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This experiment adapted a sensory preconditioning (SPC) procedure using human participants to determine if conditioning (Cond) to one flavor (the conditioned flavor) will enhance liking for another flavor (the SPC flavor) associated with it prior to training. Participants in one of three groups (N=40 per group) consumed and rated plain or sweetened cherry and grape kool-aids in four phases. In baseline and SPC phase, ratings for a plain cherry, grape, and cherry-grape mixture were similar. In training, one flavor was sweetened (SPC+Cond and Cond Only groups) or unsweetened (SPC Only group) and ratings increased only for the flavor that was sweetened. In test, Group SPC+Cond rated the conditioned flavor and the SPC flavor as more liked and tasting sweeter. Group Cond Only rated only the conditioned flavor as more liked and tasting sweeter. Group SPC Only showed no change in ratings from baseline to test. These are the first data to show SPC learning using a flavor preference paradigm with human participants.

Lesion studies have suggested that the prefrontal cortex is involved in memory for contextual details surrounding the prior observation of objects or events, but it is unknown whether it is crucial for encoding details about the location at which cues are experienced, or for recall of that information. We used intracranial infusions of the GABA A receptor agonist muscimol in rodents to directly assess the role of the medial prefrontal cortex (mPFC) during incidental encoding and retrieval of information about the location of a cue during a spatial sensory preconditioning procedure. Rats experienced a single, discrete, sensory cue as they explored an open platform, and then were tested after a 24 h delay on recollection of the prior location of the cue. Activity in the mPFC was suppressed with muscimol during either encoding or retrieval of the information, with a control group receiving saline infusions before both phases. We found that mPFC suppression during the encoding phase blocked the formation of incidental memory about the cues but mPFC suppression during retrieval had no effect. Moreover, animals with suppressed frontal cortical activity in the encoding phase expressed smaller cue-directed orienting responses, indicating they attended less to the cue. These results suggest that the frontal cortex may be required to sustain attention to incidental cues in order to later recollect the location in which they have been previously experienced, but that once the location information is encoded the frontal cortex is not required for retrieval of that information.

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.

We tested the hypothesis that conceptual similarity promotes generalization of conditioned fear. Using a sensory preconditioning procedure, three groups of subjects learned an association between two cues that were conceptually similar, unrelated, or mismatched. Next, one of the cues was paired with a shock. The other cue was then reintroduced to test for fear generalization, as measured by the skin conductance response. Results showed enhanced fear generalization that correlated with trait anxiety levels in the group that learned an association between conceptually similar stimuli. These findings suggest that conceptual representations of conditional stimuli influence human fear learning processes.

Activation of N-methyl-D-aspartate receptors (NMDAr) in the basolateral complex of the amygdala (BLA) is crucial for the acquisition and extinction of Pavlovian first-order fear. It is unknown whether these substrates also mediate higher-order fear. Higher-order fear has been observed using two procedures. In second-order conditioning, pairings of a tone (S1) and shock are followed by pairings of a light (S2) and the tone (S1); in sensory preconditioning, pairings of a light (S2) and tone (S1) are followed by pairings of the tone (S1) and shock. In each procedure, test presentations of the light alone elicit fear responses which extinguish across such presentations. This thesis examined whether activation of NMDAr in the BLA is necessary for the acquisition and extinction of higher-order fear. Inactivation of the BLA via infusion of the GABAA agonist muscimol, systemic injection of the NMDAr antagonist MK-801, and BLA infusion of the NMDAr NR2B subunit selective antagonist ifenprodil, disrupted acquisition and extinction of second-order fear. Extinction of sensory preconditioned fear was impaired by BLA infusion of muscimol or ifenprodil and by systemic MK-801. Acquisition of the neutral S2-S1 association and extinction of this association before conditioning of S1 was impaired by MK-801 but not by BLA infusion of muscimol. The final experiment examined the role of the perirhinal cortex (PRh) in the acquisition of higher-order fear. Muscimol inactivation of the PRh prior to S2-S1 pairings blocked sensory preconditioning but not second-order conditioning. These findings can be summarised as follows. First, activation of BLA NMDAr is necessary for the acquisition and extinction of second-order fear. Second, the acquisition and pre-extinction of sensory preconditioning requires NMDAr activity but not BLA activation. Third, once the fear circuit is engaged, learning to inhibit sensory preconditioned fear becomes dependent on BLA NMDAr activation. Finally, the PRh is necessary for the acquisition of an association between two neutral stimuli but not between a neutral stimulus and a learned danger signal. These findings are consistent with current views of amygdala function. They are also consistent with the claim that the contents of second-order conditioning and sensory preconditioning differ, the former involving associations between S2 and the fear responses elicited by S1 and the latter consisting in associations between the sensory properties of S2 and S1.

