Temporal Control of Behavior: Effects of Trial Duration and Rate of Reinforcement on Discrimination

A 2-alternative free-operant psychophysical choice procedure was used to examine the effect of trial duration and relative rate of reinforcement on discimination. There were two trial types 100-s trials and 30-s trials. At the start of a trial both left or right keys were illuminated red (on long trials) or green (on short trials), respectively. Pigeons were required to discriminate between the 1st and 2nd halves of a trial. Left- and right-key responses were reinforced according to independent Variable Interval schedules. Left-key responses were only during the 1st half of a trial, and right-key responses were only reinforced in the 2nd half of a trial. The VI schedule pairs were (VI30s/VI30s, VI18s/VI90s, VI90s/VI18s, VI180s/VI180s, VI270s/VI54s & VI270s/VI54s). Psychometric functions relating proportion of right-key responses to time since trial onset were sigmoidal, and when plotted as a function of relative time did not reliably superpose. When overall rate of reinforcement was greater, and when trials were longer rather than shorter, the distribution of responses shifted from the left to the right key earlier in a trial. The data will be discussed in relation to models of timing and choice.