Purpose. To investigate the behaviour of visual evoked potentials (VEP) in response to combined colour and luminance stimulation.Method. The multi-focal cortical visual evoked potential was studied using pseudo-random (m-sequence) colour stimulation (VERIS). Different green/red luminance ratios (ranging from 0.2-4.5) were employed in order to alter the achromatic content of the stimuli while the chromaticity remained unchanged. Isoluminant stimulation produced triphasic negative-positive-negative waves in both first and second order kernels. Results. Significant enhancement of the amplitude, alteration of the waveform and prolongation of the latency was observed in the first order kernel at the minimun value of the green/red luminance scale (i. e. where red light was maximally bright and green light maximally dim) while the opposite extreme of the green / red luminance scale (maximal brightness of the green colour) produced a response which was virtually identical to the achromatic VEP recorded at the same luminance contrast. Alteration of the green/red luminance ratio also affected the first two slices of the second order kernel in a systematic fashion. We have also studied the effect of gradual desaturation of both green and red colour using a grey/colour stimulation. Desaturation led to a marked change in form and amplitude of the red VEP signal in both the first and second order kernels while the green VEP signal was not affected. The residual colour component (following subtraction of the waveform for achromatic stimulation at the same luminance contrast) demonstrated practically linear dependance on the level of saturation of the red colour. Colouranomals, by contrast, produced quite stable waveforms, both in terms of waveform and symmetry (relative to the point of silent substitution of the extant cone type), which was not affected by desaturation. Conclusion.The electrophysiological results show a clear separation of the luminar ce and chromatic channels.
|Number of pages||1|
|Journal||Investigative Ophthalmology and Visual Science|
|Publication status||Published - 15 Feb 1996|