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Thomas Sprague, David Eagleman; Color-motion asynchrony depends on stimulus repetition. Journal of Vision 2010;10(7):1404. doi: 10.1167/10.7.1404.
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© ARVO (1962-2015); The Authors (2016-present)
Color-motion asynchrony depends on stimulus predictability To craft a useful model of the world, the visual system must combine information about different stimulus features processed at different times in different networks in the brain. This perceptual binding can be fooled by certain types of visual stimuli. For example, when two stimulus attributes (e.g., color and motion) are simultaneously alternated between two states (e.g., red/upward motion and green/downward motion), the color is perceived as changing ∼80 ms before the motion direction. Previous investigations into this color/motion asynchrony (CMA) illusion have used a repetitive stimulus which alternates between two colors. In contrast, we here measure perceptual asynchrony using repeated (grey-blue-grey-blue-…) and random (grey-blue-grey-orange-…) color sequences paired with alternating directions of vertical motion. The CMA was found to be 17% smaller in the randomized condition (68 ms) than in the repeated condition (82 ms). This result suggests that the asynchrony illusion is related to, or at least modified by, neural repetition suppression–the phenomenon of a diminishing neural response to a repeated stimulus. Using functional neuroimaging, we measured the BOLD signal amplitude in the posterior fusiform gyrus to be 19.3% smaller in the repeated condition than in the random condition. All reported characteristics of the CMA illusion appear to be explained by a model of perceptual decision-making in which neural evidence for each alternative, defined as the concurrent response of the relevant color and motion populations, is accumulated over time and compared. The alternative with the greater evidence is the end result of the decision. In this model, a change in the relative latencies or firing rates of these signals can lead to a change in the final perceptual decision. Our findings demonstrate that stimulus repetition–and thus the amplitude of neural responses–are important factors in the CMA illusion.
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