The procedures of TSD are designed to provide the psychophysicist with data in the form of response proportions that can be readily converted into the theoretical constructs of sensitivity, criterion, distribution variance, and distribution shape. TSD can be tested by comparing the values of the constructs predicted from the theory with those that are derived from response proportion data. In those circumstances where the data support the applicability of TSD, the theory can be used to solve many empirical problems. The situation in which a variable is found to have a large effect on response proportion is illustrative. By converting response proportion data into theoretical terms such as d’, A z , C, and β, an investigator can determine whether the effect was due to changes in the observer’s sensitivity, criterion, or both sensitivity and criterion. Today, there are several basic procedures of TSD used to solve such problems in psychophysics.