DOES SO-CALLED INTERHEMISPHERIC-TRANSFER TIME DEPEND ON ATTENTION

To our knowledge none of many past attempts to experimentally modulate the crossed-uncrossed differential (CUD) or so-called ''interhemisphe ric transfer time'' derived from appropriate visual reaction time expe riments has ever succeeded. The present 4 experiments were designed to establish that (a) under normal attentional constraints, significant CUDs would be obtained, but that (b) lateral mobilization of attention by probabilistic (valid and invalid) cuing as to target location woul d significantly and systematically alter the CUDs. In a baseline exper iment, a significant CUD was obtained. In Experiments 2-4, CUDs were r endered nonsignificant by probabilistic cuing. Specific experimental c onditions generally did not significantly influence the CUD in a syste matic direction. In only one of many analyses of those results did an experimental effect on the CUD reach significance: In Experiment 3 int rasubject mean reaction times yielded a significant complex dissociati on of CUDs as a function of type of cuing (valid or invalid) and stimu lus onset asynchrony. It was concluded that the CUD can be significant ly modulated by target location ruing, but only under very specific co nditions. The direction of the trends in all the experiments, and in t he significant finding, suggests that the CUD component that is most m arkedly influenced by such cues is a postcallosal, motor component.