Hemispheric Specialization and Interhemispheric Interaction in Self-Recognition

1. Hemispheric Specialization and Interhemispheric Interaction in Self-Recognition 86.12 Lucina Uddin, Janice Rayman, and Eran Zaidel Department of Psychology, University of California Los Angeles Introduction Results Summary of Main Findings The ability to recognize an image of oneself has often been used as an index of self-awareness. Recently, evidence for hemispheric specialization for self-recognition has been marshaled. Here, we assessed psychophysically the abilities of the two hemispheres to independently discriminate between morphed images containing varying degrees of “self” and investigated whether self-recognition is aided by interhemispheric cooperation. The just noticeable difference (JND) is the minimum amount by which a stimulus intensity must be changed in order to produce a noticeable variation in sensory experience. We apply this concept to evaluate hemispheric competence for discriminating “self” and “familiar” images morphed to various extents. • Subjects were more accurate at “same” judgments in “between” comparisons, but more accurate for “different” judgments in “within” comparisons. • The JND for “self” was same in the “within” and “between” conditions (<50). The JND for “familiar” was smaller in the “within” condition (30<JND<40) than in the “between” condition (40<JND<50). • Both hemispheres show a smaller JND for recognizing “familiar” faces (30<JND<40) than “self” faces (40<JND<50). There were no hemispheric differences in the JNDs for recognizing “familiar” or “self” faces within the resolution of this experiment (morph difference of 10%). Methods Discussion • Participants: 29 (15 female) right-handed UCLA undergraduates. • Stimuli: Two face images were presented simultaneously for 180ms to both hemispheres (“Between VF” condition) or one hemisphere (“Within VF” condition). We used (1) Face images morphed to different extents (0-100%, 10% increments) between the subject and an unknown, gender-matched face (“Self” condition), and (2) morphs between a familiar face and an unknown, gender-matched face (“Familiar” condition). • Self(Familiar)-Unknown Morph Series • Task: Participants completed four blocks (Self-Between VF, Self-Within VF, Familiar-Between VF, Familiar-Within VF), responding bimanually by button-press to indicate whether the two images presented were the “same” or “different”. Half the trials contained two identical images, while the other half contained two different images. Condition x Distance interaction: (F(18, 504) = 2.7, p = 0.002) Our experiment manipulated the distance (morph difference) between the target faces, and used a same/different judgment task. Previous “morph” studies of self-recognition abilities in the cerebral hemispheres have reported right (Keenan, 2000) or left (Turk, 2002) hemispheric biases. Here we demonstrate that though biases may differ, the two hemispheres do not differ in their ability to discriminate subtle differences between morphed self-face images. In a previous same/different study, St. John (1981) showed a LVF advantage in reaction time for same/different comparisons between two faces. Instead, we see no VF differences in discriminating either “self” or “familiar” face images. These results are in general agreement with our previous findings in a face identification paradigm, where both normal subjects and a split-brain patient showed similar abilities to detect self-face images presented to the RVF and LVF. Within VF Only 0%………20%………40%………60%………..80%………100% Conclusions • Interhemispheric interaction does not improve the JND in either the “self” or the “familiar” discrimination tasks. • “Familiar” faces are more easily distinguished than “self” faces (within each cerebral hemisphere). • The RH and LH are equally and independently competent on the “self” face discrimination task. Here, the hemispheres were also equally able to discriminate “familiar” faces. Task: “Same” or “Different”? Between VF: Within VF: References + + • Keenan, J. P., Wheeler, M. A., Gallup, G. G. Jr., Pascual-Leone, A. (2000) Self-recognition and the right prefrontal cortex. Trends in Cognitive Sciences;4: 338-344. • Sperry, R. W., Zaidel, E., Zaidel, D. (1979) Self recognition and social awareness in the deconnected minor hemisphere. Neuropsychologia; 17:153-66. • St. John, R. C. (1981) Lateral asymmetry in face perception. Canadian Journal of Psychology; 35(3):213-223. • Turk, D. J., Heatherton, T. F., Kelley, W. M., Funnell, M. G., Gazzaniga, M. S., Macrae, C. N. (2002) Mike or me? Self-recognition in a split-brain patient. Nature • Neuroscience; 5(9):841-842. Funding NIH Grant R01 NS20187 and NSF Graduate Research Fellowship Contact: lucina@ucla.edu +