Acquired equivalence and distinctiveness of cues: I. Exploring a neural network approach

Rats were placed in 4 contexts (A, B, C, D) where they received 2 auditory stimuli (X, Y); in A and B, presentations of X were paired with food and those of Y were not, and in C and D, Y was paired with food and X was not. Rats then received combinations of contexts that had provided congruent (AB, CD) or incongruent (AD, CB) information about X and Y's relationship to food. Responding was more variable during congruent than incongruent trials (Experiment 1) and was systematically increased and decreased during congruent (relative to incongruent) trials by the presentation of food or no food, respectively (Experiment 2). These results support a connectionist approach to acquired changes in stimulus distinctiveness.     

Acquired equivalence and distinctiveness of cues: II. Neural manipulations and their implications

Neural manipulations were used to examine the mechanisms that underlie the acquired equivalence and distinctiveness of cues in rats. Control rats and those with excitotoxic lesions of either the hippocampus (HPC) or entorhinal cortex (EC) acquired the following conditional discrimination: In Contexts A and B, Stimulus X-->food and Stimulus Y-->no food, and in Contexts C and D, Y-->food and X-->no food. Rats then received many food pellets in A but not in C. After this treatment, control rats showed more magazine activity in B than in D--an acquired equivalence-distinctiveness effect. This effect was also evident in HPC rats but not in EC rats. These results indicate that changes in stimulus distinctiveness are dissociable from the process of conditional learning.     

Imitative learning of stimulus-response and response-outcome associations in pigeons

A novel automated procedure was used to study imitative learning in pigeons. In Experiments 1 and 2, observer pigeons witnessed a demonstrator pigeon successfully performing an instrumental discrimination in which different discriminative stimuli indicated which of 2 topographically distinct responses (R1 and R2) resulted in the delivery of seed. The observers were then presented with the discriminative stimuli and given access to the response panel. Observer pigeons' behavior during the discriminative stimuli was influenced by how the demonstrator had responded during these stimuli. In Experiment 3, observers witnessed demonstrator pigeons performing R1 for Outcome 1 and R2 for Outcome 2. Observers then received a procedure designed to devalue Outcome 1 relative to Outcome 2 and were subsequently less likely to perform R1 than R2. These results suggest that pigeons can learn both stimulus response and response-outcome associations by observation.     

Associative change in the representations acquired during conditional discriminations: further analysis of the nature of conditional learning

Three experiments with rats investigated how the associative strengths of the representations that underlie conditional learning change when they are conditioned in compound. The results of each experiment suggest that the representation whose associative strength is most discrepant from the asymptote supported by the outcome of the trial undergoes the greatest change in associative strength. These results parallel those from simple Pavlovian conditioning (e.g., R. A. Rescorla, 2000). are inconsistent with unique-cue and configural accounts of conditional learning, and support a connectionist analysis of learning in which a "winner-takes-all" rule applies to the hidden units that can be activated and acquire associative strength at a given point in time.     

Generalization of contextual fear as a function of familiarity: the role of within- and between-context associations

Three experiments in rats investigated the generalization of conditioned fear from one context (B) to both a preexposed context (A) and a novel context (C). In each experiment, when the conditioning context (B) had been preexposed, there was greater generalization to context A than to context C; but when B was novel at the outset of conditioning this difference between A and C was not observed. The implications of these results for associative treatments of the development of contextual memories are evaluated.     

Encoding specific associative memory: evidence from behavioral and neural manipulations

Within-subjects procedures with rats assessed the associative structures acquired during conditioning trials in which the interval between the stimuli and food was either short or long (i.e., A-10 s→food and B-40 s→food). In Experiments 1 and 2, after these conditioning trials, A and B served as second-order reinforcers for 2 further stimuli (i.e., X→A and Y→B); whereas Experiment 3 used a sensory preconditioning procedure in which X→A and Y→B trials occurred before the conditioning trials, and rats were finally tested with X and Y. In each experiment, Y elicited greater responding at test than did X. This finding supports the contention that the long-lived trace of B (associated with food on B-40 s→food trials) is more similar to the memory of B that was associatively provoked by Y, than is the short-lived trace of A (associated with food on A-10 s→food trials) to the memory of A that was associatively provoked by X. These conclusions were reinforced by the effects of a neural manipulation that disrupted discrimination learning involving the short traces of stimuli but not the long traces of the same stimuli.     

Perceptual learning and acquired face familiarity: Evidence from inversion,use of internal features,and generalization between viewpoints

Pairs of similar faces were created from photographs of different people using morphing software. The ability of participants to discriminate between novel pairs of faces and between those to which they had received brief, unsupervised, exposure (5×2 s each) was assessed. In all experiments exposure improved discrimination performance. Overall, discrimination was better when the faces were upright, but exposure produced improved discrimination for both upright and inverted faces (Experiment 1). The improvement produced by exposure was selective to internal face features (Experiment 2) and was evident when there was a change in orientation (three-quarter to full face or vice versa) between exposure and test (Experiment 3). These findings indicate that perceptual learning observed following brief exposure to faces exhibit well-established hallmarks of familiar face processing (i.e., internal feature advantage and insensitivity to a change of viewpoint). Considered in combination with previous studies using the same type of stimuli (Mundy, Honey, & Dwyer, 2007), the current results imply that general perceptual learning mechanisms contribute to the acquisition of face familiarity.     

The Experimental Psychology Society Prize Lecture: Associative Priming in Pavlovian Conditioning

Any occasion on which an animal is placed in an experimental setting or context and receives pairings of one event with another provides the opportunity for a variety of associative structures to be acquired. These structures range from simple associations, which allow the presentation of one event to activate or prime a memory of the other, to hierarchical associations, which allow a simple association to be primed by some other event (e.g. the context in which the simple association was acquired). Experiments with rats that reveal priming effects consistent with both of these putative associative structures are reviewed.     

Perceptual learning in humans: Roles of preexposure schedule, feedback, and discrimination assay

In three experiments, humans received preexposure to two compound flavours (AX and BX: saline-lemon and sucrose-lemon) that were presented either in an intermixed (e.g., AX, BX, . . . BX, AX, . . .) or a blocked (e.g., AX, AX, . . . BX, BX. . .) fashion. Subsequently, AXwas paired with an unpleasant bitter taste, and the discriminability of AX and BX was assessed using the accuracy of same/different judgements and by the extent to which any learned dislike of AX generalized to BX. When participants received feedback about the accuracy of their same/different judgements during preexposure those given intermixed preexposure were more accurate in making these judgements during the test than those given blocked preexposure (Experiments 1 and 2A), however, there was no evidence of any learned dislike in these experiments. In Experiment 2B, in which participants did not receive feedback about the accuracy of their judgements, there was no effect of the preexposure regime on same/different judgements, but there was a learned dislike of AX, and this generalized less to BX in participants given intermixed than in those given blocked preexposure. The beneficial effects of intermixed preexposure are consistent with results from other species (chicks and rats), but the differences created by the presence or absence of feedback place constraints on the analysis of these effects.