Attention and oculomotor control: a high-density ERP study of the gap effect

In a gap paradigm, healthy adult subjects performed visually triggered saccades to peripheral targets either with the fixation stimulus remaining on (overlap trials) or going off before target onset (gap trials). All subjects showed faster reaction times in the gap trials (the gap effect). High density scalp event-related potentials were recorded time-locked to both the target stimuli and the eye movement onset. We observed three neural correlates of the gap effect: (i) a prefrontal positivity that precedes the target presentation which may reflect specific preparatory processes, (ii) an enhancement of the early cortical visual responses (PI) to the peripheral target in the gap trials, and (iii) a prolongation of parietal activity in the overlap trials relative to the gap trials prior to the saccade execution. These results suggest that several factors contribute to the gap effect, each having its own neural basis.