Idiosyncratic exceptions to the probability-matching decision-rule in visual discrimination

Human “Yes-No” signal-detection performance was tested under a modified perceptual-defense procedure. A majority of Ss tended to match the relative frequency with which they gave affirmative responses to the relative frequency at which signals were presented. These Ss thereby replicated the “probability-matching” behavior found in previous signal-detection and discrimination studies. However, in marked contrast to those previous results, another large set of Ss showed a tendency toward preponderant use of one of the two responses (typically, of “No”) rather than toward probability-matching. The evidence failed to suggest that the latter effect was related to a lesser ability to make the requisite sensory discrimination or to response inhibition induced by taboo stimuli.