The overlay interference task and object-selective visual attention

A series of experiments was carried out to examine object-based visual attention in an interference task. Observers were presented with two transparently overlapping equilateral triangles forming a "Star of David". One of these triangles was darker than the background, the other was lighter than the background. The observers were required to make a speeded choice response to the orientation of the darker triangle. The presence of the light triangle produced a robust interference effect that manifested as a slower response time. This effect was strongly modulated by the relative contrast of the target and distractor triangles. It was reduced when the light distractor triangle was separated in depth from the target triangle. Since the configuration rules out the possibility of 2-D spatial selection, it is concluded that object-based selection occurs in interference tasks and that the effectiveness of this selection is modulated by visual attributes that are not directly relevant to the task.