Whisker-mediated texture discrimination learning in freely moving mice

Texture is often used as a convenient stimulus dimension to study aspects of discrimination learning in rodents. However, the basis of texture discrimination learning is often left untested: Although learning could involve the whisker system, it could also be based on other senses (e.g., olfactory or visual). Here, we investigated whether mice use their whisker system to learn texture discriminations. Mice were placed in an apparatus illuminated with a dim red light, and the mice had to learn which of 2 sawdust-filled bowls contained a buried reward. The outer surfaces of the bowls were 3-D printed with different textures (grooved or smooth). Within a 60-min session, mice learned to dig in 1 bowl (e.g., grooved) rather than the other (e.g., smooth) to gain the reward. This texture discrimination and an equivalent odor discrimination were retained overnight (Experiments 1 and 2); and whisker trimming disrupted learning based on the texture of the bowls but not learning based on the odor of the sawdust in the bowls (Experiments 3 and 4). These results provide a secure basis upon which to investigate the behavioral and brain basis of texture learning in rodents. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The nature of phenotypic variation in Pavlovian conditioning

Pavlovian conditioning procedures result in dramatic individual differences in the topography of learnt behaviors in rats: When the temporary insertion of a lever into an operant chamber is paired with food pellets, some rats (known as sign-trackers) predominantly interact with the lever, while others (known as goal-trackers) predominantly approach the food well. Two experiments examined the sensitivity of these two behaviors to changing reinforcement contingencies in groups of male and female rats exhibiting the different phenotypes (i.e., sign-trackers and goal-trackers). In both phenotypes, behavior oriented to the food well was more sensitive to contingency changes (e.g., a reversal in which of two levers was reinforced) than was lever-oriented behavior. That is, the nature of the two behaviors differed independently of the rats in which they were manifest. These results indicate that the behavioral phenotypes reflect the parallel operation of a stimulus-stimulus associative process that gives rise to food-well activity and a stimulus-response process that gives rise to lever-oriented activity, rather than the operation of a single process (e.g., stimulus-stimulus) that generates both behaviors. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

The origins of individual differences in how learning is expressed in rats: A general-process perspective

Laboratory rats can exhibit marked, qualitative individual differences in the form of acquired behaviors. For example, when exposed to a signal-reinforcer relationship some rats show marked and consistent changes in sign-tracking (interacting with the signal; e.g., a lever) and others show marked and consistent changes in goal-tracking (interacting with the location of the predicted reinforcer; e.g., the food well). Here, stable individual differences in rats’ sign-tracking and goal-tracking emerged over the course of training, but these differences did not generalize across different signal-reinforcer relationships (Experiment 1). This selectivity suggests that individual differences in sign- and goal-tracking reflect differences in the value placed on individual reinforcers. Two findings provide direct support for this interpretation: the palatability of a reinforcer (as measured by an analysis of lick-cluster size) was positively correlated with goal-tracking (and negatively correlated with sign-tracking); and sating rats with a reinforcer affected goal-tracking but not sign-tracking (Experiment 2). These results indicate that the observed individual differences in sign- and goal-tracking behavior arise from the interaction between the palatability or value of the reinforcer and processes of association as opposed to dispositional differences (e.g., in sensory processes, “temperament,” or response repertoire).

Observational Learning of Instrumental Discriminations in the Rat: The Role of Demonstrator Type

In two experiments, observer rats saw a pretrained demonstrator rat of either the same or a different strain engaging in a discrimination task in which the presentation of a discriminative stimulus indicated whether performing a particular response (pulling a chain) would be reinforced. In both experiments an effect of demonstrator familiarity was found: Observers of a demonstrator from a different strain behaved in a manner that was consistent with the demonstrator whereas observers of a demonstrator from the same strain did not. These results suggest that an effect akin to latent inhibition operates in the social domain: Familiarity with the demonstrator retards the readiness with which observational learning proceeds.

Perceptual Learning during Filial Imprinting: Evidence from Transfer of Training Studies

Chicks were first imprinted by exposing them to a moving training stimulus, B or C, that was projected onto a screen at one end of an experimental cabinet. Subsequently, subjects selectively approached the stimulus to which they had been exposed. On the following day, the chicks were placed into a chilled experimental cabinet (15°C) and received trials on which two stimuli (A and B) were projected onto screens located at opposite ends of the cabinet. If the subject approached Stimulus A, a stream of warm air was delivered; if it approached B, the trial terminated, and no heat was presented. For subjects that had been imprinted with Stimulus B, those in Group B, Stimulus A was novel, and Stimulus B was familiar. For chicks that had been imprinted with Stimulus C, Group C, both A and B were novel. In two experiments, Group B acquired the discrimination more rapidly than did Group C. This observation, made using a novel training procedure, was taken to support the suggestion that imprinting results in a form of perceptual learning in which the familiar imprinting object has become more discriminable from other novel objects.

