The effects of stimulus-driven attention on subjective organization

Background: Perceptual organization results from objective (stimulus-driven) and subjective (task-driven) organization. Objective organization is derived primarily from bottom-up gestalt principles; subjective organization can be considered a top-down attentional process. In a localization search task, a Subjective Boundary Effect (SBE) indicates that performance is impaired when the target appears at locations adjacent to subjective boundaries, which are induced by the task instruction (e.g., report whether the target appeared on the left, middle or right three columns; Carrasco & Chang, 1995). Goal: To pinpoint the level of visual processing at which the SBE is established, we investigated whether stimulus-driven covert attention would attenuate the SBE. We assessed the effect of a transient, peripheral pre-cue on overall performance in a localization task, and on the SBE, in particular. Methods: In a 2-IFC task, observers searched for a tilted (45°) line among vertical or horizontal distracters and indicated which interval contained the target. Prior to each interval, a pre-cue indicated either both target location and display onset (peripheral cue) or just the display onset (neutral cue). Subjective organization was controlled by instructing observers to parse the display vertically. Objective organization was reinforced using the gestalt principles of proximity, good continuation and color, and could either be parallel or orthogonal to the direction of the subjective organization. These configurations are known to minimize and maximize the SBE, respectively. Results & Conclusions: There was an overall effect of attention, observers performed more accurately and faster in the peripheral pre-cue condition. The SBE emerged for all configurations of subjective and objective organization; however, the peripheral pre-cue did not attenuate the SBE. The resilience of this phenomenon suggests that the SBE is established in early visual processing.