"Animals were first given food reinforcement in a straight-alley runway, using a variable-ratio scheduling procedure, so that the running behavior could be elicited on many nonreinforced trials. A bar was then inserted into the starting box, and the animals could produce the onset of an extinction trial by pressing it. No further food reinforcement was given, but it proved possible to develop bar-pressing behavior and maintain it at high strength on variable-ratio and fixed-ratio schedules, solely by releasing a run to the empty goal box. An animal's performance lasted from 10 to 14, 1½-hr. daily sessions during which thousands of responses were made. The behavior was comparable to that generated by variable-ratio and fixed-ratio schedules of primary reinforcement. Although the runway behavior became disrupted after several sessions during the test phase of the experiment, a fragment of it--jumping from the starting box into the runway--persisted much longer and permitted the bar-pressing behavior to be maintained." From Psyc Abstracts 36:02:2EL53Z. (PsycINFO Database Record (c) 2006 APA, all rights reserved)