Human orientation discrimination tested with long stimuli.

Human orientation discrimination was measured for single long lines presented sequentially. Orientation sensitivity is better for a narrow range of orientations around the principal meridians. Both the orientation sensitivity and its meridional variation increase with stimulus length. Control experiments show that the "oblique effect" can be obtained as well with a signal detection method as with the method of constant stimuli and that the subjects used a visual orientation cue in their judgments. Comparison of these findings with properties of visual cortical cells suggest that cells similar to S cells of cat and monkey striate cortex, carry the neuronal representation used in the decision process. And indeed the meridional variation in orientation sensitivity can be predicted from the number of monkey S cells preferring different orientations.