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Robert B. Post, Christopher Coker; Inverted vision-action dissociation with induced motion. Journal of Vision 2005;5(8):355. doi: 10.1167/5.8.355.
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© ARVO (1962-2015); The Authors (2016-present)
In vision-action dissociation, visual illusions influence motor responses directed toward the stimulus less than might be predicted from the size of the illusion. One example may be provided by induced motion (IM), wherein a dot appears to move opposite the real motion of a surrounding stimulus. Open loop pointing directed at the apparent endpoints of the dot's motion is displaced in the direction of the preceding IM, but less than would be predicted from the IM's velocity and duration. The comparison of pointing measures of the apparent location of the dot with measures of perceived motion of the dot is problematic, however, as the motor and perceptual measures concern different properties of the stimulus. Specifically, open loop pointing addresses the dot's perceived location, whereas perceptual IM measures typically address the target's perceived velocity. To avoid this potential confound, we assessed the same property of the stimulus (apparent location) with both perceptual and motor measures following IM. Specifically, perceptual measures of perceived location obtained with a vernier task were compared to open loop pointing measures of perceived location. Consistent with prior reports, results showed a small, but reliable effect of IM on open loop pointing. However, there was no effect on the perceived location of the stimulus as assessed by the vernier task. Therefore, IM was found to influence motor measures, but not perceptual measures. This is the inverse of the pattern typically reported as vision-action dissociation. The lack of an effect of IM on the vernier task also suggests that IM does not display the flash-lag effect, as the vernier markers were flashed briefly near the IM target and their alignment was perceived correctly.
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