Response resurgence in the peak procedure

In separate experiments the timing abilities of brushtail possums and domestic hens on the peak procedure was investigated. This procedure involved animals responding on two trial types within an experimental session. On some trials responding was reinforced according to a Fixed Interval (FI) schedule, and on other trials, Peak Interval (PI) trials responding was not reinforced with food. Possums lever pressed and hens key pecked for food reinforcers on different FI schedules, and the duration of the PI was varied across a range. For 20% of trials, responding was not reinforced longer than the FI schedule that was in effect on the other 80% of trials when responding was reinforced. Response rates typically increased to a maximum at about the time the responses were normally reinforced and then decreased after the time that food would normally be reinforced, before increasing again towards the end of the PI regardless of the duration of the PI trial. When relative response rates were plotted as a function of relative time the function typically superposed for the ascending, but not descending portions of the function. The results are discussed in terms of Weber's law, and various quantitative models timing.