The Hebb repetition effect as a laboratory analogue of novel word learning

The present study tests the hypothesis that a common ordering mechanism underlies both short-term serial recall of verbal materials and the acquisition of novel long-term lexical representations, using the Hebb repetition effect. In the first experiment, participants recalled visually presented nonsense syllables following a typical Hebb effect learning protocol. Replicating the Hebb repetition effect, we observed improved recall for repeated sequences of syllables. In the second experiment, the same participants performed an auditory lexical decision task, which included nonwords that were constructed from the syllables used in the first experiment. We observed inhibited rejection of nonwords that were composed of the repeated Hebb sequences, compared to nonwords that were built from nonrepeated filler sequences. This suggests that a long-term phonological lexical representation developed during Hebb learning. Accordingly, the relation between immediate serial recall and word learning is made explicit by arguing that the Hebb repetition effect is a laboratory analogue of naturalistic vocabulary acquisition.     

The Hebb repetition effect as a laboratory analogue of novel word learning

The present study tests the hypothesis that a common ordering mechanism underlies both short-term serial recall of verbal materials and the acquisition of novel long-term lexical representations, using the Hebb repetition effect. In the first experiment, participants recalled visually presented nonsense syllables following a typical Hebb effect learning protocol. Replicating the Hebb repetition effect, we observed improved recall for repeated sequences of syllables. In the second experiment, the same participants performed an auditory lexical decision task, which included nonwords that were constructed from the syllables used in the first experiment. We observed inhibited rejection of nonwords that were composed of the repeated Hebb sequences, compared to nonwords that were built from nonrepeated filler sequences. This suggests that a long-term phonological lexical representation developed during Hebb learning. Accordingly, the relation between immediate serial recall and word learning is made explicit by arguing that the Hebb repetition effect is a laboratory analogue of naturalistic vocabulary acquisition.     

The role of overt language production in the Hebb repetition effect

The Hebb repetition effect (Hebb, 1961) occurs when recall performance improves for a list that is repeated during a serial-recall task. This effect is considered a good experimental analogue to language learning. Our objective was to evaluate the role of overt language production in language learning by manipulating recall direction during a Hebb repetition paradigm. In each trial, seven nonsense syllables were presented auditorily. Participants had to orally recall the items either in the presentation order or in reverse order. One sequence was repeated every third trial. In Experiment 1, we compared learning from a group that had recalled the items in their presentation order to learning from a group that had recalled the items in the reverse order. The two groups yielded similar learning rates. In Experiment 2, recall direction was varied between trials. The learning rate was not affected when recall direction varied between trials, suggesting a limited role of overt language production in language learning.     

Overt language production plays a key role in the Hebb repetition effect

When asked to recall verbatim a short list of items, performance is very limited. However, if the list of items is repeated across trials, recall performance improves. This phenomenon, known as the Hebb repetition effect (Hebb, 1961; Brain Mechanisms and Learning: A Symposium, pp. 37–51), is considered a laboratory analogue of language learning. In effect, learning a new word implies the maintenance of a series of smaller units, such as phonemes or syllables, in the correct order for a short amount of time before producing them. The sequence of smaller units is typically presented more than once. In the present study, we investigated the role of overt language production in language learning by manipulating recall direction. If the learning of a repeated list of items relies on overt language production processes, changing list production order by manipulating recall direction should impact the learning of the list. In Experiment 1, one list was repeated every third trial, and recall direction of the repeated list changed on the ninth repetition. In Experiment 1a, the repeated list changed from a forward to a backward order recall, where participants had to recall the items in reverse presentation order. In Experiment 1b, the repeated list changed from a backward to a forward order recall. Results showed a cost in recall performance for the repeated list when recall direction switched from forward to backward recall, whereas it was unaffected by the change from backward to forward recall. In Experiment 2, we increased the number of trials before introducing the change from a backward to a forward order recall. Results showed a decrement in recall performance for the repeated list following the change in recall direction, suggesting that language production processes play a role in the Hebb repetition effect.     

Learning nonwords: the Hebb repetition effect as a model of word learning

Page and Norris [(2008). Is there a common mechanism underlying word-form learning and the Hebb repetition effect? Experimental data and a modelling framework. In A. Thorn &; M. P. A. Page (Eds.), Interactions between short-term and long-term memory in the verbal domain; (2009). A model linking immediate serial recall, the Hebb repetition effect and the learning of phonological word forms. Philosophical Transactions of the Royal Society B: Biological Sciences, 364(1536), 3737–3753. doi:10.1098/rstb.2009.0173] have suggested that the Hebb [(1961). Distinctive features of learning in the higher animal. In J. F. Delafresnaye (Ed.), Brain mechanisms and learning (pp. 37–46). Oxford: Blackwell] repetition paradigm can be considered as a laboratory analogue of word learning. In Hebb learning experiments, the lists of items to be learned are presented as discrete sequences. In contrast, novel words are, by definition, always heard as a single coarticulated whole. Might this undermine the claim that Hebb learning can shed light on word learning? Here we report an experiment comparing learning sequences of isolated syllables with learning the same sequences spoken as a single coarticulated nonword. The pattern of learning was similar in the two cases, suggesting that the Hebb repetition paradigm can indeed provide valuable insights into the way novel word forms are learned.     