Three conditioned suppression experiments with rats investigated contrasting predictions made by the extended comparator hypothesis and acquisition-focused models of learning, specifically, modified SOP and the revised Rescorla–Wagner model, concerning retrospective revaluation. Two target cues (X and Y) were partially reinforced using a stimulus relative validity design (i.e., AX–Outcome; BX–No outcome; CY–Outcome; DY–No outcome), and subsequently one of the companion cues for each target was extinguished in compound (BC–No outcome). In Experiment 1, which used spaced trials for relative validity training, greater suppression was observed to target cue Y for which the excitatory companion cue had been extinguished in relation to target cue X for which the nonexcitatory companion cue had been extinguished. Experiment 2 replicated these results in a sensory preconditioning preparation. Experiment 3 massed the trials during relative validity training, and the opposite pattern of data was observed. The results are consistent with the predictions of the extended comparator hypothesis. Furthermore, this set of experiments is unique in being able to differentiate between these models without invoking higher-order comparator processes.

We developed a single-trial cue-location memory task in which rats experienced an auditory cue while exploring an environment. They then recalled and avoided the sound origination point after the cue was paired with shock in a separate context. Subjects with medial prefrontal cortical (mPFC) lesions made no such avoidance response, but both lesioned and control subjects avoided the cue itself when presented at test. A follow up assessment revealed no spatial learning impairment in either group. These findings suggest that the rodent mPFC is required for incidental learning or recollection of the location at which a discrete cue occurred, but is not required for cue recognition or for allocentric spatial memory.

In the present experiments, we examined the role of within-compound associations in the interaction of the overshadowing procedure with conditioned stimulus (CS) duration, using a conditioned suppression procedure with rats. In Experiment 1, we found that, with elemental reinforced training, conditioned suppression to the target stimulus decreased as CS duration increased (i.e., the CS duration effect), whereas, with compound reinforced training (i.e., the overshadowing procedure), conditioned suppression to the target stimulus increased as CS duration increased. In subsequent experiments, we replicated these findings with sensory preconditioning and demonstrated that extinction of the overshadowing stimulus results in retrospective revaluation with short CSs and in mediated extinction with long CSs. These results highlight the role of the duration of the stimulus in behavioral control. Moreover, these results illuminate one cause (the CS duration) of whether retrospective revaluation or mediated extinction will be observed.

Three experiments were conducted to examine the interaction of overexpectation treatment and trial massing using a Pavlovian fear conditioning procedure with rats. In first-order conditioning, Experiment 1 found the overexpectation effect (i.e., decreased conditioned responding to a cue after compound training when the elements were previously reinforced), the trial spacing effect (i.e., decreased responding to a cue when reinforced trials are massed), and a counteraction between overexpectation treatment and trial massing (i.e., an alleviation of the decrement in responding seen with overexpectation treatment or trial massing alone when the two treatments are conjointly administered). Experiment 2 replicated Experiment 1 with the critical treatments embedded within a sensory preconditioning preparation. The overexpectation effect, the trial spacing effect, and the mutual counteraction of overexpectation treatment and trial massing all proved significant. In Experiment 3, either the nontarget conditioned stimulus of overexpectation treatment or the excitatory context resulting from trial massing was extinguished. Results are best explained by the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001).

Three experiments investigated the way participants construct causal chains from experience with the individual links that make up those chains. Participants were presented with contingency information about the relationship between events A and B, as well as events B and C, using trial-by-trial presentations. The A-B and B-C contingencies could be positive, negative, or zero. Although participants had never experienced A and C together, A-C ratings were a multiplicative function of the A-B and B-C contingencies. These findings can be generated by an auto-associator using the delta rule. This explanation is also useful for understanding sensory preconditioning and second-order conditioning.

