Critical Duration, the Differential Luminance Threshold, Critical Flicker Frequency, and Visual Adaptation: A Theoretical Treatment*

A quantitative model formally analogous to an electrical filter containing a cascade of RC elements with output-controlled variation of time constant (parametric feedback) is shown to predict the relations between the differential luminance threshold, critical duration, critical flicker frequency, and adapting luminance in human psychophysical data; the model also treats some of the properties of frequency-response characteristics for sinusoidally-modulated flicker. Critical duration in human luminance discrimination and membrane resistance recorded from eccentric cells in Limulus both follow the same decreasing function of adapting luminance that is predicted by the model. Fitting the model to luminance discrimination and to CFF data requires a constant increment of peripheral neural response at threshold rather than a constant ratio to ongoing peripheral activity. A hypothesis regarding central neural adaptation provides a bridge between the latter result and signal/noise theories of visual discrimination.