Charlotte Bonardi

Context specificity of conditioning in flavor-aversion learning: Extinction and blocking tests

In three experiments using rats as subjects, we investigated the degree to which a conditioned flavor aversion transfers from one context to another. Experiment 1, using a one-trial conditioning procedure, found no effect of a change of context on a conditioned aversion. Experiment 2 employed a multitrial procedure and demonstrated that a conditioned aversion was extinguished more rapidly after a change of context. Experiment 3 showed that context change decreased the effectiveness with which a conditioned flavor could block acquisition of an aversion by a second flavor. It is argued that these data cannot be explained in associative terms, and that they constitute evidence of conditionality in a simple aversive conditioning procedure.

Enhanced stimulus-reward learning by intra-amygdala administration of a D3 dopamine receptor agonist

Abstract The amygdala is considered to be a critical neural substrate underlying the formation of stimulus-reward associations, and is known to receive substantial innervation from dopaminergic neurons located within the ventral mesencephalon. However, relat- ively little is known about the function of the mesoamygdaloid dopamine projection in stimulus-reward learning. Recently, we have found post-session intra-amygdala microinjections of d-amphetamine to enhance appetitive Pavlovian conditioning as assessed in a discriminative approach task. In the present study, we have examined the effects of dopamine receptor agonists possessing relative selectivity for the D1, D2 and D3 receptor subtypes in order to examine more fully the role of the mesoamygdaloid dopamine projection in stimulus-reward learning. Thus, subjects were trained to associate an initially neutral stimulus (CS+) with 10% sucrose reward (US). A second, control stimulus (CS−) was also presented but never paired with sucrose reward. In order to measure specifically the conditioned response to CS+/CS− presentation, responding during CS and US presentations was measured separately. Immediately following each training session, subjects received bilateral intra-amygdala infusion of 0.1, 1 or 10 nmol/side of SKF-38393, quinpirole or 7-OH-DPAT. Infusions of SKF-38393 or quinpirole were without effect on CS+ approach. However, post-session intra-amygdala infusions of 7-OH-DPAT enhanced selectively CS+ approach in a dose-dependent fashion. No dose of any drug affected CS−approach, US behaviours, or measures of extraneous behaviour. Subsequent acquisition of a novel conditioned instrumental response was also unaffected. Thus, the present data indicate a selective involvement of the D3 dopamine receptor subtype in the modulation of stimulus-reward learning by the mesoamygdaloid dopamine projection.

Enhancement of Latent Inhibition in Rats With Electrolytic Lesions of the Hippocampus

Two groups of rats--1 with electrolytic lesions of the hippocampus and 1 consisting of sham-operated controls--received flavor-aversion conditioning with 2 flavors. All subjects had received prior nonreinforced exposure to Flavor A. Latent inhibition was apparent in slower acquisition of the aversion to Flavor A than to Flavor B. Hippocampal lesions had no effect on acquisition to the nonpreexposed Flavor B but produced a marked enhancement of the latent inhibition effect. The contrast between this result and previous findings of an attenuation of latent inhibition in subjects with hippocampal lesions is discussed.

Acquired equivalence between cues trained with a common antecedent.

In Experiment 1, rats experienced 2 stimuli (A and N) each preceded by the same event (food) or by different events (food preceded 1 but not the other). N was then paired with shock, and the generalization of conditioned suppression to A was assessed. Generalization was more marked when A and N had been experienced along with a common antecedent. In Experiment 2, 3 stimuli (A, B, and N) were presented in initial training. For 1 group, A and N were preceded by food and B was not; for a 2nd group A alone was preceded by food. In each group, suppression generalized more readily from N to the stimulus that had received the same initial training as had been given to N. Experiment 3 found that generalization was not enhanced between stimuli when 1 had preceded food in initial training and 1 had followed it. These results demonstrate that stimuli that have shared a common antecedent will come to be treated as equivalent.

Learned Irrelevance: No More Than the Sum of CS and US Preexposure Effects?

In the 1st experiment, 1 group of rats (Group Learned Irrelevance [LIRR]) experienced uncorrelated presentations of a noise and shock; a 2nd group (Group Control [CON]) experienced noise and shock in separate phases of training. Six conditioning sessions followed, each consisting of a single noise-shock pairing. Group LIRR conditioned to the noise more quickly than Group CON. The 2nd experiment was identical to the 1 st, except that rats were given 6 noise-shock pairings in each conditioning session. In this experiment, Group LIRR learned more slowly than Group CON. These results suggest that learned irrelevance is in part the product of context specificity of latent inhibition, in which the context is the aftereffect of shock presentation. The implications of this for theories of learned irrelevance are discussed.

