Using eye saccades to assess the selectivity of search movements.

The degree of selectivity or guidance underlying search was tested by having subjects search for a target (a red vertical or green horizontal bar) among Similar (red horizontal and green vertical bars) and Dissimilar distractors (blue and yellow diagonal bars). If search is indeed a guided process, then the Dissimilar items should not be given the same scrutiny as elements sharing a feature with the target. The frequency of eye movements directed to the two distractor types was used as an indicator of this scrutiny. The analysis revealed almost equal percentages of saccades to Similar and Dissimilar elements (55% and 45%, respectively). Although indicating some evidence for selectivity during oculomotor search, this finding suggests that simpler and less optimal strategies may undermine the more efficient guided search algorithm.