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| Paper IPM / Cognitive / 7470 |
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| Abstract: | ||
| 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 to spiral motion is preserved in crowding conditions. Logarithmic spirals, similar to those used by Cavanagh | Favreau (Cavanagh |
Favreau, 1980) 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 a 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 target's rotational direction and identified it at chance levels, the direction of rotation reported by the observers during the test phase (motion aftereffect) was contrarotational to the adapting spiral's direction. Since all contours of the adapting and test stimuli were 90 degrees apart, local motion detectors tuned to the directions 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 units responding to complex configurations of moving stimuli (i.e. rotation detectors). Since rotation selective cells are located in area MST/V5a, we conclude that activation of this area is not necessarily correlated with conscious perception.
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