The role of the corpus callosum in visual orienting: importance of interhemispheric visual transfer

In a tachistoscopic visual search task, the effects of ipsi- and contralateral distractors on target search were investigated in two complete commissurotomy patients. Pop-out distractors slowed the search for contralateral targets in both patients, i.e. search was not independent in both hemifields. In normals, we previously observed an extinction-like asymmetry in that distractors in the right visual hemifield interfered with target search in the left visual hemifield, but not vice versa. This pattern was also found in one of our patients, N.G., whereas the other, L.B., showed a reversed laterality effect. While N.G. is able to transfer visual shape information between hemispheres, L.B. is not. The data suggest that the reversal of the contralateral distractor asymmetry in L.B. is due to the disruption of ipsilateral visual input to the right hemisphere.

[1]  K. Heilman,et al.  Right hemispheric dominance for mediating cerebral activation , 1979, Neuropsychologia.

[2]  Kenneth M. Heilman,et al.  Hemispace and Hemispatial Neglect , 1987 .

[3]  M. Kinsbourne.  Mechanisms of Unilateral Neglect , 1987 .

[4]  Stefan Pollmann,et al.  A pop-out induced extinction-like phenomenon in neurologically intact subjects , 1996, Neuropsychologia.

[5]  M. A. Steinmetz,et al.  Neurophysiological evidence for a role of posterior parietal cortex in redirecting visual attention. , 1995, Cerebral cortex.

[6]  M. Mesulam.  A cortical network for directed attention and unilateral neglect , 1981, Annals of neurology.

[7]  Steven A. Hillyard,et al.  Independent Attentional Scanning in the Separated Hemispheres of Split-Brain Patients , 1994, Journal of Cognitive Neuroscience.

[8]  G. Rizzolatti,et al.  Afferent properties of periarcuate neurons in macaque monkeys. II. Visual responses , 1981, Behavioural Brain Research.

[9]  Larry E. Johnson.  Bilateral visual cross-integration by human forebrain commissurotomy subjects , 1984, Neuropsychologia.

[10]  J. Bogen,et al.  Completeness of callosotomy shown by magnetic resonance imaging in the long term. , 1988, Archives of neurology.

[11]  K. Heilman,et al.  Right hemisphere dominance for attention , 1980, Neurology.

[12]  Jordan Grafman,et al.  Handbook of Neuropsychology , 1991 .

[13]  J. Wolfe,et al.  Guided Search 2.0 A revised model of visual search , 1994, Psychonomic bulletin & review.

[14]  M. Jeannerod.  Neurophysiological and neuropsychological aspects of spatial neglect. , 1987 .

[15]  J. Sprague,et al.  Interaction of Cortex and Superior Colliculus in Mediation of Visually Guided Behavior in the Cat , 1966, Science.

[16]  E. Zaidel,et al.  Letter Matching within and between the Disconnected Hemispheres , 1994, Brain and Cognition.