Carrasco, M. & Chang, I. (1995). The interaction of objective and subjective organizations in a localization search task. Perception & Psychophysics, 57 (8), 1134-1150.

We investigated how both objective and subjective organizations affect perceptual organization and how this perceptual organization, in turn, influences observers' performance in a localization search task. Two groups of observers viewing exactly the same stimuli (objective organization) performed in significantly different ways, depending on how they were induced to parse the display (subjective organization). In Experiments 1 and 2, the observers were asked to descibe the location of a tilted target among a varying number of vertical or horizontal distractors. Subjective organization was induced by instructing observers to parse the display into either three horizontal regions (rows) or three vertical regions (columns). The position of the targer was critical: location performance, as assessed by reaction time and errors, was consistently impaired at the locations adjacent to the boundaries defining the regions, producing what we refer to as the subjective boundary effect. Furthermore, te extent of this effect depended on whether the stimulus-driven and sonceptually driven information concurred or conflicted. This made location information more or less accessible. In Experiment 1, the strength of objective grouping was a function of the proxmity of the items (near ot far conditions) and their orientation in a 6 x 6 matrix. In Exeriment 2, the strength of objective grouping was a function of similarity of color (items were color coded by rows or columns) and the orientationof the items in a 9 x 9 matrix. The subjective boundary effect was more pronouced when the display promoted grouping in the direction orthognal to that of the task (e.g., when observers parsed rows but vertical distractors were closer together [Experiment 1] or were color coded [Experiment 2] to induce global rows). A localization search tak proved to be an ideal forum in which objective and subjective organizations interacted. We discuss how these results indicated that observers' performance in a localization task was determined by the interaction of onjective and subjective organizations, and that the resulting perceptual organization constrained coarse location information.