Field sensitivity of the "red" mechanism derived from primate local electroretinogram.

Using the local ERG in response to a long-wavelength stimulus as an indicator, field sensitivity functions have been obtained from cynomolgus macaque monkeys (Macaca fascicularis) with flashed and sinusoidally flickering test stimuli. These functions show the reciprocal of the relative radiance, for various adapting wavelengths, required to reduce a 667-nm test response to a criterion level. The resulting functions resemble both Stiles's pi 5 and the SR function of Smith and Pokorny, provided that pi 5 and SR are displaced about 7 nm toward longer wavelengths, in agreement with microspectrophotometric evidence. When field sensitivity functions are obtained with a 20 Hz sinusoidal test stimulus, using a continuous change of field wavelength, the direction of a slow spectral traverse has a large effect upon the shape of the sensitivity and phase functions--a hysteresis effect These effects do not occur at 5 Hz. The test light is proven to be ineffective upon G cones, and it appears unlikely that measurably significant signals are significantly induced into G cones as an indirect result of the modulation of R cones. Therefore, the steady background light absorbed in the G cones seems to be influencing the response of the R cones.