AN ABSTRACT OF THE THESIS OF Rafael Robles for the degree of Master of Science in Psychology presented on May 30, 2019. Title: The Lateralization of Emotional Perception. Abstract approved: ______________________________________________________ Frank Bernieri There is consensus among researchers that some form of hemispheric lateralization exists when perceiving emotions. However, conclusions regarding the exact organization have been inconsistent with some studies supporting an overall right hemisphere lateralization and others suggesting differential lateralization for positively and negatively valenced emotions. The main objective of this study was to examine the validity of experimental methodologies generating these conclusions in an attempt to resolve the inconsistencies found across previous works. In the current study, right handed participants (N = 90) completed three experiments testing for visual field biases when perceiving emotional faces as a proxy measure of lateralization. Participants completed a free-view emotional chimeric face task (Experiment 1), a tachistoscopic version of this task (Experiment 2), and two divided visual field tasks (Experiment 3). A consistent left visual field bias (i.e., right hemisphere lateralization) was found when judging the emotional intensity of positive and negative emotions in both the free-view and tachistoscopic chimeric face tasks. The divided visual field tasks of Experiment 3 uncovered an unexpected right visual field bias (i.e., left hemisphere lateralization) for the emotional face recognition task. These results suggest that judging emotional intensity and recognizing emotions may be distinct processes, though both are under the umbrella of “emotional perception.” ©Copyright by Rafael Robles May 30, 2019 All Rights Reserved The Lateralization of Emotional Perception by Rafael Robles A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented May 30, 2019 Commencement June 2019 Master of Science thesis of Rafael Robles presented on May 30, 2019. APPROVED: Major Professor, representing Psychology Director of the School of Psychological Science Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Rafael Robles, Author ACKNOWLEDGEMENTS The author expresses sincere appreciation to Dr. Bernieri for the hours of meetings and editing, to the members of the Interpersonal Sensitivity Lab for your help and support (tangible and emotional), to Oregon State University’s School of Psychological Science for giving me this opportunity, and to my wife Kelly for supporting me through the many late nights and roadblocks along the way. TABLE OF CONTENTS Page 1 Introduction...……………………………………………………………………… 1 1.1 Lateralization of Facial Perception: From Identity to Emotion....................4 1.2 Is Facial Perception All Right? Right Hemisphere vs Valence Hypothesis.8 1.3 Methodological Considerations……………………………………………9 1.4 Overview of the Current Study…………………………………………...14 2 General Methods.……………………………………………………….…….........16 2.1 Participants………………………………………………………………16 2.2 Apparatus………………………………………………………………...17 2.3 Procedure…………………………………………………………….......17 3 Experiment 1: Free-View Chimeric Face Task……………………………………21 3.1 Method ………………………………………..…………………………21 3.1.1 Free-view chimeric face task……………..….……………………21 3.2 Results………………………………………………………………........27 3.3 Discussion………………………….........................................………….30 4 Experiment 2: Sequential Chimeric Face Task……………………………………31 4.1 Method…….….….………………………………………………………31 4.2.1 Sequential chimeric face task……………………………………...31 4.2.2 Fixation-check.......………………………………………….……..34 4.2 Results.................................................................................................…...34 4.5 Discussion.…………………………………………………………….....36 5 Experiment 3: Divided Visual Field....………………………………….................36 TABLE OF CONTENTS (Continued) Page 5.1 Method...........................................………………………………………38 5.1.1 Word recognition task…………………………………………..38 5.1.2 Emotion recognition task……………....………………………..41 5.1.3 Fixation-check….……………………………………………….44 5.2 Results..........……………………………………………………………44 5.3 Discussion...……………………………………………………………..47 6 General Discussion...................................................................................................48 6.1 Chimeric Test of Lateralization................................................................48 6.2 Order Effects in the Chimeric Face Task..................................................50 6.3 Differential Lateralization in Emotion Perception....................................52 6.4 Limitations................................................................................................54 6.5 Future Directions.......................................................................................56 7 Conclusion................................................................................................................59 Bibliography ………………………………………………………………………..61 Appendix A: Measures………………………………………………………………69 Appendix B: Instructions and Debriefing........................……………………………74 LIST OF FIGURES Figure Page 1. Simple visual field pathway adapted from Bourne (2006)......………………......…2 2. Composite face conditions from Gilbert and Bakan (1973)…..…………………...5 3. Chimeric face example: Female right hemiface and male left hemiface.........….....6 4. Campbell’s (1978) emotional chimeric faces......………………………………….7 5. Experimental chin rest example.....……………………………………………….12 6. Facial photos and edited chimeric displays.............................................................23 7. Free-view chimeric face task (Experiment 1) response screen......……………….24 8. Free-viewing chimeric bias quotient by order and valence…………………........29 9. Stimulus array for sequential chimeric face task (Experiment 2)......….…………33 10. Stimulus array for divided visual field word recognition task (Experiment 3).....40 11. Stimulus array for divided visual field emotion recognition task (Experiment 3)43 12. Divided visual field task accuracy between visual fields for.................................45 emotional face and word recognition tasks LIST OF TABLES Table Page 1. Measures of eligibility and lateralization………………………………….....20 2. Bias quotient scoring example………………………………….....................26 1 The Lateralization of Emotional Perception In 1861, Pierre Broca reported on a patient with damage to their left hemisphere that left them unable to produce speech. Four years later, after assessing 25 additional patients with similar damage and an unaffected patient with an equivalent lesion on the right hemisphere, Broca definitively claimed the left hemisphere was solely responsible for the production of speech (see Berker, Berker, & Smith, 1986 for a translation of Broca's report). This was the first discovery in which the physically symmetrical hemispheres of the cortex were found to be functionally distinct. In the 150 years since, neurological and psychological research has continued to uncover instances of functions that are lateralized to (i.e., dominated by) one hemisphere over the other (Hugdahl, 2005). With each instance, the field of neuropsychology inches closer towards its ultimate goal, “the perfect mapping of the psychological states on cerebral states” (Pierre Feyereisen, 1991, p. 32). As the field progressed, researchers created methodologies other than lesioning to uncover similar lateralized functions. One such methodology involved the selective presentation of information to the left or right visual fields. In order to do so, information was simply presented to either side of a central fixation point. The organization of the visual pathway results in information from each eye traveling through the optic nerve to a central optic chiasm. Here the information from each eye is combined and the left and right visual field are split and sent to contralateral hemisphere (Snowden, Thompson, & Troscianko, 2011). This results in the right 2 hemisphere processing any visual information appearing to the left of center and the left hemisphere processing any information to the right of center (see Figure 1 for a visualization of this pathway). Figure 1. Simple visual field pathway adapted from Bourne (2006). Controlled movements have also been found to have a contralateral neural organization similar to that of visual fields. In an early study, Penfield and Boldrey (1937) applied electrical stimulation to the motor strip right of the cortex. When applied to the right hemisphere muscle movements occurred on the opposite side of the body. In other words, the process of moving one’s left arm originates in right hemisphere and right body movements originate in the left hemisphere. 3 The consistent organization of visual field and movement was used to study split-brain patients by researchers Sperry and Gazzaniga (see Gazzaniga, 1967 for overview). These split-brain patients had undergone a surgical operation to severe the nerve tract that facilitates communication between the left and right hemisphere (i.e., the corpus collosum). This resulted in two separate hemispheres without no method to communicate information to one another. This complete separation of hemispheres resulted in limited use the visual information depending on the visual field