human (15) and animal (1) subjectE have appeared in

the literature recently. Studies of human nursing experi-

ences, finger-sucking, restraint of movement, social

isolation, etc., are not pertinent to the present study,

and most of the animal research reported in the review by

Beach and Jaynes (1) is, at best, of tangential importance.

The literature reported below is, therefore, restricted

to those studies from which the present investigation
directly stems.

Scattered studies appeared early, but the first

major problem that arose in this general area was the
attempt to determine the relative importance of maturation

and practice in the perfection of responses. Shepard and

Breed (19), working with pecking behavior in chickens, re-

ported one of the first studies concerned with this

problem. Interest continued to grow and was afforded
further impetus in 1926 when the first of Carmichael's

studies on the swimming behavior of larval amphibians was

published (4). Although interest in the problem of early

experience and its effect on future behavier never has

wanted, renewed enq gpearter interest was stirred in present

day psychology as a result of theories stressing the

importance of perceptual learning in early life. "A

leader in this field is Hsbb, whose ]gg~L Organisabbe~ Sf,

Behagvior has been directly or indirectly responsible for

a number of experiments reported in psychological journals

during the past two or three years" (1, p. 240).

In an attempt to learn more concerning the effect

of early learning on Iature behavior, Hebb (8, 9) conducted

exploratory research. It was labelled as such because it,
"was not certain that such effects could be found in rat

behavior, even if they exist for man; but if one could

find some trace of them in rat behavior their nature could

be investigated much more easily in a species that reaches

maturity in three months than in one that takes fifteen

years (9, p. 296-297). La a first study it was found that

rats blinded at maturity, 90 days of age, were superior to

litter mates blinded in infancy when tested on the Hebb-

Willinies appbaurau. No differences in performance were

obsr~ved on two rote learning taskts requiring 200 or more

trials for mastery. It was also found that these differ-

enees were relatively permrane~nt; at eight moenths of age,

five months After being blinded, the late-blinded greetp

was still superior. A second study, al-so exploratory in

nature, compared animals reared in ordinary laboratory

cages with a group reared at home as pets. The latter

group was superior on the Hebb-Villiams test. The con-

clusions drawn from this work were that infant experience

has a lasting effect on problem-solving behavior in the

rat and that this effect is not detectable from rote

learning scores. Such an effect appears when a method

similar to a human intelligence test is used--that is, one

yielding an index based on a large number of problems.

Although his interpretation was in terms of the

animals' early perceptual experience, Hebb (9) indicates

that the differences between the cag~e- and pet-reared

groups may be interpreted by some as a result of the pet

group being tamer, more used to handling, and less disturbed

by testing in general. But if this is true the longer

testing proceeded the better the cage-reared animals should

have become in relation to the pet group. However, just

the reverse occurred; the pet group maintained and increased

its superiority. "This means that the richer experience of

the pet grouP, dur14gr development, ggad thggg better agle to

profit MI Day experiences at rmaturityv--one of the charac-

teristics of the 'intelligent' human being"n (9, p. 298-299).

Two studies add weight to the argument that the

relationship to the experimenter was of major importance

in producing the superior performance of the pet group.

Shurrager (20), in a discussion of why some of his *spinal"

cats partially regained their ability to walk, prefers

this explanation to all others. He describes at length

the type of close relationship that existed between

experimenter and animal and feels that this relationship

was the mtain factor in their recovery. Bernstein (2)

starting with this hypothesis raised two groups of rats

identically, except that the experimental group was

handled a great deal. When faced with a discrimination

task the experimental animals made significantly feweor

errors. Qualitatively, they showed more exploratory

behavior throughout the study as well as more activity

in their home cages. These findings suggested to Bernstein

an alternate interpretation to Hebb's emphasis on "early

exploratory experience," and he hypothesized that, with

early experience held constant, the group of animals

petted and handled by the experimenter would show learning

superior to that of animals that have broad exploratory

experience only.

Because Heb~b's work was exploratory and conducted

to determine if any effects could be elicited, it was not

well controlled and, therefore, the results required

correbe-ration under more stringenltly controlled conditions.

Hymoviteh (11) did this in an extesion of Hebb's original

research. In the first part of a fairly extensive Study he

blinded one group at 17 to 18 days of age (early-blinded)

and another group at 78 to 80 days (late-blinded). At 21

to 27 days of age half of the early-blinded and late-blinded

groups were placed in a large free-environmental area (FE)

for 2# hours a day on 46 to 49 occasions. The PE was a

wooden box 6 ft. long, 4 ft. wide, and 6 in. high, covered

with hardware cloth and containing playthings within its

confines. The playthings consisted of blind alleys,

inclined runways, small enclosed areas, and apertures. At

80 days of age, training on an adaptation of the Hebb-

Williams apparatus (8) was started. Scores indicated that

those exposed to the FE were superior to animals never pro-

vided with this experience. No significant differences were

observed between the early- and late-blinded groups although

the mean error scores of the early-blinded were consistently

higher than those of the late-blinded animals.

The second phase of the study consisted of placing

six rats in individual stovepipe cages (covered metal

cylinders 8 in, in diameter and 16 in. high) designed to

restrict total experience, eight in mesh cages designed to

restrict movement but permit considerable visual experience,

six in enclosed activity wheels to restrict visual experi-

ence but allow physical movement while restricting the

area, and twenty in PE. All mesh cages were periodically

moved through eight locations, six of which were located

within FB, in order to provide a perceptually rich environ-

ment for these animals. Once the animals were placed in

their experimental cages at approximately 27 days of age

none was handled. Training on the test apparatus was

started at 79 days of age. N~o differences existed between

the FE and mesh-cage groups or between the activity wheel-

and stovepipe-cage groups. But the FE and mesh-cage groups,

the only groups permitted wide visual experience, were

clearly superior to those deprived of visual experience.

When given a maze problem to test their rote learning

ability, no group differed from any other. This part of

the study clearly demonstrates the effect, of wide visual

experiences in early life on later problem-solving behavior.

It further demonstrates that this effect is independent of

any handling or relationship established since no animal

was touched by the experimenter during the experimental


In the third part; of the study one group was raised

in normal cages but placed in PE for 39 three-hour periods

spread over the age range of 30 to 75 days. A second group

was kept in stovepipe cages for the same period. From the

age of 75 to 85 days all were moved into normal cages and

treatment was then reversed during the following 45 days.

