Formation of excitatory and inhibitory associations between absent events.

Considerable evidence indicates that associations may be formed between two events even when one or both of them is absent at the time of learning. Previously, some researchers asserted that excitatory associations are formed when associatively activated representations for two events are paired, whereas others claimed that inhibitory associations are formed. In three experiments, the authors investigated the nature of tone-sucrose learning when associatively activated representations of those events were paired in the absence of either of the events themselves. Experiment 1 found substantial excitatory learning when the tone surrogate preceded the sucrose surrogate in training. Experiment 2 evaluated other accounts for the results of Experiment 1, and Experiment 3 found evidence for inhibitory tone-sucrose learning when the tone and sucrose surrogates were presented in simultaneous or backward order. The results indicated that the nature of representation-mediated learning is influenced by some of the same variables as more standard associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned inhibition in the spatial domain.

Using a variation on the standard procedure of conditioned inhibition (Trials A+ and AX?), rats (Rattus norvegicus) in a circular pool were trained to find a hidden platform that was located in a specific spatial position in relation to 2 individual landmarks (Trials A → platform and B → platform; Experiments 1a and 1b) and to 2 configurations of landmarks (Trials ABC → platform and FGH → platform; Experiment 2a). The rats also underwent inhibitory trials (Experiment 1: Trials AZ → no platform; Experiment 2a: Trials CDE → no platform) interspersed with these excitatory trials. In both experiments, subsequent test trials without the platform showed both a summation effect and retardation of excitatory conditioning, and in Experiment 2a rats learned to avoid the CDE quadrant over the course of the experiment. Two further experiments established that these results could not be attributed to any difference in salience between the conditioned inhibitors and the control stimuli. All these results contribute to the growing body of evidence consistent with the idea that there is a general mechanism of learning that is associative in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concurrent learning of temporal and spatial sequences.

In a serial reaction time task, stimulus events simultaneously defined spatial and temporal sequences. Responses were based on the spatial dimension. The temporal sequence was incidental to the task, defined by the response-to-stimulus intervals in Experiment 1 and stimulus onset asynchronies in Experiment 2. The two sequences were either of equal length and correlated or of unequal length. In both experiments, spatial learning occurred regardless of sequence length condition. In contrast, temporal learning occurred only in the correlated condition. These results suggest that timing is an integrated part of action representations and that incidental learning for a temporal pattern does not occur independently from the action. Interestingly, sequence learning was enhanced in the correlated condition, reflecting the integration of spatial-temporal information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Blocking and Unblocking in Human Causal Learning.

Three experiments sought to develop the suggestion that, under some circumstances, common associative learning mechanisms might underlie animal conditioning and human causal learning, by demonstrating, in humans, an effect analogous to the unblocking by reinforcer omission observed in animal conditioning. Experiment 1 found no such effect. Experiment 2, designed to prevent inhibitory influences that might have masked excitatory unblocking in Experiment 1, demonstrated unblocking, indicating common human-animal associative learning mechanisms in which the associability of a stimulus varies as a function of its predictive history. Experiment 3, using a similar design but with a procedure promoting application of rational inference processes, failed to detect the same unblocking effect, indicating that associative and cognitive mechanisms may influence human causal learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning of event sequences is based on response-effect learning: Further evidence from a serial reaction task.

Four experiments provide converging evidence that serial learning in a serial reaction task is based on response–effect learning, mediated by the learning of the relations between a response and the stimulus that follows it. In Experiment 1, the authors varied the stimulus sequence and the response–stimulus relations while holding the response sequence constant. Learning effects depended on the complexity of the response–stimulus relations but not on the stimulus–stimulus relations. In Experiment 2, transfer of serial learning from 1 stimulus sequence to another was only found when both sequences had identical response–stimulus relations. In Experiment 3, a variation of the stimulus sequence alone had no effect on serial learning, whereas in Experiment 4 learning effects increased when the response–stimulus relations but not the stimulus–stimulus relations were simplified. These findings suggest that serial learning is based on mechanisms of voluntary action control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of the role of associative inhibition in perceptual learning by means of the same-different task.

