The Separation of Bias and Sensitivity in Multiple-Choice Tasks

With the growing realisation by psychologists of the need to take account of response biases in perception and memory, the lack of a simple and realistic model to enable ‘sensitivity’ and ‘bias’ to be measured separately in complex tasks is becoming acute. Though signal-detection theory (TSD) has proved very useful in two-alternative tasks, it is virtually intractable in multiple-choice tasks; for this reason experimenters have tended to resort to Luce's Choice Model (LCM) as an approximation to it. The relationship between TSD and LCM, however, though close in the two-alternative case, becomes increasingly tenuous as the number of alternatives is increased. Nevertheless the substitution may still be made, provided certain cautions are observed: computer simulations have been used here to study both forced- and unforced-choice tasks, and establish guidelines for experimenters who wish to apply a two-factor analysis to data from complex tasks.