A third group was restricted to normal cazges throughout

the 130 days, and a fourth group, which remained in normal


cages, was given PE experience during both halves of the

study. Results indicated that both the early FE and con-

tinued PE groups were clearly superior to the remaining

groups, but did not differ from each other; no differences

existed between the late PE and continuously restricted

groups either. This late FE group was then statistically

compared to the restricted or stovepipe-caged group in the

second phase of the study, and no differences were found.

Hymovitch concludes from this third section of the study

that FE experience provided later in life has no effect on

test performance; the scores of animals receiving late

experience did not differ from those who had no experience.

HHymovitch's work substantiated Hebb's earlier

findings that this early perceptual experience has no

effect in rote learning situations and that the effects

are relatively permanent. In Experiment III the changes

produced in problem-solving ability during the first 75

days of life were still present 75 days later. Further-

more, the superior performance of the wider-environment

group was not equalled by the group which was deprived in

early life, despite an adequate opportunity for experience

during later life. "Hence, the effects seem to be rela-

tively permanent and possibly irreversible" (11, p. 320).

Bingham and Griffiths (3) found no differences

between FE and restricted groups in discrimination learning,

emotionality, and susceptibility to audiogenic seizures.

Differences favoring the FE animals were noted when a

Warner-Warden aete was used; restricted groups required

more trials to reach the criterion. This FE group provided

with an inclined reap, an elevated pathway, and swinging

door did not differ from one which had a broken chair, a

box, and a broken cage as playthings which indicated to
the authors that direct transfer was not the factor respon-

sible for superior performance. They have demonstrated

that early perceptual experiences have a beneficial effect

but, like Hebb, have concluded that the effect is not

found equally in all forms of behavior. Bingham and

Griffiths have further demonstrated that "Thie particular

factors constituting the richness of the wide environments

did not seem related to the superior maze performance of

experim~entals over controls" (3, p. 311-312). The authors,

however, leave an important question unanswered; they

offer no explanation as to why their study is the only one

that has found differences in mate Isarning ability. Hebb

(8), Hymovitch (11), and Forgays and Forgays (6) all report
no differences in mare performance, a task in rote learning,

as a result of rich perceptual experiences early in life.

Forgays and Forgays (6), students of Hebb, sought

to delineate still further the possible experimental

variables operating. Their subjects were male rats of


several litters born approximately the same day, weaned at

26 days, and selected randomly for group placement. A

four-story structure was erected in order to subject the

appropriate groups to specific environments within the same

general environment, that is, the saea section of the

experimental room. In the stories of the structure were

found: (a) FE animals with playthings, and a mesh-cage

group; (b) PE animals and a mesh-cage group; (c) playthings

and a mesh-cage group; (d) a mesh-cage group. The

respective mesh-cage groups could then see FE animals and

playthings, FE animals but no playthings, playthings but no

FE animals, and an area with neither FE animals nor play-

things. A restricted group was housed in laboratory cages

with three solid metal walls, a grill top, and a small

mesh door. At 90 days of age the animals were removed

from their respective environments and placed randomly to

large cages. They were then given one weekc of training on

the Hebb-'dilliams test (10) followed by actual testing on

the Rabinovitch (16) adaptation. The results indicate that

FE animals that had playthings were better problea-solvers

than any other group; the FE rats without playthings were

superior to all remaining groups. The restricted group and

mesh-cage group raised in a layer with FE animals but no

playthings did not differ significantly from each other, and

both were inferior to all other groups. The remaining

aesh-cage groups, though not different from each other,

were inferior to the two Fe groups and superior to the

restricted group and mesh-cage group mentioned above.~

Although the authors recognize that this abudy is not

directly comparable to that of Mgmovitch (11), they feel

it necessary to account for the differences observed in the

respective studies with regard to the performance of the

aesh-cage group housed with the FE animals with playthings

and the FE group. Hysovitch found no difference between

these groups in probles-solving behavior, but Feorgray an~d

Forgays found the FE group to be superior. The authors

state that in their study the mesh groups were housed three

per oage restricting them more than Hymottitch who housed

them individually. In addition, Forgays and ForgayB State

that a few animals of the FE group consistently used the

mesh cage as a resting spot, lying; down on it, which

resulted in restriction of the group's perosptual experi-

enees. The results of the study were viewed as further

tapportive evidence of Hebb's theory, that these animals

provided with a perceptually rich or varied environment

during early life will be superior problee-solvers as adults.

In the final study to be reviewed, Forgue (7) rakwed

one group in Pi with plaything~s; a seetnd group was raised

in the bame type of FE but was confined to the innear 8Qaere

foot -by glass panes. Group 1 thus had a ooeemlex visual and

proprioceptive environment and Group 2 a complex visual

but minimally stimulating proprioceptive one. TPhe third

group confined to a small black box with no furnishings had

an environment which provided minimal stimulation in both

these areas. Testing which included problea-solving in

situations similar to those devised by Mater, as well as

form discrimination and generalitation showed Group 3

consistently poorer than either of the other groups which

differed from each other only on the form discrimination

test. On this test Group 2 was significantly superior.

Forgue concludes that early experience and learning are

important determinants of cognitive ability in the rat, and

that the quality of infant experience determines the kinds

and number of "hypotheses" they can test when solving prob-

less in adulthood. La accord with these conclusions he

explains the difference between Groups 1 and 2 in fore dis-

crimination as follows: "... since group 2 animals were

physically, but not visually restricted during their develop-

ment, there was a greater tendency that visual stimuli would

be perceptually proqinqqt for these" (7, p. 335). Group 1,

on the other hand, had other stimuli which were prominent in

addition to visual cues as a result of being raised in an

environment which exposed them to more and wider stimulatim~;

although visual cues were important for thema, they were not

as completely dependent on visual stimulation as was Group 2.

Wlhat Are Bowen of the possible criticise which

might be lateled Against the r~eults of these studies sad
how would proponents of Nebb's theoretical approach 8efend

their position against these arguments? It eight be sutgget-

tod that superior performaance was metivational in origin.

With the numerous and aridd studies at hand it would appear

very unlikely that all animals raised in perceptually
enriched environmaents were more highly motivated on the

various tests in which their performance was superior; these

tasks include the ))ebb-Williams apparatus and its revisions,

problems similar to those used by Haler, and som meses.
With respect to the Hebb-Williams test, the criterion of

readiness which aust be met by all animals prior to testing

should have equated all subjects or, at laest, sh~nisized

motivational factors.

