The influence of intertrial interval food on extinction and devaluation in chain schedules.

The authors exposed pigeons to 2 equal 3-link chains by using variable-interval schedules of reinforcement. An intertrial interval (ITI) bisected by free food separated the chains. After baseline training, the authors presented terminal links in a successive discrimination to devalue 1 terminal link: The authors reinforced responses to 1 terminal link and extinguished responses to the other. The authors then presented full chains in extinction, except that they continued to deliver free food during the midpoint of the ITI. There were 2 principal findings. First, across all extinction conditions, responding decreased but did not extinguish. Second, when extinction testing revealed a terminal link devaluation effect in the 3rd condition, responding to the initial link was affected, but not middle-link responding. Overall, the results suggested that ITI food presentations can exert a substantial effect on responding in 3-link chain schedules, and they appear to influence both the pattern of extinction and devaluation effects.