Revisiting places passed: Sensitization of exploratory activity in rats with hippocampal lesions

We examined the involvement of the hippocampus in short-term changes in exploratory behaviour in an open field (Experiment 1) and experimental contexts (Experiment 2). In Experiment 1, rats with excitotoxic lesions of the hippocampus were more likely to revisit recently visited zones within the open field than were control rats. Similarly, in Experiment 2 rats with hippocampal lesions showed greater exploration of a context that they had recently explored than a context that they had less recently explored. This short-term sensitization effect was not evident in control rats. These findings are consistent with the suggestion that the recent presentation of a stimulus has two opposing effects on behaviour, sensitization, and habituation, and that hippocampal lesions disrupt the short-term process responsible for habituation, but not that responsible for sensitization.

Mediated configural learning in rats

Three experiments investigated mediated configural learning in male rats. In Experiment 1, after exposure to audio-visual compounds AX and BY, rats received trials where X was paired with shock, and Y was not. The idea that conditioning with X enables the evoked configural representation of AX to be linked to shock received support from the facts that while AX provoked more fear than BX, there was no difference between BY and AY. Similarly, Experiment 2 showed that after exposure to AX and BY, separate pairings of X and Y with shock resulted in more fear to AX and BY than AY and BX. In Experiment 3, rats in group consistent received separate exposures to A and X in Context C, and B and Y in D, while those in group inconsistent received A and X (and B and Y) in both C and D. After rats had received shocks in both C and D, rats in group consistent showed more fear to AX and BY than to BX and AY, but this was not the case in group inconsistent. These results indicate that configural representations, formed either by presenting auditory and visual stimuli as parts of a compound or in a shared context, are subject to a process of mediated learning.

Perceptual learning with tactile stimuli in rats: Changes in the processing of a dimension

Four experiments with male rats investigated perceptual learning involving a tactile dimension (A, B, C, D, E), where A denotes 1 end of the continuum (e.g., a rough floor) and E the other (e.g., a smooth floor). In Experiment 1, rats given preexposure to A and E learned an appetitive discrimination between them more readily than those not given preexposure. Experiment 2a showed that rats preexposed to B and D acquired a discrimination between A and E more readily than those preexposed to A and E; and in Experiment 2b the same preexposure treatments had no effect on the acquisition of a discrimination between B and D. In Experiments 3a and 3b, rats given preexposure to C learned a discrimination between A and E more readily than those not given preexposure. Experiment 4 demonstrated that preexposure to a texture (e.g., B) that was adjacent to the to-be-discriminated textures (e.g., C and E) facilitated a discrimination between them relative to preexposure to their midpoint (D). These novel perceptual learning effects are interpreted as reflecting a redistribution of processing between the notional elements of the texture dimension.

Goal-oriented training affects decision-making processes in virtual and simulated fire and rescue environments

Decisions made by operational commanders at emergency incidents have been characterized as involving a period of information gathering followed by courses of action that are often generated without explicit plan formulation. We examined the efficacy of goal-oriented training in engendering explicit planning that would enable better communication at emergency incidents. While standard training mirrored current operational guidance, goal-oriented training incorporated "decision controls" that highlighted the importance of evaluating goals, anticipated consequences, and risk/benefit analyses once a potential course of action has been identified. In Experiment 1, 3 scenarios (a house fire, road traffic collision, and skip fire) were presented in a virtual environment, and in Experiment 2 they were recreated on the fireground. In Experiment 3, the house fire was recreated as a "live burn," and incident commanders and their crews responded to this scenario as an emergency incident. In all experiments, groups given standard training showed the reported tendency to move directly from information gathering to action, whereas those given goal-oriented training were more likely to develop explicit plans and show anticipatory situational awareness. These results indicate that training can be readily modified to promote explicit plan formulation that could facilitate plan sharing between incident commanders and their teams.

