Stimulus segmentation in the visual search task

Four experiments were conducted in order to study the segmentation process in a visual search task with relevant stimuli (target and distracters) rand omly distributed among textural elements. The basic idea was that a paralle l segmentation process of the relevant stimuli would contribute to the over all reaction time independently of the contribution of the number of releva nt stimuli. In the first experiment, with relevant stimuli and textural ele ments that differed in the orientation of their component Lines, texture pr esence interacted with number of relevant stimuli and with target presence. These results were not favorable to the parallel segmentation hypothesis. In the second and third experiments, in which the relevant and the textural stimuli differed in orientation and in the luminance contrast of their com ponent lines, the results support a parallel segmentation process for the h igher contrast conditions. In these experiments, the effect of texture pres ence was greater on target-absent than on target-present trials. Experiment 4 shows that the search can be restricted to the high-contrast relevant st imuli when the number of these stimuli is constant and the number of textur al stimuli changes from trial to trial. The present results suggest that th e relevant stimuli can be segmented in parallel and then submitted to a res tricted analysis, even when they are scattered among textural stimuli.