Two-stage model for order discrimination

Ulrich (1987), exploring the shapes of psychometric functions obtained in the ternary-response paradigm, indicated several inconsistencies between observed and predicted relationships providing evidence against most popular models of temporal-order judgment. In this paper, a new model is presented. It assumes that there are two mechanisms involved in the order discrimination task: one is responsible for the recognition of whether or not the stimuli are successive, and the second is able to determine their order. The model was tested using Allan's (1975a, 1975b) and Ulrich's (1987) data; the model predictions were found to be consistent with the experimental results.