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Kaoru Amano, Shin'ya Nihida, Tsunehiro Takeda; MEG responses for color-motion asynchrony. Journal of Vision 2004;4(8):554. doi: 10.1167/4.8.554.
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When an upward motion of green pattern and a downward motion of red pattern are alternated at 2Hz, changes in motion direction appear to be delayed relative to color changes by about 100 ms. Moutoussis and Zeki (1997) proposed that the apparent asynchrony reflects the delayed neural processing of motion relative to that of color. On the other hand, Nishida and Johnston (2002) showed that the asynchronous perception occurred only for rapid alternations, and the delay was not accompanied by a difference in reaction time. From these and other results, they hypothesized that the perception of the relative time of events is based on the relationship between representations of the temporal pattern of salient features (time markers), and the asynchrony could be ascribed to the difficulty in detecting the direction reversals for rapid alternations. Present study measured neural responses relating to the color-motion asynchrony by using a whole head magnetoencephalogram (MEG). We first recorded MEG responses to color reversals or motion direction reversals for the frequency of 0.25, 0.5 and 2 Hz. The results indicated that increasing the frequency clearly decreased the MEG responses to motion reversals but had no significant effect on those to color changes. This is consistent with the hypothesis that allocating time markers becomes difficult for rapid direction reversals, but not for rapid color changes. Next we recorded MEG responses when the color and motion direction were simultaneously alternated within the same pattern at 2Hz with various time lags. The results indicated that the MEG responses were increased when the color and motion were perceptually synchronized, but not when they were physically synchronized. These responses might reflect the interaction between the color and motion changes under the condition of perceptual synchrony.
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