Orientation dependency for foveal line stimuli: detection and intensity discrimination, resolution, orientation discrimination and vernier acuity.

Thresholds were measured for five tasks: line detection, intensity discrimination, two-line resolution, vernier acuity and line-orientation discrimination. For each task, 30 arcmin lines were presented foveally in eight retinal meridians to assess similarities in orientation anisotropies across tasks in the same observer. Three observers were tested. The pattern of the orientation anisotropy differs across tasks. Meridional anisotropies exist in detection, increment discrimination thresholds, and vernier acuity but the classical oblique effect is consistently found only in orientation discrimination.