The deployment of spatial attention among multiple targets

The present study explored the deployment of visual attention among multiple targets as a function of their position (same or opposite hemifield) within the visual array. Twentythree participants were presented with circular search arrays (70 ms of exposure time) that contained one or two targets (numbers or letters) among distractors. In the double target condition, the two targets could appear in the same or in opposite hemifields. Target identification performance as well as ERPs to the onset of the visual array were measured. The percentage of double target reports was generally higher for targets presented in opposite, compared to the same, hemifields, indicating that competition between multiple targets increases within the same hemifield, consistent with prior findings. Interestingly, the early lateralized N2pc was clearly modulated by the number of targets identified as well as their spatial position in the array. The largest N2pc was measured when two targets were identified within the same hemifield, whereas the smallest one for two targets in opposite hemifields. Moreover, N2pc amplitude for single target reports was not affected by the actual number of targets in the array (one vs. two), consistent with the hypothesis that this early lateralized ERP component solely reflects top-down visual selective attention.