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Disentangling specific temporal frequency channels of motion processing in awake monkey V4 using color and luminance| old_uid | 7728 |
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| title | Disentangling specific temporal frequency channels of motion processing in awake monkey V4 using color and luminance |
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| start_date | 2009/11/30 |
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| schedule | 11h |
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| online | no |
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| summary | Evidence both from both psychophysics (Gegenfurtner and Hawken, 1995) and functional imaging (Tootel et al., 2004) challenges the classical concept of separate motion and color processing, that has long been a cornerstone in the argument for separate pathways. Alternatively, it has been proposed that both motion and color information is being processed along two channels, neither of which is color-blind or motion-insensitive (Gegenfurtner and Hawken, 1996): The first one, specialized in processing rapid movement, has a high sensitivity to luminance-defined stimuli, depends only weakly on contrast and processes color variations like small variations in luminance. Based on neuronal data, MT, the first area fully belonging to the dorsal stream, has been proposed as a neuronal substrate for this channel. The second channel, specialized for slow movements, has a high sensitivity to color contrast and codes movement in a highly contrast dependent manner. Concerning the neuronal substrate of his second channel, the question has been risen of whether a suitable candidate might not be V4, being the earliest visual area that fully belongs to the ventral stream, which deals with object identification and is therefore optimized for the extraction of the objects’ surface characteristics, such as color and texture.
To test this hypothesis, we measured responses to fast and slow isoluminant and isochromatic stimuli at various contrasts in V4 of the awake macaque. Our data, obtained using optical imaging of both intrinsic signals and voltage-sensitive dyes, show that, at low contrast, slowly moving isoluminant chromatic stimuli elicit larger responses than fast ones, whereas the opposite was true for isochromatic luminance-based stimuli. |
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| responsibles | Vezoli |
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