Eye movements and the span of the effective stimulus in visual search

The span of the effective stimulus during visual search through an unstruct ured alphanumeric array was investigated by using eye-contingent-display ch anges while the subjects searched for a target letter. Ln one condition, a window exposing the search array moved in synchrony with the subjects' eye movements, and the size of the window was varied. Performance reached asymp totic levels when the window was 5 degrees. In another condition, a foveal mask moved in synchrony with each eye movement, and the size of the mask wa s varied. The foveal mask conditions were much more detrimental to search b ehavior than the window conditions, indicating the importance of foveal vis ion during search. The size of the array also influenced performance, but p erformance reached asymptote for all array sizes tested at the same window sizer and the effect of the foveal mask was the same for all array sizes. T he results indicate that both acuity and difficulty of the search task infl uenced the span of the effective stimulus during visual search.