Modulation of the Initial Light Reflex during Affective Picture Viewing

MISSING IMAGE

Material Information

Title:
Modulation of the Initial Light Reflex during Affective Picture Viewing
Physical Description:
1 online resource (6 p.)
Language:
english
Creator:
Henderson, Robert Raymond
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Psychology, Clinical and Health Psychology
Committee Chair:
LANG,PETER J
Committee Co-Chair:
BRADLEY,MARGARET M
Committee Members:
PERLSTEIN,WILLIAM MICHAEL
MCCRAE,CHRISTINA SMITH
BOGGS,STEPHEN R

Subjects

Subjects / Keywords:
affect -- emotion -- eye -- pupil
Clinical and Health Psychology -- Dissertations, Academic -- UF
Genre:
Psychology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
When pictures of natural scenes are viewed, they first prompt a brief, reflexive, parasympathetic constriction of the pupil, varying in amplitude with the brightness of the image. When the scene is emotionally arousing, reflex constriction is followed by enhanced, sympathetically mediated pupil dilation. The present research was designed to determine whether the initial light reflex itself might also be modulated by emotion. Erotic, violent, and neutral scenes were presented in both natural and scrambled versions, which were identical in brightness. Significantly less initial constriction was found when participants viewed emotional, relative to neutral, natural scenes, with no differences in pupil size as a function or original content when viewing the scrambled versions. Thus, viewing emotionally evocative images modulates both early and late changes in pupil diameter that are not due to differences in brightness, suggesting early central inhibition of the parasympathetically-mediated light reflex.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Robert Raymond Henderson.
Thesis:
Thesis (M.S.)--University of Florida, 2014.
Local:
Adviser: LANG,PETER J.
Local:
Co-adviser: BRADLEY,MARGARET M.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2014
System ID:
UFE0046854:00001


This item is only available as the following downloads:


Full Text

PAGE 1

MODULATION OF THE INITIAL LIGHT REFLEX DURING AFFECTIVE PICTURE VIEWING By ROBERT R. HENDERSON A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2014

PAGE 2

2014 Robert R Henderson

PAGE 3

To my loving and supportive parents

PAGE 4

ACKNOWLEDGMENTS I thank the chair, Dr. Peter Lang, and cochair, Dr. Margaret Bradley, for their ongoing mentorship and guidance, as well as my fellow lab members of the Center for the Study of Emotion and Attention for their input and support on this project and other endeavors. I would also like to thank the members of my supervisory committee, Dr. William Perlstein, Dr. Christina McCrae, and Dr. Stephen Boggs, for their feedback and advice, as well as the undergraduates who took part in this study for their honest and open participation. I thank my parents, Robert and Eileen Henderson, my brother, Mike Henderson, and my friends and classmates for their continuous support and encouragement. 4

PAGE 5

TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 8 ABSTRACT ..................................................................................................................... 9 CHAPTER 1 INTRODUCTION .................................................................................................... 10 The Initial Light Reflex ............................................................................................ 10 Neur al Mechanisms of Pupillary Control ................................................................. 11 Factors Affecting Light Reflex Amplitude ................................................................ 12 Pupillary Changes and Emotion .............................................................................. 13 Research Aims ....................................................................................................... 16 2 METHOD ................................................................................................................ 19 Participants ............................................................................................................. 19 Design and Materials .............................................................................................. 19 Apparatus ............................................................................................................... 21 Procedure ............................................................................................................... 21 Data Reduction ....................................................................................................... 22 Statistical Analyses ................................................................................................. 23 3 RESULTS ............................................................................................................... 2 7 Primary Pupil Anal ysis ............................................................................................ 27 Light Reflex ...................................................................................................... 27 Late Pupil Diameter .......................................................................................... 27 Picture Analysis ................................................................................................ 28 Full Triplet Pupil Analysis ........................................................................................ 29 Light Reflex. ..................................................................................................... 29 Late Pupil Diameter .......................................................................................... 30 Picture Analysis ................................................................................................ 30 4 DISCUSSION ......................................................................................................... 35 Interpretation a nd Significance ............................................................................... 35 Limitations and Future Research Directions ........................................................... 38 Summary ................................................................................................................ 39 5

PAGE 6

LIST OF REFERENCES ............................................................................................... 40 BIOGRAPHIC AL SKETCH ............................................................................................ 43 6

PAGE 7

LIST OF TABLES Table page 2 1 Physical features and standardized ratings of intact pictures. ............................ 23 3 1 Mean p upil diameter change (mm) during freeviewing of intact erotic, neutral, and violent s cenes. ................................................................................ 31 3 2 Mean pupil diameter change (mm) during freeviewing of scrambled images. ... 31 7

PAGE 8

LIST OF FIGURES Figure page 1 1 Mechanisms of pupillary c ontrol. ........................................................................ 18 2 1 Example of identical brightness triplets. ............................................................. 24 2 2 Experiment set u p. ............................................................................................. 25 2 3 An example of the calibration procedure. ........................................................... 26 3 1 Change (mm) in pupil diameter from a 1s baseline preceding picture onset when viewing original erotic, neutral, and violent scenes.. ................................. 32 3 2 Pupil diameter change (mm) when viewing low and high brightness natural scenes.. .............................................................................................................. 33 3 3 Pupil Diameter change (mm) using only full triplet trials. .................................... 34 8

PAGE 9

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science. MODULATION OF THE INITIAL LIGHT REFLEX DURING AFFECTIVE PICTURE VIEWING By R obert R. Henderson Jr. May 2014 Chair: Peter J. Lang Co Chair: Margaret M. Bradley Major: Psychology When pictures of natural scenes are viewed, they first prompt a brief, reflexive, parasympathetic constriction of the pupil, varying in amplitude with the brightness of the image. When the scene is emotionally arousing, reflex constriction is followed by enhanced, sympathetically mediated pupil dilation. The present research was designed to determine whether the initial light reflex itself might also be modulated by emotion. Erotic, violent, and neutral scenes were presented in both natural and scrambled versions, which were identical in brightness. Significantly less initial constriction was found when participants viewed emotional, relative to neutral, natural scenes, with no differences in pupil size as a function or original content when viewing the scrambled versions. Thus, viewing emotionally evocative images modulates both early and late changes in pupil diameter that are not due to differences in brightness, suggest ing early central inhibition of the parasympathetically mediated light reflex. 9

PAGE 10

CHAPTER 1 INTRODUCTION The Initial Light Reflex Pupil diameter during visual perception is modulated by several factors, the most important of which is the overall brightness of the visual field. In dark light, pupil diameter increases in order to increase the size of the visual field and lower the threshold for light, and in bright light the pupil constricts in order to decrease glare and improve depth of focus and visual acuity. Constriction of the pupil when viewing bright stimuli serves to protect photoreceptors and prevent damage to the eye (Loewenfeld, 1993). The pupillary light reflex is an early occurring constriction that occurs immediately in response to changes in luminance. It is typically elicited by light shining into the right or left pupil; in healthy individuals directing light onto one eye causes si milar amplitude constriction in both the stimulated and unstimulated eye (Beatty, 1986). The onset of the light reflex depends on brightness intensity and physical characteristics of the pupillary musculature. With increases in brightness, the rate and am plitude of initial pupillary constriction, as well as rate of subsequent pupillary dilation back to resting pupil diameter, are enhanced (Ellis, 1981). The light reflex does not occur simultaneously with increases in brightness of the visual field, but instead has a built in delay period due to mechanical limitations of the pupillae sphincter muscle. In humans the light reflex has a minimum built in delay of 200ms and can be additionally delayed by about 250ms depending on the intensity of the light source (Loewenfeld, 1993). 10

PAGE 11

Neural Mechanisms of Pupillary Control Pupil diameter is determined by an antagonistic set of muscle groups, the pupillae dilator and pupillae sphincter muscles, which together regulate the amount of light entering the pupil (Beatty & LuceroWagner, 2000). Figure 11 depicts the general mechanisms controlling the pupillae dilator and pupillae sphincter muscle groups. Contraction o f the sphincter muscles causes constriction whereas contraction of the dilator muscles elicits dilation. T hese muscle groups work together in accordance with Sherringtons Law, such that contraction of the agonist muscle group is accompanied by relaxation of the antagonistic muscle group, allowing for smoother muscle movements and faster reflex responses (Loew enfeld, 1993). Activation of the pupillae dilator and sphincter muscles is determined by the relative contributions of the sympathetic and parasympathetic branches of the autonomic nervous system. The parasympathetic branch controls pupillary constriction through its influence on the pupillae sphincter muscles. Pupillary constriction is elicited via projections from the Edinger Westphal complex of the oculomotor nucleus (the Edinger Westphal Nucleus) in the midbrain to the pupillae sphincter muscles (Stein hauer, Siegle, Condray, & Pless, 2004), causing them to contract and resulting in a rapid reduction in pupil diameter. This constriction occurs primarily in response to increases in brightness of the visual field. On the other hand, the sympathetic branch of the autonomic nervous system controls pupillary dilation via direct stimulation of pupillae dilator muscles, which is mediated by posterior hypothalamic nuclei (Steinhauer, et al., 2004). Because of their radial orientation (Beatty & LuceroWagner, 2000 ), contraction of the pupillae dilator muscles increases overall pupil diameter, allowing additional light to enter the iris. 11