Negative priming in associative learning: Evidence from a serial-conditioning procedure

Three experiments investigated the suggestion that a predicted or primed stimulus commands less processing and consequently elicits a weaker conditioned response (CR) than a stimulus that is not primed. In each experiment rats received initial training in which the presentation of each of 2 serial compounds, A-X and B-Y, was followed by the delivery of food. Subsequently, Xs capacity to elicit the CR, approaching the site of food delivery, was assessed when X was preceded by Stimulus A (i.e., primed) or was presented after Stimulus B. Stimulus X elicited a more vigorous response when it was presented after B than when it followed A. These results show that the ability of one event to elicit its CR is reduced if its presentation has been predicted by some other event. This negative priming effect supports one aspect of Wagners (1981) model of Pavlovian conditioning.

Acquired equivalence of cues in pigeon autoshaping: Effects of training with common consequences and with common antecedents

In three experiments, we sought evidence for the acquired equivalence of cues in pigeons trained in an autoshaping paradigm. In Experiment 1, presentations of each of a pair of cues (different keylight stimuli) preceded a common consequence (a different keylight stimulus). The pattern of response then established by further training given to one member of the pair was found to generalize preferentially to the other, demonstrating equivalence between cues that had shared a common consequence. The same test procedure was used in Experiment 2, but with a training procedure in which each cue of a pair was preceded by a given stimulus. This too resulted in enhanced generalization between members of the pair, showing that equivalence can be established when cues have been experienced along with a common antecedent. Both training procedures were combined in Experiment 3 to confirm the reliability of the effects previously obtained. The discussion is focused on ways in which the associative explanation offered for cases of equivalence mediated by a common consequence might be extended to accommodate equivalence mediated by a common antecedent.

Acquired distinctiveness and equivalence in human discrimination learning: Evidence for an attentional process

In a first stage of training, participants learned to associate four visual cues (two different colors and two different shapes) with verbal labels. For Group S, one label was applied to both colors and another to both shapes; for Group D, one label was applied to one color and one shape, and the other label to the other cues. When subsequently required to learn a task in which a given motor response was required to one of the colors and one of the shapes, and a different response to the other color and the other shape, Group D learned more readily than Group S. The task was designed so that the associations formed during the first stage of training could not generate differential transfer to the second stage. The results are consistent, however, with the proposal that training in which similar cues are followed by different outcomes will engage a learning process that boosts the attention paid to features that distinguish these cues.

Contextual Control of Conditioned Responding in Rats With Dorsal Hippocampal Lesions

The control exerted by contextual cues over classically conditioned responding was assessed for rats with electrolytic lesions of the dorsal hippocampus and sham-operated controls. In 3 experiments the rats received initial training with 2 reinforced cues, each presented in its own distinctive context, followed by a nonreinforced test in which the cues were presented in the other context. Both control and operated subjects showed context specificity, as evidenced by less vigorous responding to these cues than to cues presented on test in their original contexts. The groups did not differ in their ability to learn an explicit discrimination in which a given cue was reinforced in one context and nonreinforced in a different context (although the groups did differ on a simple autoshaping task). It is concluded that a special role for the hippocampus in the contextual control of conditioned responding still remains to be demonstrated.

Inhibitory discriminative control is specific to both the response and the reinforcer

In two experiments an S delta was established which signalled the absence of an instrumental contingency between a particular response, R1, and a particular reinforcer, Rf1. The S delta suppressed operant responding, and the specificity of this suppression to the elements of the response-reinforcer association, R1 and Rf1, was explored. Experiment 1 showed that the S delta suppressed performance of R1 more effectively than it suppressed performance of a second response, R2. Experiment 2 showed that the S delta suppressed performance of a response rewarded with Rf1 more effectively than it suppressed performance of a response that had been rewarded with a second reinforcer, Rf2. These results suggest that an S deltas suppressive effects are specific to the particular response and reinforcer, which were uncorrelated in its presence during training. The implications of these results for theories of inhibitory discriminative control and for theories of occasion setting are discussed.