Backward Associations Research Articles

Dopamine Release in the Nucleus Accumbens Core Encodes the General Excitatory Components of Learning.

Dopamine release in the nucleus accumbens core (NAcC) is generally considered to be a proxy for phasic firing of the ventral tegmental area dopamine (VTADA) neurons. Thus, dopamine release in NAcC is hypothesized to reflect a unitary role in reward prediction error signaling. However, recent studies reveal more diverse roles of dopamine neurons, which support an emerging idea that dopamine regulates learning differently in distinct circuits. To understand whether the NAcC might regulate a unique component of learning, we recorded dopamine release in NAcC while male rats performed a backward conditioning task where a reward is followed by a neutral cue. We used this task because we can delineate different components of learning, which include sensory-specific inhibitory and general excitatory components. Furthermore, we have shown that VTADA neurons are necessary for both the specific and general components of backward associations. Here, we found that dopamine release in NAcC increased to the reward across learning while reducing to the cue that followed as it became more expected. This mirrors the dopamine prediction error signal seen during forward conditioning and cannot be accounted for temporal-difference reinforcement learning. Subsequent tests allowed us to dissociate these learning components and revealed that dopamine release in NAcC reflects the general excitatory component of backward associations, but not their sensory-specific component. These results emphasize the importance of examining distinct functions of different dopamine projections in reinforcement learning.

Do Backward Associations Have Anything to Say About Language?

In this letter, we argue against a recurring idea that early word learning in infants is related to the low-level capacity for backward associations-a notion that suggests a cognitive gap with other animal species. Because backward associations entail the formation of bidirectional associations between sequentially perceived stimulus pairs, they seemingly mirror the label-referent bidirectional mental relations underlying the lexicon of natural language. This appealing but spurious resemblance has led to various speculations on language acquisition, in particular regarding early word learning, which we deconstruct here.

Association learning: Dopamine and the formation of backward associations

The activity of dopamine neurons is critical for the ability to learn and update cue-reward associations. New work in rats shows that dopamine transients are also critical for the formation of backward associations in which the reward precedes the neutral stimulus.

A theory of repetition and retrieval in language production.

Repetition appears to be part of error correction and action preparation in all domains that involve producing an action sequence. The present work contends that the ubiquity of repetition is due to its role in resolving a problem inherent to planning and retrieval of action sequences: the Problem of Retrieval. Repetitions occur when the production to perform next is not activated enough to be executed. Repetitions are helpful in this situation because the repeated action sequence activates the likely continuation. We model a corpus of natural speech using a recurrent network, with words as units of production. We show that repeated material makes upcoming words more predictable, especially when more than one word is repeated. Speakers are argued to produce multiword repetitions by using backward associations to reactivate recently produced words. The existence of multiword repetitions means that speakers must decide where to reinitiate execution from. We show that production restarts from words that have seldom occurred in a predictive preceding-word context and have often occurred utterance-initially. These results are explained by competition between preceding-context and top-down cues over the course of language learning. The proposed theory improves on structural accounts of repetition disfluencies, and integrates repetition disfluencies in language production with repetitions observed in other domains of skilled action. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Bidirectional conditioning: Revisiting Asratyan's 'alternating' training technique.

The study of bidirectional conditioning began more than a century ago, yet it has failed to take strong root in psychology and neuroscience. We revisit this topic by exploiting E. A. Asratyan's alternating procedure of stimulus presentation, in which both forward (e.g., A→B) and backward (e.g., B→A) training trials are concurrently given, in order to analyze their potential interaction. Specifically, using a two-alternative, forced-choice task, we trained humans and pigeons to learn associations between stimuli depending on whether they were presented as sample stimuli or choice stimuli. Trials were selected from an associative network in which forward and backward associations between sample and choice stimuli were synergistic (bidirectional network) or from an associative network in which these associations were not synergistic (unidirectional network). Humans were faster to learn associations from the bidirectional network than from the unidirectional network; additionally, they performed poorly on unidirectional trials that allowed for the expression of (incorrect) bidirectional associations. Unlike humans, pigeons showed no evidence of bidirectional associations. The reasons for this species difference as well as future directions for research deploying Asratyan's two-way training technique are discussed.

Memory asymmetry of forward and backward associations in recognition tasks.

