Meridional variations in the line orientation discrimination of the cat.

Cat's differential orientation thresholds were measured with single lines presented in succession. Differential orientation thresholds measured at horizontal or vertical orientations were smaller (median 2.9 degrees) than those measured at oblique orientation (median 4.7 degrees). Replications of the experiments showed that the oblique effect was stable over a period of 2 years. Using the same behavioral methods grating acuity was measured and did not show an oblique effect. These behavioral observations are compared with the physiological data on orientation specificity of area 17 cells. This comparison suggests that the most likely explanation of the meridional variation in orientation discrimination is the meridional variation in orientation preference of area 17 S cells.