Absence of differential protection from extinction in human causal learning

Elemental models of associative learning typically employ a common prediction-error term. Following a conditioning trial, they predict that the change in the strength of an association between a cue and an outcome is dependent upon how well the outcome was predicted. When multiple cues are present, they each contribute to that prediction. The same rule applies both to increases in associative strength during excitatory conditioning and the loss of associative strength during extinction. In five experiments using an allergy prediction task, we tested the involvement of a common error term in the extinction of causal learning. Two target cues were each paired with an outcome prior to undergoing extinction in compound either with a second excitatory cue or with a cue that had previously undergone extinction in isolation. At test, there was no difference in the causal ratings of the two target cues. Manipulations designed to bias participants toward elemental processing of cue compounds, to promote the acquisition of inhibitory associations, or to reduce generalization decrement between training and test were each without effect. These results are not consistent with common error term models of associative learning. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

EXPRESS: Temporal Distortion for Angry Faces: Testing Visual Attention and Action Preparation Accounts

When asked to judge the duration of a face people typically overestimate the duration of angry compared to neutral faces. A novel feature of the current research was the inclusion of secondary manipulations designed to distort timing performance namely, the effects of visual cues (Experiment 1) and action preparedness (Experiment 2). Furthermore, to establish whether the effects are multiplicative with duration, the effects were examined across 2 duration ranges (200 to 800 ms and 400 to 1600 ms). Visual cues and instructions to prepare to act increased the tendency to judge faces as lasting longer. Experiment 1 revealed an unexpected underestimation effect for angry faces presented for short durations (200 to 800 ms). However, the effect was not replicated in Experiment 2 where the results were generally consistent with either an increase the speed of a pacemaker mechanism that resides within an internal clock (Gibbon, Church, & Meck, 1984; Treisman, Faulkner, Naish, & Brogan, 1990; Treisman, 1963) or the widening of an attentional gate (Zakay & Block, 1996) - the temporal overestimation effect for angry faces grew in magnitude from the short to long duration. Experiment 2 also showed that the temporal overestimation for angry faces was reduced in magnitude when participants were asked to prepare to either push or pull a joystick.

Competing contextual processes rely on the infralimbic and prelimbic medial prefrontal cortices in the rat

Ambiguous relationships between events may be established using interference procedures such as latent inhibition, extinction or counterconditioning. Under these conditions, the retrieval of individual associations between a stimulus and outcome is affected by contextual cues. To examine the roles of the dorsal (prelimbic) and ventral (infralimbic) medial prefrontal cortex in the contextual modulation of such associations, we investigated the context specificity of latent inhibition. Male Lister hooded rats were pre-exposed to two separate stimuli, one in each of two distinct contexts. Both stimuli were then paired with the delivery of mild foot-shock in the same one of these contexts. Finally, the strength of the resultant conditioned emotional response (CER) to each stimulus was assessed in each context. For the sham-operated control rats, the CER was attenuated for each stimulus when it was tested in the context in which it had been pre-exposed. Rats who had received lesions to the infralimbic cortex showed this effect only in the conditioning context, whereas rats with lesions to the prelimbic cortex showed the effect only in the context in which conditioning had not taken place. These findings indicate that infralimbic and prelimbic cortices play distinct, and competing, roles in the contextual modulation of initial and later learning.

Acute Itch Induces Attentional Avoidance of Itch-related Information

Attention is known to modulate itch intensity. In contrast, the reverse relationship, i.e. the degree to which the presence of an acute itch affects attention, is currently not well understood. The aims of this study were to investigate whether acute itch induces an attentional bias towards or away from visual itch-related stimuli, and if so, whether it occurs in the early or later stages of processing. A volunteer sample of 60 healthy individuals were subjected to a skin prick (either histamine or placebo), followed by completion of a spatial cueing paradigm using itch-related and neutral words as cues, in order to obtain reaction time estimates of attentional bias. The results suggest that experience of acute itch induces attentional avoidance of visual itch threats. This attentional avoidance occurs at a later processing stage in the form of facilitated disengagement of attention from itch and/or delayed disengagement from neutral information.

