Abstract
When signal intensity was set at either 20 or 21 dB SL, O was required to report whether the 60-Hz vibration on his fingertip was strong or weak. If trial-by-trial feedback was given, increasing the probability of a strong signal led to an increase in the probability of a “strong” response. The shape of receiver-operating-characteristic curves was consistent with the assumption of the theory of signal detection that performance optimization is accomplished by O making an appropriate change in the location of his decision criterion. When O was not told the signal probability or given trial-by-trial feedback the proportion of strong responses decreased as signal probability was increased. The performance optimization that occurred when feedback was given was facilitated by also telling O the signal probabiliry. When signal-probability information but no feedback is given, performance is likely to be unaffected by changes in signal probability.
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