Resurgence Following Higher or Lower Quality Alternative Reinforcement.

Resurgence is a temporary increase in a previously suppressed target behavior following a worsening in reinforcement conditions. Previous studies have examined how higher rates or magnitudes of alternative reinforcement affect suppression of the target behavior and subsequent resurgence. However, there has been no investigation of the effects of higher versus lower qualities of alternative reinforcement on resurgence. Using a three-phase resurgence preparation with rats, the present experiments examined the effects of an alternative reinforcer that was of higher (Experiment 1) or lower (Experiment 2) quality than the reinforcer that had previously maintained the target behavior. The results of both experiments showed greater reductions in target behavior with a higher quality alternative reinforcer and larger increases in target responding when a higher quality alternative reinforcer was removed. Along with prior findings with higher rates and magnitudes of alternative reinforcement, these findings suggest that variations in reinforcer dimensions that increase the efficacy of alternative reinforcement also tend to increase resurgence when alternative reinforcement is removed. The results are discussed in terms of the resurgence as choice in context model and in terms of potential clinical implications.

Consummatory successive positive contrast with aversive solutions in infant rats: Replication and generalization to a higher concentration of a bitter solution.

Successive positive incentive contrast is typically demonstrated when a group of subjects shows a higher consumption of a reinforcer than a control group, if they were previously exposed to a similar one of lower magnitude. Recently, a similar effect was observed by lowering the concentration of a quinine solution in the experimental group. On the other hand, the presence of a familiar odor has been shown to attenuate responses elicited by aversive stimuli in infant rats. This experiment was designed to assess if the presence of a familiar odor decreases the responses elicited by an aversive solution. Two groups of rats were exposed to a consummatory positive successive contrast procedure, decreasing the concentration of a quinine solution (i.e., 0.2-0.01 %). Half of the subjects in each group was tested in the presence of the homecage odor during the postshift phase. A positive successive contrast effect was evidenced by subjects in the experimental group, consuming more of the lower-concentration solution during the postshift phase. The presence of the odor, however, exerted no effect. Results are discussed in the context of the social buffering and positive successive contrast effects.

The presence of chemosensory cues transmitted through the mother's milk increases the search and ingestion responses toward bitter and sour solutions.

Olfaction is of major importance during early stages of life in altricial species. This sense allows newborns to develop different behaviors that will allow them to survive. Odors tend to be associated to contextual stimuli (such as warmth); this, in turn, enables the pups to recognize when to withdraw or approach. At the same time, olfaction modulates the acceptance of aversive flavors. The increase of approach responses toward a bitter substance during early life is enhanced by stimulation with familiar, pre-exposed odors. Newborn rats exhibit heightened grasp responses toward an artificial nipple dispensing quinine, and drink more of this bitter solution, in the presence of a pre-exposed odor (lemon or the mother's odor). The present research assessed the replicability of previous results by pre-exposing the subjects to the scent through maternal milk and using solutions with different aversive tastes. Half of the subjects (3 day-old Wistar rats) were pre-exposed to lemon odor through the maternal milk (the mother had previously ingested the lemon essence via an intragastric injection); 4 h later, all the rats were evaluated in the presence of the lemon odor with an artificial nipple containing quinine, citric acid, saline solution, or water. The results showed enhanced seeking and intake of the bitter (quinine) and sour solution (citric acid). However, this did not occur when the nipple contained water or saline solution. The evidence suggests that: During the early stages of development, familiar odors regulate the acceptance of non-palatable, otherwise rejected, flavors; and that the route of transmission of the pre-exposed odor can be through air, or through food (amniotic fluid in previous studies and, in this case, breast milk), that is, via the retronasal and orthonasal routes.

Event-related potential correlates of stimulus equivalence classes: A study of task order of the equivalence based priming probes with respect to the stimulus equivalence tests, and among the distinct trial types with each other.