Bernstein and others raised the objection that In

Hebb's original study (8) the pet-group was handled more and

wee, therefore, tamer. His study (2) supported this conteA-
tion that those handled more frequently will perform better.

But HMrovitch (11) handled all of his anteals equally sat in

the second part of his study none wed handled. Differentet

in both instances were in the expected direction. The re-

sults to not necessarily indicate that either Hebb er

Bernatein is in error, but rather that each is concernetwith
a Variable that has a someawht siailr effect on behavior.


There is the possibility that FE contains elements

present in the test situation which would account for the

superiority of the PE groups; direct transfer may be

operating. If simple transfer such as not entering blind

alleys is in operation, it would be expected to show itself

in consistently superior maze performance, but this has not

been demonstrated. Bingham and Griffiths (3) showed that

the elements contained in FE had little to do with the per-

formance in the test situation. Hymovitch (11) and Forgus

(7) showed that animals permitted visual experience alone

performed as well as those permitted actual contact with

playthings. And finally, Forgays and Forgays in comparing

the performance of the FE groups with and without playthings

state that playthings which are the most obvious agent of

direct transfer in the situation apparently benefit the

animals over and above the large open field. "Either of

these rearing environments, however, leads to superior

problem-solving ability. It would appear, then, that the

effect of free-environmental experience, as such, is not

simple transfer* (6, p. 326).

Superior performance may have resulted from greater

opportunity of FE animals for muscular exercise and its con-

commritant stimulation. Weakening this attack are Hymovitch's

(11) results indicating no differences between the activity

wheel- and stovepipe-cage groups and none between the FE and

mesh-cage group. Perges's (7) findings supported this


It would then appear that the effects are not the

result of _motivation, acquisition of specific stimulue-

res~ponse relationships, or purely motor factors. It
rather appears that the differential opportunities for

perceptual learning were responsible for the fewetts

Experimental evidence (8, 11) further suggests that these
wider experiences must occur early in life, and when pro-

vided at maturity differences in performance are not

erased. Finally, results indicate (9, 11) that these

effects are fairly permanent, that they persist over

relatively long periods of time. Hebb's theory, which

grew out of his first exploratory studies, is summparized

by Beach and Jaynes who state that it predicts that

animals permitted large amounts of pereeptual experience

during early life will prove better learners than those

deprived of such experience. "Further, it is predicted

that the magnitude of this facilitative effect is, within

limits, inversely related to ,the age at which the per-

oeptual experience is gained" (1, p. 255). It is the

purpose of the present study to attempt to define these
limits and further, to investigate the effect of variationsr

in teount of pE experience on later learning, as measured

in problem-solving situations of the Hobb-'dilliaue type.



Rous ing
The FE or experimental area was a four-story

structure measuring 5 ft. in height, 4 ft. in width, and

2 ft. in depth as described by Forgays and Forgays (6).

It was a white wooden structure with 1/4-in3. wire mesh

sides, m~asonite floors painted black and covered to a

depth of 1/2-3/4 in, with wood shavings. Each level within

the structure was 12 in. high with its ceiling serving as

the floor for the level above. (See Fig. 1.) Within these

areas were playthings designed to duplicate those of the

above mentioned study. They consisted of a tunnel with

wood sides and masonite top, a see-saw, and a small enclosed

area open at the top measuring 12 in. square with archway

entrances and two 1/4-in. plywood baffles jutting into the

area. All were 12 in. long, painted white, and constructed

of 3/4-in. lumber except where indicated. The tunnel and

enclosed area were 4 in. high. The see-saw measured 6 in,

in height. Placement of the playthings is shown in Fig. 1.

The control group was housed in standard laboratory

cages (9x10x16 in.) fitted with masonite sides. Laboratory

paper was placed above and below each of the cages





C- -**~- -~
- __ --


s tru13t\Ictur.

Photograph of the free-environmental

restricting the animals' visual environment to the area

within the cage. Except for the periods during which the

various experimental groups were placed in FE, they were

housed and treated exactly as the control group. Males

and females of each group were housed separately with each

cage containing 7-8 animals. Tfhe fourteen cages required

for the seven groups were placed on a double tiered rack;

eight on the upper and six on the lower level with no

special attention given to the cage placement, since the

animals could not see outside.

One hundred five albino rats of the Charles River

strain were used. This number contained fifteen litters

of seven animals each born the same day. Each litter

contained 3-4 animals of each sex for a total of 52 males

and 53 females. A split-litter control was exercised so

that each of the seven groups, described below, contained

only one animal of each litter. All were weaned at 21 days

of age and arrived at the laboratory the following day.

La the course of the study two animals died.

All were fed Purina Laboratory Chow each morning.

The ration per cage was 1/10 the approximate weight of an

average rat in grams, as given in an age-weight chart,

multiplied by the number of animals per cage. An additional


grea was Allott~e those in estes to allOw for food falling
through the 1/2 in, wire merph floor; water was available

at all times. This diet wse supplemented weeely with

lettuce. Cage doors were Opened twice daiily, at feeding

tim~e And again in the eating, to permit inspection.

IrE .aerience

After having spent varying lengths of time in

crowded cages, an environment both visually and physically

restrictive, each of the six experimental groups was

placed in FE. The three odd-numabered groups (I, III, V)

were exposed to this environment for 20 days, the even-

numbered groups (II, IV, VI) for 10 days. Group VII, the

control group, never entered FE. The groups were so

arranged that both a 10- and a 20-day Group received their

FE experience at the same mesan age; for Groups I and II

this wras 35 days, for Groups III and IV it was 55 days,

and for Groups V and VI it was 75 days. The various

groups were placed in PE as follows: Group I from 26 to

45 days; Group II fromR 31 to 40 days; Group III from 46

to 65 days; Group IV from 51 to 60 days; Group v from 66

to 85 days; and Group VI free 71 to 80 days. Thet 20 days

which Groups I, II.1I, and V spent in FE were divided into

four 5-day periods and at the conclusion of eamh period

the animal s ere meoved to a different level within the


experimental structure. The matching 10-day groups, there-

fore, entered FE at the start of the second 5-day period and

were removed at the conclusion of the third period. The

placement of the groups for each of the 5-day periods is

shown to Table 1. All groups were handled as little as

possible, but to equate for this variable it was necessary

to handle all animals six times, the number required in

moving a 20-day group into, within, and out of FE. When the

experimental groups were removed from FE they were returned

to their cages and treated exactly as the control group.

