Biomedical subjects

R C Barnet

Publications and source records attributed to R C Barnet.

11 recordsLinked to original sources

PubMed1998

Temporal coding in Pavlovian conditioning: Hall-Pearce negative transfer.

The Hall-Pearce (1979) negative transfer effect in rats was used to examine whether temporal relationships are coded as part of the informational content of associations that results from CS-US pairings. The transfer effect consists of a deficit in conditioned responding following CS-USstrong pairings in Phase 2 that results from prior CS-USweak pairings in Phase 1. Using conditioned bar-press suppression, we found that gaps of different duration between CS termination and US onset in the two training phases resulted in less of a Hall-Pearce negative transfer effect than did an equivalent gap in the two training phases. The results are discussed with respect to the temporal coding hypothesis (Matzel, Held, & Miller, 1988), the Pearce and Hall (1980) model, and Bouton's (1993) interference model.

Animals↗

PubMed1996

Second-order excitation mediated by a backward conditioned inhibitor.

Conditioned suppression studies with rats explored the informational content of a backward conditioned inhibitor. Pairings of an unconditioned stimulus (US) and Stimulus 1 (US-->S1) established S1 as an inhibitor in Experiment 1. Pairing the inhibitor S1 with a novel S2 (S2-->S1) promoted excitatory second-order conditioning (SOC) to S2, which suggested S1 was well associated with the US. Degrading presumed S1-US associations in Experiment 2 by S1- (extinction) treatment eliminated S2's excitation while preserving S1's inhibition. Experiments 3 and 4 converged in showing that S2 was not an excitor when Pavlovian conditioned inhibition (CI) was the inhibitory treatment prior to the SOC phase, but instead acted as a second-order inhibitor. Results are discussed in relation to the temporal coding hypothesis, the SOP ("sometimes opponent process") and Rescorla-Wagner models of conditioning, and the associative structure of SOC. Also, the data suggest that backward inhibition is special and that not all forms of CI are equal.

Animals↗

PubMed1995

Effect of relative stimulus validity: learning or performance deficit?

This research examined whether the effect of relative stimulus validity (A.R. Wagner, F.A. Logan, K. Haberlandt, & T. Price, 1968) is a deficit of acquisition or performance. Experiment 1 demonstrated the relative validity effect using rats in a conditioned lick suppression. task. A target cue trained in the presence of another cue that was a more valid predictor of reinforcement exhibited less behavioral control than a target cue that had been trained in the presence of an equally valid predictor of reinforcement. In Experiment 2, the more valid predictor was extinguished after training. This manipulation increased responding to the target cue, thereby attenuating the effect of low relative validity. This outcome suggests that the relative validity effect is a performance deficit. In addition, recovery from the relative validity deficit was specific to the particular target stimulus that was trained in the presence of the subsequently extinguished cue.

Animals↗

PubMed1995

Assessment of the Rescorla-Wagner model.

The Rescorla-Wagner model has been the most influential theory of associative learning to emerge from the study of animal behavior over the last 25 years. Recently, equivalence to this model has become a benchmark in assessing connectionist models, with such equivalence often achieved by incorporating the Widrow-Hoff delta rule. This article presents the Rescorla-Wagner model's basic assumptions, reviews some of the model's predictive successes and failures, relates the failures to the model's assumptions, and discusses the model's heuristic value. It is concluded that the model has had a positive influence on the study of simple associative learning by stimulating research and contributing to new model development. However, this benefit should neither lead to the model being regarded as inherently "correct" nor imply that its predictions can be profitably used to assess other models.

Association Learning↗

PubMed1994

Trial spacing and trial distribution effects in Pavlovian conditioning: contributions of a comparator mechanism.

A potential basis for trial spacing and trial distribution effects was investigated in rats. In Experiment 1, a conditioned stimulus (e.g., CS A) was trained with either massed (e.g., A---->A---->A) or spaced (e.g., A-->A-->A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Experiment 2, different CSs were trained in either a massed (e.g., A-->A-->A--> B-->B-->B-->C-->C-->C) or a distributed (e.g., A-->B-->C-->A-->B-->C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects are at least in part reversible deficits in performance rather than failures of learning.

Animals↗

PubMed1994

Second-order conditioning and Pavlovian conditioned inhibition: operational similarities and differences.

