Effects of Reinforcer Magnitude Variability on Operant Responding and Choice in Rats

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Havens, Crane Alexander
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The current study determined the effects of either a constant-sized (e.g., 2 pellets) or a variable-sized (averaging 2 pellets but ranging from 0-12 pellets) reinforcer on random-ratio responding in rats. Dependent measures of interest included within-session patterns of responding under a two-component multiple schedule, resistance to extinction, and preference under a concurrent schedule. Under a multiple schedule in which the two components alternated every 5 min, the component associated with the variable-sized reinforcer engendered greater responding later in the session. Responding in this component also was considerably more resistant to extinction than responding maintained by a constant-sized reinforcer; in fact, response rates increased considerably and these elevated rates were maintained for four consecutive extinction sessions in some rats. Despite this, under the concurrent schedule, the constant-reinforcer alternative was preferred in all rats. The results are discussed within the context of habituation, the partial reinforcement effect, and implications to gambling.
Variability, Reinforcement Variability, Random Ratio, Choice