The closed-field testing apparatus was the same as

that devised by Hebb and Williams (10) and modified by

Rabinovitch and Rosvold (17). It consisted of a box with

entrance and food compartments at opposite corners of an

open field. It is shown in Fig. 2. The floor of 1/4-in.

plywood was unpainted. The walls, painted black, were made

of 1/2-in. plywood 4 in. high. There were thirty-six 5-in.

squares outlined in black on the floor of the open field
which served to define error zones and act as markers for

accurate and reliable placement of barriers. The barriers

used to construct the various problems were painted black,

made of 1/2-in, plywood 4 in. high. They were constructed

so that when set on edge they reached from the floor to the

FIve+ Ba PeakM
4 11. 17.1 S
Ckroup sure of age Level

Ya a64-45 1 2 3 4
UP nc 4 ) 1
IiAl 3140 1 4
IIP ;6; 4 1
IIIx 64 4 3 2 1
~IIIF 1 a 3 14
IVM 51-4e c 1
IVF* *r 1 4
YaI 66r t 2 3
a9 c r4 2 1
VI 7-8 1 4
VIP1 r 4 1

VIIMI) Control


IIax YImmonR ~ P~resC~Ya

Fig. 2r Photograph of test apparatus.

1/4-in. screen top of the box. Ttere were 14 barriers

varying in length as follows: 3 barriers, each 5 in. lems;
4 barriers, eacch 10 in. long; 3 barriers, each 15 in. long;

2 barriers, each 20 in. leng; and 2 barriers, each 25 in.

long. A smell piece of sheet metal, 2il/2 in, was nailed to
the bottom of each barrier to insure its standing on ebge.

To prevent its being moved once the aerean top wee fweeted,

a 3/4-in. bred was put into the top of the barrier at each

end as that it engaged the me~sh top.

The practice and test problem were constructed by

placing various barriers within the open field in defined
locations (17). The practice problems, although eiailer

in nebure to those* used in testing, were simpler. TPhey

generally consisted of fewer barriers and required the
animele to make fewer turns. The animals on release from

the starting box found their way around the barriers to

the food box. (See~ Fig. 3,)

In the original article by Hobb and Williams, the

close61fi616 test it described as "a method of evaluating

anical intelligence which appeert to hav6 several impor~ant

advan~tagee, of efficiency, and validity" (10, p. 59). In

its genral2 apprach, it is claimed to be applicable to

any specite. They further state, "The most valid and

valuable ratings of human intelligence are not basdd on

learning scene but on an analysia of perforamace in a


2 3


FiSTAR S. Slo lno rcie a~ts rbe








large number of short tasks." Rote learning sceree such

as those obtained in maze learning may be a meearure of

timidity, of need for food, or a complex of these with

intellectual factors. This method minisiaes motivational

variations and bases its score on a large number of per-

formances. This is probles-solving as contrasted to rote

learning (8).

The test-retest reliability of the Hebb-k'1111sas

apparatus is .84, as reported by Hebb (8). In the most

recent standardization, Rabinovitch and Roarold (17) found

a rho of .84 when all animals (normals, brain operates, and

free-environmental) were compared. This was reduced to .80

when only the unoperated animals were considered. The

ability of the test to differentiate the various groups,

and its high test-retest reliability are both indicators

of its essential validity.

Those animals making better scores may have

superior perceptual capacities--the situations were Meant

to make a fairly ismmdiate visual solution possible--or

they may have a better immediate memory of the preceding

run. However, in either case it may be assumed that an

intellectual function is measured which is not equivalent

to the result of long termr training in the test situation.

Motivation did not appear to be an important variarbl6 einoe

the animals were not tested until all signs of timidity

had disappeared in the training period. There was no

indication that those who made poorer scores were less

eager for food. There were, also, no indications of any

exploratory activity, and none that the poorer scorer

tended to follow the walls--when all barriers were removed

all animals went directly to the food (10).

The test, then, appears to have reliability, some

degree of validity, and be well suited for studies of this


Pre-test _Tralatag

Because of the large number of animals used in the

study, it was impossible to train and test all of them at

the same time. It was, therefore, decided to begin the

training and testing of half of each group at 90 days of

age, five days after the last PE group was returned to its

cages. The animals included in this early-tested group

were the females of Group I, males of Group II, females

of Group III, and so on. Balf of Group VII consisting of

males and females was also included. Testing was completed

on the early-tested group before the remaining animals,

the late-tested group, were started on the pre-test training.

This training began at the age of 116 days, 31 days after

the last group had been removed from FE,

The pre-test training period, consisted of


adaptation sessions and preliminary reme on the prestice

problea4. Its purpose was to beach the anirrstl Y1her foot

was to be found, to obtabli~sh the habit of sating: in the

food box, and to adapt thee to the apparatus and handling,

so that when they were released from the starting box they

would go to the food with a sinimum of exploratory behavior

and without fear (17).

The adaptation sessions consisted of placing 3-4

rats in the box simultaneously after 23 hours of food

deprivation. They were then allowed to find their way

around the barriers of problems A.F (Frig. 3) to the food

compartme~nt where they were permitted to eat moist ground

food for 45 minutes. Thereafter, they were never fed in

their cages. Problems A was set up on the first day,

problem 8 an the second, and so on until the series was

completed. This procedures was repeated until all rata

ran to the food box irsediately upon being released.

As soon as theyr were eating well and gave the

imipression of being adapted to the apparatus, the animals

were run individually in the preliminary runs with as

such handling as possible. Time wae then recorded from

released until the first bite of food. They were permitted

a few bites and were then replaced in the entrance cea-

parteent, being timed as previously. This process was

repeated nine times, once a day, until all animrral ireched


the criterion of making nine runs to food in a total of

60 seconds or less on two consecutive problems. When an

animal was not running as fast as it should, eating time

of 30 minutes was reduced. For those that reached the

criterion training; was continued, but the usual nine runs

were reduced to three per practice problem. Previous work

(17) indicates that subsequent test scores are not influ-

enced by these extra runs and that those animals who reach

the criterion quickly are no more likely to perform better

than others on the test problems.

