Peripheral visual field is radially organized

The visibility of vertical, horizontal, and 45 degrees oblique square wave gratings was measured at 10 to 45 degrees of eccentricity along the vertical, horizontal, and the 45 degrees oblique meridians. A forced-choice orientation identification response to the stimulus grating and a subjective rating of the confidence in response accuracy were the response measurements. The best seen grating orientation was always the one parallel to the meridian upon which it was presented. Along the vertical and horizontal meridians the most poorly seen orientation was the one perpendicular to the meridian. Along the 45 degrees oblique meridians the horizontal grating was as poorly seen as the meridian perpendicular to the grating orientation, except in the infranasal quadrant of the field. Pinhole experiments show these results unlikely to be due to off-axis optical aberrations. It is hypothesized that the radial organization of the peripheral visual field is due to underlying neural factors ontogenically determined, not due to environmental adaptations.