In two experiments, rats received sensory preconditioning treatment in which an auditory conditioned stimulus (CS) X was followed by visual CS A in Phase 1, and CS A was followed by an appetitive US (sucrose) in Phase 2. Rats also received presentations of auditory CS Y unpaired with other events. At test, rats looked for sucrose more following CS X than following CS Y on non-reinforced probe test trials only if the light bulb on which CS A had been presented during training was removed from the chamber at the time of testing. With the light bulb present (but unlit), rats showed nodifference in amount of nose poking between CS X and CS Y. These results suggest that rats distinguish between the explicit absence of events and lack of information

Learning when and how to generalize knowledge from past experience to novel circumstances is a challenging problem many agents face. In animals, this generalization can be caused by mediated conditioning--when two stimuli gain a relationship through the mediation of a third stimulus. For example, in sensory preconditioning, if a light is always followed by a tone, and that tone is later paired with a shock, the light will come to elicit a fear reaction, even though the light was never directly paired with shock. In this paper, we present a computational model of mediated conditioning based on reinforcement learning with predictive representations. In the model, animals learn to predict future observations through the temporal-difference algorithm. These predictions are generated using both current observations and other predictions. The model was successfully applied to a range of animal learning phenomena, including sensory preconditioning, acquired equivalence, and mediated aversion. We suggest that animals and humans are fruitfully understood as representing their world as a set of chained predictions and propose that generalization in artificial agents may benefit from a similar approach.

Sixteen five- to seven-year-old children were exposed to two colour-form compounds. The compounds were presented successively. Pointing to the compounds was reinforced. Eight children received compounds A1B1 and A2B2; the others A1B2 and A2B1. This task was mixed with a two-choice discrimination task that provided the colours A1 and A2 simultaneously. Colour A1 was correct for four children in each group. Finally, tests were given that offered a choice between forms B1 and B2, without A1 or A2. The children preferred the form that had been paired with the correct colour of the two-choice discrimination task. The results can be explained with the assumption that functions transfer between stimuli if the stimuli occur contiguously. This assumption also accounts for transfer of functions between stimuli paired in matching-to-sample tasks.

In each of two experiments, two groups of rats were exposed to three flavoured solutions: A (citric acid), B (salt), and AX (a compound of citric acid and saccharin). Both experiments used a between-subjects design in which a paired group received presentations of A followed by B, alternating with presentations of AX (i.e., A → B/AX), and an unpaired group received alternating presentations of A, B, and AX (i.e., A/B/AX). This arrangement was expected to establish X as an inhibitor of B in group paired but not in group unpaired. In Experiment 1, after preexposure all subjects received a single presentation of an XB compound, then experienced sodium depletion, and were tested for their consumption of X, which was greater in group unpaired than in group paired. In Experiment 2, after preexposure, all subjects received four presentations of a new flavour, C, in compound with B and subsequently, under sodium depletion, were tested for consumption of XC. Intake of the XC compound was less in group paired than in group unpaired. These results suggest that, in group paired, X acquired an inhibitory relationship with B both retarding the acquisition of an excitatory association with B (retardation test, Experiment 1) and reducing the response to a new stimulus, C, strongly associated to B (summation test, Experiment 2). These results provide direct evidence of inhibition between two neutral stimuli and, therefore, of inhibitory sensory preconditioning.

We used an appetitive sensory preconditioning procedure to investigate temporal integration in rats in two experiments. In Phase 1, rats were presented with simultaneous compound trials on which a 10-sec conditioned stimulus (CS) X was embedded within a 60-sec CS A. In Group Early, CS X occurred during the early portion of CS A, whereas in Group Late, CS X occurred during the latter portion of CS A. In Phase 2, CS X was paired simultaneously with sucrose. On a subsequent test with CS A, the rate of magazine entries peaked during the early portions of the stimulus in Group Early and during the latter portions of the stimulus in Group Late (Experiments 1 and 2). Similar response peaks were not observed on tests with a control stimulus that had been presented in compound with a stimulus that did not signal reward (Experiment 2).

In Experiment 1, a potentiation paradigm was used to test the relative influence of odor and taste with two 2 basic tastants (i.e., salt and sweet) in conditioned aversion learning. Experiment 1 showed that aversions to tastants (salt or sweet presented in a manner by which it could be tasted) were established only in subjects trained with the tastant, not the odor (i.e., salt or sweet presented in a manner by which it could not be tasted). Experiment 2 demonstrated, with a sensory preconditioning procedure, that the expression of an aversion to tastants was dependent on previous tastant experience prior to odor aversion training. These results suggest that while subjects can smell salt and sweet solutions, these odors are neither sufficient nor necessary for the expression of a conditioned tastant aversion.