PAGE 12

Because of the reciprocal nature of the activity of the pupillae dilator and sphincter muscle, contraction of either muscle group is paired with central inhibition of outputs to the opposing muscle group. Thus, the extent of initial pupillary constriction to visual stimuli (i.e. light reflex amplitude) is determined by the degree of parasympathetic activation of the Edinger Westpha l Nucleus and its effects on the sphincter pupillae muscles, as well as to central inhibition of motor outputs to the dilator muscle. Pupil dilation, on the other hand, can be elicited by a combination of central sympathetic inhibition of the Edinger Wesph al nucleus and direct sympathetic stimulation of the pupillae dilator muscles (Loewenfeld, 1993). Thus, pupil size at any given moment is dependent upon the relative central and peripheral contributions of the sympathetic and parasympathetic branches of th e autonomic nervous system. Factors Affecting Light Reflex Amplitude The amplitude of the light reflex response may be affected by a variety of physical characteristics, but is most strongly modulated by the intensity of light shining onto the eye. Althoug h brightness is a major contributory factor in determining light reflex amplitude, a number of other features have been proposed to affect the light reflex and overall pupil size. In a largescale review of her own and other studies, Loewenfeld (1993) found that light reflex amplitude is likely influenced by color and spatial dispersion of the light source, retinal distribution, adaptation of the retina, and speed of onset and duration of the light source. Recent studies are consistent with the notion that many physical features of visual stimuli can impact pupil diameter. In addition to brightness, recent studies have shown that latency and amplitude of pupillary reactions are modulated by spatial frequency (Link, et al., 2006), luminancecontrast, color contrast (Carle, James, & Maddess, 2013; Rockefeller, & Kennish, 1993), shifting 12

PAGE 13

gaze from far to near visual stimuli (Kasthurirangan & Glasser, 2005), and different wavelengths of light (Kimura, & Rockefeller, 1996). Although the light reflex is typically elicited by physical characteristics of stimuli, when these features are controlled nonphysical factors can also impact its modulation. For example, light reflex amplitude is attenuated when subjects anticipate receiving an electric shock, and the size of light reflex attenuation is associated with evaluative ratings of anxiety (Bitsos, Szabadi, & Bradshaw, 1996). This effect is not solely due to anticipating the upcoming stimulus since a low amplitude burst of noise is insufficient to reduce light reflex amplitude (Bitsios, Szabadi, & Bradshaw, 2004). Anticipating aversive stimuli is believed to reduce the light reflex response through central inhibition of parasympathetic outputs to the pupillae sphincter muscles rather than sympathetic stimulation of t he dilator muscles (Hourdaki, Giakoumaki, Grinakis, Theou, Karataraki, & Bitsos, 2005). Light reflex amplitude is also reduced when subjects engage in tasks that are cognitively demanding (subtract 7), compared to notask conditions, with light reflex att enuation again reflecting central inhibition of the Edinger Westphal nucleus (Steinhauer, Condray, & Kasparek, 2000) rather than direct sympathetic stimulation. Overall, attenuation of the light reflex during aversive anticipation and when completing diffi cult cognitive tasks is likely due to central inhibition of parasympathetic output to the pupillae sphincter muscles, consistent with pupillary mechanisms modulating the amplitude of the light reflex to physical features of visual stimuli. Pupillary Changes and Emotion Research on effects of psychological processes on pupil size came into prominence in the United States during the 1960s, following publication of a series of 13

PAGE 14

research studies conducted by Eckhard Hess and James Polt, in which the pupil strongly dilated when individuals viewed pleasant pictures and strongly constricted when viewing unpleasant pictures (Hess & Polt, 1960). Although very popular, these studies were afflicted with numerous methodological flaws, including small sample sizes ( e.g. n=5), ambiguous stimuli, small picture sets (e.g. n=5), no mention of control for physical characteristics of the stimuli, and no formal statistical analyses. Other researchers reported contradicting results in their own investigations of pupillary c hanges during affective picture viewing. For example, Nunally, Knott, Duchnowski, and Parker (1967) recorded pupillary changes while 30 male college students viewed pictures of a semi nude female model, as well as male and female models (pleasant), neutral people, and individuals with cancerous growths (unpleasant). Although this study also utilized a small number of images (4 semi nude, 3 pleasant, 3 neutral, 3 unpleasant), the authors attempted to minimize the likelihood of pupil dilation to physical char acteristics by preceding each image with a control image that was adjusted to be darker than the upcoming pictures. In the first part of the experiment, statistical analyses revealed that pupil diameter increased when students viewed the semi nude female m odel relative to viewing the same model fully clothed. In the second part of the experiment, pupil dilation occurred when participants viewed pleasant, relative to neutral and unpleasant, pictures, which did not differ from one another. In a more recent st udy, Aboyoun and Dabbs (1998) found that pupil diameter increased when participants viewed images of unclothed, relative to clothed, individuals. Unpleasant pictures were not presented in this research. 14

PAGE 15

Early investigations of pupillary reactions were lim ited by the time resolution of pupil recordings, as pupil size was typically measured by using a camera and developing images were hand scored. Head movements were typically limited by locking the participant into a chinrest. Recent technological improvements have allowed for increased temporal resolution and accuracy when recording pupillary changes. Modern eyetracking software is able to record small changes in pupil size under a variety of ambient conditions by reflecting an infrared light source off of the participants eye while using facial recognition to track small movements and adjusting the camera to keep the pupil in focus. This allows for a more comfortable and natural experience for the participant than the earlier methodology. More importantl y, these advances allow for more frequent monitoring of changes in pupil diameter, with temporal resolutions of 60 to 120 Hz, and much more precise measurement (e.g. +/ 0.5 degree of visual angle). Using more modern technology, Bradley, Miccoli, Escrig, & Lang, (2008) explored changes in pupil diameter during emotional picture viewing. Unlike the earlier studies, they found that, subsequent to the initial light reflex, pupil diameter was larger when participants viewed either unpleasant or pleasant pictur es. That is, pupil diameter was related to emotional arousal rather than the specific hedonic content: Pupil diameter was largest relative to neutral when participants viewed either content, pleasant or unpleasant. In addition, the amplitude of pupil chang e covaried with the amplitude of skin conductance activity during picture viewing, consistent with an interpretation that these changes in pupil dilation may be sympathetically mediated. Follow up analyses of these data suggested that highly arousing pict ures might also 15

PAGE 16

modulate amplitude of the initial light reflex. This conclusion was not clear, however, because of associated variations in stimulus brightness -prompting the current study. Research Aims Although multiple investigations have since repli cated the Bradley et al. (2008) findings (e.g. Dietz, Bradley, Okun, & Bowers, 2011; Hermans, Henckens, Roelofs, & Fernandez, 2013), there are as yet no findings confirming that emotional arousal also modulates the amplitude of the initial light reflex dur ing affective picture viewing. In the current study, this issue was examined more closely by presenting highly arousing (erotic and violent) and neutral pictures that were exactly matched in brightness to each other. Moreover, as an additional control for assessing effects of brightness on the initial light reflex, each picture was presented in both an intact and scrambled version. In the scrambled version, pixels were randomly shuffled such that brightness was identical to the intact version but no conte nt (semantic or emotional) remained. If emotional arousal modulates the initial light reflex, we expected that viewing emotional scenes would elicit an attenuated light reflex compared to viewing neutral scenes, but that the light reflex for scrambled images of identical brightness would not vary as a function of original picture content. We also expected to replicate results from previous studies (e.g. Bradley, et al., 2008) showing increased pupillary dilation following the light reflex when participants view emotional, relative to neutral, natural scenes. To further assess the relationship between brightness, emotional arousal, and pupillary reactions, an additional analysis using each intact picture as the unit of analysis was conducted. We predicted t hat brightness would account for a substantial amount of variance in light reflex amplitude, replicating previous studies (Bradley, et al., 2008). If the light reflex is modulated when viewing high arousal scenes, we expected 16

PAGE 17

that, after removing effects o f brightness, ratings of emotional arousal would covary with residual light reflex amplitude. On the other hand, if emotional modulation of pupil diameter does not begin until later in the picture viewing interval, we expected that ratings of emotional arousal would not account for additional variance in the residual light reflex. In summary, this investigation sought to first replicate and then significantly extend prior findings, clarifying the time course of emotional modulation of pupillary changes duri ng affective picture viewing. 17

PAGE 18

Figure 11. Mechanisms of pupillary c ontrol. Parasympathetic projections to the sphincter muscles elicit constriction, whereas sympathetic stimulatio n of the dilator muscles increases pupil diameter. 18

PAGE 19

CHAPTER 2 METHOD Participants Twenty seven 1821year old (13 male, 82% Caucasian) University of Florida undergraduate students enrolled in General Psychology courses at the University of Florida participated in this study for course credit. Participants were recrui ted through the universitys online research participation scheduling system. The study was approved by the University of Florida Institutional Review Board, and all participants signed an informed consent form prior to participation in the study. Due to l imitations of the eyetracking system, students were ineligible to participate if they required glasses to see the pictures on the screen, although contacts were allowed. Design and Materials Stimuli were 36 pictures selected from the International Affect ive Picture System (IAPS: Lang, Bradley, & Cuthbert, 2008), consisting of 12 erotic (mean pleasure/arousal= 6.6, 6.4), 12 neutral (mean pleasure/arousal=5.2, 3.6), and 12 violent scenes (mean pleasure/arousal= 1.9, 6.4). Table 21 shows means and standard deviations of physical features and standardized ratings of emotional arousal, valence, and figureground complexity, for the original erotic, violent and neutral pictures. Arousal ratings of erotic and violent pictures were identical, and significantly different from arousal ratings of neutral pictures. Pleasure ratings necessarily differed between each hedonic content, with erotic pictures rated significantly more pleasant than neutral or violent pictures, and violent images rated significantly less pleasant than neutral pictures. All pictures portrayed people, were landscape in orientation and displayed in 19

