Search performance with discrete-cell stimulus arrays: filtered naturalistic images and probabilistic markers.

In order to partially fill the gap between search studies with artificial and naturalistic stimuli, experiments with segmented and spatially filtered images of real stimuli in the discrete cells of search arrays were conducted. RT × set size functions obtained with the spatially filtered arrays were compared with those obtained with geometric and other types of arrays. With the aid of Fourier analysis, components of target certainty/uncertainty, target-distractor similarity/dissimilarity, and distractor homogeneity/heterogeneity were evaluated for their effects on search performance and efficiency. The comparative effects of valid/invalid and ambiguous/unambiguous markers of search items were included in the experiments to probe the potential contributions of top-down and bottom-up control to search with naturalistic stimuli. Visual coding in the form of spatial frequency passbands and top-down preferences for distractor search were used to explain the results.