Avoidance but not aversion following sensory preconditioning with flavors: a challenge to stimulus substitution

After two neutral stimuli have been paired (AB), directly conditioning a response to one of them (A) will also be reflected in a change in responding to the other (B). Standard accounts of this sensory preconditioning effect assume that it is mediated by a memory involving the stimulus that was directly conditioned (i.e., A). The reliance on this shared pathway implies that sensory preconditioning (involving B) and direct conditioning (involving A) should support qualitatively similar patterns of responding. In three experiments, directly pairing A with lithium chloride (LiCl) delivery resulted in both a reduction in consumption of A (i.e., avoidance) and a reduction in the size of licking clusters it elicits (i.e., aversion). In contrast, the sensory preconditioning effect resulted in a reduction in the consumption of B but no change in the nature of the licking response that it elicited; and a similar dissociation was observed after trace conditioning. These dissociations involving direct conditioning and sensory preconditioning, observed over a range of flavor concentrations and different doses of LiCl, undermine standard accounts of sensory preconditioning that are based on the assumption of stimulus substitution.

Re-assessing causal accounts of learnt behavior in rats

Rats received either a common-cause (i.e., A→B, A→food) or a causal-chain training scenario (i.e., B→A, A→food) before their tendency to approach the food magazine during the presentation of B was assessed as a function of whether it was preceded by a potential alternative cause. Causal model theory predicts that the influence of an alternative cause should be restricted to the common-cause scenario. In Experiment 1, responding to B was reduced when it occurred after pressing a novel lever during the test phase. This effect was not influenced by the type of training scenario. In Experiment 2, rats were familiarized with the lever prior to test by training it as a potential cause of B. After this treatment, the lever now failed to influence test responding to B. In Experiment 3, rats given common-cause training responded more to B when it followed a cue that had previously been trained as a predictor of B, than when it followed another stimulus. This effect was not apparent in rats that received causal-chain training. This pattern of results is the opposite of that predicted by causal model theory. Thus, in three experiments, the presence of an alternative cause failed to influence test responding in manner consistent with causal model theory. These results undermine the application of causal model theory to rats, but are consistent with associative analyses.

Working memory and multidimensional schizotypy: dissociable influences of the different dimensions

Compromised working memory is considered a core deficit of schizophrenia and a potential endophenotype for the liability to develop schizophrenia. In keeping with this suggestion, working memory has also been found to be disrupted in people with high levels of schizotypy. However, it is unclear whether this disruption is linked to positive, negative, or disorganized symptoms/characteristics. This issue is the focus of the present investigation. The relationship between multidimensional schizotypy and working memory performance was investigated in 289 participants. Working memory was measured using an n-back task with three conditions; 0-back, 1-back, and 2-back. Covarying for the effect of shared variance between the schizotypy dimensions, we found reduced working memory performance in participants who displayed high levels of positive schizotypy and, to some extent, in participants with low levels of negative schizotypy. The results are discussed in terms of Baddeley's (1986) model of working memory and potential underlying neurological mechanisms.

Analysis of the content of configural representations: the role of associatively evoked and trace memories

Two experiments examined the content of configural learning in rats. In Experiment 1, after simple pre-exposure to two hybrid contexts (AB and CD), rats acquired a configural discrimination involving two of the contexts (A and C) and two auditory stimuli (X and Y; AX→food, AY→no food, CX→no food, and CY→food). When rats were then placed in context B, they were more likely to respond to X than Y, and when they were placed in context D the reverse was the case. Experiment 2 demonstrated that rats can acquire a configural discrimination involving the presence of context (A) and its memory trace (a; AX→food, AY→no food, aX→no food, and aY→food). These results show that associatively provoked memories (Experiment 1) and memory traces (Experiment 2) can participate in configural discriminations.

"Causal reasoning" in rats: a reappraisal

It has recently been argued that rats engage in causal reasoning and they do so in a way that is consistent with Bayes net theories (Blaisdell, Sawa, Leising & Waldmann, 2006). This argument was based upon the finding that the tendency of cues to elicit approach to a food-well was reduced when their presentation was contingent on lever pressing. There is, however, an alternative interpretation of the critical experimental findings that is based on the simple principle of response competition: wherein lever pressing interferes with the tendency to approach the food well. Here the authors replicated Experiments 1 and 2a of Blaisdell et al. (2006) and found reciprocal patterns of lever pressing and food well approach during the critical cues. These results lend direct support for an interpretation in terms of response competition while providing evidence contrary to Bayes net theories, and are readily interpreted within the theoretical framework provided by traditional associative learning theory.

