Grating and flicker sensitivity in the near and far periphery: naso-temporal asymmetries and binocular summation.

A variety of recent physiological and psychophysical experiments provide evidence for a large asymmetry between nasal and temporal processing outside of the central 40 degrees of visual field. Binocular processing has also been found to be reduced outside of this region even though the individual left and right eye fields continue to overlap for a full 120 degrees. In an effort to help quantify these findings, monocular and binocular grating and flicker contrast sensitivities were measured in the fovea and in the near and far periphery. The results show a large asymmetry between nasal and temporal retinal grating sensitivity in the far periphery especially at high spatial frequencies. A smaller asymmetry was found for flicker but no differential effect of flicker frequency was found. The summation results are consistent with previous findings in showing greatly reduced binocular processing outside of the central 40 degrees; this is especially true for the grating stimuli. These results are discussed with respect to possible physiological mechanisms.