Hemispheric lateralization of event-related potentials in a cued reaction-time task

Subjects were tested in a cued reaction-time task wherein warning stimuli (S1) of 5-letter words or dot patterns inter-mixed across trials were briefly presented. After 2 sec a second stimulus (S2) of th same category as the S1 appeared and the subject pressed a key with the left or right hand. The right key was pressed if S2 was a synonym of S1 or if the second dot pattern was the same as the first. The left key was pressed for antonyms or different patterns. It was predicted that CNVs would be larger over the left than right hemisphere on word trials and vice-versa on pattern trials in accordance with speculations concerning hemispheric specialization. The CNV was lateralized as expected, most prominently on pattern trials. In addition a negative transient evoked by S2, and a late negative post-imperative slow wave were similarly lateralized. P300 waves were very large and largest to the S2 when it differed from S1. Factor analysis confirmed these results and indicated, in addition, that P300 was larger in the hemisphere least relevant to the task.