Visual search without attentional displacement

The time needed to search for an object in a complex environment increases with the number of distracting stimuli, a phenomenon known as the "set-size effect." This observation has led to the view that, during visual search, several attentional shifts are performed, suggesting that visual information is processed serially. In an attempt to find direct evidence for such attentional shifts, we implemented several dual tasks combining a covert visual search (CVS) task or a cued target detection task with a character reporting task which allowed us to determine, a posteriori, the attentional allocation. We found that, in the cueing task, subjects preferentially reported characters displayed at different locations, demonstrating that the attention spotlight actually shifted in this condition. In contrast, in both feature and conjunction CVS, subjects predominantly reported several characters flashed at the same location, whatever the delay between their presentations, indicating that, despite a clear "set-size effect," attention remained static. These results demonstrate that CVS can be performed without shifting attention and that the "set-size effect" does not necessarily attest that visual information is processed serially. The present study therefore supports the hypothesis that parallel mechanisms are involved in visual information processing during visual search, in agreement with previous theoretical studies.