Redundancy gains for visual search after complete commissurotomy

Redundant-targets effects (RTE) for visual search were investigated in 2 co mmissurotomy patients (L.B., N.G.). L.B., who showed no evidence of visual interhemispheric transfer, exhibited a paradoxical enhancement of the redun dancy gain in the bilateral compared with the within-hemifield redundant-ta rgets conditions, whereas N.G., who showed evidence of interhemispheric tra nsfer of visual information, exhibited no enhancement of the bilateral redu ndancy gain. When only uncrossed responses were considered, both bilateral and within-held RTE were evident only when attentional demands were high. B ilateral redundant targets led to stronger gains, some indicative of coacti vation, in the slower response hand. The authors suggest that the enhanceme nt of the bilateral RTE comes about by neural coactivation, which is especi ally pronounced when the slower hemisphere elicits the response.