I recently reported on a negative component in the foveal local electroretinogram (LERG) of the primate that is dependent on the sensitivity differences between the R and G cones. This R–G-cone difference signal is most readily resolved in the foveal LERG in response to low-frequency sinusoidally flickering stimuli. In this paper, I report on changes in the R–G-cone difference signal (elicited with a 670-nm test stimulus) that are induced by 670- and 470-nm chromatic adaptation and flicker frequency. Both long- and short-wavelength backgrounds reduce the cone difference signal, but the long-wavelength reduction is associated with a phase shift that is absent with short-wavelength adaptation. Following extinction of the long-wavelength background, the R–G-cone difference signal is initially absent and increases in amplitude and phase for 5 min. In contrast, following extinction of a short-wavelength background that is about equally effective on the R cones, the cone difference signal is always present and at full amplitude. The R–G-cone difference signal has a low-pass frequency response that falls off at a higher frequency and more abruptly than the accompanying positive component.
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