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Paper   IPM / Cognitive Sciences / 7443
School of Cognitive Sciences
  Title:   Interhemispheric visual interaction in a patient with posterior callosectomy
1.  S.R. Afraz
2.  L. Montaser Kouhsari
3.  M. Vaziri Pashkam
4.  F. Moradi
  Status:   Published
  Journal: Neuropsychologia
  No.:  5
  Vol.:  41
  Year:  2003
  Pages:   597-604
  Supported by:  IPM
The role of anterior corpus callosum in visual interactions was investigated in a partial split brain patient (MD) whose posterior and middle parts of the corpus callosum where surgically resected, and only anterior portion of corpus callosum was spared. We tested three different visual tasks. In our first experiment we tested a crowding paradigm in MD. Crowding is an attentional location selection task in which recognition of a visual target is impaired when flanked by other similar visual stimuli (distractors). We found that although primary visual areas of the two hemispheres are disconnected in MD, visual distractors presented to one hemispheres can impair recognition of the target stimulus presented to the other hemisphere in our patient. In the second experiment the same crowding task with texture defined stimuli, which are not detected by subcortical structures, were tested. Again an interhemispheric interaction was found, confirming the role of the remained cortical commisures in transferring distractor information. We also replicated a classic match-to-sample task, to ensure that simple visual properties of a stimulus can not transmit through the sparing part of the corpus callosum in MD. At last we tested a visual search as an attentional object selection task in MD and five normal subjects. In contrast with the crowding results, opposite hemifield distractors had no deleterious effect on visual search. Considering the dissociation between these two tasks, we conclude that anterior corpus callosum contributes to interhemispheric interactions in attentional selection of location.

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