Abstract

Psychophysical studies have shown that the rod system can reduce the flicker sensitivity of the cone system at temporal frequencies near 10 Hz, apparently through the interference of out-of-phase rod and cone signals. Light-adapting or bleaching the rod system improves flicker sensitivity. We have examined an electrophysiological correlate of this rod-cone interaction by measuring ERG responses to a long-wavelength (Wratten No. 23A) Ganzfeld stimulus flickering at 10 Hz, either in the dark-adapted eye, against a steady Ganzfeld background, or following a Ganzfeld bleach. Consistent with the psychophysical finding, the amplitude of the cone component of the b wave is larger if the eye is moderately light-adapted or partially bleached rather than completely dark-adapted. A comparison of the ERG responses to scotopically matched short- and long-wavelength Ganzfeld flickering stimuli shows that in the dark-adapted eye, a negative-going rod response subtracts from the positive cone b-wave response, reducing its amplitude. Light adaptation shortens the implicit time of the rod response and reduces its amplitude, so that its negative influence on the cone b wave is reduced. The effect of light adaptation on the cone flicker ERG is therefore predictable from the algebraic summation of phase-shifted rod and cone ERG subcomponents.

© 1985 Optical Society of America