Elias R, Stanley, D & Carrasco
M (2002, May). The effects of stimulus-driven attention on subjective
organization. Vision ScienceS Society, Sarasota, FL. 488-B4.51.
Background: Perceptual organization has two components, objective (or
stimulus driven) organization and subjective (or task-driven) organization.
Whereas objective organization is derived primarily from bottom-up gestalt
principles, subjective organization can be considered as a top-down, attentional
process. It has been shown that in a localization search task, performance
is consistently impaired when the target appears at locations adjacent
to boundaries induced by task instruction (i.e., the way observers were
instructed to parse the display). This effect is termed the Subjective
Boundary Effect (SBE; 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
a localization performance task, in general, and on the SBE, in particular.
Methods: Twelve observers performed a localization visual search task,
searching for a tilted (45°) line among vertical or horizontal distracters.
Observers indicated the interval that contained the target (2-IFC task).
Subjective organization was controlled by instructing observers to parse
the display vertically. Objective organization was strongly 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 have been shown to minimize and maximize
the SBE, respectively.
Results & Conclusions: The SBE was replicated in all experiments. There
was an overall effect of attention, observers performed more accurately
and faster in the peripheral pre-cue than the neutral pre-cue condition.
However, for all configurations of subjective and objective organization
tested, the peripheral pre-cue did not attenuate the SBE. The resilience
of this phenomenon suggests that the SBE is established in early visual