Procedures for establishing second-order excitation (conditioned stimulus [CS] 1-unconditioned stimulus [US] trials followed by CS2-CS1 trials) are highly similar to those for Pavlovian conditioned inhibition (CS1-US trials interspersed with CS2-CS1 trials). Conditioned suppression in rats was used to identify the critical operational differences that result in second-order excitation as opposed to Pavlovian inhibition. No, few, or many CS2-CS1 trials were either interspersed with or given after CS1-US trials. CS2 proved excitatory only after few CS2-CS1 trials, either interspersed or sequential (Experiment 1). In contrast, CS2 proved inhibitory on both summation (Experiment 2) and retardation (Experiment 3) tests only after many CS2-CS1 trials, and then only when the excitatory status of CS1 was preserved. Apparently, the critical difference for establishing second-order excitation or Pavlovian inhibition is the number of CS2-CS1 pairings.

Animals↗

PubMed1993

Temporal encoding as a determinant of blocking.

A blocking paradigm with rats was used to evaluate whether different temporal information is encoded in simultaneous rather than forward associations. During Phase 1, the blocking conditioned stimulus (CS) was simultaneously or forward paired with an unconditioned stimulus (US). During Phase 2, the pretrained CS occurred in compound with a novel target CS that was paired in a simultaneous or forward manner with the US. Forward pretraining resulted in more blocking of a forward than a simultaneously trained target CS, and simultaneous pretraining resulted in more blocking of a simultaneously than a forward trained target CS. Thus, greater blocking occurred when the blocking and blocked CSs had the same temporal relation to the US. The results support the temporal coding hypothesis and question the necessity of predictive information in blocking.

Animals↗

PubMed1993

Local time horizons in Pavlovian learning.

Responding to a conditioned stimulus (CS) is impaired if the CS is trained in the presence of excitatory local context cues. Four lick suppression experiments with rats explored whether this local context effect arises from the influence of excitatory cues that precede or that follow a reinforced target CS. Pretrained nontarget stimuli served as local context cues that occurred (a) immediately before and after the target CS trial, (b) immediately before or after the target CS trial, or (c) only before or after the target CS trial with varying intervals between the nontarget stimulus and target CS. Results indicated similar control over responding to the target CS by the preceding and following nontarget cues. This outcome implies a symmetrical window of memory integration (local time horizon) for a Pavlovian CS. Possible mechanisms underlying the detrimental effect of embedding a CS in an excitatory local context are discussed.

Animals↗

PubMed1992

Responding to a conditioned stimulus depends on the current associative status of other cues present during training of that specific stimulus.

The comparator hypothesis is a response rule stating that responding to a Pavlovian conditioned stimulus (CS) reflects the associative strength of the CS relative to that of other cues (comparator stimuli) that were present during CS training. Thus, modulation of the associative strength of a CS's comparator stimulus should alter responding to that CS. These studies examined the stimulus specificity of this effect using within-subjects designs. Rats were trained on 2 CSs, each with a unique comparator stimulus, to determine the degree to which posttraining extinction of the comparator stimulus for one CS influences responding to the other CS. Using negative contingency (Experiments 1 and 2), overshadowing (Experiment 3), and local context (Experiment 4) preparations, stimulus specificity was observed. In each case, posttraining extinction of the comparator stimulus for one CS had greater impact on responding to that CS than on responding to the alternate CS.

Animals↗

PubMed1991

Irrelevance of sample stimuli and directed forgetting in pigeons.

A successive matching procedure was used to investigate which aspect of the test-omission procedure is responsible for establishing a postsample stimulus as a cue to forget in pigeons. It was found that a postsample stimulus that reliably followed a sample that was irrelevant to performance functioned as a cue to forget. This result was obtained regardless of whether termination of that postsample stimulus was followed by reinforcement or by the presentation of sample-independent discriminative stimuli. It was also found that a postsample stimulus that functioned as a cue to forget at the beginning of training lost that function when it was repeatedly presented on trials in which the sample was relevant to performance. These findings reveal that (a) neither a reduction in reinforcement rate nor the omission of the opportunity for discriminated responding is necessary to establish an effective cue to forget and (b) irrelevance of the sample to performance is a sufficient condition to establish a cue to forget. These results suggest that a postsample stimulus that is presented on trials in which remembering the sample is not reinforced differentially will come to set the occasion for not remembering the sample.

Journal Article↗

PubMed1990

Suboptimal choice in a percentage-reinforcement procedure: effects of signal condition and terminal-link length.

Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.

Animals↗