Effect of pattern luminance profile on the pattern ERG in man and pigeon

Pattern electroretinograms (PERGs) have been recorded in man and pigeon using phase reversing patterns. Studies were made in both species of the effect of grating spatial frequency, grating profile (sine or square) or the size of the squares of a checkerboard on the amplitude of the responses. The results obtained in the two species were similar. In general, the ratio of the amplitudes of the sine wave:square wave responses is that predicted by the Fourier fundamentals of the pattern, and is thus not determined by changes in local luminance or contrast as it is normally defined. Checks however gave larger responses than sine or square wave profile bars matched to the Fourier fundamental on the diagonal. The results are not explicable in terms of any single stimulus parameter and suggest that the PERG generator has a degree of center/surround organisation similar to retinal ganglion cells. It is however argued that, because of the known physiological properties, generators cannot be unequivocally localised by varying the stimulus or comparing retinal, cortical and perceptual response dynamics.