Abstract

We measured orientation discrimination threshold at 7.5° increments around the clock for an 8-cycle/deg grating subtending 1.0° that was located 1.25° from the foveal center. Threshold was lowest for vertical and horizontal gratings. However, rather than rising monotonically to maxima for oblique orientations, threshold rose sharply to submaxima for gratings inclined at only ~20° to hori­zontal or vertical before falling to weak subminima at oblique orientations. This finding held for both subjects tested. It is consistent with the idea that orientation discrimination is determined by the reltive activity of two or more orientation-tuned neural elements,¹ and that the retinal area tested addressed only 4-8 such elements. This idea can also explain how subjects unconfound orientation change from covarying stimulus parameters even though cortical neurons are generally sensitive to several stimulus parameters.

© 1986 Optical Society of America