Abstract

According to Kelly's analysis (1961) of the psychophysical measurements of flicker thresholds, human visual sensitivity is inversely proportional to the mean light level at low temporal frequencies (i.e., ΔI/I = constant, Weber's Law), but is mostly determined by absolute amplitude of modulation (ΔI) at high temporal frequencies. This pattern of response was later replicated in electrophysiological measures of retinal responses, such as in monkey ganglion cells (Purpura et al., 1990) and in the human focal electroretinogram (Seiple et al., 1992). From the electrophysiological results it has been suggested that the temporal frequency dependent adaptation must occur at the retinal level, and in the case of Seiple et al's study, at the level of the photoreceptors. However, the relation of this frequency- dependent adaptation pattern to the modulation depth of the flickering stimulus has not been characterized. In a previous study (Wu et al., 1993) we found that the flicker ERG exhibited a nonlinear frequency dependent adaptation. In this study we further investigate the relation of the frequency dependent adaptation to luminance adaptation at different modulation depths. Since the flicker ERG is nonlinear at all modulations (Burns et al., 1992), and the relation of response amplitude to modulation varies nonlinearly across frequencies (Wu et al., 1994), characterization of the temporal response of the system requires response measurements at a series of modulations and luminance levels. In this study we report results from such measurements, and relate the temporal frequency adaptation results to those from several classic luminance adaptation studies.

© 1995 Optical Society of America