Repetition learning in the immediate serial recall of visual and auditory materials

In 5 experiments, a Hebb repetition effect, that is, improved immediate serial recall of an (unannounced) repeating list, was demonstrated in the immediate serial recall of visual materials, even when use of phonological short-term memory was blocked by concurrent articulation. The learning of a repeatedly presented letter list in one modality (auditory or visual) did not transfer to give improved performance on the same list in the other modality. This result was not replicated for word lists, however, for which asymmetric transfer was observed. Inferences are made about the structure of short-term memory and about the nature of the Hebb repetition effect.     

Visual Hebb repetition effects survive changes to both output order and concurrent articulation*

Building upon the work of Guerrette, Guérard, and Saint-Aubin [(2017). The role of overt language production in the Hebb repetition effect. Memory and Cognition, 45(5), 792–803. doi:10.3758/s13421-017-0693-4], we examine the effect of output order on the visual Hebb repetition effect. We limit opportunities for forward recall at test by using a novel positional recall procedure, employing non-verbal visual stimuli, and requiring participants to undertake concurrent articulation (CA). During encoding, participants received sequences of six unfamiliar-faces. Every third sequence, participants received the same faces in the same serial order (the Hebb sequence). At test, participants were required to either select the faces in their order of original presentation (SR) or recall the serial position of each individually re-presented face tested in a randomised order (PR). For both recall conditions, and following CA, the Hebb repetition effect persisted, demonstrating that the Hebb repetition effect is not dependent upon forward recall.     

Tactile order memory: evidence for sequence learning phenomena found with other stimulus types

We examine serial order memory for sequences of tactile stimuli and investigate whether established characteristics of order memory, namely serial position effects, error distributions, and Hebb repetition learning, are observed with tactile memory. Visually obscured participants received six tactile stimulations: one to each of six fingers. At test, participants lifted the six fingers in the order of stimulation. For every third trial participants received the same order of stimulation (i.e. the Hebb sequence). Serial recall accuracy produced the canonical bowed serial position function found for immediate serial recall. In addition, recall for the Hebb sequence improved relative to the filler sequences, providing the first demonstration of the Hebb repetition effect with tactile stimuli. Analysis of errors revealed close similarities to that reported with verbal and visual stimuli. This experiment further generalises established features of order memory to tactile memory, supporting the utilisation of an analogous order memory mechanism across stimuli.     

Hebb repetition effects for non-verbal visual sequences: determinants of sequence acquisition

We report four experiments premised upon the work of Horton et al. [(2008). Hebb repetition effects in visual memory: The roles of verbal rehearsal and distinctiveness. Quarterly Journal of Experimental Psychology, 61(12), 1769–1777] and Page et al. [(2013). Repetition-spacing and item-overlap effects in the Hebb repetition task. Journal of Memory and Language, 69(4), 506–526], and explore conditions under which the visual Hebb repetition effect is observed. Experiment 1 showed that repetition learning is evident when the items comprising the non-repeated (filler) sequences and the repeated (Hebb) sequences are different (no-overlap). However, learning is abolished when the filler and Hebb sequences comprise the same items (full-overlap). Learning of the repeated sequence persisted when repetition spacing was increased to six trials (Experiment 2), consistent with that shown for verbal stimuli (Page et al., 2013). In Experiment 3, it was shown that learning for the repeated sequence is accentuated when the output motor response at test is also repeated for the Hebb sequence, but only under conditions of no-overlap. In Experiment 4, repetition spacing was re-examined with a repeated motor output response (a closer methodological analogue to Page et al., 2013). Under these conditions, the gradient of Hebb repetition learning for six trial repetition intervals was markedly similar to that for three trial intervals. These findings further support the universality of the Hebb repetition effect across memory and are discussed in terms of evidence for amodality within-sequence memory.     

Hebb learning, verbal short-term memory, and the acquisition of phonological forms in children

Recent work using the Hebb effect as a marker for implicit long-term acquisition of serial order has demonstrated a functional equivalence across verbal and visuospatial short-term memory. The current study extends this observation to a sample of five- to six-year-olds using verbal and spatial immediate serial recall and also correlates the magnitude of Hebb learning with explicit measures of word and nonword paired-associate learning. Comparable Hebb effects were observed in both domains, but only nonword learning was significantly related to the magnitude of Hebb learning. Nonword learning was also independently related to individuals' general level of verbal serial recall. This suggests that vocabulary acquisition depends on both a domain-specific short-term memory system and a domain-general process of learning through repetition.     