In Experiment 1a, participants were exposed, over a series of trials, to separate presentations of 2 similar checkerboard stimuli, AX and BX (where X represents a common background). In one group, AX and BX were presented on alternating trials (intermixed), in another, they were presented in separate blocks of trials (blocked). The intermixed group performed to a higher standard than the blocked group on a same-different test. A superiority of intermixed over blocked exposure was also evident in a within-subject design (Experiment 1b) and when the test required discrimination between a preexposed stimulus and the background (e.g., AX vs. X), even if the background changed between preexposure and test (AY vs. Y) (Experiment 2). In Experiment 3, the intermixed/blocked effect was observed when, in preexposure, stimulus presentations were alternated with the background alone (e.g., AX/X). This suggests that the perceptual learning effect is not the consequence of inhibitory associations between unique features but to increased salience of those features. Experiment 4 confirmed this finding and also ruled out an account of the effect in terms of trial spacing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning across the duration of a backward conditioned stimulus.

Five conditioned suppression experiments examined the extent to which an appetitively motivated lever-press response can be punished by different components of a backward conditioned stimulus (CS). Using a 0-s unconditioned stimulus UCS–CS interval, Experiments 1 and 2 showed that the initial 3 s of a normally 30-s backward CS served as a more effective punisher than the CS as a whole, Experiment 3 found no such effect if the UCS–CS interval were 3 s rather than 0 s. Experiments 4A and 4B found that if the UCS–CS interval were 0 s, the initial part of the backward CS acquired excitatory properties although the CS as a whole passed a summation test for conditioned inhibition. By contrast, the 3-s UCS–CS interval supported inhibitory conditioning across the whole duration of the backward CS. Taken together, these findings support a modified version of Wagner's sometimes opponent process model, which suggests that different components of a backward CS become either excitatory or inhibitory depending on the components' temporal proximity to the UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

I like it because I said that I like it: Evaluative conditioning effects can be based on stimulus-response learning.

Evaluative conditioning (EC) effects are often assumed to be based on a learned mental link between the CS (conditioned stimulus) and the US (unconditioned stimulus). We demonstrate that this link is not the only one that can underlie EC effects, but that if evaluative responses are actually given during the learning phase also a direct link between the CS and an evaluative response—a CS-ER link—can be learned and lead to EC effects. In Experiment 1, CSs were paired with USs and participants were asked to evaluate the pairs during the conditioning phase. Resulting EC effects were unaffected by a later revaluation of the USs, suggesting that these EC effects can be attributed to CS-ER learning rather than to CS-US learning. Experiment 2 replicated Experiment 1 with the difference that no evaluative responses were given during the learning phase. EC effects in this study were influenced by US revaluation, suggesting that these EC effects are mainly based on CS-US learning. In Experiment 3, it was shown that EC effects can be found even if the USs are entirely removed from the procedure and the CSs are only paired with enforced evaluative responses. Together the experiments show that the valence of a stimulus can change because of a contingency with an evaluative response. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Intertrial interval as a contextual stimulus: Further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short?), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long?), discrimination learning was much slower. Experiment 1 compared Long+/Short? and Short+/Long? discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long? learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long? learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short? learning may be faster than Short+/Long?because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A?) are learned quicker than feature-negative discriminations (A+/AB?). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation by the stimulus properties of excitation

Three experiments with pigeons investigated the role of excitation in a Pavlovian modulatory paradigm where the reinforcement contingencies of a conditioned stimulus (CS) were signaled by modulatory stimuli. In Experiment 1, excitatory training of the modulator that signaled reinforcement, the positive modulator, had a greater facilitative impact on discrimination learning than did excitatory training of both modulators. Although this could have resulted from simple excitatory summation, Experiment 2 revealed that excitatory training of the negative modulator also enhanced learning more than did excitatory training of both modulators. In Experiment 3, responding to CSs that had come under the control of differentially excitatory modulators was similarly controlled by new stimuli that had received simple differential excitatory training. Results suggest that excitation can play a modulatory role in Pavlovian conditioning.     