Testing Procedure

The early-tested animals required 11 days to reach

the training criterion, and the late-tested group required

10 days; therefore, testing began at 102 and 127 days of

age, respectively. Following 23 hours of food deprivation

each animal was given eight runs in the first problem

situation and then allowed to eat in a movable and dupli-

cate food box for 30 minutes. Approximately 23 hours

later the procedure was repeated with the second problem,

and so on until all 12 problems were completed at the

rate of one a day.

An attempt was made to vary the order in which

the groups were exposed to the test problems so that each

group would be placed to as many different serial positions

as possible ktle maintaintag an appJe~ximate 23-hear heager~

drite, rhere was home difficulty in this sinet beatkng~ a

sinpgle gresp of 7-8 animals took appPexisetely oat hear;

therefore, no group's position could be shifted extensivel

fror day to day.

The animales score in each problems was the total

number of error sonied entered. Time was not recorded.

An error was counted each time the animal's two forefi*t

crossed into a~n error rsne, The error zones are indicate

in Fig. 3 by broken lines~. Where an alley contains two

error zones, two errors were scored if the animal crotead

the second line, but none was scored when~ he emerged from

the alley through the first error zoe*, If, after hiring

emerged with both forefeet, the anteel turned around and

went back, an additional error was ecored. The amisel's

score on the entire test wee the total number of error

sones entered on the 12 problem. These provided the

critied1 data in terms of which the hypothesis was




While planning the study, it was recognized that

although the total number of animals used would be large,

each group would contain only a small number of subjects.

Since the rasumHptions underlying traditional statistical

procedures would be difficult, if not impossible, to

satisfy with such small groups, other sethods of analysis

were sought. Non-paramtetric statistical methods, as

described by Moses (14), appeared applicable in the

present situation since tests of significance do not

depend upon assumptions concerning the population dis-

tribution. Of the methods described, Wilcoxon's matched

pairs signed ranks test (24) appeared the most adequate

since it deManded a more stringent experimental control,

that of a split-litter control in the present study.

This technique consists of computing the difference

between the scores of the various pairs, always subtracting

in the same direction. These differences without regard

to sign are then ranked, and the ranks derived from scores

of the same sign are sume~ed. The smaller of these two

totals is then used directly in entering the probability

tables supplied by Wilcoxon (25). In some cases our own


probehility ralras had be be computed free the foresia

he provides since sae comparisent contained a nuelber of

paire greater than pr'ovided for in hisr tables. A rinagl6

exlampleQ of the computations involved in this analysis is

provided in Appendix Table 2.

TPhe result of tht analysis in which each of the

groups use compared to every other group are presented th

Table 2. From this table we can see a marked Somrn~ey

toward superior performance in the test situebion~ by

Group III, exposed to FE for 20 days from 46 to 65 days of

age. This group is significantly better than Groups Y

and VII and shows a tendency toward superiority ever

Groups I, II, and VI. Groups III and Iv did not differ

in their #Ffrerihano+. Group IV which was exposed to FE for

10 days from 51 to 60 days old and, therefore, rteceied its

experionse at the same aban age as Group III, performed

significantly better than the control group which was nevri

exposed to the experimental environment. It would then

appear that a 10-day exposure to this perceptually rich

environrrest at an age approximating 55 days has an effect

sufficient enough to diffbrentibbe this group froe those

restricted throughout. But exposure for 20 days results in

performance that temis to be superior to that of all groups

exposed At othtr ages. W~posure at rety early ages (26 to

45 days) or at ages close to materityr (66 to 85 days),


I (20, 35)** >.95 >.e5 >.05 >.05 >.05
II (lo, 35) >.05 >.*5 >.oj >.oS;
III (20, 55) >.05* >.05* >.oS <.05 >.eS*<,o
IV (lo, 55) >.oS >.05* (.02
V (20, 75) >.05 >.05
VI (lo, 75) >.05*
VII (Control)

Note.--Where differe~nces are or tend to be sig-
nificant groups along, the vertical axis wrre superior.
wApproaches significance.



**Length of and measn age at FE exposure.

whether of 10- or 29-days duration, does not improve per-

formaemoe; none of these groups was significantlyl different
free the restricted group. When the gresps with the anaee

mean e~tposure cge (I and II; III and IV; V ant VI) rwre
combined and coapared with the other two groups as in

Table 3, exposure at 55 days of age is seen to resrult in

performance in the problem-solving or testing situation
which is significantly superior to the performance of

those groups exposed at 35 or 75 dayS of age. However,
the length of exposure, per se, whether 10 or 20 days,

without regard to the age at which it occurs, hase no

appetent effect on probles-solving behavior. The animrals
on whee testing was started when 102 days old did not differ

in their performance from those started at 127 days of age,~

neither were there any sex differences. These final coe-

parisone are based on 1 tests.



35 75

35 >.oS
55 (.oj <.02

Note.--Yhere significant difference are indicated
groups along the tertical axis werer superior.



La general ag~~sree~t with the findings of Nebt

(8, 9), Vymovitch (11)I and Forgays and Porgays (6)
theri- poeYg to be little question that free-environmebedJ

or pes~ceptually enriched experieneesl in early life are
refleettd in superior probleavrsolving ability in the

mature rat. However, the present abudy has served the

funebther9n of defining the previously nebulous period during

which these experiences will affect subsequent performance;
it sorted to delimit within a fairly restricted range the

age at which exposure to this enriched environment pro-

duces geeatest enhancement in problee-solving behavior at

maturity. Tfhis age range isl roughly between 46 to 65

days, and does not appear to support fully Hecbb's general
notion that the sise of the effect is inerseoly related

to the age at which these experiences are provided.

It might be seuggested that superior perforamace

was motivationall in origin. However, all animals met the

smee criterion of readiness, mine runs in a total of 60
secondsa or less on two ceneecutive training probleag.

This criterion should have equated the animals or, at

least, edAieiked motivational factors. Q~ualitatively,


no exploratory behavior was observed in any of the animals

during the testing period.

Bernatein (2) showed that tamer groups of animals

perform significantly better than less tame groups. In

the present study the variable, handling, was held constant.

