Anisotropies of perceived contrast and detection speed.

Gratings of different orientations were compared in terms of both apparent contrast and detection speed. Magnitude estimates demonstrated that oblique gratings appear perceptually to have lower contrasts than horizontal or vertical gratings of the same physical contrast. This anisotropy of perceived contrast holds across a wide suprathreshold range of physical contrasts. Even when gratings of the different orientations are equated in terms of perceived contrast, an oblique effect of detection time remains. The magnitude of this residual anisotropy of detection speed decreases as contrast is increased from threshold, such that this second anisotropy is observed only at a restricted range of lower contrasts.