PAGE 20

256bit grayscale. Pictures were selected to represent a range of brightness, contrast, and ratings of figureground complexity. Pictures were arranged into twelve sets of three pictures (i.e. triplets of eroti c, violent, and neutral images) ; each set varied in brightness from the other sets. Thus, pictures were selected to include one picture of each hedonic content at twelve different brightness lev els. At each brightness level, the triplet included one erotic, one neutral, and one violent picture, all of which were initially very similar in brightness. Pictures within a triplet were then adjusted to be identical in brightness using Adobe Photoshop ( version 7.01; Adobe Systems Inc., San Jose, CA). A scrambled version of each picture was then created which randomly rearranged pixels to produce a version that was identical in brightness to the original intact picture. Figure 21 shows an example of low and high brightness original triplets and their scrambled versions. The final set of stimuli consisted of 36 intact and 36 scrambled pictures, for a total of 72 pictures. Each picture was displayed for a 6 s freeviewing period, followed by a varying inte rtrial interval of 9 12 s that presented a fixation cross on a gray screen. Pictures were arranged such that within a block of 18 trials, participants viewed one intact and one scrambled version of each content at low, medium, and high brightness levels. Picture presentation was counterbalanced such that an intact and scrambled version of each content ( i.e. erotic, neutral, violence) was presented within a block of 6 trials; within this block two pictures of low, medium, and high brightness were presented. Across participants, three presentation orders were constructed which counterbalanced whether a specific picture was presented early, middle or late in the series. 20

PAGE 21

Apparatus Pictures were presented using an IBM compatible computer running Presentation s oftware (Neurobehavioral Systems, San Francisco, CA). Pictures were displayed on a 19inch monitor located in the experimental room, at a distance of 30 inches (76.2 cm) from where the participant was seated, subtending 8.9 x 9.1 degrees of visual angle. Pupil diameter was continuously sampled at 60 Hz from 2s before picture onset to 250 ms before the end of the inter trial interval using an ASL model D6 desk mounted remote eye tracker (Applied Science Laboratories, Bedford, MA; see F igure 22 c). This system consists of a video camera and an infrared light source, which is focused on the participants right eye. Face recognition is used to track head movements and keep the pupil in focus. The recording video camera was located in front of the participant, situated just below the stimulus presentation monitor. The height of the monitor and eye tracker was adjusted between participants to ensure that each participants pupil was level with a fixation cross in the center of the screen. Figure 22 depicts the setup of the participant room, experimenter view, and eyetracking camera. Procedure After arriving at the laboratory, each participant signed a consent form and was seated in an upright chair in a small, soundattenuated, dimly lit room. A calibrati on procedure was conducted in order to ensure accurate measurement of pupil diameter at different gaze locations. The dot distribution and example gaze locations are depicted in Figure 23. The participant was instructed to sequentially look at 9 dots tha t appeared one at a time on the screen while pupil diameter and gaze location were recorded. Several scrambled images of varying brightness were then presented in order to ensure 21

PAGE 22

reliable pupil diameter measurement at different levels of picture brightnes s. This procedure was repeated until pupil diameter was successfully obtained at each gaze location and brightness level. The participant was then instructed to view each picture for the entire time that it was on the screen and to look at the fixation cr oss at all other times. It was emphasized that participants should sit still throughout the experimental session, as small movements would interfere with data collection. The experimenter monitored gaze location and pupil diameter during each session and adjusted camera focus during the inter trial interval when necessary (see Figure 22 b for an example of accurate pupil and gaze location measurement). Data Reduction Pupil diameter was converted offline from arbitrary units to millimeters and linear interpolation was used to estimate pupil size for samples in which the pupil was occluded due to blinking. For each trial, pupil diameter during a onesecond baseline prior to picture viewing was subtracted from each of the following pupil samples. Five partici pants were not included in the final analysis due to unsuccessful pupil discrimination on more than 15% of trials. Based on the average waveform, the initial light reflex was calculated as the mean pupil change in a window from .5 to 1.3 s after picture o nset (Figure 31 a). Trials in which pupil discrimination was less than 50% accurate in this time window were counted as missing (3.2% of total trials). Late pupil diameter was calculated as the mean pupil change in a window from 2 to 6 seconds following picture onset (Figure 31b) and included the same trials as in the analysis of the light reflex. To ensure that any potential differences in pupil size for each picture content were not due to differences in brightness after removing trials, a separate analysis was 22

PAGE 23

conducted using only those trials with full triplets for both intact and scrambled versions of the images (i.e. for each subject, removing all trials which did not have a corresponding samebrightness trial in all six conditions). After removal of these trials 86.4% of original trials remained. The initial light reflex and late pupil diameter were calculated using the same time windows (Light reflex: 0 .5 1.3s; late pupil diameter : 2 6s) as in the primary pupil analysis. Statistical Analyses Data were analyzed using a Content (3: erotic, neutral, violent) X Mode (2: intact, scrambled) repeated measures analysis of variance for each of the dependent variables (initial light reflex, later pupil diameter), with appropriate follow up univariate ANOVAs when warranted. GreenhouseGeisser was used to correct degrees of freedom for sphericity. Tables 31 and 32 display means and standard errors for all comparisons. Table 21. Physical features and standardized ratings of intact pictures. Mean (SD) Erotic Neutral Violent Physical Features Brightness 0.45 (0.13) 0.45 (0.13) 0.45 (0.13) Contrast 0.05 (0.02) 0.06 (0.02) 0.05 (0.03) Standardized Ratings Hedonic Valence 6.61 (0.34) 5.17 (0.42) 1.88 (0.24) Arousal 6.37 (0.36) 3.57 (0.39) 6.45 (0.32) Complexity 3.90 (0.36) 3.70 (2.06) 3.99 (2.06) Note: Pictures depicting erotica, neutral events, and violence were selected to be identical in brightness, and highly similar in contrast and ratings of figureground complexity. Erotic and violent pictures were identical in ratings of emotional arousal and significantly different from neutral scenes. Erotic, neutral, and violent pictures necessarily differed in ratings of hedonic valence. Scrambled versions were identical in brightness to intact images. 23

PAGE 24

Figure 21. Example o f identical brightness triplets. A. Example of a low brightness triplet. B. Example of a high brightness triplet. Brightness was varied across triplets but identical between erotic, violent, and neutral images within each tripl et. 24

PAGE 25

Figure 22. Experiment set u p A. Participants were seated 30 inches away from the monitor. The height of the monitor and eyetracker were adjusted so that each participants eye was level with the fixation cross in the center of the screen. B. Experimenter view of monitors showing participants point of gaze and accuracy of pupil size measurement. C. The eyetracking camera, which uses infrared light to maintain pupil discrimination and face recognition to adjust for head movements. 25

PAGE 26

Figure 23. An example of the calibration procedure. A. E xample of an accurate calibration to the center dot. B. An example of unsuccessful calibration to the center dot. Calibration was repeated until accurate pupil discrimination and point of gaze coor dinates were obtained for all dots on the screen and at varying levels of brightness. 26

PAGE 27

CHAPTER 3 RESULTS Primary Pupil Analysis Light Reflex Figure 31a illustrates the change in pupil diameter during freeviewing of natural scenes, showing a clearly att enuated light reflex response when viewing intact erotic and violent, compared to neutral, scenes Significant main effects of picture content, F(2,20) = 23.5, p < .001, and mode, F(1,21) = 179.9, p < .001, were accompanied by a significant interaction between content and mode, F(2,20) = 13.4, p < .001. Follow up analyses revealed significant effects of picture content when viewing intact F(2,20) = 35.1, p<.001, but not scrambled, pictures. For intact pictures, viewing either erotic or violent scenes prompted significantly less early pupil constriction, compared to neutral pictures, F(1,21) = 107.7, p< .001 and F(1,21)= 14.5, p < .005, respectively. Viewing e rotic scenes prompted less constriction than violent scenes, F(1, 21) = 15.4, p < .001. Early modul ation of the initial light reflex was not due to differences in brightness, as size of the initial light reflex did not differ by original hedonic content when participants viewed scrambled versions of these pictures that were identical in brightness F(2, 20) = 0.48, p> .6 (see f igure 3 1, inset). Overall, pupil constriction was larger when viewing scrambled, compared to intact, scenes (all Fs 1(1, 21) > 58, p < .001). Late Pupil Diameter Pupil diameter later in the viewing interval was also modulated, with a larger response for emotional than neutral scenes (Figure 31b). Significant main effects were obtained for picture content, F(2,20) = 55.3, p< .001, mode, F(1,21) = 169.1, p < .001, 27

PAGE 28

a nd their interaction, F(2,20) = 28.7, p < .001. Follow up analyses revealed significant effects of picture content for intact pi ctures only, F(2,20) = 72.0, p<.001. Viewing erotic and violent pictures was associated with significantly larger increases in late pupil diameter, compared to neutral scenes, F ( 1,21 ) = 200.6, p < .001 and F ( 1, 21) = 19.1, p < .001, respectively, with viewing erotic scenes again eliciting larger changes than violent scenes, F(1,21) = 49.3, p < .001. Overall, pupil diameter during the later viewing interval was reduced when participants viewed scrambled, compared to intact, images (all Fs (1,21) > 70, p < .001). Again, pupil diameter did not vary among scrambled pictures. Picture Analysis Figure 32 depicts average pupillary changes when participants viewed intact erotic, violent, and neutral pictures at low and high brightness levels. As can be seen, light reflex amplitude was strongly associated with picture brightness. To further determine whether the initial light reflex is reliably modulated by emotional content, a hierarchical regression was conducted using each intact picture as the unit of analysis, assessing first effects of brightness and then emotional arousal. As expected, light reflex amplitude was highly correlated w ith picture brightness, F(1, 34) = 106.6, p < .001, R2 =.75, with pictures higher in brightness prompting significantly larger light reflexes than lower brightness pictures. After removing effects due to brightness, however, rated emotional arousal of each picture (Lang et al., 2008) continued to account for significant variance in the amplitude of the initial light reflex, F(2,33) = 74.9, p < .001, R2 increase = .06. 28

