N2pc and attentional capture by colour and orientation-singletons in pure and mixed visual search tasks

Abstract

The capture of attention by singleton stimuli in visual search is a matter of contention. Some authors propose that singletons capture attention in a bottom–up fashion if they are salient. Others propose that capture is contingent upon whether or not the stimuli share task-relevant attributes with the target. This study assessed N2pc elicited by colour and orientation singletons in a mixed task (the singleton defined as target changed block-to-block), and a pure task (the target was the same across the whole task). Both singletons elicited N2pc when acting as targets; when acting as non-targets, orientation singletons elicited N2pc only in the mixed task. The results suggest that the singletons were not salient enough to engage attention in a purely bottom–up fashion. Elicitation of N2pc by non-targets in the mixed task should be attributed to top–down processes associated with the current task. Stimuli that act as targets in part of the blocks become not completely irrelevant when non-targets