White light was temporally modulated and subjects gave magnitude estimations of the apparent depth of modulation. Three stimulus parameters were varied: level of time-average luminance, amplitude of modulation, and frequency of modulation. At the lowest luminances, apparent depth of modulation decreased monotonically as modulation frequency increased toward fusion. At the higher luminances, only large amplitudes of modulation produced monotonic functions relating apparent depth of modulation to frequency; smaller amplitudes of modulation produced nonmonotonic functions with maxima in the region of 5–10 Hz. Derived contours relating modulation amplitude to frequency for constant apparent depth of modulation generally resemble functions relating modulation amplitude to frequency for threshold.
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