Pigeon performance on a variable-interval omission schedule at different levels of food deprivation

After modifying a variable-interval schedule to include an omission contingency, we investigated rates of responding and performance at different levels of food deprivation in pigeons. The variable-interval schedule had intervals which averaged 30 s in duration. Any response made during a particular interval cancelled the food delivery at the end of the interval. Following intervals in which no response occured, the first response produced a 6-s access to grain. Sessions lasted until 150 of these intervals had been presented. Food deprivation was manipulated in two ways. In the first, pigeons started at 90% of their free-feeding weights and were gradually reduced to their 70% levels. In the second, pigeons were maintained at three specific levels of their free-feeding weights: 70, 80, and 90%. During all sessions, rates of responding and the percentage of reinforcers omitted were recorded. The results from both methods of deprivation were similar: (1) rates of responding systematically increased as pigeon's body weights decreased; and (2) performance, as indicated by the percentage of reinforcer omissions, worsened as pigeon's body weights declined.