Each animal was handled six times from the day they were

placed in the various groups, at 22 days of age, through

the start of preliminary training, at 90 or 116 days of

age. It may be speculated that the age at which handling

took place was an important variable, and that as the

animals grew older it had a more taming effect. This

would account for the superiority of the 55 day group

when comapared with the 35 day group. But,1it would also

lead to the prediction that the 75 day group would be

superior to all younger groups. This prediction is not

borne out in the data which indicates that the 55 day

group was stgnificantly superior to either of the other

groups. It might then be suggested that the handling

schedule of the 55 day group had the greatest taking effect.

If this was true the control group which had the same han-

dling schedule should be indistinguishable from it in test

performance. This is contradicted by the daPta.

Had transfer or the opportunity for muscular

exercise been important variables all experimental group

should have been superior to the control group. In


addittena e1 le. and all 20-46f~ group+ should have perfessed

equally. Beth of these "predi~ctioat are contradicted by the)

It then appears that the effeetr ear net the result

of activational differepnces the operation of tr`adfor, or

motor faebers., It rather appears that the opportunity

presented the ~tarious groups for peroeptual learning ass

responsible for thb resu~lts.
Attempts to account for results in teims of Felevant

and prominent; stimull are seen in the studies of Forgus (7)

and Theapean and Heron (22), Discussing the findings that

free-environmental animals did poorer on a form discrllis

nation task, Forgue (7) shebe, "sintce group 2 animals were

physioally, but not visually, restricted during their
developewrrt, there wat a greater tendenoy that vitnal

stimuli would be perceptually prominent for thee"

(7, p. 335), while the free-environmental aniimals had
additiemal prominent srtiaelt becaese they had bee expoeed

to meay more. In aountiing for the poor performace of

restricted dogs, lUbepsoon and tcaron (22) state that the

exset mebure~ of the deficit shown by these dege is not

easily &*@iast, but Appeare best described as a lack of

ability to di~dtidib~te ielevant from irrelevant aspcts

of the enirPeneent.

Wehat expeasse to the experilmenta envriron~men had

no effect on the young animals (Oroups I and II) may be

explained in either of two ways neither of which can be

validated from the data of this experiment. It is possible

that these very young animals (26 to 45 days old) were

incapable of organizing the complex stimull to which they
were exposed into a meaningful or useful pattern. If this

is true, then it may be concluded that they were too young

or maturation had not progressed far enough to enable them

to benefit from this type of experience.

The second possible reason for no improvement in

probles-solving behavior is that during the period of

restriction following FE experience, reliance upon visual

cues disappeared since they were no longer important for the

animalsa. This account differs from the first in that it

assumes an organization of the stimuli by the young animals,

but that in the following period the usefulness of visual

oues practically disappeared. Therefore, when placed in a

situation in which these cues were important, hypotheses
other than those based on visual stimuli were tested since

they steamed from cues which had becomet laportant in the

animals' behavioral repertoire during the long period of

restriction. From this account it would appear that after

additional visual experience, probles-solving ability should

improve so that their performance would not differ from that

of the 55 day old group. This conclusion, which is easily


testabli, 6hesae free the ***umption that an erganizatism
of atimult was pPrei~wely~ presnti that the aniaeals hat,

in Wssase*, dari~sed so benefit free their experince; ab&
that only 941eenning the importance of visual ones eas

necessary. In contrast, the first account based on a
inability to organise the stimruli would not predict tapreoed

performance relative to this 55 day old group, since newr
learning, ra~ther than relsarning, is necessary which app~er

unlikely to occur sinee Hymrotitch (11) ahoew6 that *zpeawre

after 85 days of age following previous restriction he8 no

beneficial effect on problea-solving behavior.

Thd present study indicates that if the first

expsare~ to extensive visual stimulation comesr as late as
66 to 8F; A~s there is no enhancement in probler-selving

ability. TPhese results can again be accounted for in towns

of preeineaowr of stimuli. Since these animals were n*For

required to use visual stimull to anly extent, they never
beess impertalnt or preeinent for them, and by the time the

animals were placed in th& free-environmental situation

they were set or fixed in relation to the stimuli to which

they would attend. In this situation, them, visual cues
were of miaor importance to the animals and performance

based upeA thee wea, therefore, poor.

Chang~ing our frame of refereseo and l~belling1 at

speculathom that whiah follows, we may ask how the present


results and attempted explanations fit with what we knew

about childhood behavior and development.

Our first explanation of the poor performance of

early-exposed animals was based on the assumption that they

were unable to organize the stimulus field and, hence, were

incapable of benefiting from this experience. In line with

this, one Is reminded of James's description of the infant's

consciousness as a "blooming buzzing confusion" probably

incapable of separating or differentiating various aspects

of the environment. We are allaware that many cues which

stimulate adults or even older children apparently escape

or, at least, do not affect the young child's behavior.

I'esec environmental features, behaviorally, are meaningless

for his because he is incapable of organizing them into a

meaningful pattern, Even with practice many forms of

behavior are not improved as Mccraw (12) has shown, because

maturation has not progressed far enough to permit bene-

ficial effects to be derived from this experience.

The second attempt to account for the poor per-

formance of the early-exposed animals assumed that they

were capable of organizing the stimluli, but; that during;

the following period these same cues, because they were no

longer depended upon, lost their importance or prominence.

This can be summarized in terms of forgetting through lack

of practice. The young child learns various routines and

habits with comparative ease, but cons-tant repetition is

nee*$eary if this behavior is to have any pareemengce. He

is attremelf flexible and adaptable in that a pattern which

is new, different, or bven the opposite of the previously

established oen can be learned with relatively little

difficulty. Stimsuli, at this age, which waee previously

unattended and unimportant, can suddenly spring into premi-

nonce and those of previous importance, slip into obecurity.

Older-exposed animals, it was suggested, may be set

or fixed in relation to the stimaull to which they attend or

react. Still in the province of speculation, we see its

counterpart in older children who are fairly close to

maturity. Social learning is just about completed by this

age, methods of adaptation and adjustment are well rooted,

and they are more difficult to change. The comparative

speed with which young children respond in therapy as come

pared with that of the individual near maturity supports

the position that firmly entrenched patternls of behavior are

less susceptible or, at 16ast, more difficult to change.

Present results indicate that there is probably a

period when environmental influences have a tremendous

imPrct upon the individual which is relatively permanent.

In the rat, this period appears to be abut aidway between

weaning and seturity. Speculating with reference to

children, the compapeble period would extend roughly free

5 to 9 years of age. La support of the laportance of this

age, Gole and Morgan (5i) state that the period between
entrance to primary school and adolescence is extremely

important in the development of social behavior, and
Wechaler's curve of mental growth shows this period to

include the start of, as well as, a period of rapid

growth (23).

