Trial spacing is a determinant of cue interaction.

Four conditioned lick suppression experiments with rats examined the effect of trial spacing on cue interaction. Experiments 1 and 2 found overshadowing to be eliminated with massed compound stimulus- outcome pairings and the usual trial spacing effect to be reversed with compound acquisition trials. Experiment 3 found that whether acquisition compound- outcome pairings were massed or spaced determined the effect of posttraining extinction treatment. Extinction of the overshadowing cue reduced responding following massed training and increased responding following spaced training. Extinction of the context decreased responding following massed training. Experiment 4 found the conditioning and devaluation results to be associative and stimulus specific. These results are in accord with the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting reduced overshadowing and blocking.

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ→O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X→O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X→O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparator view of Pavlovian and differential inhibition.

In 3 experiments using rats as subjects, the authors varied trial spacing to investigate the conditions under which Pavlovian and differential inhibition are observed. Experiment 1 compared Pavlovian and differential inhibition with spaced training trials. Spaced trials resulted in only the Pavlovian inhibitor passing both summation and retardation tests. Conversely, Experiment 2 compared these 2 types of inhibition with massed training trials. This training resulted in only the differential inhibitor passing both tests for conditioned inhibition. Finally, in Experiment 3 all subjects experienced Pavlovian inhibition training with massed trials. Although this training by itself did not result in behavior indicative of inhibition, subjects that also experienced posttraining extinction of the training context did pass both tests for inhibition. Overall, these results are anticipated by the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) but are problematic for most contemporary associative learning theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overexpectation and trial massing.

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

Lesions of basolateral and central amygdala differentiate conditioned cue preference learning with and without unreinforced preexposure.

In the separated arms conditioned cue preference (CCP) task rats are trained by confining them in one arm of an eight-arm radial maze with food and in another arm on the opposite side of the maze with no food on alternate days. After two such trials, rats prefer the food-paired arm when allowed to move freely between the two arms, neither of which contains food. However, if the rats are preexposed to the maze by exploring it without food before training, no preference is observed and at least 4 training trials are required to produce a CCP, suggesting that unreinforced preexposure to the maze latently inhibits acquisition. If this interpretation is correct, preexposure should reduce the size of the preference acquired with both 2 and 4 training trials. In Experiment 1, this prediction was replicated for 2 training trials; however, with 4 training trials, eliminating preexposure also eliminated the CCP. A previous finding that basolateral amygdala lesions impair the CCP with preexposure and 4 training trials was replicated in Experiment 2, but similar lesions had no effect on the CCP in nonpreexposed rats given 2 training trials. In contrast, lesions of the central nucleus impaired the 2 training trial CCP but had no effect on the 4 training trial CCP. This double dissociation suggests that the BLA-mediated 4 training trial CCP may be due to learning about the reward features of the maze space, while the central-nucleus-mediated 2 training trial CCP may be due to a conditioned approach response. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Massed extinction trials produce better short-term but worse long-term loss of context conditioned fear responses than spaced trials.

A series of experiments studied the effects of the interval between extinction trials on the loss of context conditioned freezing responses. Rats were shocked in one context (A) but not in another (B) and subjected to extinction trials in context A. In Experiment 1, massed trials produced more rapid loss than spaced trials. A shift from spaced to massed trials maintained this loss, but the shift from massed to spaced trials restored lost responses. Experiments 2-5 examined this effect of massed trials on responding across spaced trials. They provided evidence that (a) a single trial was as effective as multiple daily massed trials, (b) learning occurred on the first of the massed trials but not on later ones, and (c) the first trial reduced the amount learned across subsequent massed trials. Finally, alternating extinction trials in A and B produced more response loss across spaced trials than blocks of trials in A and B. The results were discussed in terms of the role accorded to self-generated priming in the models developed by A. R. Wagner (1978, 1981). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trial spacing and trial distribution effects in Pavlovian conditioning: Contributions of a comparator mechanism.

Two experiments, involving a total of 144 rats, investigated a potential basis for trial spacing and trial distribution effects. In Exp 1, a CS (e.g., CS A) was trained with either massed (e.g., A?→?A?→?A) or spaced (e.g., A A A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Exp 2, different CSs were trained in either a massed (e.g., A?→?A?→?A?→?B?→?B?→?B?→?C?→?C?→?C) or a distributed (e.g., A?→?B?→?C?→?A?→?B?→?C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects were, at least in part, reversible deficits in performance rather than failures of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditional Discrimination Learning in Patients With Bilateral Medial Temporal Lobe Amnesia.

