PATTERN-REVERSAL ELECTRORETINOGRAM IN RESPONSE TO CHROMATIC STIMULI .1. HUMANS

We have studied the steady-state PERG in human subjects in response to red-green plaid patterns modulated either in luminance or in chromati city or both. By varying the relative luminance of the red and green c omponents, a value could be obtained at which the PERG amplitude was e ither minimum or locally maximum. This always occurred at equiluminanc e, as measured by standard psychophysical techniques. PERG amplitude a nd phase were measured as a function of spatial and temporal frequency of sinusoidal contrast reversal. In both space and time, the response to chromatic patterns was low-pass, while that to luminance was band- pass, and extended to higher spatial and temporal frequencies. The pha se of the PERG to chromatic stimuli was systematically lagged compared with that to luminance stimuli, by an amount corresponding to about 2 0 ms under our experimental conditions. The variation of phase with te mporal frequency suggested an apparent latency of about 67 ms for colo r contrast compared with 47 ms for luminance. These estimates were con firmed with separate measurements of transient PERGs to abrupt contras t reversal. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectori ally the responses to appropriate luminance and chromatic contrasts, w e were able to predict with accuracy the response as a function of col or ratio (ratio of red to total luminance). The above findings all agr ee with those reported in the accompanying paper for the monkey PERG ( Morrone et al., 1994), and indicate that the differences in response l atency and integration time of luminance and chromatic stimuli observe d by psychophysical and VEP techniques may arise at least in part from the properties of retinal mechanisms.