An anisotropy of orientation-tuned suppression that matches the anisotropy of typical natural scenes.

Broadband oriented-noise masks were used to assess the orientation properties of spatial-context suppression in 'general' viewing conditions (i.e., a fixated, large field of 'naturalistic' noise). Suppression was orientation-tuned with a Gaussian shape and bandwidth of 40 degrees that was consistent across test orientation (0 degrees, 45 degrees, 90 degrees, and 135 degrees). Strength of suppression was highly anisotropic following a "horizontal effect" pattern (strongest suppression at horizontal and least suppression at oblique test orientations). Next, the time course of anisotropic masking was investigated by varying stimulus onset asynchrony (SOA). A standard "oblique effect" anisotropy is observed at long SOAs but becomes a "horizontal effect" when a noise mask is present within approximately 50 ms of the test onset. The orientation-tuned masking appears to result from an anisotropic gain-control mechanism that pools the weighted responses to the broadband mask, resulting in a changeover from oblique effect to horizontal effect. In addition, the relative magnitude of suppression at the orientations tested corresponds to the relative magnitudes of the content of typical natural scenes at the same orientations. We suggest that this anisotropic suppression may serve to equalize the visual system's response across orientation when viewing typical natural scenes, 'discounting' the anisotropy of typical natural scene content.