Functional cerebral asymmetry and performance II. Individual differences in reaction time to word and pattern stimuli triggered by asymmetric alpha bursts.

The difference in mean square values of EEG alpha in left and right hemispheres recorded from parietal scalp regions of 5 female and 6 male human Ss was used to trigger 50 msec presentations of words or random dot patterns, and reaction times to correctly detected target stimuli were obtained. In 9 of 11 Ss the effect of left and right triggering was opposite for word and pattern stimuli, although in only 4 Ss were results consistent with a simple interpretation of alpha as an "idling" rhythm. The results support the hypothesis of complementary hempheric specialization and indicate that overt performance depends on the state of functional cerebral asymmetry.