Abstract

In the analysis of psychophysical thresholds, both signal detection theory and the quick high-threshold theory assume a linear contrast transducer function (CTF). That is, for small signals there is no physiological threshold, but the internal response grows linearly with stimulus contrast from the zero level. However, data from psychometric functions are equally compatible with a nonlinear CTF, corresponding to a true threshold below which there is no internal response. In studies of infant vision it is desirable to use the visual evoked potential (VEP) as an index of visual sensitivity. Many analyses of VEP contrast sensitivity assume the existence of an electrophysiological threshold of zero VEP response for such visual sensitivity measurements. This corresponds to the assumption of a nonlinear CTF for the electrophysiological response, in opposition to the assumption of a linear CTF in psychophysics.

© 1986 Optical Society of America