Multiple levels of orientation anisotropy in crowding with Gabor flankers.

Using oriented Gabor patches, we found that for nearly cardinal target orientations, oblique flankers' orientations induced more interference than did cardinal flankers' orientations. This pattern was observed both at the local and global levels of flankers' orientation. With respect to the global orientation (flankers' global arrangement around the target), there was no difference between the effects of the two cardinal orientations, and both induced the same amount of interference. With respect to the local orientation (Gabors' orientation), in accordance with previous reports, a difference was found between the effects of the two cardinal orientations--a considerable amount of interference with flankers equal in orientation to the target (although less than with the oblique flankers) and almost no interference from flankers orthogonal to the target. Crowding was also affected by an anisotropy based on the target-fixation axis (radial, tangential, and diagonal) and by the flankers' relations. The magnitude of these latter factors was small relative to that of the former ones. The multiple factors that affected crowding, as well as the similarities and the differences between the effects at the two orientation levels, suggest that crowding is determined by multiple sources of interference operating at several levels of representation.