Learning correct responses and errors in the Hebb repetition effect: two faces of the same coin

In a serial recall task, the Hebb repetition effect occurs when recall performance improves for a sequence repeated throughout the experimental session. This phenomenon has been replicated many times. Nevertheless, such cumulative learning seldom leads to perfect recall of the whole sequence, and errors persist. Here the authors report evidence that there is another side to the Hebb repetition effect that involves learning errors produced in a repeated sequence. A learning measure based on past recalls (correct or incorrect) shows that the probability of a given response increases with the number of prior occurrences of that response. The pattern of results reveals another manifestation of the Hebb repetition effect and speaks to the nature of implicit learning.     

Order or disorder? Impaired Hebb learning in dyslexia

The present study offers an integrative account proposing that dyslexia and its various associated cognitive impairments reflect an underlying deficit in the long-term learning of serial-order information, here operationalized as Hebb repetition learning. In nondyslexic individuals, improved immediate serial recall is typically observed when one particular sequence of items is repeated across an experimental session, a phenomenon known as the Hebb repetition effect. Starting from the critical observation that individuals with dyslexia seem to be selectively impaired in cognitive tasks that involve processing of serial order, the present study is the first to test and confirm the hypothesis that the Hebb repetition effect is affected in dyslexia, even for nonverbal modalities. We present a theoretical framework in which the Hebb repetition effect is assumed to be a laboratory analogue of naturalistic word learning, on the basis of which we argue that dyslexia is characterized by an impairment of serial-order learning that affects language learning and processing.     

Learning to reproduce a list and memory for the learning.

The ability to reproduce from memory a short list of verbal items immediately following presentation is known to improve over successive trials on that list, even if these trials are embedded in a sequence of trials on other lists of the same sort (Hebb, 1961). Less clear is whether this "Hebb effect" arises without the list repetition being noticed. This question has long been pondered and has recently taken on particular theoretical significance, but the available evidence is scant and inconsistent. Two experiments are described in which, in essence, a sequence of immediate reproduction trials was followed by tests that called for list recognition (Experiments 1 and 2) and/or estimates of list presentation frequency (Experiment 1). These tests provided quantitative measures of repetition awareness. Typical Hebb effects were found, but there was no evidence that the effects occurred without the subjects' being aware of the repetition; effect-size analyses indicated that both the recognition and frequency responses were more sensitive to repetition than were the reproduction responses. Therefore, not only could the recognition and frequency responses not have been made solely on the basis of how readily the test lists were reproduced, but the Hebb effect could have required an awareness of repetition.     

Implicit serial learning: Questions inspired by Hebb (1961)

Implicit serial learning occurs when indirect measures such as transfer reveal learning of a repeating sequence even when subjects are not informed ofthe repeating sequence, are not asked to learn it, and do not become of aware of it. This phenomenon is reminiscent of an experiment by Hebb(1961), who studied the repetition of sequences in a serial recall task. Two experiments investigated the relation between implicit serial learning and ideas about learning forwarded by Hebb and others who used his method. The experiments showed that implicit serial learning occurs even when the repeating sequence is intermixed with randomly generated sequences instead of being repeated continuously, that the organization of the sequence into regularly or irregularly grouped subsequences determines the extent of learning, and that the repetition effect observed does not depend on subjects' ability to recognize the repetition.     

The role of awareness in anticipation and recall performance in the Hebb repetition paradigm: implications for sequence learning

Sequence learning has notably been studied using the Hebb repetition paradigm (Hebb, 1961) and the serial reaction time (SRT) task (Nissen & Bullemer, Cognitive Psychology 19:1–32, 1987). These two paradigms produce robust learning effects but differ with regard to the role of awareness: Awareness does not affect learning a repeated sequence in the Hebb repetition paradigm, as is evidenced by recall performance, whereas in the SRT task, awareness helps to anticipate the location of the next stimulus. In this study, we examined the role of awareness in anticipation and recall performance, using the Hebb repetition paradigm. Eye movements were monitored during a spatial reconstruction task where participants had to memorize sequences of dot locations. One sequence was repeated every four trials. Results showed that recall performance for the repeated sequence improved across repetitions for all participants but that anticipation increased only for participants aware of the repetition.     