Preexposure along a continuum: Differentiation and association

In 5 experiments, we assessed the effects of preexposure to simple auditory stimuli on subsequent conditioning and discrimination learning. Experiment 1 showed that preexposure to a single stimulus retarded acquisition of conditioned responding to that stimulus. The same preexposure regimen facilitated the subsequent acquisition of a discrimination between 2 stimuli that flanked the preexposed stimulus along the frequency dimension. Experiment 2 replicated this midpoint preexposure effect on discrimination learning but also found that alternating preexposure to the discriminative stimuli retarded discrimination learning. Experiments 3 to 5 explored the causes of these effects. These experiments are the first to examine perceptual learning in animals using simple auditory stimuli, and their results suggest that in at least some circumstances alternating preexposure to auditory stimuli results in an increase in generalization between them. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The representation of stimulus conjunction in theories of associative learning: A context-dependent added-elements model

This article briefly reviews 3 theories concerning elemental and configural approaches to stimulus representation in associative learning and presents a new context-dependent added-elements model (C-AEM). This model takes an elemental approach to stimulus representation where individual stimuli are represented by single units and stimulus compounds activate both those units and configurational units corresponding to each conjunction of 2 or more stimuli. Activity across these units is scaled such that each stimulus always contributes the same amount of activity to the system whether it is presented in isolation or in compound; the configurational units "borrow" activity from representational units for individual stimuli (and from each other). This scaling is affected by the extent to which stimuli interact with each other perceptually. Hence, the model is conceptually similar to Wagner's (2003) replaced elements model but lacks features that explicitly code for the absence of stimuli (i.e., inhibited elements). Simulations of the model are reported for a range of generalization and discrimination learning tasks, conflicting results from which have previously been taken to provide support for either configural or elemental theories of learning. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Disentangling the effects of attentional weighting and associative mediation in perceptual learning reveals no evidence for associative mediation

Learning to categorize perceptually similar stimuli can result in people becoming more sensitive to differences along perceptual dimensions that are relevant to category membership and/or less sensitive to equivalent differences along irrelevant perceptual dimensions. These effects of acquired distinctiveness and acquired equivalence may be caused by changes in the representations of stimuli which come about through adjustment to the relative attentional weighting of perceptual features or dimensions. Alternatively, the development of associations between individual stimuli and category labels could result in those labels being incorporated into the stimulus representation, hence increasing or decreasing generalization between the stimuli. For many categorization tasks, the expected effects of attentional weighting and associative mediation on stimulus similarity are the same. We report 3 experiments using complex category structures, which allowed us to assess the independent influence of each mechanism on stimulus similarity. The results suggest that, in these categorization tasks, attentional weighting affects perceptual similarity but associative mediation does not. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

A computational implementation of a Hebbian learning network and its application to configural forms of acquired equivalence

We describe and report the results of computer simulations of the three-layer Hebbian network informally described by Honey, Close, and Lin (2010): A general account of discrimination that has been shaped by data from configural acquired equivalence experiments that are beyond the scope of alternative models. Simulations implemented a conditional principle-components analysis Hebbian learning algorithm and were of four published experimental demonstrations of configural acquired equivalence. Experiments involved training rats on appetitive biconditional discriminations in which discrete cues (w and x) signaled food delivery (+) or its absence (-) in 4 different contexts (A, B, C, and D): Aw+ Bw- Cw+ Dw- Ax- Bx+ Cx- Dx+. Contexts A and C acquired equivalence. In 3 of the experiments acquired equivalence was evident from subsequent revaluation, from compound testing or from whole-/part-reversal training. The fourth experiment added concurrent biconditional discriminations with the same contexts but a pair of additional discrete cues (y and z). The congruent form of the discrimination, in which A and C provided the same information about y and z, was solved relatively readily. Parametric variation allowed the network to successfully simulate the results of each of the 4 experiments. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Effects of Short-term Temperature Change in the Innocuous Range on Histaminergic and Non-histaminergic Acute Itch

