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 Ra ndom-interval 15-s schedule on one (food) lever in a rodent operant co nditioning chamber. They were then exposed to a condition in which foo d could only be obtained during a timein period which lasted 10 s or l onger dependent upon whether or not subjects pressed another (avoidanc e) lever. If subjects did not press the other lever during the 10-s ti mein, a 50-s timeout was presented during which food could not be obta ined. Subjects first had the opportunity to avoid timeout presentation by pressing the avoidance lever during timein or to escape the timeou t by pressing the lever during timeout. A changeover delay of 2-s prev ented food presentation immediately following avoidance lever-food lev er sequences. All subjects pressed the avoidance lever to avoid or esc ape timeout, but only one of the subjects consistently pressed the avo idance lever when escape was no longer available. One more subject acq uired consistent avoidance responding after reexposure to the avoidanc e/escape and avoidance only conditions. The four remaining subjects we re then exposed to a signalled avoidance procedure in which a 5-s stim ulus change preceded timeout presentation. Three of the subjects came to respond reliably on the avoidance lever when switched back to the u nsignalled avoidance procedure. One of the subjects never acquired con sistent avoidance responding. Functional control by the avoidance cont ingency was demonstrated during the final two experimental conditions in which the contingencies associated with the avoidance lever were sy stematically removed and reintroduced.