Hebb repetition effects in visual memory: the roles of verbal rehearsal and distinctiveness

A version of the Hebb repetition task was used with faces to explore the generality of the effect in a nonverbal domain. In the baseline condition, a series of upright faces was presented, and participants were asked to reconstruct the original order. Performance in this condition was compared to another in which the same stimuli were accompanied by concurrent verbal rehearsal to examine whether Hebb learning is dependent on verbal processing. Baseline performance was also compared to a condition in which the same faces were presented inverted. This comparison was used to determine the importance in Hebb learning of being able to visually distinguish between the list items. The results produced classic serial position curves that were equivalent over conditions with Hebb repetition effects being in evidence only for upright faces and verbal suppression as having no effect. These findings are interpreted as posing a challenge to current models derived from verbal-domain data.     

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.     

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.     

Exploring the characteristics of the visuospatial hebb repetition effect

Using the dot task (see Jones, Farrand, Stuart, & Morris, 1995)--regarded as a good visuospatial analogue of the verbal serial recall task--we examined whether the Hebb repetition effect and its characteristics can be extended to visuospatial material. Classically, the Hebb effect has been associated with serial verbal memory: Repetition of a to-be-remembered sequence of verbal items every third trial markedly improves serial recall of that sequence. In the present study, Hebb effects were observed with visuospatial information, and a direct comparison between verbal and spatialsequence learning revealed that the Hebb repetition effect for visuospatial information shares similar characteristics with its verbal analogue. Our results cast some doubt regarding the parsimony of the view that the classical verbal Hebb effect is driven by a store specialized for phonological information and impose some further constraints on modeling serial memory and implicit sequence learning.     

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.     

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 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.     

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.     

The contributions of encoding,retention, and recall to the Hebb effect

The article reports an experiment testing whether the Hebb repetition effect—the gradual improvement of immediate serial recall when the same list is repeated several times—depends on overt recall of the repeated lists. Previous reports which suggest that recall is critical confound the recall manipulation with retention interval. The present experiment orthogonally varies retention interval (0 or 9 s) and whether the list is to be recalled after the retention interval. Hebb repetition learning is assessed in a final test phase. A repetition effect was obtained in all four experimental conditions; it was larger for recalled than non-recalled lists, whereas retention interval had no effect. The results show that encoding is sufficient to generate cumulative long-term learning, which is strengthened by recall. Rehearsal, if it takes place in the retention interval at all, does not have the same effect on long-term learning as overt recall.     

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.     

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.     

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.     

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.     

Children retain implicitly learned phonological sequences better than adults: a longitudinal study

Whereas adults often rely on explicit memory, children appear to excel in implicit memory, which plays an important role in the acquisition of various cognitive skills, such as those involved in language. The current study aimed to test the assertion of an age‐dependent shift in implicit versus explicit learning within a theoretical framework that explains the link between implicit sequence memory and word‐form acquisition, using the Hebb repetition paradigm. We conducted a one‐year, multiple‐session longitudinal study in which we presented auditory sequences of syllables, co‐presented with pictures of aliens, for immediate serial recall by a group of children (8–9 years) and by an adult group. The repetition of one Hebb sequence was explicitly announced, while the repetition of another Hebb sequence was unannounced and, therefore, implicit. Despite their overall inferior recall performance, the children showed better offline retention of the implicit Hebb sequence, compared with adults who showed a significant decrement across the delays. Adults had gained more explicit knowledge of the implicit sequence than children, but this could not explain the age‐dependent decline in the delayed memory for it. There was no significant age‐effect for delayed memory of the explicit Hebb sequence, with both age groups showing retention. Overall performance by adults was positively correlated with measures of post‐learning awareness. Performance by children was positively correlated with vocabulary knowledge. We conclude that children outperform adults in the retention over time of implicitly learned phonological sequences that will gradually consolidate into novel word‐forms. The findings are discussed in the light of maturational differences for implicit versus explicit memory systems that also play a role in language acquisition. A video abstract of this article can be viewed at: https://youtu.be/G5nOfJB72t4     

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.     

The effect of old age on the learning of supraspan sequences

Two experiments examined age-related differences in sequence learning using computerized versions of the D. O. Hebb (1961) paradigm. In this learning task, the participant executes immediate serial recall of 24 supraspan sequences. Without the participants' knowledge, 1 sequence is presented several times. Repetition leads to improved recall of this repeated sequence relative to random sequences. Results showed a dissociation in age-related learning deficits depending on the nature of the to-be-remembered material. The effect of repetition is similar for younger and older adults with familiar and unfamiliar verbal material (words and pseudowords) but is significantly reduced in older adults when learning is assessed with a visuospatial version of Hebb's supraspan learning task (P. M. Corsi, 1972).     

Discrimination learning of rotated faces: a Markov analysis of coding and association processes]

30 subjects participated in a discrimination experiment learning face-letter associations under four rotation conditions (45 degrees, 90 degrees, 135 degrees, 180 degrees). Under each condition two thirds of the faces were presented twice, upright and rotated away from the vertical; the remaining faces were presented once, upright or rotated. Learning is described by a joint Markov model: For faces that are presented twice it assumes a separate association and encoding process (two-stage-model), for faces that are presented once it assumes an association process (all-or-none-model). The Markov model fits the data for all four rotation conditions. The angle of rotation does not affect learning for faces that are presented once. For faces that are presented twice it influences both the association and the encoding process. For the angles employed, the effect of rotation can be approximated linearly. The results suggest that the encoding of a rotated face differs increasingly from an upright face as a function of these angles of rotation. This confirms analogous conclusions from mental rotation experiments.     

Effects of motion and audio-visual redundancy on upright and inverted face and feature preferences in 4-13-month old pre- and full-term NICU graduates

NICU infants are reported to have diminished social orientation and increased risk of socio-communicative disorders. In this eye tracking study, we used a preference for upright compared to inverted faces as a gauge of social interest in high medical risk full- and pre-term NICU infants. We examined the effects of facial motion and audio-visual redundancy on face and eye/mouth preferences across the first year. Upright and inverted baby faces were simultaneously presented in a paired-preference paradigm with motion and synchronized vocalization varied. NICU risk factors including birth weight, sex, and degree of CNS injury were examined. Overall, infants preferred the more socially salient upright faces, making this the first report, to our knowledge, of an upright compared to inverted face preference among high medical risk NICU infants. Infants with abnormalities on cranial ultrasound displayed lower social interest, i.e. less of a preferential interest in upright faces, when viewing static faces. However, motion selectively increased their upright face looking time to a level equal that of infants in other CNS injury groups. We also observed an age-related sex effect suggesting higher risk in NICU males. Females increased their attention to the mouth in upright faces across the first year, especially between 7–10 months, but males did not. Although vocalization increased diffuse attention toward the screen, contrary to our predictions, there was no evidence that the audio-visual redundancy embodied in a vocalizing face focused additional attention on upright faces or mouths. This unexpected result may suggest a vulnerability in response to talking faces among NICU infants that could potentially affect later verbal and socio-communicative development.