The ability of bilateral medial temporal lobe amnesic patients (MT; n=8) and normal participants (NC; n=8) to acquire a conditional discrimination in trace and delay eyeblink conditioning paradigms was investigated. Experiment 1 assessed trace conditional discrimination learning by using a light conditional stimulus (S+/S-) and tone conditioned stimulus (CS) separated by a 1-s trace. NCs responded differentially on S+ trials (mean percent conditioned responses=66) versus S- trials (30). Whereas MTs were impaired in their acquisition of the conditional discrimination (S+=51, S-=43). In Experiment 2, the temporal separation was eliminated. NCs acquired the conditional discrimination (S+=70, S-=29). MTs were unable to respond differentially (S+=42, S-=37). The findings indicate that the hippocampal system is essential in acquiring a conditional discrimination, even in a delay paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal response patterns during discriminative eyeblink/jaw movement conditioning in the rabbit.

Rabbits were given concurrent training in eyeblink (EB) and jaw movement (JM) conditioning in which 1 tone predicted an airpuff and another tone predicted water. After 10 days of discrimination training, the animals were given 10 days of reversal training. In the discrimination phase, acquisition of the 2 conditioned responses was not significantly different; however JM discrimination errors were much more frequent than were EB errors. In the reversal phase, correct performance on EB trials increased gradually, as was expected, whereas there was immediate behavioral reversal on JM trials. Differences in size and topography of dorsal CA1 multiple-unit responses reflected the ability of the hippocampus to discriminate between stimuli in trained animals, corresponding to the performance of the behavioral discrimination. During JM trials, the rhythmicity of the neural response was further modulated by the type of the prior trial, suggesting the coding of sequential events by the hippocampus. Thus, hippocampal conditioned activity can rapidly change its magnitude and pattern depending on the specific trial type during a concurrent EB/JM discrimination task and its reversal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of practice and positional variables in acquisition of a complex psychomotor skill

40 Navy subjects practiced a three-dimensional tracking task in two positions (the apparatus either in front of,, or above, the subject) under distributed and massed practice schedules to determine the effects of these variables on acquisition of skill. Distributed and massed practice were defined in terms of trial (4 1/2 and 9 min.) and session (1 and 2 hr.) lengths with the subjects equally divided into these four groups: distributed trials, distributed sessions; distributed trials, massed sessions; massed trials, distributed sessions; and massed trials, massed sessions. Total training (practice and rest) time was identical for all groups. Results indicated that task position was a relevant variable in acquisition of skill, i.e. different practice schedules were optimal for the two positions studied.     

Overshadowing and associability change.

Three appetitive Pavlovian conditioning experiments with rats examined the associability of stimuli A and B that had a history of compound conditioning (AB+), relative to stimuli X and Y that had a history of conditioning in isolation (X+, Y+). Following this training, Experiment 1 revealed that conditioned responding was higher to X and Y than to A and B (overshadowing). In a subsequent AY+, AX?, BY? test discrimination, the AY/BY discrimination was solved more readily than the AY/AX discrimination. In Experiment 2, following AB+, X+, Y+ training, A and Y were presented as a compound and signaled the availability of reinforcement upon the performance of an instrumental response. Test trials in which A and Y were presented alone, and in extinction, revealed that A acquired greater control of instrumental responding than Y. Experiment 3 revealed that following AB+, X+, Y+ training, A and B served as more effective discriminative stimuli for instrumental responding than X and Y. Overall, these results imply that the associability of stimuli conditioned in compound is higher than stimuli conditioned in isolation. These results are discussed in terms of attentional theories of associative learning. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Characteristics of associative learning in younger and older adults: Evidence from an episodic priming paradigm.

Two experiments investigated age differences in the encoding of associative information during a speeded naming task. In both experiments, semantically unrelated prime-target word pairs were presented 4 times, in either massed or spaced fashion, during the learning phase. An immediate or delayed test trial was presented following the fourth presentation. In Experiment 1, participants named both the primes and the targets. Younger and older adults showed similar benefits when naming targets that were part of a consistent prime-target pairing compared with targets presented with different primes at each presentation. In Experiment 2, participants named only the target word. Younger adults showed a benefit for consistently paired words, whereas older adults showed no benefit for consistently paired words. The results of the test trials showed a greater benefit for massed repeated words than for spaced repeated words at the immediate test and a reversed pattern at the delayed test. This spacing by test delay interaction was evident in response latency in Experiment 1 and in cued recall performance in Experiment 2. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Repeated acquisition of a spatial navigation task in mice: effects of spacing of trials and of unilateral middle cerebral artery occlusion

The working memory version of the Morris water escape task, the repeated acquisition task, consists of trial pairs in which an animal is started twice from the same start position. Animals have mastered this task when they need less time to find the platform in the second of the two trials. In this study, study, male C57BL mice were trained on this task with massed, spaced, or spaced delay trials in which there was a 90-min delay between the first and second trials of a pair. The mice trained with spaced trials learned the repeated acquisition task, whereas the mice trained with massed or spaced delay trials were not consistently able to do so. When the mice had reached a stable baseline performance, the middle cerebral artery (MCA) was occluded or the mice were sham-operated. Then, the effects of the MCA occlusion (MCA-O) on the performance in the repeated acquisition tasks were studied. MCA occlusion hardly affected the performance in this task, irrespective of the spacing condition of the trials, although surgery per se seemed to have a transient disruptive effect.     

