FATE OF NEGLECTED TARGETS - A CHRONOMETRIC ANALYSIS OF REDUNDANT TARGET EFFECTS IN THE BISECTED BRAIN

The authors examined some of the sensorimotor effects of the split-bra in operation to understand how a ''dual mind'' can produce unified beh avior. They report psychophysical evidence of extinction to bilateral simultaneous stimulation in callosotomy patient J.W.: Although he coul d verbally report the occurrence of a unilateral left br right visual field target, left field report accuracy dropped by 34% when targets o ccurred bilaterally. Paradoxically, the same stimulus conditions produ ced abnormally robust redundant signal effects on simple manual and vo cal reaction times, which exceeded predictions that were based on prob ability summation. Neural summation is often inferred from redundancy gain of this magnitude. Because this seems less likely after callosoto my, the authors suggest a model that is based on response competition between the disconnected hemispheres to account for J.W.'s redundant t arget effects. The dissociation between explicit report and motor perf ormance is discussed.