Abstract
The Pavlovian autoshaping paradigm has often been used to assess the behavioral effects of reward omission on behavior. We trained pigeons to receive a food reward (unconditioned stimulus or UCS) following illumination of a response key (conditioned stimulus or CS). In Experiment 1, one group of pigeons was trained with two 100% predictive CS-UCS associations (reward certainty) and another group with two 25% predictive CS-UCS associations (reward uncertainty) for 12 sessions. In both groups, the two CS durations were 8 s. Then, in each group, the duration of one CS remained unchanged and that of the other CS was suddenly extended from 8 to 24 s for 6 sessions. In Experiment 2, some experienced individuals (from Experiment 1) and naïve individuals formed two groups trained with a 24-s CS throughout for 18 sessions. Our results show that pigeons (a) pecked less at the uncertain than the certain CS, (b) decreased and then increased CS-pecking after extending CS duration, especially in the certainty condition, (c) were unresponsive to the 24-s CS in the absence of previous experience, and (d) decreased their response rate close to the end of a trial irrespective of the reinforcement condition, CS duration, and amount of training. These results are discussed in relation to several theoretical frameworks.
Highlights
Title Decreased Key Pecking in Response to Reward Uncertainty Followed by Surprising Delay Extension in Pigeons
A post-hoc pairwise comparison revealed that the pigeons pecked significantly more at the rewarded conditioned stimulus (CS) than at the nonrewarded CSs
The nonrewarded grey CS was not included in those analyses because it was only present for the pigeons from Group Uncertainty, and a paired-samples t-test indicated that responding to the grey CS did not significantly differ from that to the other nonrewarded CSs [grey vs. blue: t(7) = 0.17, p = 0.867; grey vs. brown: t(7) = 1.25, p = 0.252]
Summary
Title Decreased Key Pecking in Response to Reward Uncertainty Followed by Surprising Delay Extension in Pigeons. Besides reward uncertainty, another traditional approach to reward omission is the consummatory successive negative contrast (cSNC) procedure, in which organisms are repeatedly exposed to a given reward concentration (e.g., a 32% sucrose solution), which is suddenly reduced to a noticeably lower nonzero value (4% sucrose). We analyzed the number of key-pecking responses that occurred after shifting the duration of an initial-link CS presentation from 8 s to 24 s for several sessions Another indicator of frustration might be revealed through a second-by-second analysis of responding within a trial, as the anticipation of frustration near the end of a trial is assumed to inhibit approach behavior among uncertain, but not certain, individuals due to a possible absence of reward delivery (e.g., Amsel et al, 1964; Chen et al, 1980)
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