Some functional characteristics of avoidance of timeout from response-dependent food presentation in rats.

Three male and three female rats were first trained to respond on a Random-Interval 15-s schedule on one (food) lever in a rodent operant conditioning chamber. They were then exposed to a condition in which food could only be obtained during a timein period which lasted 10 s or longer dependent upon whether or not subjects pressed another (avoidance) fever. If subjects did not press the other level during the 10-s timein, a 50-s timeout was presented during which food could not be obtained. Subjects first had the opportunity to avoid timeout presentation by pressing the avoidance level during timein or to escape the timeout by pressing the lever during timeout. A changeover delay of 2-s prevented food presentation immediately following avoidance lever-food lever sequences. All subjects pressed the avoidance lever to avoid or escape timeout, but only one of the subjects consistently pressed the avoidance lever when escape was no longer available. One more subject acquired consistent avoidance responding after reexposure to the avoidance/escape and avoidance only conditions. The four remaining subjects were then exposed to a signalled avoidance procedure in which a 5-s stimulus change preceded timeout presentation. Three of the subjects came to respond reliably on the avoidance lever when switched back to the unsignalled avoidance procedure. One of the subjects never acquired consistent avoidance responding. Functional control by the avoidance contingency was demonstrated during the final two experimental conditions in which the contingencies associated with the avoidance lever were systematically removed and reintroduced.