We demonstrated a sensory preconditioning in the pond snail, Lymnaea stagnalis. An appetitive sucrose solution (a conditioned stimulus: CS1) and weak vibration (another conditioned stimulus: CS2) were first associated, and then the CS2 and an aversive KCl solution (an unconditioned stimulus: UCS) were done. To build the conditioning, two different training procedures, spaced and massed, were examined. After the both training, the sensory preconditioning was built: significantly fewer feeding response to the CS1 became elicited; slower latency to the first bite to the CS1 was induced. No significant differences on the memory retention between these training procedures were found in the sensory preconditioning.

Exposure to banana scented salty water produced a preference for that smell in rats tested under a sodium appetite (experiment 1), and exposure to almond scented sweet water produced avoidance of that smell when rats were tested after developing an aversion to the sweet taste (experiment 2). The consolidation of this within-event learning was disrupted when exposure to the solutions were followed by social isolation. These results duplicate the disruptive effect of social isolation on context learning and raise the possibility that within-event learning like context learning may involve the hippocampal formation.

Three conditioned lever-press suppression experiments with rats investigated the interaction between overshadowing and outcome-alone exposure effects. Experiment 1 found in first-order conditioning that combined overshadowing and outcome-preexposure treatments attenuate the response deficit produced by either treatment alone. Experiments 2 and 3 investigated the interaction between overshadowing and outcome pre- and postexposure effects in sensory preconditioning, varying retention intervals to engage recency and primacy effects with respect to treatment order. Contrary to when a solitary cue is conditioned, responding to a cue conditioned in compound appeared positively correlated with the context's associative status. These findings suggested that some of the basic laws of learning applicable to cues conditioned alone do not similarly apply to a component of a compound cue.

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.

The authors used a touch screen-based visual-search task to investigate spatial integration in pigeons. First, pigeons were presented with a consistent spatial relationship between compound visual landmarks (LMs) A-X and B-Y, separately. Next, pigeons learned to find a hidden goal on the monitor in the presence of LMs A and B. The goal bore a consistent spatial relationship to LM A, but not to LM B. On nonreinforced probe tests, the peak and distribution of responses to LM X suggest that pigeons computed a novel X-goal spatial relationship on the basis of X-A and A-goal spatial vectors. Responses to LM Y, however, revealed no evidence of spatial integration. These results replicate and extend those of A. P. Blaisdell and R. G. Cook (2005) using an open-field task.

The integration of spatial maps in pigeons was investigated using a spatial analog to sensory preconditioning. The pigeons were tested in an open-field arena in which they had to locate hidden food among a 4x4 grid of gravel-filled cups. In phase 1, the pigeons were exposed to a consistent spatial relationship (vector) between landmark L (a red L-shaped block of wood), landmark T (a blue T-shaped block of wood) and the hidden food goal. In phase 2, the pigeons were then exposed to landmark T with a different spatial vector to the hidden food goal. Following phase 2, pigeons were tested with trials on which they were presented with only landmark L to examine the potential integration of the phase 1 and 2 vectors via their shared common elements. When these test trials were preceded by phase I and phase 2 reminder trials, pigeons searched for the goal most often at a location consistent with their integration of the L --> T phase 1 and T --> phase 2 goal vectors. This result indicates that integration of spatial vectors acquired during phases I and 2 allowed the pigeons to compute a novel L --> goal vector. This suggests that spatial maps may be enlarged by successively integrating additional spatial information through the linkage of common elements.

In two experiments rats were preexposed to neutral stimuli. Both experiments used a between-subjects design in which a paired group was preexposed to intermixed presentations of A→ Band AX, and an unpaired control group was preexposed to intermixed presentations of A, B, and AX. After the conditioning of B, in Experiment 1, conditioned responding to X was acquired more slowly in the paired than in the unpaired group. Furthermore, in Experiment 2, Xreduced conditioned responding to a separately trained excitor in a summation test but only in the paired group. Together, these results provide evidence of an inhibitory form of sensory preconditioning.

Infants’ memories are highly specific to their training stimuli; they rarely transfer learned responding. In two experiments, we asked whether sensory preconditioning facilitates the transfer of deferred imitation. In Experiments 1A and 1B, 6-month-olds were simultaneously preexposed to Puppets A and B and then saw target actions modeled on Puppet A. The infants associated the paired puppets and imitated the actions on Puppet B. In Experiment 2, the preexposure procedure was repeated, but the actions were modeled on Puppet A with a toy train in view. The infants also associated Puppet A and the train: Either object effectively reactivated both forgotten memories; thereafter, the infants again imitated the actions on Puppet B. These findings reveal that infants form specific and enduring associations between stimuli they have merely seen together. These associations facilitate the transfer of deferred imitation, both directly and indirectly, through connections to other associations.