There is an intensive debate on whether memory for serial order is symmetric. The objective of this study was to explore whether associative asymmetry is modulated by memory task (recognition vs. cued recall). Participants were asked to memorize word triples (Experiments 1-2) or pairs (Experiments 3-6) during the study phase. They then recalled the word by a cue during a cued recall task (Experiments 1-4) and judged whether the presented 2 words were in the same or in a different order compared with the study phase during a recognition task (Experiments 1-6). To control for perceptual matching between the study and test phase, participants were presented with vertical test pairs when they made directional judgment in Experiment 5. In Experiment 6, participants also made associative recognition judgments for word pairs presented at the same or the reversed position. The results showed that forward associations were recalled at similar levels as backward associations and that the correlations between forward and backward associations were high in the cued recall tasks. On the other hand, the direction of forward associations was recognized more accurately (and more quickly) than backward associations, and their correlations were comparable to the control condition in the recognition tasks. This forward advantage was also obtained for the associative recognition task. Diminishing positional information did not change the pattern of associative asymmetry. These results suggest that associative asymmetry is modulated by cued recall and recognition manipulations and that direction as a constituent part of a memory trace can facilitate associative memory.

Sleep Enforces the Temporal Order in Memory

BackgroundTemporal sequence represents the main principle underlying episodic memory. The storage of temporal sequence information is thought to involve hippocampus-dependent memory systems, preserving temporal structure possibly via chaining of sequence elements in heteroassociative networks. Converging evidence indicates that sleep enhances the consolidation of recently acquired representations in the hippocampus-dependent declarative memory system. Yet, it is unknown if this consolidation process comprises strengthening of the temporal sequence structure of the representation as well, or is restricted to sequence elements independent of their temporal order. To address this issue we tested the influence of sleep on the strength of forward and backward associations in word-triplets.Methodology/Principal FindingsSubjects learned a list of 32 triplets of unrelated words, presented successively (A-B-C) in the center of a screen, and either slept normally or stayed awake in the subsequent night. After two days, retrieval was assessed for the triplets sequentially either in a forward direction (cueing with A and B and asking for B and C, respectively) or in a backward direction (cueing with C and B and asking for B and A, respectively). Memory was better for forward than backward associations (p<0.01). Sleep did not affect backward associations, but enhanced forward associations, specifically for the first (AB) transitions (p<0.01), which were generally more difficult to retrieve than the second transitions.Conclusions/SignificanceOur data demonstrate that consolidation during sleep strengthens the original temporal sequence structure in memory, presumably as a result of a replay of new representations during sleep in forward direction. Our finding suggests that the temporally directed replay of memory during sleep, apart from strengthening those traces, could be the key mechanism that explains how temporal order is integrated and maintained in the trace of an episodic memory.

Temporal integration and temporal backward associations in human and nonhuman subjects.

Two experiments are reported that demonstrate temporal integration of independently acquired temporal relationships, including backward associations, in both human (Experiment 1) and nonhuman (rats, Experiment 2) subjects. The experiments were designed and analyzed in the framework of the temporal coding hypothesis (e.g., Matzel, Held, & Miller, 1988; Savastano & Miller, 1998) as a strategy toward illuminating the use of temporal information and assessing the existence of temporal backward associations. Both experiments provided evidence of retrieval of associations to an event that was expected to occur prior to the moment in time at which a stimulus was presented (i.e., backward associations). In addition, Experiment 1 constitutes the first controlled demonstration of temporal integration by human subjects.

An autoassociative neural network model of paired-associate learning.

Hebbian heteroassociative learning is inherently asymmetric. Storing a forward association, from item A to item B, enables recall of B (given A), but does not permit recall of A (given B). Recurrent networks can solve this problem by associating A to B and B back to A. In these recurrent networks, the forward and backward associations can be differentially weighted to account for asymmetries in recall performance. In the special case of equal strength forward and backward weights, these recurrent networks can be modeled as a single autoassociative network where A and B are two parts of a single, stored pattern. We analyze a general, recurrent neural network model of associative memory and examine its ability to fit a rich set of experimental data on human associative learning. The model fits the data significantly better when the forward and backward storage strengths are highly correlated than when they are less correlated. This network-based analysis of associative learning supports the view that associations between symbolic elements are better conceptualized as a blending of two ideas into a single unit than as separately modifiable forward and backward associations linking representations in memory.

Reader Control in Reading: Effects of Language Competence, Text Type, and Task

Reader control was examined with native and nonnative readers of Japanese who thought aloud during reading and later recalled. Two types of text (stories and essays) and 2 types of tasks (read freely and read for coherence) were used. It was found that (a) native readers generated more backward inferences and general knowledge associations for essays and more forward inferences for stories; (b) when reading an essay for coherence, native readers generated more backward inferences, more comments on text structure, and fewer general knowledge associations in contrast to when reading it freely; (c) nonnative readers generated more elaborative inferences and more comments on text structure for essays; and (d) nonnative readers did not process an essay differently between when reading it freely and when reading it for coherence, although in the read-for-coherence condition, their recall was as good as that of native readers. These results suggest that native readers engage in different modes of processing according to text type and task, whereas nonnative readers' processing is strategic but inefficient, especially with more demanding text.

