Free-operant Avoidance of Time-out From Response-independent Food Presentation by Pigeons Pecking a Key

Abstract:
The present experiments examined the behavior of food-deprived pigeons pecking a small translucent disc ("key"). Food was occasion- ally presented independently of responding, except during signaled "time-out" periods, during which food was never presented. Key pecking during "time-in" postponed the next time-out according to a free- operant avoidance paradigm. Successive time-outs followed one an- other at 5-sec intervals (i.e., the time-out--time-out interval=5 sec) unless a response occurred during time-in, in which case the next time-out occurred x sec after the last response, where x was the length of the response--time-out interval.
During Experiment I, stimuli correlated with time-in and time- out were projected on the key. Lengthening the response--time-out interval while maintaining a constant time-out--time-out interval progressively decreased response rates during time-in for all subjects.
During Experiment II, the importance of the delay contingency in maintaining the key pecking observed was examined by presenting time-outs response-independently at variable intervals matched to ones obtained under a proceeding free-operant avoidance condition.
Response rates for all subjects decreased when the delay contingency was suspended in this manner.
The independent contributions of responding maintained by time- out-postponement and responding elicited by the time-in and time-out stimuli were examined with a two-key procedure during Experiment III.
Responses to a continuously illuminated "delay" key during time-in postponed time-out, signaled by stimuli projected on a separate "signal" key. Response rates on the delay key during time-in for two subjects decreased as the response--time-out interval was lengthened. Responding on the signal key was unsystematically related to the response--time-out interval, and generally occurred at very low rates. The third subject responded on the delay and signal keys at comparable rates, and response rates on the delay key during time- in were unaffected by changes in the response--time-out interval.
Thus, free-operant time-out-postponement may control key pecking in the relative absence of elicited pecking, but elicited responding may contribute to the behavior observed.
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