Amplitude and phase of responses of macaque retinal ganglion cells to flickering stimuli.

1. We have measured responses of macaque retinal ganglion cells to a uniform flickering field, with variation in luminance, chromaticity or both (heterochromatic flicker). 2. With heterochromatic flicker, as the luminance ratio of the flicker components was varied, phasic ganglion cell activity went through a minimum and an abrupt phase change close to equal luminance. Tonic ganglion cell responses underwent a gradual phase change without any minimum close to equal luminance. For red on-centre cells, when wavelengths above 570 nm were altered with white, a progressive phase advance occurred as luminance ratio (L lambda/LW) was increased. With wavelengths below 570 nm a progressive phase lag occurred. For green on-centre cells, the opposite pattern was found. For all tonic cells, the higher the temporal frequency, the more rapidly did such phase changes occur. A simple model incorporating a centre-surround delay of 3-8 ms could quantitatively account for these changes. 3. With luminance flicker of different dominant wavelengths, amplitudes and phase of responses of phasic ganglion cells were independent of wavelength at all frequencies. The amplitude and phase of the responses of tonic ganglion cells was very dependent on wavelength, as well as on flicker frequency. Their characteristics hardly ever resembled results from phasic cells. 4. For achromatic flicker, response phase of tonic cells at or above 10 Hz was variable, probably due to the centre-surround delay. Such variability was not seen among phasic cells. 5. An interesting implication of these results is that the ability of tonic ganglion cells to unambiguously signal rapid chromatic or spatial change is limited.