While temperatures in the noxious range are well-known to inhibit acute itch, the impact of temperature in the innocuous temperature range is less well understood. We investigated the effect of alternating short-term temperature changes in the innocuous range on histamine and cowhage-induced acute itch, taking into account individual differences in baseline skin temperature and sensory thresholds. Results indicate that cooling the skin to the cold threshold causes a temporary increase in the intensity of histamine-induced itch, in line with previous findings. Skin warming increased cowhage-induced itch intensity. Potential mecha-nisms of this interaction between thermosensation and pruritoception could involve cold-sensitive channels such as TRPM8, TREK-1 or TRPC5 in the case of histamine. The rapid modulation of cowhage induced itch - but not histamine-induced itch - by transient skin warming could be related to the lower temperature threshold of pruriceptive polymodal C-fibres (cowhage) as compared to the higher temperature threshold of the mechanoinsensitive C-fibres conveying histaminergic itch.

Stimulus similarity affects patterning discrimination learning

In four experiments, participants' performance on a variety of nonlinear patterning discriminations was assessed using a predictive learning task and visual patterns. Between groups, the similarity of the stimuli that composed these visual patterns was manipulated. When the stimuli were of low similarity, participants' performance was consistent with the predictions of one version of Pearce's (1987, 1994, 2002) configural theory of learning (Kinder & Lachnit, 2003); they were better able to discriminate between different patterns when they shared few, rather than many, stimuli. This effect was not observed when the similarity of the stimuli was high. Under these conditions, the results were more consistent with predictions of elemental theories of learning (e.g., Rescorla & Wagner, 1972; Wagner, 2003). This is the first time that these different patterns of performance on complex patterning discriminations have been shown within a single stimulus modality in the same experiment. The overall pattern of results is difficult to reconcile with either elemental or configural models of associative learning. (PsycINFO Database Record

Placebo Analgesia From a Rubber Hand

Placebo analgesia, reductions in pain after administration of an inert treatment, is a well documented phenomenon. We report, to our knowledge, the first demonstration that placebo analgesia can be experienced when a sham analgesic is applied onto a rubber hand. The effect was obtained by exploiting the rubber hand illusion, in which ownership is felt over a rubber arm that is unattached to the body. Under conditions of synchronous as well as asynchronous visuotactile stimulation, a thermal pain stimulus was delivered on the real arm of 20 participants and seemingly also on the rubber arm, before and after applying a sham analgesic and a control cream only to the rubber arm. During synchronous visuotactile stimulation, pain was experienced on the rubber arm, and the application of the sham analgesic to the rubber arm significantly decreased the severity of reported pain. This shows that experience of the body can modulate expectations and the induction of placebo analgesia.

PERSPECTIVE

This article presents an experiment suggesting that a placebo treatment applied to a rubber hand during the rubber hand illusion can produce placebo analgesia. This finding indicates that embodiment may influence the placebo effect, a previously unexamined factor in the treatment process with potential applications to treatment administration.

Attention and associative learning in humans: An integrative review

This article presents a comprehensive survey of research concerning interactions between associative learning and attention in humans. Four main findings are described. First, attention is biased toward stimuli that predict their consequences reliably (learned predictiveness). This finding is consistent with the approach taken by Mackintosh (1975) in his attentional model of associative learning in nonhuman animals. Second, the strength of this attentional bias is modulated by the value of the outcome (learned value). That is, predictors of high-value outcomes receive especially high levels of attention. Third, the related but opposing idea that uncertainty may result in increased attention to stimuli (Pearce & Hall, 1980), receives less support. This suggests that hybrid models of associative learning, incorporating the mechanisms of both the Mackintosh and Pearce-Hall theories, may not be required to explain data from human participants. Rather, a simpler model, in which attention to stimuli is determined by how strongly they are associated with significant outcomes, goes a long way to account for the data on human attentional learning. The last main finding, and an exciting area for future research and theorizing, is that learned predictiveness and learned value modulate both deliberate attentional focus, and more automatic attentional capture. The automatic influence of learning on attention does not appear to fit the traditional view of attention as being either goal-directed or stimulus-driven. Rather, it suggests a new kind of “derived” attention.

