Psychometric function

It models the relationship between a given feature of a physical stimulus, e.g. velocity, duration, brightness, weight etc., and forced-choice responses of a human or animal test subject.

The psychometric function therefore is a specific application of the generalized linear model (GLM) to psychophysical data.

The probability of response is related to a linear combination of predictors by means of a sigmoid link function (e.g. probit, logit, etc.).

This is equal to the transition range of the psychometric function and the sensory threshold corresponds to visual acuity.

(Strictly speaking, a typical optometric measurement does not exactly yield the sensory threshold due to biases in the standard procedure.)

Simulated example of a psychometric function, showing how the proportion of correct detections may increase with increasing luminance of the stimulus.