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)     

The intermixed-blocked effect in human perceptual learning is not the consequence of trial spacing.

A robust finding in humans and animals is that intermixed exposure to 2 similar stimuli (AX/BX) results in better discriminability of those stimuli on test than does exposure to 2 equally similar stimuli in 2 separate blocks (CX_DX)--the intermixed-blocked effect. This intermixed-blocked effect may be an example of the superiority of spaced over massed practice; in the intermixed, but not the blocked exposure regime, each presentation of a given stimulus (e.g., AX) is separated from the next by the presentation of its partner (BX). Two experiments with human participants replicated the intermixed-blocked effect and showed that the effect was not due to the spacing of exposure trials. A mechanism for the intermixed-blocked effect is proposed, which combines theories from associative learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on spatial and cued leaning

An investigation was made of the effects of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the acquisition and retention of two operantly conditioned discrimination tasks. Twenty Long-Evans rats were conditioned to approach one of two spatial locations that was either held constant across trials (spatial task) or was associated with a visual cue (illuminated lamp) that was randomly assigned to one of the locations on each trial (cued task). Rats were assigned to one of two treatment groups in which they received intraperitoneal injections of either NG-nitro-L-arginine methyl ester or saline approximately 2 h before sessions on each day of training. Analysis was made of the trial-by-trial performance in order to identify the characteristics of learning under each condition. Assessment of learning acquisition was based on the number of trials required to reach a criterion of 80% correct responses, whereas retention was assessed by the number of trials to criterion on each day after the criterion was initially reached. Analysis indicated that treatment groups did not differ significantly on acquisition or retention of either the spatial or cued task. These results indicate that inhibition of nitric oxide synthase does not interfere with the learning or retention of basic operant tasks that involve simple spatial or visual analysis. Whereas results from biochemical and physiological investigations have suggested an impact of nitric oxide synthase on behavioural function, behavioural investigations indicate a limited impact of nitric oxide synthase inhibition on learning and memory. Although these results do not discount the role of nitric oxide synthase in a hippocampal mechanism, they illustrate that behavioural analysis should be made in the context of multiple interacting neural systems. Viewed with previous behavioural research on the effects of NG-nitro-L-arginine methyl ester, these results indicate that nitric oxide synthase inhibition results in impairment of certain forms of learning whereas other forms are preserved.     

Detrimental Influence of Contextual Change on Spacing Effects in Free Recall.

Two experiments were conducted to determine the mechanism underlying the spacing effect in free-recall tasks. Participants were required to study a list containing once-presented words as well as massed and spaced repetitions. In both experiments, presentation background at repetition was manipulated. The results of Experiment 1 demonstrated that free recall was higher for massed items repeated in a different context than for massed items repeated in the same context, whereas free recall for spaced items was higher when repeated in the same context. Furthermore, a spacing effect was shown for words repeated in the same context, whereas an attenuated spacing effect was revealed for words repeated in a different context. These findings were replicated in Experiment 2 under a different presentation background manipulation. Both experiments seem to be most consistent with a model that combines the contextual variability and the study-phase retrieval mechanism to account for the spacing effect in free-recall tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Classical conditioning of proboscis extension in honeybees (Apis mellifera).

Conditioned extension of the proboscis in restrained honeybees with odor as the CS and sucrose solution—delivered to the antenna (to elicit extension of the proboscis) and then to the proboscis itself—as the UCS. In a 1st series of experiments, acquisition was found to be rapid, both in massed and in spaced trials; its associative basis was established by differential conditioning and by an explicitly unpaired control procedure. Both extinction and spontaneous recovery in massed trials were demonstrated. In experiments on the nature of the UCS, eliminating the proboscis component lowered the asymptotic level of performance, whereas eliminating the antennal component was without effect; reducing the concentration of sucrose from 20% to 7% slowed acquisition but did not lower the asymptotic level of performance; and second-order conditioning was demonstrated. In experiments on the role of the UCS, an omission contingency designed to eliminate adventitious response-reinforcer contiguity was found to have no adverse effect on acquisition. In experiments designed to analyze the resistance to acquisition found after explicitly unpaired training in the 1st experiments, no significant effect was found of prior exposure either to the CS alone or to the UCS alone, although the unpaired procedure again produced resistance that was shown to be due to inhibition rather than to inattention; extinction after paired training was found to be facilitated by unpaired presentations of the UCS. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting predictions of extended comparator hypothesis and acquisition-focused models of learning concerning retrospective revaluation.

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