The effect of background spatial contrast on electroretinographic responses in the human retina

The electroretinogram (ERG) was obtained to contrast modulation (CM). This stimulus is a product of temporal modulation of the contrast of a spatial sinusoid at constant mean luminance. Mean contrast (10-40%), and modulation depth (25-1.0) were modulated at 7.5Hz to record the pattern electroretinogram (PERG). The spatial pattern was a foveally fixated grating pattern with sinusoidal luminance profile with spatial frequency of 4.6c/deg. CM resulted in significant first and second harmonic ERG responses. First harmonic amplitude increases then flattens as a function of mean contrast with DeltaC=constant, while the second harmonic response remains unaffected by mean contrast. Apparently the first harmonic represents summed signals of local luminance responses arising from on and off neurons. Mean spatial contrast signals modulate preganglionic local luminance responses.