In laboratory studies, the assessment of memory is typically associated with overt behavioral responses. Thus, it has been difficult to determine whether the enhancement of hippocampal sensory-evoked potentials that often accompany memory formation are the neurophysiological manifestation of a memory "trace" or are a secondary product of the behavioral expression of the memory. We addressed this issue by examining changes in evoked hippocampal field potentials during sensory preconditioning, a form of behaviorally silent relational learning that requires an intact hippocampus for execution. Rats were exposed to presentations of a white noise (S1) that terminated with a tone (S2). These pairings of ostensibly "neutral" stimuli supported no change in the behavior elicited by the noise. However, if the tone was subsequently paired with mild footshock (US), suppression of ongoing licking behavior (indicative of fear) was elicited by the noise, indicating that the animal had associated the noise with tone (S1-S2), and had represented the noise-tone-shock (S1-S2-US) relationship. Pre-training neurotoxic lesions of the hippocampus had no effect on conditioned suppression to tone after tone-shock (S2-US) pairings, but disrupted the expression of continued suppression to noise (S1) after tone-shock pairings. In a second experiment, sensory-evoked field potentials in the dorsal hippocampus were recorded with extracellular electrodes. No changes in the hippocampal response evoked by white noise were observed after pairings of noise and tone, i.e., no evidence for a memory trace could be detected. In contrast, after tone was paired with footshock, two short-latency negative potentials within the noise-evoked field response increased in amplitude, a response often presumed to reflect a neurophysiological correlate of memory storage. In total, these results suggest that although the hippocampus critically contributes to the processing of a behaviorally silent associative memory, there may be no role for changes in the amplitude of hippocampal sensory-evoked field potentials in storing representations of the relationships between sensory experiences.

The associative analysis of conditioning assumes a conceptual nervous system consisting of a set of units (nodes). Some nodes are are activated by specific external stimuli; others, when activated, result in the emission of particular patterns of behavior (responses). The behavioral changes produced by conditioning procedures are explained in terms of the formation of links between nodes that allow activity in one to excite activity in another. The aim of this chapter is to specify what nodes are involved in a given conditioning procedure and the pattern of interconnections that forms among them. Three procedures are considered: Excitatory conditioning, in which a Pavlovian conditioned stimulus reliably precedes the occurrence of an unconditioned stimulus or, for the instrumental case, in which a given response reliably produces a given outcome; inhibitory conditioning, in which the association between the relevant events is discontinued (the conditioned stimulus or the response occurs without consequence); and complex conditioning, in which the consequence of the conditioned stimulus or of the response varies according to which other events are presented. It is demonstrated that the standard assumptions of associative theory can explain the results of the first of these procedures; that the second requires the further assumption that links can inhibit the tendency of nodes to be activated; and that the last requires further new assumptions (that nodes can encode the configural properties of stimuli, or that links can operate on other links as well as on nodes, or both). Keywords: activation; associations; excitatory conditioning; blocking; conditioned response (CR); conditioned stimuli (CSs); event processing; extinction; feature negative; feature positive; inhibitory conditioning; instrumental conditioning; occasion setting; outcomes (O); overshadowing; Pavlovian conditioning; persistence of associations; reinstatement; revaluation; R-O associations; S-O associations; S-R associations; S-R theory; S-S theory; second-order conditioning; sensory preconditioning; transfer tests; unconditioned response (UR); unconditioned stimuli (USs)

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.

Equivalence of flavour cues, each of which had been paired with a common antecedent, was demonstrated with rats in a three-stage design. In the first stage, a group of thirsty rats were given each of two target flavour cues after a common antecedent flavour (Xright arrowA and Xright arrowB), while a second group of rats were given A and B after differential antecedent flavours (Xright arrowA and Yright arrowB). Another group of rats was allowed to drink A and B after familiar tap water. In the second stage, aversion to A was established by a lithium chloride injection after drinking A. The acquired equivalence effect was verified in the third stage by strong aversion to B in the group trained with the common antecedent compared with the remaining two groups. The representation-mediation, rather than response-mediation, hypothesis seems to fit the backward acquired equivalence effect obtained here.

