Investigated adaptation to lines of specific orientation, a process that occurs in primary visual cortex. When a single grating is presented in the periphery of the visual field, human observers were aware of its orientation, but when it was flanked by other similar gratings (crowding), its orientation became impossible to discern. Results show that orientation-specific adaptation is not affected by crowding, implying that spatial resolution is limited by an attentional filter acting beyond the primary visual cortex. Consistent with this, attentional resolution is greater in the lower than in the upper visual field, whereas there is no corresponding asymmetry in the primary visual cortex. It is suggested that the attentional filter acts in 1 or more higher visual cortical areas to restrict the availability of visual information to conscious awareness. (PsycINFO Database Record (c) 2007 APA, all rights reserved)

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