"The Influence of Pre-Attentive Processing
of Illusory Contours on Crowding"

Abstract of a paper by Naveen Krishnan

What is the neural basis of conscious awareness? Some studies have suggested that consciousness occurs very early in processing. However, numerous studies have demonstrated that extensive processing can occur in the absence of conscious awareness. I explored the amount of processing that can occur in the absence of conscious awareness by means of the "crowding" effect, in which flanking distractors make it harder to identify a peripherally presented target (He et al. 1996; Ramachandran et al. 1998). He et al have suggested that crowding is due to the limited resolution of visual attention. Physiological recordings and studies of patients with neglect suggest that illusory contours may arise at an early stage of perception, prior to attention. To determine whether illusory contour perception occurs before attention, I tested twenty subjects with four open or closed Pac-men stimuli that would corm either an illusory contour (IC) or an amodally completed (AC) rectangle, either crowded (IC-C, AC-C) or non-crowded (IC-NC, AC-NC). If IC perception preceded crowding, subjects should be better in the IC condition than in the AC condition. To assess the magnitude of crowding, our observers judged whether rectangles of different aspect ratios were "taller" or "wider." Performance was similar on IC-NC and AC-NC trials. However, performance on AC-C trials was significantly impaired relative to non-crowded trials. In the critical IC-C condition, performance was significantly better than in the AC-C condition. These results show that crowding occurs late in processing, and that extensive processing can occur in the absence of conscious awareness.

Senior Level, First Place, Naveen Krishnan; Torrey Pines High School, Grade 11.
Advisor: Victoria Coordt

Naveen Krishnan