PAGE 29

Full Triplet Pupil Analysis Pictures of erotica, violence and neutral content were origi nally designed as triplets in which brightness was exactly matched. Because some trials were lost due to excessive pupil loss or poor pupil discrimination, it is possible that, in the preceding analyses, brightness may have still varied among data retained in the analysis. To confirm that these effects were not do to subtle differences in brightness resulting from missing trials, a second analysis was conducted using only those trials in which data was available for both the intact triplet and its scrambled version. In this analysis, approximately 86% of the previous data was retained. Light Reflex. Pupillary reactions during freeviewing of natural scenes again resulted in attenuated light reflex responses when viewing intact erotic and violent, compared to neutral, natural scenes (Figure 33a). Results were identical to those in the full analysis. Significant main effects of picture content, F(2,20) = 12.31, p < .001, and mode, F(1,21) =, 228.5, p < .001, were found, accompanied by a significant interac tion between content and mode, F(2,20) = 13.9, p < .001. Significant effects of picture content were found w hen participants viewed intact, F(2,20) = 26.0, p<.001 but not scrambled, pictures, with viewing intact erotic and violent images prompting attenua ted light reflex amplitudes relative to viewing intact neutral scenes, F ( 1,21 ) = 51.8, p< .001 and F(1,21) = 15.9, p < .001, respectively The light reflex was further attenuated when participants viewed erotic, compared to violent, scenes, F(1, 21) = 10.04 p < .005. Light reflex amplitude did not differ when participants viewed scrambled versions of these pictures that were identical in brightness, F(2,20) = 0.07, p>.9 (see Figure 33, inset). As in the previous analysis, light reflex amplitude was att enuated 29

PAGE 30

when participants viewed scrambled, compared to intact, pictures (all Fs (1, 21) > 48, p < .001). Late Pupil Diameter As in the original analysis, later pupil diameter was als o modulated by picture content, F(2,20)= 44.8, p<.001, mode, F(1,21)= 196.1, p<.001, and their interaction, F (2,20) = 25.9, p<.001. Significant effects of picture content were elicited when parti cipants viewed intact pictures, F(2,20) = 52.3, p<.001, with no differences when viewing scrambled images, F(2,20) = 0.51, p>.6. Si gnificantly larger changes in late pupil diameter were found when participants viewed erotic or violent, compared to neutral, scenes, F ( 1,21 )= 105.6, p < .001 and F ( 1, 21) = 17.8, p < .001, respectively Pupil diameter was again greater when participants v iewed erotic, relative to violent, pic tures, F(1,21) = 42.7, p < .001. Late Pupil diameter was similarly reduced when participants viewed scrambled, compared to intact, images (all Fs ( 1,21) > 60, p < .001). Picture Analysis Assessing effects of brightne ss and emotional arousal via a hierarchical regression analysis using intact picture as the unit of analysis revealed similar results to the primary pupil analysis. Light reflex amplitude remained strongly associated with picture brightness, F(1,34) = 196. 3, p<.001, R2= .76 with ratings of emotional arousal accounting for significant variance in light reflex amplitude once effe cts of brightness were removed, F (2,33) = 16.3 p<.001, R2 increase= .07. 30

PAGE 31

Table 31. Mean p upil diameter change (mm) during free viewing of intact erotic, neutral, and violent scenes. Mean (SD) Analysis Erotic Violent Neutral Light Reflex Primary 0 .07 ( 0 .04) 0 .20 ( 0 .06) 0 .32 ( 0 .04) Full Triplet 0 .04 (0.21) 0.15 (0.30) 0.30 (0.26) Late Pupil Diameter Primary 0.52 (0.07) 0.15 (0.08) 0.12 (0.06) Full Triplet 0.53 (0.36) 0.20 (0.43) 0.10 (0.35) Note: Means (standard errors) of pupil diameter change (mm) during freeviewing of erotic, neutral, and violent scenes during the initial light ref lex (.5 1.3 seconds) and late pupil diameter (2 6 seconds). Results of the primary and full triplet analyses revealed identical patterns of modulation. Table 32. Mean pupil diameter change (mm) during freeviewing of scrambled images. Mean (SD) Analysis Erotic Violent Neutral Light Reflex Primary 0.61 (0.04) 0.63 (0.05) 0.64 (0.05) Full Triplet 0.60 (0.23) 0.61 (0.23) 0.60 (0.33) Late Pupil Diameter Primary 0.57 (0.07) 0.60 (0.05) 0.67 (0.06) Full Triplet 0.58 (0.35) 0.60 (0.25) 0.58 (0.35) Note: Means (standard errors) of pupil diameter change (mm) during freeviewing of scrambled versions of each original hedonic content (erotic, neutral, and violent) during the initial light reflex (.5 1.3 seconds) and late pupil diameter (2 6 seconds). Pupil diameter was not modulated during viewing of scrambled images of original hedonic content in either time period. Results of the primary and full triplet analyses revealed identical patterns of modulation. 31

PAGE 32

Figure 3 1. Change (mm) in pupil diameter from a 1s baseline preceding picture onset when viewing original erotic, neutral, and violent scenes. a) The mean light reflex was averaged in a window from .5 to 1.3 s following picture onset, and b) later pupil diamet er was averaged in a window from 2 to 6 s post picture onset. Inset: Pupil size when viewing scrambled versions did not differ as a function of original picture content in either time period. 32

PAGE 33

Figure 32. Pupil diameter change (mm) when viewing low and high brightness natural scenes. A. Mean pupil change during viewing of low brightness erotic, neutral, and violent scenes. B. Mean change in pupil diameter when viewing high brightness natural scenes. The light reflex was enhanced when participants viewed high brightness, relative to low brightness, pictures. The light reflex and later pupil diameter were consistently modulated by emotional content during viewing of both darker and lighter natural scenes. 33

PAGE 34

Figure 33. Pupil Diameter change (mm) using only full triplet trials. Change (mm) in pupil diameter from a 1 s baseline preceding picture onset when viewing the original erotic, neutral or violent scenes using only full triplet trials. a) Initial light reflex; b) Late pupil diameter. Inset: P upil size when viewing scrambled versions. Results were identical to the primary analysis. 34

PAGE 35

CHAPTER 4 DISCUSSION Interpretation and Significance When viewing emotionally engaging pictures, modulatory effects on pupil diameter are apparent as early as th e initial light reflex. Although the light reflex is much more strongly modulated by perceptual factors such as brightness, this early constriction was nonetheless significantly attenuated when participants viewed highly arousing pictures of erotica and v iolence, compared to neutral images (see Figure 31) When participants viewed scrambled versions of each intact scene, which were identical in brightness but without semant ic content, neither the initial light reflex or later pupil dilation varied as a function of original picture content, confirming that the attenuation in light reflex amplitude found when viewing intact emotional, compared to neutral, pictures did not reflect subtle differences in brightness. Furthermore, ratings of emotional arousal sub stantially predicted differences in light reflex amplitude once effects of brightness were removed, again demonstrating early modulation of pupil diameter when viewing emotionally engaging natural scenes. Because the pupil is sensitive to slight variations in brightness, pictures were originally selected to form samebrightness triplets of erotic, violent, and neutral content. However, since some trials were lost due to poor pupil discrimination, it was possible that brightness may have varied when using a ll remaining trials in the primary analysis. Therefore, a follow up analysis using only those trials in which complete data was available for the original triplet and its scrambled version (see Figure 33) was conducted, confirming findings of attenuated l ight reflex amplitudes when participants viewed erotic or violent, compared to neutral, pictures, and of a significant association 35

PAGE 36

between emotional arousal and light reflex amplitude after removing effects of brightness. Modulation of the initial light reflex was larger when participants viewed erotic, compared to violent, scenes. This is consistent with previous studies finding greater physiological reactivity when young adults view pictures of erotic couples, compared to when viewing other pictures rated similarly in emotional arousal. For example, Schupp, Cuthbert, Bradley, Hillman, Hamm, and Lang (2004) recorded startle reflexes and event related potentials during freeviewing of emotional pictures varying in terms of their motivational significance. P ictures depicting erotica elicited significantly greater late positive potentials and increased inhibition of the P3 component to startle probes, compared to viewing other pictures which were rated similarly in terms of emotional arousal (e.g. human threat animal threat, mutilation) suggesting greater allocation of attentional resources when viewing erotica. Erotic stimuli also prompt greater electrodermal reactions than similarly rated arousing unpleasant pictures in young adults (Lang, Bradley, & Cuthbert, 1997), suggesting that erotic pictures are more emotionally arousing in this population and that self report may not identify these differences as well as physiological measures. Despite this heightened response when viewing erotica, pupil diameter was nonetheless reliably and significantly modulated when participants viewed arousing pictures of erotica and violence, compared to neutral images. Pupil diameter at any given moment is determined by the amount of coactivation of sympathetic and parasympathetic influence on pupillary musculature. Although the specific mechanism behind emotional modulation of the light reflex has not been 36