Extreme Elemental Processing in a High Schizotypy Population: Relation to Cognitive Deficits

The cognitive deficits observed in schizophrenia have been characterized as a failure to utilize task-setting information to guide behaviour, especially in situations in which there is response conflict. Recently, we have provided support for this account; high schizotypy individuals demonstrated inferior biconditional discrimination performance compared to low scorers, but were not impaired on a simple discrimination that did not require the use of task-setting cues. These results may, however, also be explained by the way in which individuals with high schizotypy process stimulus compounds . Here, we examine the initial approaches to solving biconditional and control discrimination tasks of participants with high and low schizotypy scores. In particular, we focus on performance during the first block of training trials to capture processing style before the acquisition of the discrimination tasks. Participants scoring highly on the introvertive anhedonia subscale (which has been allied to the negative and cognitive symptoms of schizophrenia) demonstrated better biconditional performance during the first block of training trials than did low-schizotypy individuals, consistent with a highly elemental approach to stimulus processing. Subsequent recognition tests confirmed this analysis demonstrating that the pattern of performance observed in participants with high schizotypy was associated with a failure to discriminate conjunctions of items that had been seen before from those that had not. These results suggest that the negative/cognitive symptoms of schizophrenia may reflect an extreme bias towards elemental, as opposed to configural, processing of stimulus conjunctions.

Dissociation of prefrontal cortex and nucleus accumbens dopaminergic systems in conditional learning in rats

There is converging evidence that the prefrontal and mesolimbic dopaminergic (DAergic) systems are involved in the performance of a variety of tasks that require the use of contextual, or task-setting, information to select an appropriate response from a number of candidate responses. Performance on tasks of this nature are impaired in schizophrenia and in rats exposed to psychotomimetics; impairments that are often attenuated by administration of dopamine (DA) antagonists. Rats were trained on either a complex instrumental discrimination task, that required the use of task-setting cues, or a simple discrimination task that did not. Following training, microdialysis probes were implanted unilaterally in either the medial prefrontal cortex (mPFC) or nucleus accumbens (NAc) and samples were collected in freely moving animals during a behavioural test session. In Experiment 1, we found no difference in levels of DA in the mPFC of rats while they were performing the two discrimination tasks. Rats that performed the complex task did, however, show significantly higher mPFC DA levels relative to rats in the simple discrimination condition following the end of the behavioural test session. In Experiment 2, rats performing the conditional discrimination showed lower levels of DA in the NAc compared to the simple discrimination group both during the test session and after it. These results provide direct evidence that conditional discrimination tasks engage frontal and mesolimbic DAergic systems and are consistent with the proposal that regulation of fronto-striatal DA is involved in aspects of cognitive control that are known to be impaired in individuals with schizophrenia.

Rapid communication: Impaired conditional task performance in a high schizotypy population: Relation to cognitive deficits

Cognitive impairments in schizophrenia have been characterized as reflecting a core deficit in the maintenance or use of task-setting cues to mediate appropriate ongoing behaviour. This analysis suggests that cognitive deficits in schizophrenia will be particularly evident when different task-setting cues dictate when different responses are required by the same stimuli. One simple task in which task-setting cues are required is a biconditional discrimination. Here we examined the performance of participants with high and low schizotypy scores (Mason, Claridge, & Jackson, 1995) on a biconditional discrimination and an otherwise equivalent, control discrimination that did not require the use of task-setting cues. Participants scoring highly on the Introvertive Anhedonia subscale (which has been allied to the negative and cognitive symptoms of schizophrenia) performed poorly on the biconditional, but not on the control, discrimination. No other subscales demonstrated a significant influence on either biconditional or control performance.

