THE OPTIMUM DECISION RULES FOR THE ODDITY TASK

This paper presents the optimum decision rule for an m-interval oddity task in which m-1 intervals contain the same signal and one is differ ent or odd. The optimum decision rule depends on the degree of correla tion among observations. The present approach unifies the different st rategies that occur with ''roved'' or ''fixed'' experiments (Macmillan & Creelman, 1991, p. 147). It is shown that the commonly used decisio n rule for an m-interval oddity task corresponds to the special case o f highly correlated observations. However, as is also true for the sam e-different paradigm, there exists a different optimum decision rule w hen the observations are independent. The relation between the probabi lity of a correct response and d' is derived for the three-interval od dity task. Tables are presented of this relation for the three-, four- , and five-interval oddity task. Finally, an experimental method is pr oposed that allows one to determine the decision rule used by the obse rver in an oddity experiment.