Solving XOR

Three experiments examined the way in which exclusive-or (XOR) problems are solved by rats. All rats first received food-rewarded positive and negative patterning problems with two stimulus sets: either A+, B+, AB- and C-, D-, CD+, or A-, B-, AB + and C+, D +, and CD-. Subsequently, rats received revaluation trials in which A was paired with shock and C was not, prior to generalization test trials with B, D, AB, and CD (Experiments 1 & 2); or received A-->shock trials prior to tests with B and CD (Experiment 3). There was greater generalized fear to B than to either D (Experiments 1 & 2) or AB (Experiment 2) and CD (Experiments 2 & 3). These results are inconsistent with configural, connectionist models, but are consistent with an alternative connectionist model that can represent the logical structure of XOR problems.

Latent inhibition, learned irrelevance, and schizotypy: assessing their relationship

INTRODUCTION

Previous research suggests that latent inhibition is reduced in patients with acute schizophrenia and in healthy participants with high levels of schizotypic characteristics. Other evidence indicates the disruption of a related effect (learned irrelevance) in patients with acute schizophrenia.

METHOD

This study used a recently developed latent inhibition procedure, that avoids methodological limitations of previous studies, and a related learned irrelevance procedure to assess the relationship between these phenomena and schizotypic characteristics in undergraduate participants.

RESULTS

Participants preexposed to a letter (S) learnt the predictive relationship between that letter and another letter (X) slower than the relationship between a novel letter and X (a latent inhibition effect). Experiment 1 found reduced latent inhibition in the high schizotypy group after 10, but not 20 preexposures. In Experiment 2, participants preexposed to both S and X learnt a subsequent relationship between them slower than the relationship between a novel letter and X (a learned irrelevance effect). This effect was abolished in participants with high levels of schizotypy.

CONCLUSIONS

These results are both the first demonstration of abolished learned irrelevance and of a significant reduction in latent inhibition without employing an explicit masking task in participants with high levels of positive schizotypy.

Configural Learning without Reinforcement: Integrated Memories for Correlates of What, Where, and When

In 2 experiments we examined the ability of rats to form configural memories of what auditory stimulus (X or Y) was presented where (Context A or B) and when (morning or afternoon). In both experiments, rats received morning presentations of X in Context A and Y in Context B and afternoon presentations of X in B and Y in A. Subsequently, at midday the rats were exposed to trials where X was paired with footshock whereas Y was not. We then assessed the degree of contextual fear in A and B in the morning and the afternoon. In the morning, rats showed more fear in A than in B, and in the afternoon they showed more fear in B than in A. These results indicate that rats can form configural memories that represent what (X or Y) was presented, where (A or B), and when (morning or afternoon).

Role of the medial prefrontal cortex in acquired distinctiveness and equivalence of cues

In the present study, the authors examined the role of the medial prefrontal cortex in acquired equivalence and distinctiveness of cues. Rats were placed in 4 experimental contexts (A, B, C, and D) where they received presentations of 2 auditory stimuli (X and Y). In Contexts A and B, X was paired with food and Y was not, whereas in Contexts C and D, Y was paired with food and X was not. Rats that received sham lesions and those with lesions of the medial prefrontal cortex acquired this configural discrimination equally readily. Rats then received many pellets in A but not in C. After this training, sham-lesion rats exhibited more magazine activity in B than in D (an acquired distinctiveness/acquired equivalence effect), whereas those with medial prefrontal cortex lesions did not. These results indicate that the medial prefrontal cortex is involved in the process by which experience with stimuli influences the degree of generalization between them.

Simultaneous presentation of similar stimuli produces perceptual learning in human picture processing

Human participants received unsupervised exposure to difficult-to-discriminate stimuli (e.g., A and A'), created with a morphing procedure from photographs of faces, before learning a discrimination between them. Experiments 1 and 2 demonstrated that prior exposure enhanced later discrimination and that intermixed exposure (A, A', A, A'...) resulted in better subsequent discrimination than blocked exposure (B, B, ...B', B'...). Experiments 3 and 4 showed that simultaneous exposure to 2 similar stimuli facilitated the later acquisition of both a simultaneous and a successive discrimination, and this effect was observed even though simultaneous exposure to 2 stimuli fostered the development of an excitatory association between them (Experiment 5). The findings of Experiments 1 and 2 revealed a perceptual learning effect with pictures of faces, and the findings of Experiments 3-5 are difficult to reconcile with associative analyses of perceptual learning.