This study investigates the influences of: 1) the task order of two stimulus equivalence classes (SEC) probes, and 2) the possible differences within the equivalence trial types. These factors were analyzed together on both behavioral and event-related potentials (ERP) data. Two groups of normal subjects participated in two successive sessions. In the first session, all participants were trained in the baseline relations among visual stimuli (pseudo-words). In the second session, one group performed the matching-to-sample (MTS) equivalence tests before the equivalence-relatedness-priming (EBRP) task, while the other group performed both tasks in reverse order. In the EBRP task related trial types included trained, symmetrical and equivalence relationships while the unrelated trial types included the same stimuli but without relationships. Event related potentials were recorded separately for related and unrelated conditions during the EBRP task. Results showed that response times to related trials were shorter than those to unrelated ones. At the electrophysiological level, two late waveforms were sensitive to the differences among the stimulus pairs of the EBRP task: Both waveforms were larger for the unrelated than the related conditions. Conversely, there were no main influences of the task order or of the trial types with each other. These results provide evidence that 1) the EBRP task exhibits priming effects among the SEC stimuli, 2) the behavioral and electrophysiological effects were similar regardless of whether the EBRP task was done before or after the MTS tests, and 3) there were no differences within the baseline and derived trial types in the EBRP task.

Ensombreciendo el surgimiento de clases de equivalencia / Overshadowing the formation of equivalence classes

Investigaciones actuales postulan que el condicionamiento respondiente (CR) es suficiente para establecer clases de equivalencia de estímulos (CEE). A su vez, el fenómeno de ensombrecimiento no se ha estudiado dentro del contexto de aprendizaje de CEE. Estudiar la influencia de procesos propios del CR se plantea como una forma de evaluar esta hipótesis. Tres clases de tres estímulos fueron entrenadas mediante una tarea de emparejamiento con la muestra. Cada clase estuvo compuesta por dos estímulos simples y un estímulo compuesto, conformado por dos estímulos de distinta saliencia. Luego se evaluó la emergencia de relaciones derivadas para los estímulos saliente y ensombrecido. La emergencia de CEE se observó en cuatro de 13 sujetos para el estímulo saliente y en ninguno para el estímulo ensombrecido. Estos resultados demuestran que la emergencia de relaciones derivadas es sensible al ensombrecimiento, y aporta evidencia respecto del rol del CR en la formación de CEE.

Current researches postulate that respondent conditioning (RC) is sufficient to establish Stimuli Equivalence Classes (SEC). In turn, the influency of the the overshadowing phenomenon has not been studied within the learning context of SEC. Studying the influence of RC\'s processes is posed as a way of evaluating this hypothesis. Three classes of three stimuli were trained through a matching to sample task. Each class consisted of two simple stimuli and one compound stimulus, consisting of two stimuli of different salience. The emergence of derived relationships for salient and overshadowed stimuli was then evaluated. Emergence of SEC was observed in four of 13 subjects for the salient stimuli and in none for the overshadowed stimuli. These results shown that the emergence of derived relationships is sensitive to overshadowing, and provides evidence regarding the role of RC in the formation of SEC.

Effects of mixed training structures on equivalence class formation

The experimental literature reports differences in performance when participants are tested for the emergence of derived relations after stimulus equivalences class training, depending on which training structured is used. Comparison-as-node and sample-as-node structures have shown to be more effective in producing the emergence of derived relations than linear series, with inconclusive results about which of the first two structures is more effective. Intertrial correspondence was manipulated between the stimuli via the use of mixed training structures. 48 participants were divided in four groups: the first received equivalence-class training using a sample-as-node structure, the second following a comparison-as-node structure, and the other two following a mixed structure with the same nodal density of the central node as the first two. The four groups were taught two five-member equivalence classes with a nodal density of four. Both during training and testing, the performances were higher for the sample-as-node and the comparison-as-node structures, compared to the other two structures. Results are discussed from the lens of hypotheses based on simple-discriminations learning and the role of samples and comparisons (AU)

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