PAGE 37

determined, one view is that pupil diameter reflects changes in locus coeruleus activity during processing of motivationally significant stimuli (Gilzenrat, Nieuwenhuis, Jepma, & Cohen, 2010), based on studies indicating that locus coeruleus activity is strongly associated with changes in pupil diameter. The locus coeruleus has inhibitory influences on the Edinger Westphal nucleus as well as excitatory projections to preganglionic sympathetic neurons in the spinal cord (Samuels & Szbadi, 2008), both of which can elicit changes in pupil diameter. However, in animal studies utilizing electrical stimulation of parasympathetic fibers in the oculomotor nerve, it has been demonstrated that light reflex amplitude is primarily determined by contractions of the pupillae sphincter muscles (Clarke, R. J., 2007) rather than direct sympathetic stimulation of the dilator muscle. Thus, one possibility is that viewing scenes high in emotional arousal alters the firing rate of neurons in the locus coeruleus, inhibiting projections from the Edinger Westphal nucleus to the pupillae sphincter muscles and attenuating the light reflex. On the oth er hand, increased late pupil diameter is likely due to continued inhibition of the Edinger Westphal Nucleus as well as direct sympathetic stimulation of the pupillae dilator muscles by posterior hypothala mic nuclei ( Steinhauer, et al., 2004). Pupil dilati on may also be elicited by increased activity of the superior colliculus, as microstimulation of this area in monkeys elicits reliable increases in pupil diameter (Wang, Boehnke, White, & Munoz, 2012). Future studies utilizing pharmacological blockades of appropriate receptors in the sympathetically mediated dilator and parasympathetically mediated sphincter muscles (e.g. Steinhauer, et al., 2004) will be useful in determining the specific mechanisms underlying emotional modulation of the 37

PAGE 38

light reflex (and later pupil dilation). However, previous research suggests that light reflex modulation is due to central inhibition of the Edinger Westphal nucleus, which may be mediated by changes in locus coeruleus activity, with subsequent dilation elicited by continued central inhibition of the Edinger Westphal nucleus as well as direct sympathetic stimulation of the dilator muscle. Limitations and Future Research Directions This study measured pupil diameter in a population of collegeage students at the Univ ersity of Florida. Older adults have been shown to have smaller resting pupil and reduced light reflex amplitudes to flashes of light relative to young adults (Bitsios, Prettyman, & Szabadi, 1996). Previous studies have demonstrated similar emotional modu lation of late pupil diameter in healt hy older adults (e.g. Dietz, et al., 2011) but it is unclear whether emotional modulation of the light reflex will replicate in differently aged populations. The scrambled and intact pictures used in this study necess arily differed in terms of spatial frequency and contrast. Although pupil size did not differ among scrambled versions of erotic, neutral, and violent scenes, these images did elicit a significantly larger initial constriction than the intact version of the picture. Larger light reflexes are found for stimuli higher in spatial frequency (Link et al., 2006), however, which is consistent with the enhanced constriction when viewing scrambled, compared to intact, images found here. In addition to physical differences, specific contents of erotica, and violence were used in this study. Future studies utilizing a wider range of affective pictures that are controlled for spatial frequency may be useful in better understanding the relationship between emotional arousal and light reflex amplitude. 38

PAGE 39

Summary The initial light reflex is attenuated when participants view emotionally arousing, compared to neutral, natural scenes, suggesting early and rapid effects of emotional arousal on pupillary changes during freeview ing of affective pictures. These findings cannot be explained by subtle variance in picture brightness, as scrambled versions of these same scenes, identical in brightness to the intact images, did not elicit reliable differences in pupil diameter. One interpretation is that early modulation of pupil diameter reflects changes in the firing rate of neurons in the locus coeruleus, but additional studies are needed to determine the precise mechanisms. Most broadly, these data show that differences in emotion al arousal prompt changes in the initial light reflex beyond the effects of brightness alone, suggesting that emotional effects are immediate and then continue to modulate pupillary responses over periods of picture exposure. 39

PAGE 40

LIST OF REFERENCES Aboyoun, D. C., & Dabbs, J. M. (1998). The Hess pupil findings: Sex or novelty? Social Behavior and personality, 26, 415420. Beatty, J. (1986). The Pupillary System. In Coles, M. G. H., Donchin, E., & Porges, S. W.(Eds.), Psychophysiology: Systems, proce sses, and applications (pp. 4350). New York, NY: The Guilford Press. Beatty, J., & LuceroWagoner, B. (2000). The pupillary system. In J. T. Cacioppo, L. G. Tassinary, & G. G. Berntson (Eds.), Handbook of psychophysiology (pp. 142 162). Cambridge, UK: Cambridge University Press. Bitsios, P., Prettyman, R., & Szabadi, E. (1996). Changes in autonomic function with age: A study of pupillary kinetics in healthy young and old people. Age and Ageing, 25, 432438. Bitsos, P., Szabadi, E., & Bradshaw, C. M. (1 996). The inhibition of the pupillary light reflex by threat of an electric shock: a potential laboratory model of human anxiety. Journal of psychopharmacology, 10, 279287. Bitsios, P., Szabadi, E., & Bradshaw, C. M. (2004). The fear inhibited light refle x: importance of the anticipation of an aversive event. International Journal of psychophysiology, 52, 8795. Bradley, M. M. (2009). Natural selective attention: Orienting and emotion. Psychophysiology, 46, 111. doi:10.1111/j.14698986.2008.00702.x Bradl ey, M. M., Miccoli, L., Escrig, M. A., & Lang, P. J. (2008). The pupil as a measure of emotional arousal and autonomic activation. Psychophysiology 45, 602 7. doi:10.1111/j.14698986.2008.00654.x Carle, C. F., James, A. C., & Maddess, T. (2013). The pupill ary response to color and luminance variant multifocal stimuli. Investigative Ophtalmology & Visual Science, 54, 467475). Dietz, J., Bradley, M. M., Okun, M. S., & Bowers, D. (2011). Emotion and ocular responses in Parkinsons disease. Neuropsychologia, 49, 3247 3253. doi: 10.1016/j.neuropsychologia.2011.07.029. Ellis, C. J. (1981). The pupillary light reflex in normal subjects. British Journal of Ophthalmology, 65, 754759. Gilzenrat, M., Nieuwenhuis, S., Jepma, M., & Cohen, J. (2010). Pupil diameter t racks changes in control state predicted by the adaptive gain theory of locus coeruleus function. Cognitive, affective & behavioral neuroscience, 10, 25269. doi:10.3758/CABN.10.2.252 40

PAGE 41

Hermans, E. J., Henckens, M. J. A. J., Roelofs, K., & Fernandez, G. (20 13). Fear bradycardia and activation of the human periaqueductal grey. Neuroimage, 66, 278287. doi: 10.1016/j.neuroimage.2012.10.063. Hess, E. H., & Polt, J. M. (1960). Pupil size as related to interest value of visual stimuli. Science, 132, 349350. Ho urdaki, E., Giakoumaki, S. G., Grinakis, V., Theou, K., Karataraki, M. & Bitsos, P. (2005). Parametric exploration of the fear inhibited light reflex. Psychophysiology, 42, 447455. Kasthurirangan, S., & Glasser, A. (2005). Characteristics of pupil responses during far to near and near to far accommodation. Opthalmic and physiological optics, 25, 328339. Kimura, E., Rockefeller, S. L., Y. (1996). A Chromatic cancellation property of human pupillary responses. Vision Research, 36, 15451550. Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1997). Motivated attention: affect, activation, and action. In P. J. Lang, R. F. Simons, & M. Balaban (Eds.), Attention and orienting (pp. 97135). Mahwah, NJ: Erlbaum. Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (20 08). International affective picture system (IAPS): Affective ratings of pictures and instruction manual. Technical Report A 8. University of Florida, Gainesville, FL. Link, B., Jnemann, A., Rix, R., Sembritzki, O., Brenning, A., Korth, M., & Horn, F. (20 06). Pupillographic measurements with pattern stimulation: the pupils response in normal subjects and first measurements in glaucoma patients. Investigative ophthalmology & visual science, 47, 49474955. doi:10.1167/iovs.060021 Nunally, J. C., Knott, P. D., Duchnowski, A., & Parker, R. (1967). Pupillary response as a general measure of activation. Perception and Psychophysics, 2, 149155. Loewenfeld, I.E., (1993). The pupil: Anatomy, physiology, and clinical applications (pp. 88, 97, 101, 136137, 425). Ames, Iowa: Iowa State University Press. Rockefeller, S. L.Y., & Kennish, J. (1993). Transient and sustained components of the pupil response evoked by achromatic spatial patterns. Vision Research, 33, 22392252. Samuels, E. R., & Szbadi, E. (2008). Fu nctional neuroanatomy of the noradrenergic locus coeruleus: Its roles in the regulation of arousal and autonomic function part II: Physiological and pharmacological manipulations and pathological alterations of locus coeruleus activity in humans. Current N europharmacology, 6, 254285. 41

PAGE 42

Schupp, H., Cuthbert, B., Bradley, M., Hillman, C., Hamm, A., & Lang, P. (2004). Brain processes in emotional perception: Motivated attention. Cognition & Emotion, 18, 593611. doi:10.1080/02699930341000239 Steinhauer, S. R., Condray, R., & Kasparek, A. (2000). Cognitive modulation of midbrain function: task induced reduction of the pupillary light reflex. International Journal of Psychophysiology, 39, 2130. Steinhauer, S., Siegle, G., Condray, R., & Pless, M. (2004). Sympat hetic and parasympathetic innervation of pupillary dilation during sustained processing. International journal of psychophysiology, 53, 7786. doi:10.1016/j.ijpsycho.2003.12.005 Wang, C., Boehnke, S. E., White, B. J., & Munoz, D. P. (2012). Microstimulatio n of the monkey superior colliculus induces pupil dilation without evoking saccades. The journal of neuroscience, 32, 36293636. 42

