Time-course change in attentional resource allocation during a spot-the-difference task: investigation using an eye fixation-related brain potential

During a visual search, attentional resources are allocated to various items until a target is detected. However, whether there is a time-course change in the allocation of attentional resources prior to detection of the target is unclear. In the present study, we measured an eye fixation-related brain potential (EFRP) while participants performed a spot-the-difference task to investigate the time-course change. Participants were presented with upright or inverted pairs of photographs consisting of two cooking-area photographs in which only one element was different, and they were asked to search for the different element (a target location) and to press a button as quickly and accurately as possible when they found it. A P1 amplitude in the EFRP, affected by attention, at a fixation that occurred just before the button was pressed was larger compared to those at the others. This result indicated an increase in attentional resources allocated to the target. In addition, the P1 amplitude increased in the third fixation from the stimulus presentation only when the stimulus was presented upright. These results suggest that the allocation of attentional resources prior to target detection is not constant.