Corina Jimenez-Gomez

Differential outcomes enhance accuracy of delayed matching to sample but not resistance to change.

Three experiments assessed the relation between the differential outcomes effect and resistance to change of delayed matching-to-sample performance. Pigeons produced delayed matching-to-sample trials by responding on variable interval schedules in two components of a multiple schedule. In the same-outcome component, the probability of reinforcement was the same for both samples (.9 in Experiments 1 and 2, .5 in Experiment 3); in the different-outcomes component, the probability of reinforcement was .9 for one sample and .1 for the other. In all three experiments, the forgetting functions in the different-outcomes component were higher and shallower than in the same-outcomes component. When total reinforcement was greater in the same-outcomes component (Experiments 1 and 2), resistance to disruption by prefeeding, intercomponent food, extinction, or flashing lights typically was greater in that component. In Experiment 3, when total reinforcement was equated, resistance to disruption was similar across components. Thus, the level and slope of forgetting functions depended on differential reinforcement correlated with the samples, but the resistance to change of forgetting functions depended on total reinforcement in a component. Both aspects of the results can be explained by a model of delayed matching to sample performance.

Resistance to Change and Frequency of Response-Dependent Stimuli Uncorrelated with Reinforcement

Stimuli uncorrelated with reinforcement have been shown to enhance response rates and resistance to disruption; however, the effects of different rates of stimulus presentations have not been assessed. In two experiments, we assessed the effects of adding different rates of response-dependent brief stimuli uncorrelated with primary reinforcement on relative response rates and resistance to change. In both experiments, pigeons responded on variable-interval 60-s schedules of food reinforcement in two components of a multiple schedule, and brief response-dependent keylight-color changes were added to one or both components. Although relative response rates were not systematically affected in either experiment, relative resistance to presession feeding and extinction were. In Experiment 1, adding stimuli on a variable-interval schedule to one component of a multiple schedule either at a low rate (1 per min) for one group or at a high rate (4 per min) for another group similarly increased resistance to disruption in the components with added stimuli. When high and low rates of stimuli were presented across components (i.e., within subjects) in Experiment 2, however, relative resistance to disruption was greater in the component presenting stimuli at a lower rate. These results suggest that stimuli uncorrelated with food reinforcement do not strengthen responding in the same way as primary reinforcers.

Effects of initial-link duration on preference and resistance to change in concurrent-chains schedules

Previous studies with concurrent-chains procedures have shown that preference for a terminal-link signaling a higher reinforcement rate decreases as initial-link durations increase. Using a concurrent-chains procedure, the present experiment examined the effects of manipulating initial-link duration on preference and resistance to disruption with rats nose poking for different rates of food reinforcement in the terminal links. Consistent with previous findings, preference for a terminal link with a higher reinforcement rate decreased with longer initial links. Conversely, relative resistance to disruption in the terminal link with a higher reinforcement rate increased with longer initial links. These findings are counter to the prediction of behavioral momentum theory that preference and resistance to change should be positively related.

Concurrent Chains Schedules as a Method to Study Choice Between Alcohol Associated Conditioned Reinforcers

An extensive body of research using concurrent-chains schedules of reinforcement has shown that choice for one of two differentially valued food-associated stimuli is dependent upon the overall temporal context in which those stimuli are embedded. The present experiments examined whether the concurrent chains procedure was useful for the study of behavior maintained by alcohol and alcohol-associated stimuli. In Experiment 1, rats responded on concurrent-chains schedules with equal variable-interval (VI) 10-s schedules in the initial links. Across conditions, fixed-interval schedules in the terminal links were varied to yield 1∶1, 9∶1, and 1∶9 ratios of alcohol delivery. Initial-link response rates reflected changes in terminal-link schedules, with greater relative responding in the rich terminal link. In Experiment 2, terminal-link schedules remained constant with a 9∶1 ratio of alcohol delivery rates while the length of two equal duration initial-link schedules was varied. Preference for the rich terminal link was less extreme when initial links were longer (i.e., the initial-link effect), as has been previously reported with food reinforcers. This result suggests that the conditioned reinforcing value of an alcohol-associated stimulus depends on the temporal context in which it is embedded. The concurrent-chains procedure and quantitative models of concurrent chains performance may provide a useful framework within which to study how contextual variables modulate preference for drug-associated conditioned reinforcers.

TEMPORAL CONTEXT, PREFERENCE, AND RESISTANCE TO CHANGE

According to behavioral momentum theory, preference and relative resistance to change in concurrent-chains schedules are correlated and reflect the relative conditioned value of discriminative stimuli. In the present study, we explore the generality of this relation by manipulating the temporal context within a concurrent-chains procedure through changes in the duration of the initial links. Consistent with previous findings, preference for a richer terminal link was less extreme with longer initial links across three experiments with pigeons. In Experiment 1, relative resistance to change and preference were related inversely when responding was disrupted with response-independent food presentations during initial links, replicating a previous finding with rats. However, more food was presented with longer initial links, confounding the disrupter and initial-link duration. In Experiment 2, presession feeding was used instead and eliminated the negative relation between relative resistance to change and preference, but relative resistance to change was not sensitive to relative terminal-link reinforcement rates. In Experiment 3, with more extreme relative terminal-link reinforcement rates, increasing initial-link duration similarly decreased preference and relative resistance to change for the richer terminal link. Thus, when conditions of disruption are equal and assessed under the appropriate reinforcement conditions, changes in temporal context impact relative resistance to change and preference similarly.

Matching law analysis of rats' alcohol self-administration in a free-operant choice procedure.

The generalized matching law quantitatively describes the relation between relative response allocation and relative reinforcement allocation in a choice situation and has accounted well for drug-maintained choice behavior. Earlier studies applying the generalized matching law to alcohol-maintained choice, however, have produced somewhat atypical findings (e.g. poor fits, negative sensitivity values). These findings may be the result of the procedures used in the earlier alcohol studies (e.g. two-bottle choice procedure, variations in relative concentration of alcohol, volume consumed as dependent variable). This experiment examined the applicability of the generalized matching law to alcohol self-administration using procedures more similar to those typically used with other reinforcers. A free-operant choice procedure arranging concurrent variable-interval schedules of alcohol reinforcement was used to vary rates of alcohol deliveries produced by two response options. Results showed that the generalized matching law provided a good description of changes in the relative allocation of behavior with changes in the relative rate of alcohol delivery. Thus, the atypical results in earlier studies were likely a result of the procedures used. These results suggest that the parameters of the generalized matching law may provide useful quantitative measures of the impact biological and environmental variables on alcohol-associated choice behavior.