Detection of auditory signals presented at random times,II

The paper includes experimental results obtained using two procedures in which signals are presented at random times. A simple three-stage theory consisting of a sensory process, followed by a response bias, and ending in a response process, involving a random delay, and that mayor may not have a memory, is compared with the data. The free-response procedure yielded data that could not be accounted for by a first version of the theory in which the crucial assumption about the response process was that once a response process is under way it locks out all further inputs until the response is made. Alternative models, including a race between response processes with the first response suppressing all others and a simple first-in first-out queue, were equally inadequate. On the assumption that the difficulties lie in the complexities of the response process when there are two or more inputs close in time, we decided to avoid these theoretical difficulties by using a modified reaction-time procedure. The initial results are encouraging. The tails of the latency distributions appear to be exponentially distributed and a theoretical prediction that two of the time constants should be the same appears to be supported. The major indications of difficulties are inconclusive evidence that the response bias parameter may not be constant and, possibly related, that the initial portion of the tails may overshoot the predicted value. In spite of the possible variation in the bias parameter, estimates of the signal-plus-noise to noise-alone parameters increase in a systematic manner with signal strength