Spacing repetitions over 1 week

Does varying the spacing of repetitions over intervals as long as 1 week aftect recall? The answer from three experiments is yes. Subjects incidentally processed words repeated within a single list and words repeated in separate lists at list spacings of up to 1 week. Memory was tested by free recall shortly after the second presentations or after retention intervals of up to 1 week. Recall of the words repeated across separate lists conformed to a proportionality rule. When the retention interval is short relative to the spacing intervals, performance is inversely related to spacing. When the retention interval is a large proportion of the spacing intervals, performance is directly related to spacing. Does varying the spacing of repetitions within a single list affect recall after a retention interval of 2 weeks? The answer depends on the processing used while studying the words. Processing that generated interitem associations resulted in a within-list spacing effect even after a 2-week retention interval. Without the interitem associations, the effect was absent after a 1-day retention interval. Most of these findings were explained by examining the changing relationship between the retrieval context and the context stored during study.     

Bartlett revisited: Direct comparison of repeated reproduction and serial reproduction techniques

Bartlett developed the procedures of repeated reproduction (the same person repeatedly recalling information) and serial reproduction (people transmitting information from one person to another). Our experiment directly compared recall accuracy across these two techniques, which has not previously been reported, using DRM word lists. Recall of the initial study list words remained constant across repeated reproductions but declined markedly across serial reproductions. In contrast, recall of associated words that were not originally studied (i.e. critical words) was steady across both conditions. Because more of the original list words were forgotten across each link of the serial reproduction chain, the proportion of critical items recalled (relative to list words) increased significantly as the list passed between people. Using output bound scoring, serial reproduction resulted in lower accuracy than repeated reproduction by the final recall trial. Our results are broadly consistent with Bartlett's (1932) informal observations: Serial reproduction produces greater forgetting of the original material than does repeated reproduction and also leads to greater distortion relative to the proportion of correct material recalled.     

Semantic similarity and immediate serial recall: Is there an effect on all trials

In immediate serial recall, items are better recalled when they are all drawn from the same semantic category. This is usually accounted for by a two-stage retrieval-based framework, in which, at recall, long-term knowledge is used to reconstruct degraded phonological traces. The category shared by list items would serve as an additional retrieval cue restricting the number of recall candidates. Usually, the long-term search set is not defined, but some authors have suggested an extended search set and others a restricted set that is composed of the most recently presented items. This was tested in an experiment in which participants undertook an immediate serial recall task either alone or under articulatory suppression with either semantically similar or dissimilar lists. A trial-by-trial analysis revealed that, in both quiet and suppression conditions, items from similar lists were better recalled on all the trials, including the first one. In addition, there was no interaction between semantic similarity and trial, indicating that the effect of similarity was of similar size on all the trials. The results are best interpreted within a proposal suggesting an extended long-term search set.     

The influence of acoustic similarity on serial recall of letter sequences

Acoustic similarity is known to impair short-term memory (STM) for letter sequences. The present series of experiments investigated the effects of acoustic similarity on long-term retention. In the first experiment, subjects were asked to learn one of two lists of 8 letters, the letters being either of high or low acoustic similarity. Lists were visually presented for three trials, with subjects responding after each trial. Then subjects participated in an immediate memory task for digits which lasted for 20 min. Finally, subjects tried to recall the list of letters they had learned previously. Lists having items of high acoustic similarity were more difficult to recall on the first trial, but were better recalled on the delayed retention test. In a second experiment, groups of subjects were again asked to learn one of two lists of 8 letters differing in acoustic similarity, using different orders of the letters used previously. The procedures were identical except that in two groups, a STM task for digits intervened between the presentation and test of the letters. This intervening task minimized the effects of STM and eliminated the differences in retention found previously. In a third experiment, better long-term retention for material having high acoustic similarity was also obtained when subjects used a backward recall procedure. In the last experiment 14 item lists were learned to a criterion of two correct trials, and retention was tested after each trial and at a delay of 20 min. and 23 hr. No effect of acoustic similarity was found and little retention loss occurred. These results suggest that reducing the STM component by introducing a STM control or by lengthening the list caused the effect of acoustic similarity to disappear.     

Exploring the enactment effect from an information processing view: What can we learn from serial position analyses?

The focus of the present article was to analyze processes that determine the enactment and age effect in a multi-trial free recall paradigm by looking at the serial position effects. In an experimental study (see Schatz et al 2010), the performance-enhancing effect of enactive encoding and repeated learning was tested with older and younger participants. As expected, there was a steady improvement of memory performance as a function of repeated learning regardless of age. In addition, enactive encoding led to a better memory performance than verbal encoding in both age groups. Furthermore, younger adults outperformed the elderly regardless of type of encoding. Analyses in the present article show that encoding by enacting seems to profit especially from remembering the last items of a presented list. Regarding age differences, younger outperformed older participants in nearly all item positions. The performance enhancement after task repetition is due to a higher amount of recalled items in the middle positions in a subject performed task (SPT) and a verbal task (VT) as well as the last positions of a learned list in VT.