Mechanisms for categorization: Decision criteria and the form of the psychophysical function

The essential features that any satisfactory model of categorical judgement must account for are discussed. The implications of the strong evidence for the Thurstone case V model are drawn out. Then evidence for a linear learning model of criterion setting is presented including new data for isobias functions with either response speed deadlines or physical stimulus difference manipulated. A method for extending linear learning models to encompass joint setting of several criteria is suggested. It is shown that an arcsinh transformation of the Thurstone scale produces a scale which is a linear function of stimulus intensity in decibels. The scale parameter of this transformation remains constant for stimulus ranges greater than 18 dB while changing systematically when sequential presentation is manipulated to improve discrimination.