Effects of Pointing Direction and Direction Predictability on Event- related Lateralisations of the EEG

In two experiments, we investigated hemispheric EEG differences in 9(12) healthy volunteers during pointing to lateral and central targets. The questions addressed were whether horizontal pointing direction and the predictability of pointing direction modulated hemispheric differences (event-related lateralisations of the EEG = ERLs). To vary pointing direction predictability, targets were displayed either randomly at one of nine different positions on a screen (‘random’) or at the same horizontal position in five subsequent trials (‘sequenced’) while vertical positions varied randomly. ERLs varied with pointing direction. This was true across changes in target eccentricity and pointing distance. Foci of the ERLs were in premotor, motor and parietal cortex, reflecting the critical involvement of these areas in the control of visually guided reaching. Direction predictability reduced the parietal ERL before pointing onset, probably reflecting a lesser effort in visuomotor transformation. Predictability also added an additional component to the early ERLs after target onset and increased direction effects during movement.