MODELING TIMING PERFORMANCE ON THE PEAK PROCEDURE

Computer simulations based on the Scalar Expectancy Theory (SET) and t he connectionist model of Church and Broadbent (1990) were run to matc h 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 rewar d is withheld. On such a test, a period of high rate of responding (ru n) is sandwiched between periods of low rates of responding. Models we re run to match the means and standard deviations of the start, the en d, the middle, and the duration of the run, as well as the correlation s 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 rewa rd and one or two thresholds. Models sampling two thresholds, with bot h difference and ratio comparison rules, fit the data well. In the con nectionist models the memory was a matrix of vector autocorrelations, with a vector representing a clock reading on a set of oscillators. Th e thresholds were each an angle between the clock vector and a compari son vector derived from memory. These models did not fare well.