Changes in the focal electroretinogram with retinal eccentricity.

Flicker sensitivity increases in the peripheral retina when relatively large targets are used. This enhancement of cone system-mediated temporal sensitivity persists even when corrections are made for cortical magnification factors. It has been suggested that the differences in temporal frequency response characteristics across the retina are based on differences in receptor morphology between the peripheral and central cones. We have examined a possible retinal origin of this phenomenon by obtaining psychophysical and electroretinographic data at a variety of locations on the temporal retina. Psychophysical results show an increased sensitivity for high temporal frequency stimuli (above 30 Hz) with retinal eccentricity whether or not the stimulus size was scaled. Focal electroretinograms recorded with a constant size stimulus did not show an increase in amplitude with eccentricity. However, when an equal number of receptors were stimulated by scaling the target size, focal amplitudes were larger in the periphery. The electrophysiological findings are consistent with a possible retinal origin for this flicker enhancement phenomenon.