Self-recognition: Lessons from the split-brain Lucina Uddin, Janice Rayman, and Eran Zaidel

1. Self-recognition: Lessons from the split-brainLucina Uddin, Janice Rayman, and Eran Zaidel Department of Psychology, University of California Los Angeles Introduction Results: Chi square Results: Signal Detection A response was considered a “target-present” response if the subject responded “self” in the self block or “familiar” in the familiar block. Images morphed towards “other” more than 50% were designated as “target-absent” trials. Self-recognition may be an indicator of self-awareness (Keenan, 2000). To what extent is the ability to self-recognize lateralized in the human brain? The split-brain offers a unique opportunity to independently probe the abilities of the two cerebral hemispheres. In this study, tachistoscopic presentation was used to present morphed self-face images randomly to the right or left visual field (VF) in patient N.G. in order to assess rigorously the lateralization of self-recognition using two different statistical methods (hierarchical chi square and signal detection). • The subject showed a significant bias to respond “yes” to the presence of the target (54.7%, 2(1) = 11.88, p < 0.001). • The subject responded “yes” more frequently in the “familiar” task (64.2%) than in the “self” task (45.1%, 2(1) = 49.98, p < 0.001), but only when the stimulus was in the RVF (82%, 2(1) = 38.81, p < 0.001).* Methods • Participant: We tested patient N.G., a 70-year-old woman who underwent complete forebrain commissurotomy in 1963 to alleviate intractable epilepsy (Bogen and Vogel, 1976). • Stimuli: Face images morphed to different extents (0-100%, 5% increments) between the subject and an unknown, gender-matched face (“self” condition) and morphs between a familiar face and an unknown, gender-matched face (“familiar” condition) were used. Images were presented randomly to the RVF or LVF for 180ms. The subject was tested over six sessions, with 672 images presented per session. • Task: The patient responded unimanually and was instructed to press one button on a response box if the image presented looked more like an image of “self (familiar)”, and another button if the image looked more like “an unknown other face.” • Data Analysis: Data from uncrossed responses (congruent response hand and VF) were analyzed using a hierarchical chi square analysis (Winer, 1991). Additionally, signal detection analysis was used to compute d' as a measure of sensitivity of detection of “self” or “familiar” stimuli, independently of bias. *significant as 1-tailed z-scores, p < 0.05 • The effect of morph interval differed for the two tasks (2(20) = 42.78, p < 0.005). Responses in the “self” task followed an orderly descent as the stimuli contained less “self” and more “other”. Discussion Previous work has suggested a double dissociation wherein the disconnected left hemisphere (LH) shows a recognition bias for self, and the right hemisphere (RH) shows a bias for familiar others (Turk, 2002). Instead, our chi square analysis shows that the LH exhibits a general “yes” bias, which is even more pronounced in the “familiar” recognition task. This may be interpreted as an inability of the disconnected LH of N.G. to perform the “familiar” task. By contrast, it appears that the RH of this patient can do both the “self” and “familiar” tasks. The previously reported selective LH bias for self is not supported in our data. Our signal detection analysis does reveal a selective deficit in the LH for detecting familiar face stimuli. Conclusions • In the “familiar” task, this orderly progression was weaker for responses to LVF stimuli, and absent for RVF stimuli, producing a Task, VF, and Morph Interval interaction (2(20) = 39.05, p < 0.01). Both hemispheres of this patient are independently capable of self-recognition, though they may have different decision criteria. This patient’s LH is superior in self-recognition. The ability to recognize familiar others seems to be limited to the RH of this patient. Task: Self (Familiar) or Other? References • Bogen, J. E., Vogel, P. J. (1976) Neurological status in the long term following complete cerebral commissurotomy. In Les Syndromes de Disconnexion • Calleuse Chez L’Homme. Hopital Neurologique, Lyon, 69394. • 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. • 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. • Winer, B. J., Brown, D. R., Michels, K. M. (199) Statistical Principles in Experimental Design, 3rd ed., Boston, MA, McGraw-Hill. • Zaidel, E., Iacoboni, M., Zaidel, D. W., & Bogen, J. The callosal syndromes. In K.M. Heilman & E. Valenstein, E. (Eds.) Clinical Neuropsychology, 4th • Edition. New York: Oxford University Press: 347-403. + 180ms Contact: lucina@ucla.edu +