But stating that all behavior is affected equally

and during the samse short age span is to defend an

untenable position. A firmer and sounder approach is

perhaps, to postulate critical periods in development;

a position which is not new and which is supported by

physiological as well as psychological evidence. A

recent article (26) reported that a wide range of con-

genital abnormalities can be produced in baby rats by

subjecting the mothers to severe deficiencies of folic

acid, a B vitamin, for as little as two days during a
"critical period" of pregnancy. These deformities include

hair lip, cleft palate, extra and fewer digits, and club

feet. It was known previously that this could be done,

"but scientists had not realized how narrow a timse any

be involved." There are no significant abnormalities if

the deficiency occurs before the seventh or after the

twelfth day of pregnancy. A 24 hour deficiency from

7 to 12 days after the start of pregnancy had no effect,

but a 48 hour dbfisency 'pretates death or deasatating

sh~norwellitho* In 70-100k of the animale, The mothere

suffered no ill effeets.

In pi)ychologist1 literature, 4ectt ant Marsten

(18) divide the developerent of the puppyt into 094ties1

periods according to the kinds of behavior that are

possible. The first is the neonatal period lasting

appretaetely 14 dabs or up to the opening of thve

eyeC. During this ti-me the animal is som~ewhatt isolteet

free the environment. A transition period folaev ~ad

lasts until about 3a eeeks of age when conditioning is

said to become possible. This period lasts until the

puppy leaves the nest and first notices observers, which

marks the beginning of the socialisationa period. It is

during this time that the first extensive contacts with

individuals other than the petents tC~be plao*, and it

is deteribed me a critical period affecting the future

social adjusrtment of the animal. Thnis period, ending

with scantag at 8 to 10 weeks of age, is followed by the

juvenile period which lasts until sequel eatu~rity.

Following thtis~, the anise enters the adult sage.

hn_ the area of heean behavior, Freed's stages of

psycchresteml 849lopment ear well konon and need noat be

reviewed here. Other authors haer also made use of the

coakept of critical periods. Stratton (21) in his


discussion of children reared in isolation stated, "Lack

of association with adults during a certain critical period

gji early childhood Citalics maine), it seemso likely, produces
in some or all normal children marks like those of congenital

defect" (21, p. 597). On the same topic, Maslow and

Mittleeman state, "Whether this feeble-mindedness is per-

m~anent or not seems to defend on the _child's ~e whgbg social

ioolatio~n bes~os [italics mine] ." If it starts after the

development of speech "it is remediable for a long time

after, likely for several years" (13, p. 317). It appears

possible, then, that there are ages when specific types of
learning are possible and easy, but once this critical

period has past this learning is extremely difficult, if
not impossible.

In terms of the present study, it appears that

there is a critical period in the development of rats

during which visual learning or sensitivity to visual

cues takes place. This period extends approximately from

46 to 65 days of age. At earlier or later ages, it was

seen, this learning or sensitivity does not take place.
Leaving the specific results of the study and generalizing

from them, it appears that there are ages when the indi-

vidual is too young to benefit from environmental experi-

ences and that when he reaches a certain age environment

plays a relatively minor -role, that is, his behavior is

patterned, and within 10mits of severity, contem~porary

environmnclt does not alter it to any appreciable degree

or perestently.

The present study indicates a need for research

along the fg11owing lines: (a) investigations to determine

the reason for animproved problee-selving ability in rats

exposed to a rich visual environment at young ages, (b)

systeratic and comparative studies to determine other

influences that affect behavior without restricting the

behavior studied to problea-solving, (c) comaparative

research designed to investigate the existence of critical

periods in development.



The purpose of the study was to test Mobb's general
notion that the earlier rats are exposed to a perceptually

enriched environment, the greater will be their problem-

solving ability when mature. The specifle hypothesis

tested was that enhancement of the problem-solving ability

of mature rats is a function of the amount of this free-

environmental experience and the age at which it is pro-

tided. Six experimental and one control group, consisting

of fifteen animals each, were used in the study. A split-

litter control was exercised. All groups, except the

controls, were placed in a large free-environmental area

containing playthings as described by Forgays and Forgays

(6), for 10 or 20 days at mean ages of 35, 55, or 75 days.

The control group was housed in standard laboratory cages

fitted with opaque sides; the tops of the cages were always

covered with laboratory paper. The experimental groups

were also housed in these cages except for the period spent

in the free-environmental area. All animals were handled

the same number of times during rearing.

Half of each group was tested at 102 days of age

and half at 127 days on the Hebb-Williams closed-field

teet, as refig~d and stanaerdized by Babineviteh and
Ibeavold (17).

The lreults ear be summarised as followso:

A. Animals tested at 102 days of ate diA not differ

from those S~ted at 127 days ( see p. 33 ant Appendix hmlW

b. Sex does not influeae~ perform~anee in the etiH

situation (see p. 35 and Appe~ndix Table 5).

c. Longth of exposure did not appear as a sig-

nificant variable (see p. 35 and Appendix Table 3).

d. Ate at exposure appeared as a significant
variable--the group receiving free-envi~ronrmetal experience

at the mea~n age of 55 days, i~e., )roupe III and IV cor-

bined, performed significantly better than those receitt~g;

it Sk 35 or 75 days (see p. 35-36 and Asppndix table 3).

The study supports Habb's theory that wide per-

oeptleal experience provided seek in life has a beneficial
effect on the problee-rplvinrg abilityI of mature rabe. It

does net support his notion that the enhanceernt is

intersed Polated to the age at which thtis experience is

received. Untmpeeved performancet by group provided with

this ex~pewhne at very early aeye or at ages close to

maturity, eeras *eeamed for in )eam of relevant or

preatheuat )ticall.
Th ~Eesoimetal~ hylpobbeeds teseid was: The

effect of free-envirenmental experience on probleia-solving

ability of mature rats is a function of the length of this

experience and the age at which it is permitted. This

predicted that the age at the time of exposure, the length
of exposure, or an interaction of these variables would be

significant. The experimeental results support the

prediction maade with respect to the age variable.


