Neural suppression of distractors surrounding the spotlight: Evidence from steady-state visual evoked potentials

The present study investigated the allocation of spatial attention using steady-state visual evoked potentials (SSVEPs). The SSVEP is elicited in visual cortical areas by a repetitive flicker having the same fundamental frequency as the driving stimulus. Two flickers were applied with the letter stream presented in the center of the monitor and the distractor presented on either the left or right side of the target. Participants were instructed to detect the target letter in the letter stream. The distance of the two flickers was manipulated. The results show that the amplitudes of the SSVEPs elicited by the distractor were enhanced when it was in the closest position and suppressed when it was at a farther distance. But the amplitudes rebounded at the farthest distance. Meanwhile, the SSVEP elicited by the target flicker remained stable independent of the distance of the distractor. Thus, the present study indicates that focused attention involves neural suppression surrounding the classic “spotlight”, and the SSVEP paradigms open new avenues for studying the attentional suppression mechanism.