Covert object recognition at large visual eccentricity

Abstract

Numerous studies have shown quantitative and qualitative differences between foveal and peripheral vision but few studies have investigated object recognition beyond 20í. With natural scenes as stimuli Thorpe et al. (1999) reported that human subjects were able to detect the presence of an animal with a performance of 70% correct at an eccentricity of 60íbut no identification was required. We investigated explicit and covert object recognition at large visual eccentricities (30 and 60í). Covert recognition was tested by means of a priming task. In a first block of trials subjects were presented with 48 pictures of objects that they had to categorize as animal or not. Pictures were displayed randomly left or right of fixation for 80 msec each. In block 2 subjects were presented randomly with the same pictures (perceptual priming), with same name-different shape pictures (semantic priming) and with new pictures. Two groups of 12 subjects were tested at 30í and 60í respectively (for both blocks). Explicit recognition was tested in a third group at 60í. Subjects were asked to categorize pictures as animal or not in block 1. In block 2 they were asked to decide whether the picture had been presented in the first block. Both perceptual and semantic priming occurred at 30í. Only perceptual priming was observed at 60í (83% correct for identical pictures). Explicit recognition was very poor at 60í (58.3% correct). These results show that, though subjects experience difficulties to recognize pictures, covert recognition occurs at large eccentricities. E-mail: [email protected]