Effects of decision criterion on response latencies of binary decisions

The effects of decision criterion on response latencies of binary decisions were examined. The stimuli comprised two, partly overlapping, "normal" distributions of either two-digit numbers or tonal frequencies. Individual stimuli were randomly sampled from the distributions, and subjects had to decide from which distribution the stimulus was sampled. The decision goal was to maximize the expected gain using three different payoff matrices. Decision latencies with and without prior knowledge of optimal decision criteria were measured. In a control task, subjects were asked only to label stimuli as being either above or below the optimal criteria (without regard for a posteriori probabilities or expected gain). The relation between criterion and latency was examined by means of a trial-by-trial analysis of the stimuli and the responses. Response latency was inversely related both to the distance between the stimulus and the decision criterion and to the probability of the response elicited by the stimulus. Response latencies showed a maximum at the criterion in all conditions. These results were obtained with different stimulus modalities (tones or numbers), different discriminability levels within the auditory modality, and different decision tasks. It is proposed that the decision criterion is the primary determinant of response latencies of binary decisions.