Cortical slow potentials in verbal and spatial tasks--the effect of material, visual hemifield and performing hand.

Fifteen right-handed students voluntarily initiated the tachistoscopic presentation of visual stimuli containing either verbal (abstract words) or spatial (stereogeometric figures) material. Subjects had to reproduce stimulus material which had been presented either in their right or their left hemifield of vision by writing or drawing, either with their right or their left hand. Material-specific effects were found during the reproduction period: amplitudes of the performance-related negative potential shifts were larger in parietal and occipital recordings (P4, O1, and O2) when drawing as compared to writing. The opposite was true in frontal and left central leads (F3, F4, and C3) where writing was associated with larger negative amplitudes than drawing. Although subjects were informed about the nature of the forthcoming stimulus before voluntarily initiating the task, material-specific effects were missing in the preparation period. The performing hand had an influence on potentials in central leads, whereas hemifield of vision had no effect on preparation- and performance-related slow potential shifts.