A Behavior Systems Approach to the Expression of Backward Associations

In the first phase of Experiment 1 rats were trained with a backward serial conditioned stimulus (CS) with three 8-s elements (Food—Near–Intermediate–Far, where the name of the element denotes its temporal proximity to food). In the second phase of this experiment, different groups received a novel lever presented in compound with a different CS element. In the first phase of Experiment 2, rats were also trained with a similar backward serial CS; but, in the second phase, the entire serial CS was shifted to a forward pairing (Far–Intermediate–Near—Food), and again different groups received a novel lever in compound with a different CS element. In the first phase of Experiment 3, a serial CS was explicitly unpaired with food. The second phase of this experiment was identical to that of Experiment 2. The results showed that lever contact was lowest during the Near element in Experiment 1, highest during the same element in Experiment 2, and indistinguishable among all the elements in Experiment 3. These outcomes support the behavior systems hypothesis that backward CSs come to control a sequence of post-food search modes that can influence subsequent pre-food search.

Delayed matching in pigeons with food and no-food samples: Further examination of backward associations

When pigeons are trained on a delayed conditional discrimination with presence versus absence samples and tested with delays, a bias to choose the comparison associated with the absence sample is observed with increasing delay. Additionally, when the samples consist of food versus no food, this trial-type performance difference is reversed on short-delay trials: a bias to choose the comparison associated with the presence sample develops with delay testing. This reversal in comparison bias at short delays has been attributed to a preference produced by backward associations between the hedonic samples and the nonhedonic choice stimuli. In the present experiment, we tested an alternative hypothesis, that the short-delay comparison bias is produced by proactive interference— in particular, from reinforcement obtained on the previous trial—by including a group trained with reinforcement on only half of the trials with a correct response. According to the proactive interference account, this group should have shown a smaller short-delay comparison bias than would the typical 100% reinforcement group. Instead, consistent with a backward-association interpretation, the magnitude of the short-delay comparison bias shown by the 50% group was significantly greater than that shown by the 100% group.

Coding of feature and no-feature events by pigeons performing a delayed conditional discrimination

Pigeons’ performance of a delayed conditional discrimination with presence versus absence of conditional (sample) stimuli was examined in two experiments. The pigeons showed steeper retention functions with feature (i.e., presence) samples (either food or yellow) than with no-feature (i.e., absence) samples (either no food or no yellow). These results suggest that pigeons code features and respond only by default to test stimuli (comparisons) associated with no features. In contrast, the overall superiority of performance on no-feature-sample trials compared with feature-sample trials in both the food/no-food- and yellow/no-yellow-sample tasks was reversed at a 0-sec delay in the food/no-food-sample group, but not in the yellow/non-yellow-sample group. This difference in results with hedonic versus nonhedonic samples suggests that the crossover in delay performance on food/no-food-sample trials is produced by the formation of backward associations between the food-associated comparison stimulus and the food sample.

Development of excitatory backward associations during the establishment of forward associations in a delayed conditional discrimination by pigeons

The development of excitatory backward associations in pigeons was demonstrated in three experiments involving conditional discriminations with differential outcomes. In Phase 1 of all three experiments, correct comparison choices following one sample were followed by food, whereas correct comparison choices following the other sample were followed by presentation of an empty feeder. In Phase 2, the food and no-food events that served as outcomes in Phase 1 replaced the samples. When the associations tested in Phase 2 were consistent with the comparison-outcome associations developed in Phase 1, transfer performance was significantly better than when the Phase 2 associations were inconsistent with the Phase 1 associations. In Experiment 1, an identity matching-to-sample task was used with red and green samples and red and green comparisons. In Experiment 2, a symbolic matching task was used with shape samples and hue comparisons, and it was shown that the backward associations formed were between the trial outcome (food or no food) and the correct comparison. In Experiment 3, it was determined that the transfer effects observed in these experiments did not depend on either the similarity of behavior directed toward the samples in the training and test phases, or the similarity of food and no-foodexpectancies generated by the samples in Phase 1 to food and no-foodevents presented as samples in Phase 2.

Backward associations: Differential learning about stimuli that follow the presence versus the absence of food in pigeons

During training intended to establish positive and negative backward associations, pigeons received periodic 3-sec illuminations of a grain magazine, with food simultaneously available on 50% of the illuminations. For backward-positive subjects, a red keylight followed food trials only; for backward-negative subjects, it followed no-food trials only. During this training, the birds hardly ever pecked the red stimulus (no evidence of backward conditioning). However, when the red stimulus subsequently preceded and signaled grain for all birds, the backward-positive subjects pecked sooner and more often than did the backward-negative subjects, and control subjects performed at an intermediate level. Increases in the amount of original training did not significantly change the facilitatory effects of the backward-positive stimulus, but seemed to enhance the retarding effects of the backward-negative stimulus. These group differences cannot be attributed to what happened after the backward stimuli during original training. The features of the present technique that could possibly have produced strong and long-lasting positive and negative backward associations are discussed in comparison to prior research that has indicated weak or transitory evidence of true backward conditioning.

