Abstract: To investigate temporal dynamics of the spatial scaling of attention during visual search, event-related potentials (ERPs) were measured in young subjects who performed a search task in which the search array was preceded by valid cues that varied in size and hence in precision of target localization. The effects of cue size on P1 and N1 components, and the time course of these effects with variation in cue-target stimulus onset asynchrony (SOA), were examined. Reaction time (RT) to discriminate a target was prolonged as cue size increased. The amplitudes of the posterior P1 and N1 evoked by the search array were affected in opposite ways by the size of the precue: P1 amplitude increased whereas N1 amplitude decreased as cue size increased, particularly following the shortest SOA. The results showed that when top-down information about the region to be searched was less precise (larger cues), RT slowed and the neural generators of P1 became more active, reflecting the additional computations required in changing the spatial scale of attention to the appropriate element size to facilitate target discrimination. In contrast, the decrease in N1 amplitude with cue size may reflect the broadening of the spatial gradient of attention. The results provided electrophysiological evidence that changes in the spatial scale of attention modulate neural activity in early visual cortical areas and activate at least two temporally-overlapping component processes during visual search.

Key words: event-related potentials (ERPs), visual attention, spatial scale, precues