H 00> 4 #0~b~-O ON OHf0\
H I n ?u ?nOP \0 1C

H 0 90@ 0 000 vcOu00O @
3 ~ \) \O cH a t4 NOR cl


~~~EE~X~ E~x


H R NNN4 \ 10 O 00 o u e\

W gamsha anah sah
0 4cO 0 O O O NA4 O c r

H ~ N 4 I ZAOHNA4l~ lr( ~r(

Pair Group I Group II Diff. Rank

1 83 112 *29.0 8
2 145 Died
3 135 95 4oo 11
4 188 177 11.0 2
5 153 185 *32.o o9.5
6 136 122 14.0 5
7 139 136 3.0 1
8 112 166 -51.0 12
9 129 195 .66.0 13
10 123 136 -13.0 3
11 191 121 70.0 14
12 149 135 14.0 5
13 138 106 32.0 9.5
14 139 125 14,o 5
15 113 132 -19.0 7
Sum of ranks with less frequent signc52.5

P ).05



Groups Sue of Ranks N P

_ _




















10 vs. 20 days 014

35 vsr. 55 days old

35 vs. 75 says ol&

55 vs. 75 days 014
(III, IV vs. V, VI)





*Approach~e significense

Eal-rly-Tst* 134.92 5.48 1.9 >*
Late-Te t~a 142 .00




Males 133.55 193,os .05 >.05

Females 14).48

1. Baach, P. A., a Jaynes, J. 1Etf~cts of early experiment

upon the behavior of amiaale. ParakeLP. Buh1., 1954,

51. 239-263.

2. Bernsttin, L. A mote on Christie's: "Experimental

naivete and experiential naitete.* Perobab EBl.*,

1952, 49, 38-40.

3. Binghee, w. n., & Oriffithe, W. J., Jr. Th~e effect
of different environments during infancy on adult

behavior in the rat* Z*, co2MR* vbhystl. 4hrobol.,

1952, 45, 307-312.
4. Caraichael, L. The development of behavior in

verbabretes experimentally removed from the influeses

of ext~rnal stimulation. Psychel. Rev., 1926, 33,


5j. Cele, Luells, b nergan, J. J. B. Pareholonr ot

SM-lehdood ARE AdQl~rcenre. Wliw York: Rhinehart,


6. Forgape, D. G., a Porg~afe, Janet W. The nature of

the effect of free-entironmrental experience in the

ret. L. era.a hratelo Prehkol., 1952, 15, 322-328.

7. )org~ue, R. H. The effect of early perceptual learning

as the behavieral organization of adult rats. J

Iagg, shratal. Farebel., 1954, 47, 331-336.

8. Hebb, D. O. The effects of early experience on

probles-solving at naturity* AMSE Psycholooist,

1947, 2, 306-307 (Abstract).

9. Hebb, D. 0. The org~anitattoo of behargor. New York:

Wiley & Sons, 1949.

10. Hebb, D. O., A Williams, K. A method of rating animaal

intelligehnee. J. ggg. Psychol., 1946, 34, 59-65.

~11 Hymeovitch, B. The effects of experimental variations

on problem solving in the white rat, 1Z. co4g. physiol.

Prachol,, 1952, 45, 313-321.

12. McGraw, Ayrtle B., Growth: 4 study 2( Johnny and

J~iasy. New York: Appelton-Century, 1935.

13. M~aslow, A. H., & Mittleman, B. PrincipleL of abnprelS

Psucholesy: The dyassios of psychic illness.

New York: Harper & Brothers, 1951.

14. Moses, L. E. Non-parametric statistics for psycho-

logical research. Psychel. Bull... 1952, 49. 122-143.

15. orlansky, H. Infant care and personality. PSychol.

&911*1, 1949, 46, 1-48.

16. Rabinoritch, M. S. Standardization of a closed field

intelligence test for rats. Unpublished master's

thesis, McGill Univer., 1949.

17. Rabinovitch, M. S., &c Roevold, H. E. A closed-field

intelligence test for rats. Canaq. d. Psychol.,

1951, 5, 122-128.

18. Scott, J. P., &; laraton, Mary-'Veets. Critical

perieds affecting the deveclopmet of norral and~
haladjuititiv social behaviori in puppies. d. etanth

Pershalp., 1950, 77, 25-60.

19. Shepard, J. F., t Breed, F. S. Maturation and use
in the development of an instinct. J. ggil. Behar.,

1913, 3, 274-285.
20. Shurrag~er, P. S. "Spinal" cats walk. Scintif.

Arur, 1950, 183 (5), 20-22.
21. Stratton, G. M. Jungle children. Psychol. Bull.,

1934. 31, 596-597 (Abstract).
22. Thomrpson, W. R., A Heron, W. The effects of

restricting early experience on the probles-solving

capacity of dogs. C~ana. rA. Psychol., 1954, 8, 17-31.

23. Wechaler, D. jMLr aspsureten~t of attit intelligence.

~baltimore: Willisas & Wilkins, 1944.

24. Wilcoxon, F. Individual compairisons By ranking

lethods. Steeetr. Pisll, 1945, 1, 80-82.

25. wilcoxon, F. Probability tables for individual

comrparison by ranking methods. Blamphries. 1947,

3, 119-122.

26. Congenital abnormalities. Sci, Nlewrsltr., 1956,

69, 53.


Bernard Eingold was born July 19, 192?, in New York

City. He graduated from William Howard Taft High School

there in 1944. He then attended New York University, College

of Arts and Pure Science, until enlisting in the United

States Navy in June, 1945. Returning to New York University

in February, 1947, after being discharged from service, he

received his Bachelor of Arts Degree in the spring of 1949

with a major in psychology.

Mr. Eingold received his Master of Arts Degree in

psychology from the University of Missouri in August, 1951

after which he attended the University of North Carolina

for one year. He has been in attendance at the University

of Florida since the fall of 1952.

He was elected to the honorary social science

society at the University of Missouri; Alpha Kappa Delta,

the honorary sociology society at the University of Florida;

and Psi Chi, the national honorary society in psychology.

He is also an associate member of the Florida Psychological

Association and the American Psychological Association.

This dissertation was prepared under the diresetion

of the chaisrmn of the sendidate' s supervisory coasitt**

and has been approved by all members of the ceaitte*, It

was subr itted to the Dean of the College of Arts and Se6Cease~

and to the Gretuate Council and was approved as partial

fulfilla~nt of the requirements for the degree of Doctor

of Philosophy.

June re, 1956

Dean, College of Arts and Science

Dean, Graduate School



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