Evidence for an Accumulator Model of Psychophysical Discrimination

Recent theoretical approaches to the problem of psychophysical discrimination have produced what may be classified as ‘ statistical decision ’ or ‘ data accumulation ’ models. While the former have received much attention their application to judgment and choice meets with some difficulties. Among the latter, the two types which have received most attention are a ‘ runs ’ and a ‘ recruitment ’ model, but neither seems able to account for all of the relevant data. It is suggested instead that an ‘ accumulator ’ model, in which sampled events may vary in magnitude as well as probability, can be developed to give a good account of much of the available data on psychophysical discrimination. Two experiments are reported, in which the subject presses one of two keys as soon as he has decided whether the longer of two simultaneously presented lines is on the left or right. Results are found to be inconsistent with a runs or recruitment process, but to accord well with predictions from the accumulator model. Other evidence consistent with such a mechanism is briefly reviewed