Pattern evoked retinal response (PERR) in human: effects of spatial frequency, temporal frequency, luminance and...

Spatial and temporal tuning were examined for both retinal and cortical signals using low contrast sinusoidol gratings. Maximum PERR and VECP responses occurred at the 4 Hz alternation rate and at 0.68 and 2.2 cpd, respectively. A 25% low spatial frequency attenuation (LSFA) was observed for the PERR. To test the possibility that prior inability to detect LSFA of the PERR was due to the masking of a pattern contrast response by a large amplitude local luminance response, mean luminance and optical power were varied in separate experiments. Greater relative LSFA was observed with a lower mean luminance and defocus differentially affected responses elicited by high and low spatial frequency gratings. In addition greater relative LSFA was observed when power at the second harmonic rather than amplitude was the dependent measure. We conclude that LSFA may be observed. The absence of spatial tuning in previous reports is explained by the masking of pattern contrast by local lumnance responses. Detection of LSFA in the present experiments is attributed to use of stimulus conditions which minimize local luminance responses and the use of an objective response measure with a high signal-to-noise ratio, i.e., power at the second harmonic of the stimulation frequency.