Increased reaction time adherence to response criterion in a sample discrimination task

Abstract

In a signal detection task with equal-variance distributions and an unbiased criterion, the distribution of reaction times typically has a peak near the point of overlap between the two distributions. A sample discrimination task is used to determine whether slower reaction times are associated with a likelihood ratio near unity or to the placement of the decision criterion. Listeners decide whether a single presented tone was sampled from a normal distribution with a mean of 1000 Hz or a mean of 1100 Hz, with each distribution having a standard deviation of 100 Hz. Base rates are varied across conditions so that the optimal decision criterion corresponds to respective likelihood ratios of .25,.67, 1, 1.5, or 4. In all conditions, the peak of the reaction time distribution as a function of frequency is near the optimal criterion for maximizing percent correct. In conclusion, slower reaction times are found when the frequency of the tone is near the selected criterion rather than near a point where stimuli from the two distributions are most similar. The results suggest that increases in reaction time are associated with the decision stage rather than an earlier perceptual processing stage.