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Michael C. Granovetter, Leah Ettensohn, Marlene Behrmann; Stable visual discrimination behaviors in hemispherectomy patients. Journal of Vision 2020;20(11):1188. doi: https://doi.org/10.1167/jov.20.11.1188.
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Patients with pharmacoresistant epilepsy can undergo cortical resection to remove epileptogenic tissue and alleviate seizures. In extreme cases, a hemispherectomy can be performed, in which an entire cerebral hemisphere is resected or disconnected. Notably, if the procedure is performed before adulthood, overall cognitive functioning may remain intact. However, there has been no systematic investigation profiling visuoperceptual abilities of this patient population. In this study, 16 patients (6- to 34 years-old) with either a left or right hemispherectomy performed a task in which two consecutive stimuli (words in one condition, faces in another) were presented at central fixation. Participants reported, with a keypress, whether stimulus pairs were identical or different. 55 age- and gender-matched controls also performed the task, but with stimuli presented in the left or right visual fields to restrict immediate stimulus processing to a single hemisphere. Crawford & Howell statistical tests for single-subject neuropsychology cases revealed that, remarkably, 13 of the 16 patients exhibited comparable accuracy on both word and face discrimination compared to controls viewing stimuli in either the left or right visual fields (one such patient actually showed superior accuracy for face discrimination). Linear mixed effects modeling showed no main effect of group (patient versus control) or group by stimulus category (words versus faces) interaction among either left or right hemispherectomy patients. Left hemispherectomy patients did demonstrate significantly longer reaction times for word discrimination than for face discrimination, a difference not observed among controls. That said, comparable accuracies of hemispherectomy patients and controls suggest that development of a single hemisphere might be sufficient for word and face processing, thought to be the product of the left and right hemisphere, respectively, in typical controls. Future work will examine hemispherectomy patients’ performance on other tasks thought to reflect hemispheric lateralization, such as global/local precedence and spatial frequency processing.
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