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Geoffrey Boynton; Orientation-specific adaptation in human visual cortex. Journal of Vision 2004;4(11):42. doi: 10.1167/4.11.42.
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Adaptation of the fMRI signal has been increasingly used as a tool for measuring the response properties of underlying neuronal subpopulations. However, fMRI-adaptation studies with object stimuli tend not to show stimulus-specific adaptation in early visual areas, such as the primary visual cortex (V1). We specifically searched for adaptation effects in early visual areas by measuring the fMRI response to pairs of sinusoidal gratings that had either the same or orthogonal orientation. We found no orientation-specific adaptation effects in V1 but we did find increasing effects along the hierarchy of visual areas (V2, V3, and V4V). From these results, one might conclude that there are no orientation-specific neurons in human V1. However, is more likely that neurons in V1 are simply less susceptible to adaptation. Thus, our results support a general principle of the visual system in which lower visual areas maintain a veridical representation of the world, while higher visual areas represent only what is behaviorally relevant.
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