Context- but not familiarity-dependent forms of object recognition are impaired following excitotoxic hippocampal lesions in rats

Dual-process models of recognition memory in animals propose that recognition memory is supported by two independent processes that reflect the operation of distinct brain structures: a familiarity process that operates independently of the hippocampus and a context-dependent (episodic) memory process that is dependent on the hippocampus. A novel variant of an object recognition procedure was used to examine this proposal. Healthy rats showed a preference for exploring a novel object rather than a familiar object: a familiarity-dependent recognition effect. They also showed a preference for exploring a familiar object that was presented in a different spatiotemporal context rather than a familiar object that was presented either in a different spatial or temporal context: a context-dependent form of recognition that is sensitive to "what" object has been presented "where" and "when." Rats with excitotoxic hippocampal lesions showed the familiarity-dependent but not the context-dependent form of recognition. The results provide support for dual-process theories of recognition memory.

The effects of habituation training on compound conditioning are not reversed by an associative activation treatment

Rats received habituation to either 2 compound flavors (AX and BY; the activation group) or a compound and an element alone (AX and Y; the habituation group). They also received additional presentations of Y alone either after (Experiment 1) or intermixed (Experiment 2) with habituation. In the habituation group, A had undergone habituation whereas B had not; in the activation group, both A and B had undergone habituation, but presenting Y alone should result in associative activation of B and that, according to G. Hall (2003), should increase B's efficacy. A supplementary experiment demonstrated that the presentation of Y does activate a representation of B. In both experiments, an aversion was established to AB, and subsequently the habituation group showed a greater aversion to B than to A. However, in neither experiment was there any indication that the activation group showed a greater aversion to B than to A. These results are inconsistent with the suggestion that the associative activation of a stimulus representation in the absence of the stimulus reverses the effects of habituation training.

The role of similarity in human associative learning

In 2 experiments, humans received sequences of patterns that were similar (AX-->BX, AY-->BY, AZ-->BZ) or dissimilar (CX-->DY, CY-->DZ, CZ-->DX). The patterns were portrayed as bugs that could be eliminated with 2 insecticide sprays (red or blue). Either spray eliminated bugs with Features A and C, and participants learned by trial and error to use one spray (e.g., red) to eliminate bugs with Feature B and the other spray (e.g., blue) to eliminate those with Feature D. In Experiment 1, participants' spray choice for bugs with Feature A came to match that used to eliminate bugs with Feature B, but there was no such associative transfer between Features C and D. That is, similarity promoted associative transfer of responding between paired patterns when the features used to manipulate similarity (i.e., X, Y, and Z) were irrelevant. In Experiment 2, in which X, Y, and Z were relevant to the solution of configural discrimination, similarity hindered such associative transfer. These results complement those found in pigeons (R. A. Rescorla & D. J. Gillan, 1980) and indicate that similarity should not be accorded independent status as a principle of associative learning.

Transfer of configural learning between the components of a preexposed stimulus compound: implications for elemental and configural models of learning

In 2 experiments, rats received preexposure to 2 compound contexts: AB and CD for the congruent group and AC and BD for the incongruent group. Subsequently, all rats received a configural discrimination in which separate placement in contexts A or B indicated that presentations of stimulus X would be followed by food and presentations of Y would not, and separate placement in contexts C and D indicated that Y would be followed by food and X would not. In both experiments, rats in the congruent group acquired the conditional discrimination more rapidly than those in the incongruent group. These results are inconsistent with conventional associative accounts of either stimulus preexposure effects or configural learning and instead provide support for a connectionist account.

Inhibitory associations contribute to perceptual learning in humans

Perceptual learning in humans was examined in 2 experiments. In Experiment 1, participants received intermixed exposure to 2 similar compounds (AX, BX, AX, BX, . . .) and blocked exposure to a 2nd pair of similar compounds (CY, CY, . . . , DY, DY, . . .). Aversions established to AX and CY generalized less to BX than to DY. In Experiment 2, 1 pair of compounds was presented in a forward order (i.e., AX3BX), whereas the 2nd pair of compounds was presented in a backward order (i.e., DY-->CY). Aversions established to AX and CY generalized less to BX than to DY. These results indicate that inhibitory associations contribute to perceptual learning in humans and thereby establish a fundamental similarity between the mechanisms that underlie perceptual learning in humans and rats.