Information and expression of simultaneous and backward associations: Implications for contiguity theory

Five conditioned lick-suppression experiments with water-deprived rats examined the possibility that simultaneous and backward associations are learned, but are not expressed as anticipatory responses in common indexes of associative strength. Experiments 1–4 used a sensory preconditioning procedure in which clicks preceded the onset of a tone. Subsequently, the tone was paired with footshock in either a forward, simultaneous, or backward arrangement. In no case did the tone trained in the simultaneous or backward manner elicit a conditioned response. However, Experiments 1, 2, and 3 determined that the clicks, which predicted the tone, evoked equally strong conditioned responses regardless of whether the tone was paired with the shock in a forward, simultaneous, or backward manner. Experiment 4 found that responding to the clicks was degraded following postconditioning extinction of the tone, regardless of whether the tone had been paired with the shock in a forward or simultaneous manner. Experiment 5 determined that if the click and tone were paired simultaneously, the click failed a test for excitation following tone-shock simultaneous pairings but passed a test for excitation following tone-shock forward pairings. Collectively, these findings suggest that predictive information (i.e., a forward relationship between stimuli) is not necessary for the acquisition of an association, but may promote the expression of the association in an anticipatory response system. Moreover, these results suggest that associations are not simple linkages, but contain information regarding the temporal relationship of the associates.

SYMMETRY AND TRANSITIVITY OF CONDITIONAL RELATIONS IN MONKEYS (CEBUS APELLA) AND PIGEONS (COLUMBA LIVIA)

In Experiment 1 six monkeys were tested with discriminative relations that were backward relative to their training in a 0-second conditional ("symbolic") matching procedure. Although there was some indication of backward associations, the evidence was generally weak, and statistical evaluations did not reach conventional significance levels. Unlike children, who show backward associations to the point of symmetry, monkeys and pigeons display at best only weak and transient backward associations. In Experiment 2 associative transitivity was assessed across two sets of conditional matching tasks. All four monkeys tested demonstrated strong transitivity. In contrast, in Experiment 3 there was no evidence of transitivity in three pigeons tested under conditions closely comparable to those of Experiment 2. These results may identify some key features of interspecies differences and contribute to analyses of serial learning in animals.

Pre- and postlexical loci of contextual effects on word recognition.

The context in which a word occurs could influence either the actual decoding of the word or a postrecognition judgment of the relatedness of word and context. In this research, we investigated the loci of contextual effects that occur in lexical priming, when prime and target words are related along different dimensions. Both lexical decision and naming tasks were used because previous research had suggested that they are differentially sensitive to postlexical processing. Semantic and associative priming occurred with both tasks. Other facilitative contextual effects, due to syntactic relations between words, backward associations, or changes in the proportion of related items, occurred only with the lexical decision task. The results indicate that only associative and semantic priming facilitate the decoding of a target; the other effects are postlexical. The results are related to the different demands of the naming and lexical decision tasks, and to current models of word recognition.

Tests for Mediated Transfer in Pigeons

Each of five pigeons was trained on two conditional position discriminations. The two training discriminations had an element in common, either a stimulus or a response item. Following training on the two discriminations the birds were tested on a discrimination comprised of the elements of the other two discriminations with the common item omitted. Prior research with humans has shown that humans can perform with a high degree of accuracy on a third, untrained discrimination in similar situations (Sidman, Cresson, & Willson-Morris, 1974). Pigeons performed accurately on the third discrimination when they were trained with the two discriminations chained together, i.e., the common element falling in between the stimulus and response items in the test discrimination. In addition, these pigeons apparently used an overt mediating strategy. Other pigeons trained on other paradigms did not perform accurately on the test discrimination. In the latter cases the birds would have had to form backward associations in order to perform the test discrimination.

The Generality of the Retention Interval Model.

Elaborations and refinements were made for core constructs of the retention interval (RI) model that specified a major difference between anticipation and study-test methods to be short-term memory (STM) processes in differential retention intervals. Subsequent developments reinforce the model and suggest that basic processes per each type of event are, respectively, the same for both methods (except for quantitatively differential retention intervals)-the identity hypothesis. The RI model unveiled another major factor, learning difficulty, that controls performance differences between the two methods. By encompassing new developments, the generality of the RI model was tested in a variety of situations. The model seems to hold firmly for a wide range of paired-associate and verbal discrimination learning paradigms including such cross-variations as the following: mixed vs. unmixed list design, constant vs. random item presentation orders, forward vs. backward associations, part vs. whole list designs, and visual vs. auditory modalities. Other theories, in contrast, seem to lack mechanisms to cope with inconsistent data, prevalent throughout the vast scope of learning situations.