PAGE 43

BIOGRAPHICAL SKETCH Robert R. Henderson was born on July 18, 1987 in Woodbury, New Jersey. One of two children, he grew up in Upper Township and West Deptford, New Jersey, graduating from West Deptford High School in 2006. He earned his B.S. in Psychology from the University of Delaware (UD) in 2010. While at UD, Robert completed one year of research in an infant cognition lab and one year of research in a clinical psychophysiology laboratory, where he completed an honors senior thesis investigating inhibitory control in overweight children and healthy control participants. Following his graduation from UD, Robert was employed as a post baccalaureate research assistant at the Center for the Study of Emotion and Attention (CSEA) in Gainesville, Florida. While at the CSEA, Robert ran studies inves tigating psychophysiological processes during affective picture viewing and memory tasks, collected standardized ratings of affective pictures and texts, and helped to measure and record physiological data from patients with Anxiety Disorders. He also assi sted with administrative duties and data analysis for several other research projects and was able to gain valuable research exposure at annual Society for Psychophysiological Research conferences, where he presented multiple first and second author poster s. Robert is currently pursuing a Ph.D. in clinical psychology as a graduate student in the Clinical & Health Psychology program at the University of Florida. He continues to work in the CSEA, studying emotional and cognitive processes in undergraduates and patients diagnosed with anxiety disorders. After completing his Ph.D. program, Robert hopes to complete an internship in an academic clinic or VA prior to beginning a post doctoral research career utilizing psychophysiological methods in an academic environment. 43



PAGE 1

BRIEFREPORTThepupilasameasureofemotionalarousaland autonomicactivationMARGARETM.BRADLEY,LAURAMICCOLI,MIGUELA.ESCRIG, and PETERJ.LANGCenterfortheStudyofEmotionandAttention,UniversityofFlorida,Gainesville,Florida,USAAbstract Pupildiameterwasmonitoredduringpictureviewingtoassesseffectsofhedonicvalenceandemotionalarousalon pupillaryresponses.Autonomicactivity(heartrateandskinconductance)wasconcurrentlymeasuredtodetermine whetherpupillarychangesaremediatedbyparasympatheticorsympatheticactivation.Followinganinitiallightre”ex, pupillarychangeswerelargerwhenviewingemotionallyarousingpictures,regardlessofwhetherthesewerepleasantor unpleasant.Pupillarychangesduringpictureviewingcovariedwithskinconductancechange,supportingtheinterpretationthatsympatheticnervoussystemactivitymodulatesthesechangesinthecontextofaffectivepictureviewing. Takentogether,thedataprovidestrongsupportforthehypothesisthatthepupilsresponseduringaffectivepicture viewingre”ectsemotionalarousalassociatedwithincreasedsympatheticactivity. Descriptors: Pupil,Arousal,Emotion,Pleasure,Sympathetic,SkinconductanceHess(e.g.,Hess&Polt,1960)famouslyreportedbi-directional effectsofemotiononpupilchange,reportingthatthepupilconstricted(shutdown)whenpeopleviewedunpleasantpicturesand dilatedwhentheyviewedpleasantpictures.Theseresultsproved dif“culttoreplicate,however,andthisearlyresearchsuffered fromnumerousmethodologicaldif“culties,includingtheuseof veryfewpictures(e.g.,“ve),verysmallnumberofsubjects(e.g., “ve),themethodofassessingpupilchange,andnostatistical analysis.Libby,Lacey,andLacey(1973)laterconductedamore extensiveinvestigationofpupillarychangesduringaffectivepictureviewing,presenting30picturesto34participantswhileboth pupildiameterandheartrateweremeasured.Intheirstudy,the pupilwasphotographedtwotimesasecondduringa15-sexposureforeachpicture.Then,sixclerksscoredtheresulting 81,600measurementsonthebasisofawallchartontowhichthe negativewasprojected.Thereportedresultsweresomewhat confusing:Althoughattention-gettingpictures,afactoronto whichemotionalityloaded,wasassociatedwithgreaterpupil dilation,asecondpleasurefactorsuggestedthatneutralpicturespromptedlargerpupildilationthanemotionalpictures. Morerecentdatahavesuggestedthatemotionalarousalisa keyelementinmodulatingthepupilsresponse.Forinstance,ina posterabstract,Steinhauer,Boller,Zubin,andPearlman(1983) describedatainwhichpupildiameterincreasedwhenpeople viewedpleasantandunpleasantpictures,and,morerecently, AboyounandDabbs(1998)presentedpicturesofclothedand nakedindividualstomenandwomen,“ndingthatpupildilation re”ectedgeneral,ratherthangender-speci“c,arousal.Nonetheless,asystematiccomparisonofpupillaryreactionsasafunction ofpictureemotionality,andtheroleofemotionalarousalin modulatingpupillarychanges,doesnotyetexist.Onegoalofthe currentstudywastoreassesstheeffectsofhedonicvalenceand arousalonpupillaryresponsesduringpictureviewingusinga moderninfraredeye-trackingsystemandalargesetofwell-validatedpicturesfromtheInternationalAffectivePictureSystem (IAPS;Lang,Bradley&Cuthbert,2005),whichallowedexperimentalcontrolofbothratedpleasureandarousal. Asecondgoalofthecurrentstudywastoassessthecontributionofsympatheticandparasympatheticactivitytopupil changeintheaffectivepictureviewingcontext.Asdiscussed morefullybySteinhauer,Siegle,Condray,andPless(2004), changesinpupildiameterarecontrolledbytwomuscles F the dilatorandthesphincter F thataredifferentiallyin”uencedby activityinthesympatheticandparasympatheticbranchesofthe nervoussystem.Increasedsympatheticactivity increases theactivityofthedilatormuscle,promptingdilation,whereasinhibitionofparasympatheticactivitylessensconstrictionofthe sphinctermuscle,whichalsoresultsindilation.Thus,increasesin pupillarydiametercanbemediatedbyactivityineitherdivision oftheautonomicnervoussystem. Inthepictureviewingcontext,previousstudieshaveconsistentlyfoundthatskinconductancechangesarelargerwhen viewingpleasantandunpleasant,comparedtoneutral,pictures, ThisresearchwassupportedinpartbyagrantfromtheNational InstituteofMentalHealth(P50MH72850)totheCenterfortheStudyof EmotionandAttention(CSEA)attheUniversityofFlorida.Laura MiccoliandMiguelEscrigarenowattheJaumeIUniversityofCastello n,Spain. Addressreprintrequeststo:MargaretM.Bradley,Centerforthe StudyofEmotionandAttention,Box112766,UniversityofFlorida, Gainesville,FL32611,USA.E-mail:bradley@u”.eduPsychophysiology,45 (2008),602…607.WileyPeriodicals,Inc.PrintedintheUSA. Copyright r 2008SocietyforPsychophysiologicalResearch DOI:10.1111/j.1469-8986.2008.00654.x602

PAGE 2

indicatingthatthissympatheticallymediatedresponsecovaries withemotionalarousal(Lang,Greenwald,Bradley,&Hamm, 1993).Ontheotherhand,cardiacdecelerationisgenerallygreaterwhenviewingunpleasant,comparedtoeitherpleasantor neutral,pictures(Bradley,Codispoti,Cuthbert,&Lang,2001), andpharmacologicalblockadestudiesoffearbradycardiain animalssuggestthatthisdeceleratoryactivityismediatedprimarilybychangesinparasympatheticactivity(Berntson,Boysen,Bauer,&Torello,1989). Ifpupillarychangesduringpictureviewingaremediatedby differencesinparasympatheticactivity,weexpectedthatthe patternofpupillarychangeswouldcovarywiththepatternof cardiacdecelerationandbemostpronouncedforunpleasant pictures.If,ontheotherhand,pupillarychangesduringpicture viewingareinitiatedbysympatheticallymediatedchangesthat increaseactivityofthedilatormuscle,weexpectedthatpupillary responseswouldcovarywithskinconductanceactivity,withincreasesinbothmeasureswhenviewingemotionallyarousing comparedtoneutralpictures,regardlessofhedonicvalence. Themostimportantnaturalfunctionofthepupilistodynamicallyrespondtochangesinenv ironmentalillumination,and, inhumans,thepupilre”exivelyrespondstosuchchangeswithan initialconstriction(i.e.,thelightre”ex)thatisrelatedtostimulus luminosity(Beatty&Lucero-Wagoner,2000).Becausethehuman eyeisdifferentiallysensitivetolightinthegreen,red,andblue spectrums(makingitmoredif“culttoaccuratelyestimateluminanceforcolorphotographs),wepresentedpicturesingrayscale. Moreover,wecontrolledluminancebyequatingboththeaverage luminanceacrossimagesineachsetofpictures(i.e.,pleasant, neutral,andunpleasant)aswellas byequatingthedistributionof luminancevaluesineachpictureset.Weexpectedthat,although themagnitudeoftheinitialligh tre”exwouldcovarywithluminance,itwouldnotsystematical lydifferasafunctionofhedonic picturecontent,allowinganaccu rateassessmentofpupilchange thatisspeci“callyrelatedtopictureemotionality. Method Participants Twenty-seven(11female)18…22-year-oldstudentsfromaUniversityofFloridaGeneralPsychologycourseparticipatedfor coursecredit.Ofthese,85%( n 5 23)reportedtheywerewhite/ Caucasian,7%( n 5 2)Arab/MiddleEastern,and7%biracial/ multiethnic. MaterialsandDesign Stimuliwere96pictures1selectedfromtheInternationalAffectivePictureSystem(IAPS:Langetal.,2005),consistingof32 pleasant(meanpleasure/arousal 5 7.0,5.5),32neutral(mean pleasure/arousal 5 4.9,3.4),and32unpleasant(meanpleasure/ arousal 5 2.4,5.9)pictures.Ratedarousalwasequivalentfor pleasantandunpleasantstimuli.Allpicturesportrayedpeople, werebalancedforstimuluscomplexity,werelandscape(1024 768)inorientation,andweredisplayedin16-bitgrayscale.Using AdobePhotoshop(version7.01;AdobeSystemsInc.,SanJose, CA),themeanluminosityoftheselectedpictureswasmodi“ed suchthatthemeananddistributionofluminosityvaluesforeach ofthepicturessets(pleasant,neutral,unpleasant)didnotdiffer, asdepictedinFigure1(top). Thepupilasameasureofemotionalarousal 603 Picture Luminance & the Pupil12 10 8Pleasant Neutral Unpleasant Low Luminance Moderate Luminance High Luminance6 4 2 0 6.2 6.0 5.8 5.6 5.4 5.2 2.0 1.5 1.0 0.5 0.0 0 r=.73 123456 Time (s)Magnitude of Light Reflex (mm) Pupil diameter (mm)LowHigh Luminance LowHigh LuminanceNumber of Pictures Figure1. Toppanel:Themeananddistributionofluminancevaluesfor pleasant,neutral,andunpleasantpictureswerematched.Middlepanel: Pupillaryresponsefollowingpictureonsetbeginswithaninitiallight re”ex(decreaseinpupillarydiameter)thatisstronglymodulatedby luminance.Bottompanel:Themagnitudeoftheinitiallightre”exvaries withpictureluminanceonapicture-by-picturebasis(eachsquareisa picture). 1ThelibrarynumbersforIAPSpictures(Langetal.,2005)usedinthis studyare:pleasant:2208,2250,2260,2501,2560,2650,4611,4617,4640, 4653,4659,4666,4687,4694,5621,8041,8080,8090,8116,8120,8161, 8180,8200,8280,8300,8320,8330,8370,8380,8400,8420,8465;neutral:2020,2190,2200,2210,2214,2215,2220,2221,2235,2240,2270, 2272,2278,2383,2393,2410,2441,2491,2493,2514,2579,2745.1,2749, 2752,2810,2850,2870,2890,3210,5455,7550,9210;unpleasant:2120, 2205,2520,2590,2691,2730,2750,2800,3015,3030,3053,3100,3170, 3180,3181,3400,3500,3530,3550,6210,6211,6212,6821,6834,6838, 9041,9250,9254,9341,9405,9800,9921.

