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13. The essential value of the
alternatives of the suboptimal choice procedure is different for pigeons and
rats

13. The essential value of the alternatives of the suboptimal choice procedure is different for pigeons and rats

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Gabriela E. López-Tolsa-Universidad Nacional Autónoma de México José
Manuel Niño-Universidad Nacional Autónoma de México Vladimir Orduña-Universidad
Nacional Autónoma de México

Gabriela E. López-Tolsa-Universidad Nacional Autónoma de México José Manuel Niño-Universidad Nacional Autónoma de México Vladimir Orduña-Universidad Nacional Autónoma de México

Introduction. The suboptimal choice procedure consists on giving an organism a choice between a discriminative alternative with a low probability of reinforcement, and a non-discriminative alternative with higher probability of reinforcement. In most experiments, pigeons choose the discriminative alternative and rats choose the non-discriminative alternative. On the other hand, the economic concept of essential value (EV), derived from fitting an exponential model of demand to data obtained from exposing an organism to increasing fixed-ratio schedules, has been shown to predict choice among different primary and conditioned reinforcers. Objective. The main goal of this study was to calculate the EV of each of the alternatives of the suboptimal choice procedure to assess if it can predict choice. Method. Eight pigeons and 8 rats were exposed in different conditions to each of the alternatives of the suboptimal choice procedure. Throughout sessions the FR requirement in the initial link for each alternative was increased from 1 to 120 in order to obtain the demand curve and calculate the essential value. Results. Pigeons showed higher EVs in the discriminative alternative, whereas rats showed higher EVs in the non-discriminative alternative. Discussion. Results of this study support the hypothesis that EV of each alternative may predict results in the suboptimal choice procedure, so further research manipulating variables that can affect choice should be tested.

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14. Probability and Reward Amount
Differentially Affect Response Rates and Latencies

14. Probability and Reward Amount Differentially Affect Response Rates and Latencies

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Jorge Mallea - Columbia University Atara Schulhof - Barnard
College Peter Balsam - Columbia University, Barnard College

Jorge Mallea - Columbia University Atara Schulhof - Barnard College Peter Balsam - Columbia University, Barnard College

Changes in unconditioned stimulus (US) probability affect the level of conditioned responding. However, these changes are confounded with changes in uncertainty and total amount of reward. In the present experiment, we aimed to differentiate between these elements influencing subjects’ behavior. Five groups of mice varied in their probability of reinforcement (.25, .50, .50x2, .75, and 1.0). Two groups (.50 and.50x2) shared the same probability of reinforcement but group .50x2 received twice the reward amount on every reinforced trial. Thus, group .50x2 received the same total number of rewards as group 1.0. Groups .25 and .75 had the same uncertainty, even if differing in their probability of reinforcement and the amount of reward. Groups .50 and .50x2 had the highest level of uncertainty, while group 1.0 had the least uncertainty. After this phase, all subjects went through 4 sessions of extinction with no reinforcement delivery. Response rates, latencies and probability of responding are influenced by probability of reinforcement. In addition, latencies are modulated by total amount of reward. During extinction, subjects with higher probability of reinforcement showed quicker extinction (i.,e. Partial Reinforcement Extinction Effect; PREE). These results suggest that probability plays a big role in the acquisition and extinction of appetitive conditioning and this role appears to be independent of the uncertainty with which the CS signals the US. Furthermore, latencies appear to be regulated by the total amount of reward predicted by the CS.