Temporal analysis of the topographic ERG: chromatic versus achromatic stimulation.
The topographic electroretinogram evoked by multi-focal exchange of black and white or red and green stimuli was analysed into linear and non-linear Wiener kernels. The first-order (temporally linear) response showed a biphasic waveform which inverted as the luminance ratio of the exchanged colours passed through unity (established both psychophysically and photometrically). A short latency non-linearity which was dependant on luminance contrast was observed in both chromatic and achromatic ERG. However, in the chromatic second-order response, a long-latency non-linearity, foveally prominent, with a distinct skew in power towards the nasal retina, appeared around the isoluminant point, between the points of silent substitution for the L and M-cone types. Modelling of the second-order responses showed that over a wide range of luminance ratios, the chromatic ERG is well described by a linear combination of the achromatic (contrast-dependent) component and the response at isoluminance. The difference in second-order response between coloured and black and white stimulation, at the same luminance contrast, showed that the long-latency non-linearity is recorded when the red and green cone types are operating out of phase and peaks in amplitude at a green/red luminance ratio of 0.8. This interpretation was confirmed by the lack of the long-latency non-linearity in colour-anomalous subjects (whether deficient in the L or the M-cone type). A marked similarity exists between the properties of the long-latency non-linearity and the frequency-doubled response generated in the ganglion cells of the magnocellular pathway.
School of Optometry, University of New South Wales, Sydney, Australia.
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A
Klistorner
D P
DP
Crewther
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SG
Crewther
D003118:Color Perception / Q000502:physiology*; D015350:Contrast Sensitivity; D004596:Electroretinography; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D013053:Spectrophotometry; D013997:Time Factors