PAGE 3

Picturesweredisplayedfor6seach,withanintertrialinterval of10s.Agrayscaleimagewiththemeanluminositycomputed acrossallpictureswasdisplayed2sbeforepicturepresentation oneachtrialtocontrollevelofilluminationpriortopicture onset.Anacousticstartleprobewaspresentedbetween3and5s afterpictureonsetonhalf( n 5 16)ofthetrialsforeachpicture content;thestartlere”exdataarenotpresentedhere.2Pictures werearrangedinblocksofsix,withtwopicturesofeachhedonic content(pleasant,neutral,andunpleasant)ineachblock;pictureswereviewedinoneoftwodifferentordersacrossparticipants,withaspeci“cpictureviewedineitherthe“rsthalforthe secondhalfofthestudy,acrossorders. Apparatus PicturepresentationwascontrolledbyanIBM-compatiblecomputerrunningPresentationsoftware(NeurobehavioralSystems, SanFrancisco,CA).Picturesweredisplayedona19-in.monitor (SamsungSyncMaster191T)locatedintheexperimentalroom, atadistanceof99.06cm(39in.)fromwheretheparticipantwas seated. PupildiameterwasrecordedusinganASLmodel504eyetrackersystem(AppliedScienceLaboratories,Bedford,MA), whichallowsfreemovementoftheheadandconsistsofavideo cameraandaninfraredlightsourcepointedattheparticipants righteye.Amagneticsensor,attachedtoaheadband,tracked andadjustedforheadmovement.Therecordingvideocamera waslocatedinawoodboxinfrontofthesubject,andared translucentscreenobscureditfromview.Pupildiameterwas sampledat60Hzfor2spriortopictureonset,for6sduring pictureonset,and3sfollowingpictureoffset. SkinconductanceandheartrateweremeasuredusingVPM software(Cook,2001)runningonanIBM-compatiblecomputer.Skinconductancewasrecordedusingtwolargesensorsplaced adjacentlyonthehypothenareminenceoftheleftpalmarsurface afterbeing“lledwith0.05MNaClpaste.ACoulbournS71-22 skinconductancecoupler(CoulbournInstruments,Allentown, PA)sampledelectrodermalactivityat20Hz.TheelectrocardiogramwasrecordedfromtheleftandrightforearmusingstandardAg/AgClelectrodes,“lledwithelectrolytepaste.Thesignal was“lteredusingaCoulbournS75-01bioampli“er,andaSchmitttriggerinterruptedthecomputereachtimeitdetecteda cardiacR-wave.Interbeatintervalswererecordedtothenearest millisecondandreducedoff-lineintoheartrateinbeatsper minute,inhalf-secondbins. Procedure Uponarrivalatthelaboratory,eachparticipantsignedaconsent formandwasseatedinareclinerinasmall,sound-attenuated, dimlylitroom.Theheadbandfortrackingheadmovementand sensorsformeasuringheartrateandskinconductancewerethen attached.Eachparticipantwasinstructedthataseriesofpictures wouldbedisplayedandthateachpictureshouldbeviewedthe entiretimeitwasonthescreen.Followingthreepracticetrials, thesetof96pictureswaspresented.Then,thesensorswereremovedandtheparticipantwasaskedto“lloutapostexperimentalquestionnaire.Theexperimentersubsequentlydebriefed, paid,andthankedtheparticipant. DataReduction Sampleswherethepupilwasobscu redduetoblinkingwereidenti“ed,andlinearinterpolationwasusedtoestimatepupilsize.For eachtrial,a1-sprepicturebase lineaveragewassubtractedfrom eachofthefollowingpupilsamples.Basedontheaveragewaveformduringpictureviewing(seebelow),theinitiallightre”ex duringpictureviewingwasscoredasthemaximumextentofpupil constrictioninawindowfrom0.6to1.6safterpictureonset.The pupilresponsetothepicturecontentfollowingtheinitiallightre”ex wascalculatedasthemeanchan ge(frombaseline)inawindow from2to6safterpictureonset.Forbothskinconductanceand heartrate,a1-sprepicturebaselinewassubtractedfromthevalues ateachhalf-secondduringpictureviewing.Forskinconductance, themaximumchangebetween1and4safterpictureonsetwas computedandalogtranform(log[SCR 1 1])donepriortoanalysis ofvarianceinordertonormalizethedata.Forheartrate,the averagechangescoreacrossthe6-sviewingintervalwasanalyzed. Multivariatestatisticsarereportedforallanalyses. Results Figure1(middle)illustratesthemeanpupildiameteracrossthe pictureviewinginterval.Anotablefeatureistheinitiallightre”ex immediatelyfollowingpictureonset,inwhichpupildiameter decreasesduetotheincreaseinillumination.Asexpected,the magnitudeoftheinitiallightre”exwasmodulatedbypicture luminosity, F (2,25) 5 60.6, p o .0001,withsigni“cantdifferences inthemagnitudeofthelightre”exforpicturesthatwerelower, moderate,orrelativelyhigherinluminosity,asillustratedin Figure1(middle), F s(1,26) 4 42, p s o .0001.Moreover,thelight re”exwashighlycorrelatedwiththemeanluminosityonapicture-by-picturebasis,asillustratedinFigure1(bottom), F (1,94) 5 107, p o .0001. Figure2(toppanel)illustratesmeanpupildiameterasa functionofpictureemotionality.Consistentwithoureffortsto controlluminosity,therewerenosigni“cantdifferencesinthe amplitudeoftheinitiallightre”exasafunctionofpictureemotionality.Ontheotherhand,pupildiameterfollowingtheinitial lightreactionwassigni“cantlyaffectedbypictureemotionality, withasustaineddifferenceinpupildiameterwhenparticipants viewedemotional,comparedtoneutral,picturesfromabout2s untiltheendoftheviewinginterval,asillustratedinFigure2 (top).Whenpupillarychangeswereaveragedfrom2to6safter pictureonset,picturecontentresultedinamaineffect, F (2,25) 5 10.25, p o .001,withbothpleasantandunpleasant picturespromptingrelativeincreasesinpupildiameterthatwerelargerthanthoseelicitedwhenviewingneutralpictures, F s(1,26) 5 7.21and15.39,respectively, p s o .001.Thedifference inpupilsizebetweenpleasantandunpleasantpicturesdidnot reachsigni“cance, F (1,26) 5 3.04, p 5 .09. SkinConductance Skinconductancechangeparalleledthepatternofpupillary changes,asillustratedinFigure2(bottomleft).Replicating manypreviousstudies,hedoniccontentaffectedskinconductancechange, F (2,24) 5 3.62, p o .05,withlargerchangeswhen participantsviewedunpleasant, F (1,25) 5 6.79, p o .02,orpleasant, F (1,25) 5 3.69, p 5 .03one-tailed,comparedtoneutral, pictures.Totheextentthatemotionalityisthefactordriving changesinthepupilandinskinconductance,weexpectedthat bothresponseswouldbemostpronouncedforpicturesratedas highestinemotionalarousal.Toassessthisrelationship,pleasant 604 M.M.Bradleyetal. 2Thedataanalysisincludedbothtrialsonwhichastartleprobewas deliveredandno-probetrials.Whenthisfactorwasincludedintheanalysisofthepupillarydata,effectsofpictureemotionalitywereidenticalfor bothtrialtypes.

