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| Paper IPM / Cognitive / 7495 |
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| Abstract: | |
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When a single moving stimulus is presented in the peripheral visual field, its direction of motion can be easily distinguished, but when the same stimulus is flanked by other similar moving stimuli, observers are unable to report its direction of motion. In this condition, known as 'crowding', specific features of visual stimuli will not access conscious perception. The aim of this study was to investigate whether adaptation of high-level motion-processing areas is preserved in crowding conditions. Logarithmic spirals, similar to those used by Cavanagh and Favreau (1980 Perception 9 175 - 182) were used as adapting stimuli. A rotating spiral stimulus (target spiral) was presented, flanked by spirals of the same type, and observers were adapted to its motion. The observers' task was to report the rotational direction of directionally ambiguous motion (test stimulus) presented afterwards. The directionally ambiguous motion consisted of a pair of spirals flickering in counterphase, which were mirror images of the target spiral. Although observers were not aware of the rotational direction of the target and identified it at chance levels, the direction of rotation reported by the observers (motion aftereffect) was contra-rotational to the direction of the adapting spiral. Since all contours of the adapting and test stimuli were 90� apart, local motion detectors tuned to the direction of the mirror-image spiral should fail to respond, and therefore not adapt to the adapting spiral. Thus any motion aftereffect observed should be attributed to adaptation of high-level motion-processing areas responding to complex configurations of moving stimuli. Since rotation-selective cells are located in area V5a/MST, it is concluded that activation of this area is insufficient for conscious perception
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