SUMMARYShort-term memory in Drosophila melanogaster operant visual learning in the flight simulator is explored using patterns and colours as a compound stimulus. Presented together during training, the two stimuli accrue the same associative strength whether or not a prior training phase rendered one of the two stimuli a stronger predictor for the reinforcer than the other(no blocking). This result adds Drosophila to the list of other invertebrates that do not exhibit the robust vertebrate blocking phenomenon. Other forms of higher-order learning, however, were detected: a solid sensory preconditioning and a small second-order conditioning effect imply that associations between the two stimuli can be formed, even if the compound is not reinforced.

Short-term memory in Drosophila melanogaster operant visual learning in the flight simulator is explored using patterns and colours as a compound stimulus. Presented together during training, the two stimuli accrue the same associative strength whether or not a prior training phase rendered one of the two stimuli a stronger predictor for the reinforcer than the other (no blocking). This result adds Drosophila to the list of other invertebrates that do not exhibit the robust vertebrate blocking phenomenon. Other forms of higher-order learning, however, were detected: a solid sensory preconditioning and a small second-order conditioning effect imply that associations between the two stimuli can be formed, even if the compound is not reinforced.

In the present study, sensory preconditioning of human electrodermal activity was demonstrated. In the first phase of the experiment, two pairs of neutral pictures of human faces were presented (A/B and C/D) sequentially. In the second phase, one picture of one pair was immediately followed by an electrocutaneous stimulus (B+), and one picture of the other pair was not (D−). In the third phase the other picture of each pair (A and C) was tested. The effect of A and C alone presentations (pre-extinction) between the first and the second phase was investigated. When only those participants that showed reliable B+/D− differentiation were considered, the extinction group did not show stronger conditioned electrodermal activity to A than to C, whereas the control group did. These findings suggest that sensory preconditioning of anticipatory/preparatory responding only occurs when the pre-conditioned stimulus (A) actually predicts the conditioned stimulus (B).

Animals seem to learn and use internal models; they learn to anticipate predictable events, and their behavior in the sensory preconditioning paradigm reflects formation of novel associative chains. To investigate possible neural correlates, the temporal difference model (TD model) was extended to an internal model approach. The proposed model learns reward prediction error signals that resemble dopamine neuron activity. In contrast to the original TD model, the reward prediction error signals of the proposed model are influenced by the formation of novel associative chains in the sensory preconditioning experiment. This is consistent with experimental findings, as striatal dopamine concentration is influenced by the formation of novel associative chains in this paradigm. Comparison of the model architecture with biological neural networks suggests that chains of neurons with tonic anticipatory activity may underlie the formation of novel associative chains. These findings suggest that dopamine neuron activity may reflect the processing of an internal model.

The effects of lesions of the perirhinal cortex on the development of associations between two conditioned stimuli (CSs) were examined with a sensory preconditioning procedure. Rats were given either bilateral electrolytic lesions of the perirhinal cortex or control surgery. They were then given either paired or unpaired presentations of a light CS and a tone CS. All of the rats were then given eyeblink conditioning procedures that involved paired presentations of either the light or tone and a periorbital shock unconditioned stimulus (US). The rats were finally given a test session that consisted of unpaired presentations of the tone and light CSs. Sensory preconditioning was established in the control group, but not in the lesion group. The findings are consistent with the view that the perirhinal cortex is involved in forming associations between neutral stimuli (even in the absence of reinforcement).

Water-deprived rats served in a conditioned lick-suppression experiment designed to test the hypothesis that second-order conditioning is more robust than sensory preconditioning with equivalent parameters. The second-order and sensory preconditioning paradigms are identical except for the ordering of Phase 1 and Phase 2. In second-order conditioning, S1 immediately precedes the US during Phase 1 (i.e., S1→US), and S2 immediately precedes S1 during Phase 2 (i.e., S2→S1). In sensory preconditioning, these phases are reversed, such that S2 precedes S1 during Phase 1 (i.e., S2→SI) and S1 precedes the US during Phase 2 (i.e., SI→US). Thus, in second-order conditioning, S1 becomes excitatory prior to S2-S1 pairings. This would suggest a positive bias toward attending to S1 during S2-S1 pairings in second-order conditioning but not in sensory preconditioning, a condition that might render second-order conditioning more effective. The results indicated the presence of both second-order conditioning and sensory preconditioning effects, but they did not support the hypothesis that second-order conditioning is a more robust conditioning phenomenon than sensory preconditioning.

