Three groups of subjects received training in stimulus equivalence classes with a respondent-type training procedure. Stimulus contingency was positive for the first group, zero for the second, and negative for the third. Afterwards, all participants were tested with a matching-to-sample task for four baseline relations (A1-B1, A2-B2, C1-B1, and C2-B2), four symmetry relations (B1-A1, B2-A2, B1-C1, and C2-B2), and four combined symmetry and transitivity relations (A1-C1, A2-C2, C1-A1, and C2-A2). After this, they were retrained and retested twice. Explicit reinforcement was not programmed during the training or testing phases. The number of subjects who learned the baseline relations and showed the emergence of derived relations was higher in the positive contingency group than in the zero or negative contingency groups, although in all cases at least one retraining phase was required in order to reach the criteria. This finding contributes to the literature suggesting that stimulus pairing is the fundamental variable underlying emergent stimulus functions.

This review presents a critical reading of the literature on social buffering in human and non-human animals. The term social buffering has been coined to refer to an attenuation of stress responses by the presence of conspecifics. Evidence shows that the buffer seems to be specific for each stage of development, being the mother the factor that attenuates the stress responses during early development and conspecifics of the same age, later in life. An animal model of scarcity of resources revealed that when being reared by a stressed mother, the social buffering effect does not occur. The literature reviewed allows us to approach a key factor related to stress and its effects in the different stages of ontogeny.

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.

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