PAGE 4

andunpleasantpictureswereeachdividedintohighandlow arousalpicturesonthebasisofthemedianarousalratingineach pictureset.AsillustratedinFigure3,picturesratedhigherin emotionalarousal F pleasantorunpleasant F promptedequivalentchangesinelectrodermalactivity( F o 1),withbothshowing signi“cantlylargerchangescomparedtoneutralpictures, F s(1,25) 5 8.75and7.28,respectively, p s o .02.Similarly,for pupildiameter,highlyarousingpleasantpicturesandunpleasant picturespromptedequivalentpupillarychanges( F o 1),with bothtypesofpictureassociatedwithlargerchangesthanwhen participantsviewedneutralpictures, F s(1,26) 5 34.39and18.56, respectively, p s o .01.Pupilchangewhenparticipantsviewed picturesratedlowerinemotionalarousaldidnotdifferfrom whentheyviewedneutralpicturesineithermeasure,exceptfor unpleasantpicturesratedlowerinarousalinthepupillaryanalysis, F (1,26) 5 6.01, p o .05. HeartRate Forheartrate,adifferentpatternofmodulationwasfound,as illustratedinFigure2(bottomright).Amaineffectofpicture content, F (2,25) 5 8.33 p o .001,indicatedthatunpleasantpicturespromptedalargercardiacdeceleration(mean 5 1.76 beatsperminute[bpm]),whichwassigni“cantlydifferentfrom theheartratechangeselicitedwhenparticipantsviewedpleasant ( 0.87bpm)orneutral( 0.81bpm)pictures, F s(1,26) 5 11.62 and14.19, p s o .001,respectively.Heartratechangewhenparticipantsviewedpleasantandneutralpicturesdidnotdiffer. Whenheartratechangewascomputedasafunctionofboth pleasureandarousal,unpleasantarousingpicturescontinuedto promptgreaterdecelerationcomparedtoanyotherpicturecontent, F s(1,26) 5 16.94,7.74,21.66,and10.29, p o .01,forpleasantlow,pleasanthigh,neutral,andunpleasantlow,respectively. PictureAnalysis Foreachofthe96pictures,skinconductancechange,heartrate change,andpictureluminancewereenteredintoahierarchical multipleregressionanalysispredictingthemeanpupilchange (2to6safterpictureonset)duringpictureviewing.Inthisanalysis, bothluminance, F (1,92) 5 65, p o .0001,andskinconductance changes, F (1,92)5 10.7, p o .005,wereindependentpredictorsof Thepupilasameasureofemotionalarousal 605 Figure2. Toppanel:Pupillaryresponsewhenviewingaffectivepicturesshowsgreaterpupillaryincreasesfollowingtheinitiallight re”exforpleasantandunpleasant,comparedtoneutral,pictures,indicatingmodulationbyemotionalarousal.Bottomleft:Skin conductancechangesduringpictureviewingaresimilartopupillaryresponses,showinglargerincreaseswhenpleasantor unpleasant,comparedtoneutral,picturesareviewed.BottomRight:Heartratechangeduringpictureviewingshowsgreatercardiac decelerationwhenunpleasantpicturesareviewed.

PAGE 5

pupildiameterduringpictureviewing.Wheneffectsduetoluminancewereremoved,skinconductancechangeremaineda highlyreliablepredictoroftheresidualpupillarychanges, F (1,92) 5 10.5, p o .005.Heartratechangewasnotrelatedto pupillarychangesduringpictureviewing. Discussion Aninitialdecreaseinpupildiameterfollowingpictureonsetwas stronglyrelatedtoluminanceasexpected,andexperimental controlinsuredthatthisinitiallightre”exdidnotdifferasa functionofpicturecontent,allowinganassessmentofemotion onpupillarychangesduringpictureperception.Thedataclearly indicatedthat,followingtheinitiallightre”ex,pupillaryincreaseswerelargerwhenparticipantsviewedpleasantorunpleasant, comparedtoneutral,pictures.Thesedatadiscon“rmearlierhypothesesregardingdifferentialpupillarychangesasafunctionof hedonicvalence(Hess&Polt,1960)andsupportthemorerecent consensusthatpupildiameterincreaseswhenpeopleprocess emotionallyengagingstimuli,regardlessofhedonicvalence.Ina recentstudy,Partala,Jokiniemi,andSurakka(2000)reported increasedpupildilationevenwhenparticipantslistenedtoaffectivelyengaging,comparedtoneutral,sounds,suggestingthat emotionalarousalpromptspupillaryincreasesevenwhenthe perceptualcontextisnotvisual. WhereasLibbyetal.(1973)originallyreportedthelargest pupillarychangeswhenunpleasantpictureswereviewed,togetherwithanassociationbetweenpupillarychangeandcardiac deceleration,theseeffectswerenotreplicatedinthepresentstudy andmayre”ectdifferencesinpictureselection.Thus,whereasin thepresentstudy,pleasantandunpleasantpictureswerematched foremotionalarousalonthebasisofIAPSratings(Langetal., 2005),levelofarousalwasnotconsideredbyLibbyetal.(1973). Althoughtheirpicturesetapparentlyincludedpleasantstimuli typicallyratedashighlyarousing(e.g.nudeongrass,beautifulfemalemodel),somepleasantpicturesaremoredif“cultto characterizeintermsofarousal(e.g.,pieceofsandstoneshaped likenude,severallightbulbs,sexuallysuggestive),andothers donotappear,onthesurface,tobepleasant(e.g.,locomotive, viewofwheels).Becausegreatercardiacdecelerationistypically foundwhenunpleasantpicturesareviewed(Bradleyetal.,2001), anassociationbetweencardiacandpupillarychangesislikely whenpleasant,arousingpicturesarenotwellrepresentedinthe stimulusset.Supportingthisinterpretation,whenpleasantpictureswereremovedfromthecurrentanalysis,therankcorrelationbetweencardiacdecelerationandpupillarychangeacross pictureswas .33,whichisalmostidenticaltothe .35correlationreportedpreviouslybyLibbyetal. Ratherthanvaryingwithcardiacdeceleration,thecurrent studyfoundthatpupillarychangescovariedwithskinconductancereactions,providingcollateralsupportforthehypothesis thatpupildiameterduringpictureviewingpredominantlyre”ects sympatheticnervoussystemactivity.Duringpictureviewing, bothskinconductanceandpupillarychangesweregreatestfor emotional,comparedtoneutral,picturesandtheseeffectswere accentuatedforthepicturesratedasmosthighlyarousing.Furthermore,whenthepicturewasusedastheunitofanalysis,the relationshipbetweenskinconductanceandpupilchangespersisted,evenwhenspeci“ceffectsduetoluminositywereremoved usinghierarchicalmultipleregression. Instudiesthathaveexploredeffectsofmentalloadandsustainedcognitiveprocessingonpupilchange,theobservedpupillarydilationappearedtobemediatedbyparasympathetic inhibitionofthesphinctermuscle(Steinhaueretal.,2004).The closecovariationofpupildilationwithskinconductanceinthe currentstudysuggeststhat,foremotionalprocessing,themechanismmaybedifferentandinvolvedirectsympatheticinnervationofthedilatormuscle.Takentogether,thecurrentdataare consistentwiththehypothesisthatpupillarychangesduring affectivepictureviewingaremediatedbyincreasedsympathetic activity,andstronglysuggestthatpupildilationisdeterminedby emotionalarousal,independentofwhetherpicturesarepleasant orunpleasantinhedonicvalence. REFERENCESAboyoun,D.C.,&Dabbs,J.M.(1998).TheHesspupildilation “ndings:Sexornovelty? SocialBehaviorandPersonality 26 415…420. Beatty,J.,&Lucero-Wagoner,B.(2000).Thepupillarysystem.In J.T.Cacioppo,L.G.Tassinary,&G.G.Berntson(Eds.), Handbook ofpsychophysiology (pp.14…162).Cambridge,UK:Cambridge UniversityPress. Berntson,G.G.,Boysen,S.T.,Bauer,H.R.,&Torello,M.S. (1989).Conspeci“cscreamsandlaughter:Cardiacandbehavioral reactionsofinfantchimpanzees. DevelopmentalPsychobiology 22 771…787. Bradley,M.M.,Codispoti,M.,Cuthbert,B.N.,&Lang,P.J.(2001). EmotionandmotivationI:Defensiveandappetitivereactionsin pictureprocessing. Emotion 1 ,276…298. Cook,E.W.III.(2001). VPMreferencemanual .Birmingham,Alabama: Author. Hess,E.H.,&Polt,J.M.(1960).Pupilsizeasrelatedtointerestvalueof visualstimuli. Science 132 ,349…350. Lang,P.J.,Bradley,M.M.,&Cuthbert,B.N.(2005).International AffectivePictureSystem(IAPS):Affectiveratingsofpicturesand instructionmanual.TechnicalReportA-6.Gainesville,FL:UniversityofFlorida.606 M.M.Bradleyetal. Figure3. Changesinpupillarydiameterandskinconductancecovary, withthelargestreactionsforpleasantandunpleasantpicturesrated highestinemotionalarousalforbothpsychophysiologicalmeasures.

PAGE 6

Lang,P.J.,Greenwald,M.K.,Bradley,M.M.,&Hamm,A.O.(1993). Lookingatpictures:Affective,facial,visceral,andbehavioralreactions. Psychophysiology 30 ,261…273. Libby,W.L.,Lacey,B.C.,&Lacey,J.I.(1973).Pupillaryand cardiacactivityduringvisualattention. Psychophysiology 10 270…294. Partala,T.,Jokiniemi,M.,&Surakka,V.(2000).Pupillaryresponsesto emotionallyprovocativestimuli.In Eyetrackingresearch&application:Proceedingsofthe2000symposiumoneyetrackingresearchand applications (pp.123…129).NewYork:ACMPress. Steinhauer,S.R.,Boller,F.,Zubin,J.,&Pearlman,S.(1983).Pupillary dilationtoemotionalvisualstimulirevisited. Psychophysiology 20 S472.[Abstract]. Steinhauer,S.R.,Siegle,G.J.,Condray,J.,&Pless,M.(2004).Sympatheticandparasympatheticinnervationofpupillarydilationduring sustainedprocessing. InternationalJournalofPsychophysiology 53 77…86. (R eceived July17,2007;A ccepted November9,2007)Thepupilasameasureofemotionalarousal 607