Lesions to the ventral, but not the dorsal, medial prefrontal cortex enhance latent inhibition

The acquisition of a conditioned response to a stimulus when it is paired with a reinforcer is retarded if the stimulus has previously been repeatedly pre-exposed in the absence of the reinforcer. This effect, called latent inhibition, has previously been found to be insensitive to lesions of the medial prefrontal cortex (mPFC) in rats. Using an on-baseline conditioned emotional response procedure, which is especially sensitive to small variations in the absolute magnitude of latent inhibition, we found increased latent inhibition following excitotoxic lesions of the mPFC (Experiment 1) or the ventral mPFC alone (Experiment 2) as compared with sham-operated control rats. Lesions restricted to the dorsal mPFC, however, were without effect (Experiment 2). These results are consistent with those of experiments employing another type of interference procedure, extinction. Together, these findings suggest that when different contingencies between a stimulus and a reinforcer are established in separate learning phases, lesions to the ventral mPFC result in increased interference between first-learned and second-learned contingencies. As a consequence, retrieval of the second-learned contingency is impaired, and performance is dominated by the first-learned contingency. These findings are discussed in light of the use of latent inhibition to model cognitive deficits in schizophrenia.

Optional-shift behaviour in rats: a novel procedure for assessing attentional processes in discrimination learning

A novel, optional-shift procedure was used to assess changes in the attention paid to stimuli that occur over the course of discrimination learning. In Phase 1, rats were trained on a conditional instrumental discrimination using audiovisual stimulus compounds; one stimulus dimension (auditory or visual) was relevant to the solution of the discrimination, the other was irrelevant. In Phase 2, all animals received three sessions of training with novel audiovisual compounds where both dimensions were equally diagnostic. Results from probe test trials indicated that, during Phase 2, animals learnt most about cues belonging to the stimulus dimension that was relevant during Phase 1. These results suggest that over the course of discrimination learning there was an increase in the amount of attention paid to relevant stimuli and/or a decrease in the attention paid to irrelevant stimuli.

The influence of hippocampal lesions on the discrimination of structure and on spatial memory in pigeons (Columba livia)

Pigeons (Columba livia) were trained with a spatial structural discrimination, which was based on the spatial relationship among the components of a pattern, and a feature-binding structural discrimination, which was based on how different visual features within a pattern were combined. Neither discrimination was impaired by damage to the hippocampus and area parahippocampalis. The lesions impaired performance on a spatial working memory and a spatial reference memory task in open field. The results indicate an intact hippocampus is not essential for the solution of structural discriminations in pigeons and the hippocampus is important for processing some types of spatial information--that used in navigation, but not other types--that used in spatial structural discriminations.

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.

The discrimination of structure: III. Representation of spatial relationships

Pigeons received a discrimination in which the spatial relationship between 2 adjacent rectangles filled with different colors signaled the trial outcome. Test trials then involved the same rectangles separated horizontally by a gap. The tests in Experiment 1 disrupted the discrimination more when the rectangles were tall and thin than when they were short and wide. Experiment 2 revealed that the width of the rectangles rather than their height determined the extent to which separating them would disrupt the original discrimination. The results are explained in terms of a template-matching account of pattern recognition with the additional assumption, supported by Experiment 3, that the size of a template can be altered to improve its match with a test pattern.

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.

Discrimination of structure: II. Feature binding

In 3 experiments, pigeons acquired a discrimination between patterns comprising the same features. Thus vertical green bars beside horizontal red bars might have signaled food, and horizontal green bars beside vertical red bars might have signaled no food. The solution of this discrimination can be explained by assuming each pattern is represented either by a template or by structural features that are sensitive to combinations of color and line orientation. The 1st explanation predicts subjects should react to a training pattern rotated 90 degrees in the same way as the pattern on which it is based. The 2nd explanation predicts these patterns should be treated as if they signal opposing outcomes. The experiments confirmed the 2nd of these predictions.

Visual search asymmetry in pigeons

Pigeons received an odd-item search task that involved an array of 12 patterns containing 11 similar distractors and a single target. Pecks to the target resulted in the delivery of food. Accuracy was greater on trials when a distinctive feature was located in the target but not in the distractors, rather than when the feature was in the distractors but not in the target. This search asymmetry was influenced by the similarity of the target to the distractors. The results are similar to those obtained with humans.

