In two experiments, a recognition memory task, in which subjects judged whether a given five-digit number had been shown previously, was compared to a numerical decision task, in which subjects judged whether a given five-digit number represented the height of a man or a woman. Subjects were found to shift β (the cutoff point along the decision axis) with changes in prior probabilities in the direction specified by signal detection theory in the numerical decision task but not in the recognition memory task. An explanation of the results, in terms of a difference in ď (discriminability) between the two tasks, was ruled out. In contrast, explanations which cannot be ruled out involve differences between the tasks in the amount of practice required for the subject to learn the manner in which the stimuli are distributed along the decision continuum, and differences in the availability of an alternative basis for response other than the decision continuum.