In Pavlovian first-order conditioning, a conditioned response is acquired by pairing a neutral stimulus (S1) with a stimulus that has innate motivational value. In higher-order conditioning, a neutral stimulus (S2) is paired with S1 either after (second-order conditioning) or before (sensory preconditioning) first-order conditioning has been acquired. Thus, in higher-order conditioning the motivational value of the reinforcer is acquired rather than innate. This review describes some of the potential uses of higher-order conditioning in investigating the neural substrates of fearful memories. First, because in second-order fear conditioning S2 is not paired directly with a painful stimulus, any effect of a treatment on the acquisition of fear cannot be attributed to the treatment’s possible effects on transmission of nociceptive information. Second, higher-order conditioning provides opportunities for analyzing where and how different types of events, or different aspects of the same events, are represented in the brain.

Maalouf, M., A. A. Miasnikov, and R. W. Dykes. Blockade of cholinergic receptors in rat barrel cortex prevents long-term changes in the evoked potential during sensory preconditioning. J. Neurophysiol. 80: 529–545, 1998. We offer evidence that acetylcholine (ACh) is involved in the emergence of functional neuronal plasticity induced by whisker pairing. Evoked potentials were recorded within the barrel cortex of awake, adult rats before, during, and after one of five paradigms. In the pairing procedure, each of 50 deflections of a whisker (S1) was followed 150 ms later by the deflection of a second whisker (S2). The explicitly unpaired control procedure differed by the lack of contiguity and contingency between the stimulation of S1 and S2. In the three remaining groups, pairing was performed 30 min after an intraperitoneal injection of either 0.5 ml of saline (150 mM NaCl), 100 mg/kg of atropine methyl nitrate (0.5 ml of AMN in saline), or 100 mg/kg of atropine sulfate (0.5 ml of ATS in saline). Changes in responsiveness to S1 were compared with, and adjusted by, changes in responsiveness to stimulation of S2. Changes in potentials evoked by S1 were interpreted as a change in neuronal excitability occurring when the first innocuous stimulus systematically predicted the appearance of the second innocuous stimulus. When whisker pairing was performed alone or in the presence of either saline or AMN (a blocker of muscarinic cholinoreceptors that does not cross the blood-brain barrier, BBB), responses to S1 increased, whereas, in the presence of ATS (blocker of muscarinic cholinoreceptors that does cross the BBB) or following the explicitly unpaired control, they decreased. The effects of saline, AMN, and ATS on the evoked potential without vibrissae pairing were opposite to those observed when these substances were injected and pairing occurred. Analysis of the behavioral state of the animal showed that the changes observed in the evoked potential could not be attributed to changes in behavioral state. The changes in responsiveness to S1 induced by whisker pairing were independent of neuronal excitability, did not occur in the absence of contingency and contiguity between S1 and S2, were blocked by the muscarinic receptor antagonist ATS, but not by blockade of muscarinic modulation of normal synaptic transmission. Thus activation of muscarinic cholinoreceptors within the CNS were a necessary condition for this form of neuronal plasticity.

The effect of passively exposing infants to visual information in a sensory preconditioning paradigm was assessed in five experiments with seventy-eight 6-month-olds. In the basic paradigm, infants were simultaneously exposed to two contexts (S1 and S2), trained in one of them (S1), and tested in the other (S2). Infants learned an association between S1 and S2 and exhibited transfer to S2 after preexposures of 1 hr/day for 1 week but not after 2 min or 1 hr on a single occasion. When S1 was the focal cue, however, infants transferred responding after a single preexposure lasting only 2 min. Extended preexposure also produced learned irrelevance, biasing subsequent selective attention, but there was no evidence of latent inhibition. These findings demonstrate that young infants pick up fairly sophisticated information about specific stimuli in their visual surround and the relationships between them merely as a result of passive observation, without explicitly being trained to do so. Moreover, infants may not express this knowledge for several days, until finally given an opportunity to do so. Sensory preconditioning may be an instance of "unitization"-a special type of infantile learning that enables immature organisms to acquire some associations more rapidly than adults.