The effects of using stimuli from three different dimensions on autoshaping with a complex negative patterning discrimination

In two experiments pigeons received a complex negative patterning discrimination, using autoshaping, in which food was made available after three stimuli if they were presented alone (A, B, C), or in pairs (AB, AC, BC), but not when they were all presented together (ABC). Subjects also received a positive patterning discrimination in which three additional stimuli were not followed by food when presented alone (D, E, F), or in pairs (DE, DF, EF), but they were followed by food when presented together (DEF). Stimuli A and D belonged to one dimension, B and E to a second dimension, and D and F to a third dimension. For both problems, the discrimination between the individual stimuli and the triple-element compounds developed more readily than that between the pairs of stimuli and the triple-element compound. The results are consistent with predictions that can be derived from a configural theory of conditioning.

Acquisition of superexcitatory properties by an irrelevant background stimulus

Six appetitive conditioning experiments with rats demonstrated that an irrelevant X accompanying a negative patterning discrimination (XA+, XB+, XAB-) acquires extraordinarily high levels of conditioned excitation. Responding to X was similar to that evoked by 2 excitors in combination (Experiment 1) and was greater than responding to a separately reinforced Y (Experiments 2-5). Superexcitatory properties were not acquired by X in the nonpatterning discriminations of Experiments 2-4. Experiment 5 found that A and B, if anything, were weakly excitatory. Making them more strongly excitatory after conditioning did not interfere with retention of the original discrimination (Experiment 6). Results support a counterintuitive prediction of associative theories that, under carefully arranged conditions, irrelevant stimuli may acquire superexcitatory properties.

Summation in autoshaping is affected by the similarity of the visual stimuli to the stimulation they replace

Pigeons received autoshaping with 2 stimuli, A and B, presented in adjacent regions on a television screen. Conditioning with each stimulus was therefore accompanied by stimulation that was displaced from the screen whenever the other stimulus was presented. Test trials with AB revealed stronger responding if this displaced stimulation was similar to, rather than different from, A and B. For a further experiment the training just described included trials with A and B accompanied by an additional, similar, stimulus. Responding during test trials with AB was stronger if the additional trials signaled the presence rather than the absence of food. The results are explained with a configural theory of conditioning.

Discrimination of structure: I. Implications for connectionist theories of discrimination learning

In each of 4 experiments animals were given a structural discrimination task that involved visual patterns composed of identical features, but the spatial relations among the features were different for reinforced and nonreinforced trials. In Experiment 1 the stimuli were pairs of colored circles, and pigeons were required to discriminate between patterns that were the mirror image of each other. A related task was given to rats in Experiment 2. Subjects solved these discriminations. For Experiment 3, some pigeons were given a discrimination similar to that used in Experiment 1, which they solved, whereas others received a comparable task but with 3 colored circles present on every trial, which they failed to solve. The findings from Experiment 3 were replicated in Experiment 4 using different patterns. The results are difficult to explain by certain connectionist theories of discrimination learning, unless they are modified to take account of the way in which compound stimuli are structured.

Summation: further assessment of a configural theory

when A+ B+ training was conducted in the absence of CD+ trials. A further failure to observe abnormally strong responding during AB was found in Experiment 3 for which the training trials with A+ B+ CD+ were accompanied by trials in which C and D were separately paired with food. The results are explained in terms of a configural theory of conditioning, which assumes that responding during a compound is determined by generalization from its components, as well as from other compounds to which it is similar.

Discrimination of structure: I. Implications for connectionist theories of discrimination learning

In each of 4 experiments animals were given a structural discrimination task that involved visual patterns composed of identical features, but the spatial relations among the features were different for reinforced and nonreinforced trials. In Experiment 1 the stimuli were pairs of colored circles, and pigeons were required to discriminate between patterns that were the mirror image of each other. A related task was given to rats in Experiment 2. Subjects solved these discriminations. For Experiment 3, some pigeons were given a discrimination similar to that used in Experiment 1, which they solved, whereas others received a comparable task but with 3 colored circles present on every trial, which they failed to solve. The findings from Experiment 3 were replicated in Experiment 4 using different patterns. The results are difficult to explain by certain connectionist theories of discrimination learning, unless they are modified to take account of the way in which compound stimuli are structured.