Facilitation and inhibition of the human startle blink reflexes by stimulus anticipation.

The cutaneous eyeblink has 2 electromyographic components, 1 unilateral and early (R1) and 1 bilateral and late (R2), which are served by different neural pathways. These 2 reactions were measured when the eliciting stimulus was expected or relatively surprising. Forewarning was varied in 3 ways: Subjects received notice that the stimulus was about to occur on some trials (Experiment 1); delivered the stimulus to themselves on some trials (Experiments 2 & 3); or experienced a series of trials in which a tone was paired with the eliciting stimulus, followed by tone-alone trials interspersed with test trials (Experiment 4). In each case, forewarning enhanced R1 amplitudes while depressing R2 but reduced the latency of both components. This mixed pattern of effects reveals that the preparatory state provoked by forewarning focuses excitatory and inhibitory processes simultaneously on different reflex pathways: inhibition central and excitation peripheral. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Automatic and intentional activation of task sets.

Four experiments examined automatic and intentional activation of task sets in a switching paradigm. Experiment 1 demonstrated incidental task sequence learning that was not accompanied by verbalizable task sequence knowledge. This learning did not affect task shift cost and may be attributed to automatic task-set activation. In Experiment 2, both shift cost and learning effect increased when the response–cue interval was short, indicating the influence of residual, persisting activation of the preceding task set. In Experiment 3, learning disappeared with a long cue–stimulus interval (CSI), which resulted in a strong preparation effect. This preparation, however, reduced reaction time level but was not specific to task shifts. Finally, experiment 4 showed that a within-subject CSI variation also leads to reduced shift costs. Together, the data suggest an activational account of task preparation and may have relevant implications for inhibitory accounts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of automatic imitation is sensitive to sensorimotor contingency.

The associative sequence learning model proposes that the development of the mirror system depends on the same mechanisms of associative learning that mediate Pavlovian and instrumental conditioning. To test this model, two experiments used the reduction of automatic imitation through incompatible sensorimotor training to assess whether mirror system plasticity is sensitive to contingency (i.e., the extent to which activation of one representation predicts activation of another). In Experiment 1, residual automatic imitation was measured following incompatible training in which the action stimulus was a perfect predictor of the response (contingent) or not at all predictive of the response (noncontingent). A contingency effect was observed: There was less automatic imitation indicative of more learning in the contingent group. Experiment 2 replicated this contingency effect and showed that, as predicted by associative learning theory, it can be abolished by signaling trials in which the response occurs in the absence of an action stimulus. These findings support the view that mirror system development depends on associative learning and indicate that this learning is not purely Hebbian. If this is correct, associative learning theory could be used to explain, predict, and intervene in mirror system development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition Between Antecedent and Between Subsequent Stimuli in Causal Judgments.

In the analysis of stimulus competition in causal judgment, 4 variables have been frequently confounded with respect to the conditions necessary for stimuli to compete: causal status of the competing stimuli (causes vs. effects), temporal order of the competing stimuli (antecedent vs. subsequent) relative to the noncompeting stimulus, directionality of training (predictive vs. diagnostic), and directionality of testing (predictive vs. diagnostic). In a factorial study using an overshadowing preparation, the authors isolated the role of each of these variables and their interactions. The results indicate that competition may be obtained in all conditions. Although some of the results are compatible with various theories of learning, the observation of stimulus competition in all conditions calls for a less restrictive reformulation of current learning theories that allows similar processing of antecedent and subsequent events, as well as of causes and effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative time course of semantic and phonological activation in reading Chinese.

