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Declan J. McKeefry; Color in motion revealed by motion after-effects. Journal of Vision 2008;8(17):8. doi: 10.1167/8.17.8.
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The analysis of the colour and motion of visual stimuli was traditionally believed to take place within segregated processing pathways in the primate visual system. However, it has become increasingly more apparent that this segregation cannot remain absolute and that there must be some capacity for integration across these sub-modalities. In this talk I will describe some psychophysical experiments which explore the extent to which colour and luminance cues can be either combined or segregated in motion perception.
In studies of the traditional motion after-effect (MAE), where prolonged inspection of a unidirectional moving stimulus results in illusory motion in the opposite direction, we have found evidence of chromatic selectivity. Induced MAEs were strongest when the adapting and test stimuli were of the same chromatic (or luminance) contrast composition, but fell to a minimum when the two stimuli were modulated along orthogonal axes in colour space. However, when we examined the chromatic selectivity of a second after-effect, in which motion adaptation induces misperceptions in the spatial position of stationary objects, we found it to be completely insensitive to chromatic composition of the test and adapting stimuli. Similarly, in experiments where we measured misperceptions in the speed of moving grating stimuli, induced by placing flanking or ‘modifier‘ stimuli in close proximity, we found that the magnitude of the effects were the same regardless of the chromatic or luminance contrast composition of the stimuli.
The results from these experiments suggest that there are separable chromatic and luminance inputs to motion processing, at least in its earliest stages. However, when motion cues are utilised for more complex aspects of perception, such as position estimation or the computation of stimulus speed, there is the capacity to effectively combine both colour and luminance information to achieve specific perceptual goals.
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