During sensory preconditioning, rats were given two distinct flavors (saccharin and coffee) in sequence with 0, 9, or 27 sec between the two flavors. A control group received the flavors unpaired. In subsequent training, the second flavor preceded sucrose by 5 min. Later, the subjects that had had 0- or 9-sec delays between the two flavors showed a significant preference for the flavor not directly reinforced, whereas those that had had a 27-sec delay showed only a marginally significant preference. Although taste aversions have been produced using these methods, this is the first demonstration of conditioned preferences for flavors not directly associated with the reinforcers. These results offer an alternative way to study flavor-flavor learning.

The authors propose a computational theory of the hippocampal region's function in mediating stimulus representations. The theory assumes that the hippocampal region develops new stimulus representations that enhance the discriminability of differentially predictive cues while compressing the representation of redundant cues. Other brain regions, including cerebral and cerebellar cortices, are presumed to use these hippocampal representations to recode their own stimulus representations. In the absence of an intact hippocampal region, the theory implies that other brain regions will attempt to learn associations using previously established fixed representations. Instantiated as a connectionist network model, the theory provides a simple and unified interpretation of the functional role of the hippocampal region in a wide range of conditioning paradigms, including stimulus discrimination, reversal learning, stimulus generalization, latent inhibition, sensory preconditioning, and contextual sensitivity. The theory makes novel predictions regarding the effects of hippocampal lesions on easy-hard transfer and compound preexposure. Several prior qualitative characterizations of hippocampal function--including stimulus selection, chunking, cue configuration, and contextual coding--are identified as task-specific special cases derivable from this more general theory. The theory suggests that a profitable direction for future empirical and theoretical research will be the study of learning tasks in which both intact and lesioned animals exhibit similar initial learning behaviors but differ on subsequent transfer and generalization tasks.

Learning and memory processes are known to be influenced by the action of norepinephrine (NE). The present study evaluated the influence of neonatal administration of the NE neurotoxin DSP4 on sensory preconditioning (SPC) in 16- and 28-day-old rats. Rats were subcutaneously administered 50 mg/kg DSP4 or saline within 24 h after birth and tested at 16 or 28 days in two experiments. The results from Experiment 1 indicated that nondepleted 16-day-old rats exhibited strong SPC, whereas this conditioning was disrupted by neonatal administration of DSP4. No SPC was seen in either neonatal treatment group at 28 days of age, confirming previous reports of an ontogenetic decline in SPC. In Experiment 2, no effects of DSP4 were observed on first-order conditioning at either age. The brains of representative subjects were separated into forebrain, cerebellum, and brain stem samples and were analyzed to determine the extent of NE depletion. This analysis showed that DSP4 produced a marked reduction in NE concentration in the forebrain, but not in the cerebellum or brain stem. The results of this study suggest a role for forebrain NE in SPC in preweanling rats. This modulatory noradrenergic influence appears to be exerted on the formation of associations between two relatively neutral stimuli during the preexposure phase, given the absence of an effect of DSP4 on primary conditioning.

Little is known regarding the effects of acute ethanol on learning and memory among infant and juvenile rats. Two experiments were designed to evaluate the influence of various doses of ethanol administration on sensory preconditioning and primary conditioning in preweanling (16-day-old) and postweanling (28-day-old) rats. Moderate doses of ethanol facilitated conditioning at both ages. In the absence of ethanol, sensory preconditioning was not statistically significant among postweanlings in Experiment 1, although the phenomenon was clear and robust among preweanlings. Sensory preconditioning was facilitated by administration of doses of 0.8 and 1.2 g/kg ethanol in preweanlings and a dose of 1.6 g/kg ethanol in postweanlings, whereas sensory preconditioning was impaired in preweanlings by a high dose (2.4 g/kg) of ethanol. This reflected a shift to the right, between the preweaning and the postweaning periods, in the dose—response curve. It was determined in Experiment 2 that the effect of ethanol on sensory preconditioning could not be explained by stimulus generalization or an effect of ethanol on first-order conditioning, confirming the effect of ethanol on learning of the odor—odor association in the preexposure phase. The basis for a dose-dependent biphasic effect of ethanol on sensory preconditioning is discussed.

Sensory preconditioning and the Espinet effect illustrate that animals can reason about event relations. In sensory preconditioning, a combination of positive A-B and B-C relations yields a positive A-C relation. In the Espinet effect, a combination of a negative A-B relation and a positive B-C relation yields a negative A-C relation. Using analogies of Heider's balance theory of human attitudes, we predict that nonhuman animals would also infer a positive A-C relation from negative A-B and B-C relations.