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.