Modelling timing performance on the peak procedure.

Computer simulations based on the Scalar Expectancy Theory (SET) and the connectionist model of Church and Broadbent (1990) were run to match data sets from the peak procedure. On the peak procedure, a light or tone usually signals a reward for a response after a fixed interval (FI), but occasionally, the signal is left on for a long time and reward is withheld. On such a test, a period of high rate of responding (run) is sandwiched between periods of low rates of responding. Models were run to match the means and standard deviations of the start, the end, the middle, and the duration of the run, as well as the correlations among them. On a trial, the models based on SET determined the start and the end of the run according to a memory of expected time of reward and one or two thresholds. Models sampling two thresholds, with both difference and ratio comparison rules, fit the data well. In the connectionist models the memory was a matrix of vector autocorrelations, with a vector representing a clock reading on a set of oscillators. The thresholds were each an angle between the clock vector and a comparison vector derived from memory. These models did not fare well.