An ERP study on visual spatial priming with peripheral onsets.

Visual event-related potentials were measured for peripheral target stimuli that were preceded by a peripheral square. Targets appeared either at the same location as the square or in the opposite visual hemifield. In Experiment 1, 75% of the trials were same-location trials, and in Experiment 2, same- and opposite-location trials were equiprobable. The subject's overt response was dependent either on the identity or on the location of the target. In both experiments, opposite-location targets elicited an enhanced P1 at posterior electrodes ipsilateral to the position of the letter. This enhancement may be due to a sensory inhibition of same-location targets. Same-location targets elicited an enhanced negativity between 130 and 300 ms, with a first peak located parietally and a second peak broadly distributed over midline electrodes. This effect was larger in Experiment 1 than in Experiment 2 and is interpreted as enhanced processing of same-location targets due to an attentional orienting process elicited by the peripheral square.