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 connectionist networks: an addendum

The results of a recent study have provided direct support for the suggestion that conditional learning in rats is best characterized by a 3-layer connectionist network (M. J. Allman, J. Ward-Robinson, & R. C. Honey, 2004). In the 2 experiments reported here, rats were used to investigate the nature of the changes that occur when a stimulus compound is presented, whose components activate hidden units associated with food and no food, and either food or no food is presented. The results of both experiments, while controlling for the possible contribution of associations between these hidden units (within-layer links), provide evidence that the distribution of associative change between units in the hidden layer that are activated by the stimulus compound and those in the output layer (between-layer links) are unequal. They also indicate that associative change is more marked on trials on which no food was presented than on trials on which food was presented.

Excitotoxic Lesions of the Entorhinal Cortex Leave Gustatory Within-Event Learning Intact

The ability of rats with ibotenate lesions of the entorhinal cortex to form memories for events was assessed by using a gustatory within-event learning procedure. Rats first received exposure to 2 events, AX and BY, each composed of a pair of flavors. Following this exposure period, Flavor X alone was paired with the delivery of lithium chloride. Lesioned and control rats showed a greater aversion to A than to B and to AX than to BX. These results challenge theories that suppose that the entorhinal cortex plays a general role in forming representations of patterns of stimulation.

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, AX was 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.

Hippocampal lesions modulate both associative and nonassociative priming

In associative priming, rats are more likely to orient to a visual stimulus whose memory has not been recently activated (V1) than to one whose memory has been recently activated (V2). However, rats with excitotoxic hippocampal lesions are more likely to orient to the primed V2 than to the unprimed V1. This study investigated the influence of hippocampal lesions on nonassociative priming. Rats received presentations of 2 visual stimuli, V1 and V2, that had been presented more (V2, primed) or less (V1, unprimed) recently. Control rats oriented to V1 rather than to V2, whereas hippocampal rats oriented to V2 rather than to V1. These results parallel those observed in an associative priming procedure and thereby suggest that the role of the hippocampus in priming is general.

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.

Lesions of the mammillothalamic tract impair the acquisition of spatial but not nonspatial contextual conditional discriminations

This study examined the influence of selective mammillothalamic tract lesions in rats on the acquisition of two kinds of contextual conditional discrimination: one involving two contexts (A and B) that differed in their visuo-spatial properties and another involving two contexts (C and D) that differed in temperature. In contexts A (and C) presentations of a tone were paired with food whereas presentations of a clicker were not; and in contexts B (and D) presentations of the clicker were paired with food whereas those of the tone were not. Mammillothalamic tract lesions disrupted initial acquisition of the conditional discrimination involving visual contexts (A and B), but not the formally equivalent discrimination involving thermal contexts (C and D). These results provide support for the suggestion that mammillothalamic tract lesions disrupt visuo-spatial encoding.

Entorhinal cortex lesions disrupt the transition between the use of intra- and extramaze cues for navigation in the water maze

This study with rats examined the effects of excitotoxic lesions to the entorhinal cortex (EC) and hippocampus (HPC) on using extramaze and intramaze cues to navigate to a hidden platform in a water maze. HPC lesions resulted in a disruption to the use of extramaze cues, but not intramaze cues, whereas EC lesions had no effect on the use of these cues when they were encountered for the first time. However, prior navigation training in which 1 type of cue was relevant disrupted navigation with the other type in rats with EC lesions. Results show that the EC contributes to the processing of spatial information, but that this contribution is most apparent when there is a conflict between 2 sources of navigational cues in the water maze.

Representational blending in human conditional learning: Implications for associative theory

In two experiments, participants were presented with pictures of different foods (A, B, C, D, X,) and learned which combinations resulted in an allergic reaction in a fictitious patient, Mr X. In Problem 1, when A or B (but not C or D) was combined with food X an allergic reaction occurred, and when C or D (but not A or B) was combined with Y an allergic reaction occurred. In Experiment 1, participants also received Problem 2 in which A, B, C, and D interacted with foods V and W either in the same way as X and Y, respectively, or in a different way. Participants performed more proficiently in the former than in the latter condition. In Experiment 2, after training on Problem 1, participants judged whether or not novel combinations of foods (e.g., AB, CD, AD, CB) would cause an allergic reaction in Mr X. They were no more likely to indicate that AB or CD would cause an allergic reaction than AD or CB, but made their judgements more rapidly and with greater confidence on AB and CD trials than on AD and CB trials. These results (1) indicate that shared representations come to be addressed by the components of similar compounds (e.g., AX and BX) that have predicted the same outcome (an allergic reaction), and (2) are inconsistent with standard, associative theories of learning, but (3) are consistent with findings from nonhuman animals and with a connectionist interpretation of these findings.