The relative time course of semantic and phonological activation was investigated in the context of whether phonology mediates access to lexical representations in reading Chinese. Compound words (Experiment 1) and single-character words (Experiments 2 and 3) were preceded by semantic and phonological primes. Strong semantic priming effects were found at both short (57 ms) and long (200 ms) stimulus onset asynchrony (SOA), but phonological effects were either absent in lexical decision (Experiment 1), were present only at the longer SOA in character decision (Experiment 2) or were equally strong as semantic effects in naming (Experiment 3). Experiment 4 revealed facilitatory or inhibitory effects, depending on SOA, in phonological judgments to character pairs that were not phonologically but semantically related. It was concluded that, in reading Chinese, semantic information in the lexicon is activated at least as early and just as strongly as phonological information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation and inhibition.

The reciprocal relation between conditioned inhibition and conditioned facilitation was explored in both learning and performance. In five autoshaping experiments, pigeons were trained with a facilitation procedure in which a keylight was followed by food only in the presence of a diffuse stimulus. Under the conditions, the birds came to peck the keylight primarily in the presence of the diffuse stimulus (facilitator). In Experiments 1 and 2 such a facilitator was found to counter the performance decrement otherwise produced by a conditioned inhibitor. Moreover, the facilitator did so more successfully than did a simple Pavlovian excitor. In Experiments 3, 4, and 5 facilitation training was found to affect the learning of inhibition. In Experiment 3 pretraining with a facilitation paradigm was found to slow the subsequent development of conditioned inhibition more than did pretraining with an excitatory procedure. In Experiments 4 and 5 facilitation training was found to attenuate previously established inhibition more than did excitatory training. These results suggest that under some circumstances facilitation, rather than excitation, is the natural conceptual opposite to inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced discrimination between flavor stimuli: Roles of salience modulation and inhibition.

Rats were given intermixed preexposure to the compound flavors AX and BX and to the compound CX in a separate block of trials (4 presentations of each compound). In Experiment 1, rats showed less generalization of conditioned aversion from AX to BX than from CX to BX, a perceptual learning effect. Experiment 2 showed that the formation of an excitatory association proceeded more readily between A and B than between C and B, suggesting that intermixed preexposure maintains the effective salience of A and B and does not establish inhibition between them, a process that would require prolonged preexposure. According to this analysis, salience modulation and associative inhibition may contribute to perceptual learning at different stages of preexposure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of primary motivation in stimulus preexposure effects.

It is currently a matter of debate whether the deficit in conditioning observed after stimulus preexposure is one of acquisition or one of performance. The major criticism of performance-based theories is their inability to specify what is learned during nonreinforced preexposure that may influence subsequent acquisition of conditioned responding. Experiments 1 and 2 used an excitatory appetitive conditioning procedure and Experiment 3 used an inhibitory appetitive conditioning procedure, with rats as subjects, and consistently found that the effects of preexposure to a stimulus transferred to conditioning only when the reinforcer was relevant to the motivational state in which that preexposure was conducted. This finding suggests that during preexposure, rats learn that a stimulus is unrelated to events of relevance to their current motivational state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating the conditioning and the anorectic effects of estradiol in female rats.

The present series of experiments challenges the ability of the hormone estradiol to act as an unconditioned stimulus in the conditioned taste avoidance (CTA) learning paradigm. We hypothesize that reductions in sucrose consumption observed after pairing it with estradiol are not indicative of associative learning, but due to the unconditioned expression of estradiol’s anorectic effects during the time of CTA assessment. Three experiments in which a sucrose solution was paired with estradiol were conducted to test this hypothesis. Experiment 1 demonstrated that female rats expressed a reduction in post-pairing sucrose consumption even though the anorectic effects of estradiol had subsided. Experiment 2 showed that although a low dose of estradiol produced anorexia, it did not elicit post-pairing reductions in sucrose consumption. Experiment 3 revealed that contingent pairing was a requirement for post-pairing reduction in sucrose consumption even when testing was done at a time when anorexia is expressed. These findings demonstrate the dissociability of the conditioning and anorectic effects of estradiol, providing evidence against the hypothesis. The results are discussed in terms of independent neural mechanisms underlying the disparate behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)