Saccade selection in visual search: evidence for spatial frequency specific between-item interactions

We present two experiments in which subjects were required to make a saccade to a target amongst distractors. Targets were oriented Gabor patches. Analysis of errors, when subjects fail to make a saccade to the target, showed two interesting features. First, most error saccades were directed towards a distractor and not to the blank space between distractors. This suggests that although the location of the target may not be encoded correctly, the locations of the items in the display are encoded. Second, when the display items were all of the same spatial frequency, a long-range effect occurred whereby the likelihood of an error saccade in a specific direction decreased systematically as the distance from the target increases. This systematic influence of the target location extended over practically the whole display. The long-range effect appeared whenever all display items had the same spatial frequency and showed little dependence on the spatial frequency of the display items. However, when the items had different spatial frequencies the long-range effects were absent.