Asymmetries of the contingent negative variation (CNV) and its after positive wave (APW) related to differential hemispheric involvement in verbal and non-verbal tasks.

The CNV and the subsequent positive wave (including both the P300 wave and the slow positivity following it) were recorded at left and right frontal and central electrodes during the performance of tasks in which nine right-handed subjects (male and female) had to determine whether S1 and S2 were the same or different. In one task, works had to be matched for meaning while in a second, faces had to be matched for identity. Words elicited CNVs which were more negative over left than right frontal regions. This effect was reversed when the stimuli were faces. Since the CNV is presumed to reflect processes of anticipation rather than stimulus processing, the asymmetry cannot be explained in terms of the lateralisation of neural mechanisms specialised for the analysis of verbal or visuospatial stimuli. Instead the observation is regarded as evidence for mechanisms of lateral activation of a more general nature than would be necessary for the facultative selection of cognitive mode. The amplitude of the CNV relative to baseline was affected by the amplitude of P300 response to S1. This was larger to faces than words in both hemispheres. A small asymmetry in the positive wave following S2 was observed, the amplitude being greater over the right hemisphere for words and over the left for faces. This is interpreted in terms of the subjective probability of the two types of stimulus for a hemisphere ill-equipped to receive them.