Involvement of the rat medial prefrontal cortex in novelty detection

The prefrontal cortex in humans has been implicated in processes that underlie novelty detection and attention. This study examined the contribution of the rat medial prefrontal cortex to novelty detection using the targeting, or orienting, response (OR) as a behavioral index. Lesions to the medial prefrontal cortex (specifically the prelimbic and infralimbic cortices) influenced neither the OR to a novel visual stimulus from a localized light source (V1), nor the change in this OR over the course of a series of exposures to V1. However, after exposure to V1, the OR to a 2nd visual stimulus from the same source, V2, was more pronounced in control rats than in lesioned rats. These results suggest that the medial prefrontal cortex in the rat contributes to the process of novelty detection.

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.

Sensory preconditioning in rats with lesions of the anterior thalamic nuclei: evidence for intact nonspatial 'relational' processing

Rats with neurotoxic lesions centered in the anterior thalamic nuclei were trained in two versions of a nonspatial, sensory preconditioning procedure. In both versions, two stimulus compounds (AX and BY) were first presented and then X, but not Y, was paired with an aversive unconditioned stimulus. This procedure resulted in greater conditioned responding to A than B. Anterior thalamic lesions had no apparent effect on these two examples of sensory preconditioning, nor did they affect fear conditioning or conditioned taste aversion. In contrast, the same lesions led to a severe deficit on a test of spatial memory. These results help to refine our understanding of the contribution of the anterior thalamic nuclei to spatial memory.

The influence of selective lesions to components of the hippocampal system on the orienting [correction of orientating] response, habituation and latent inhibition

The contribution that components of the hippocampal system in the rat make to the modulation of attention or stimulus processing was assessed using several simple behavioural assays: the orienting response (OR) to a novel stimulus, the subsequent habituation and dishabituation of this OR, and the latent inhibition effect that typically results from repeated exposure to a stimulus. Excitotoxic lesions of components of the hippocampal system produce dissociable effects on the OR, habituation and latent inhibition: lesions of the entorhinal cortex have no effect on the OR or changes in the OR during exposure to a stimulus, but disrupt latent inhibition; lesions of the subiculum disrupt the OR but not latent inhibition; and lesions of the hippocampus disrupt the OR and latent inhibition. These effects have important implications for our understanding of habituation and latent inhibition, and the neural mechanisms involved in attentional modulation.

Involvement of the rat medial prefrontal cortex in novelty detection

The prefrontal cortex in humans has been implicated in processes that underlie novelty detection and attention. This study examined the contribution of the rat medial prefrontal cortex to novelty detection using the targeting, or orienting, response (OR) as a behavioral index. Lesions to the medial prefrontal cortex (specifically the prelimbic and infralimbic cortices) influenced neither the OR to a novel visual stimulus from a localized light source (V1), nor the change in this OR over the course of a series of exposures to V1. However, after exposure to V1, the OR to a 2nd visual stimulus from the same source, V2, was more pronounced in control rats than in lesioned rats. These results suggest that the medial prefrontal cortex in the rat contributes to the process of novelty detection.

Involvement of the entorhinal cortex in a process of attentional modulation: evidence from a novel variant of an IDS/EDS procedure

Novel behavioral assays were used to assess the role of the entorhinal cortex in modulating attention to components of stimulus compounds. In Stage 1, rats received discrimination training with compounds constructed from 3 dimensions (auditory, visual, and tactile); in each compound the combination of components from 2 dimensions (e.g., auditory and visual) were relevant to the solution of the discrimination, and the remaining dimension (e.g., tactile) was irrelevant. In Stage 2, rats received a different discrimination in which the relevant dimensions were either congruent (auditory and visual) or incongruent (auditory and tactile) with those that were relevant in Stage 1. Sham-operated rats acquired the congruent discrimination more rapidly than the incongruent discrimination--a finding indicative of a process of attentional modulation--whereas rats with excitotoxic lesions of the entorhinal cortex acquired both discriminations equally readily.