Ventral premotor cortex lesions disrupt learning of sequential grammatical structures

Far transfer of retrieval-practice benefits: rule-based learning as the underlying mechanism

Benefits of self-testing for learning have been consistently shown for simple materials such as word lists learned by rote memorization. Considerably less evidence for such benefits exists for complex, more educationally relevant materials and its application to new situations. The present study explores the mechanisms underlying this transfer. To this end, a typical retrieval-practice-effect paradigm was applied to foster the learning of an artificial language. Participants either repeatedly studied grammatically correct exemplar sentences of the artificial language or engaged in a cloze test as the interim test after learning. To assess far transfer, participants in both groups of restudy and retrieval practice engaged in a grammaticality judgment test after a delay of 5 min and 1 week. In addition, participants in both groups completed a final memory test (i.e., a cloze test identical to the initial test) 1 week after learning. In addition to a long-term memory benefit of retrieval practice, results revealed also a retrieval-practice benefit in the far-transfer test after the 1-week delay. The findings further support the view that far transfer is supported by learning the underlying grammatical rules as opposed to memorizing the material. Thus, retrieval practice is also effective for fostering learning of complex materials and, even more importantly, for promoting transfer of learning-a crucial goal in modern educational practices.

ENIGMA: A Web Application for Running Online Artificial Grammar Learning Experiments

Artificial grammar learning (AGL) is an experimental paradigm frequently adopted to investigate the unconscious and conscious learning and application of linguistic knowledge. This paper will introduce ENIGMA ( https://enigma-lang.org ) as a free, flexible, and lightweight Web-based tool for running online AGL experiments. The application is optimized for desktop and mobile devices with a user-friendly interface, which can present visual and aural stimuli and elicit judgment responses with RT measures. Without limits in time and space, ENIGMA could help collect more data from participants with diverse personal and language backgrounds and variable cognitive skills. Such data are essential to explain complex factors influencing learners' performance in AGL experiments and answer various research questions regarding L1/L2 acquisition. The introduction of the core features in ENIGMA is followed by an example study that partially replicated Chen (Lang Acquis 27(3):331-361, 2020) to illustrate possible experimental designs and examine the quality of the collected data.

Disruption to left inferior frontal cortex modulates semantic prediction effects in reading and subsequent memory: Evidence from simultaneous TMS-EEG

Readers use prior context to predict features of upcoming words. When predictions are accurate, this increases the efficiency of comprehension. However, little is known about the fate of predictable and unpredictable words in memory or the neural systems governing these processes. Several theories suggest that the speech production system, including the left inferior frontal cortex (LIFC), is recruited for prediction but evidence that LIFC plays a causal role is lacking. We first examined the effects of predictability on memory and then tested the role of posterior LIFC using transcranial magnetic stimulation (TMS). In Experiment 1, participants read category cues, followed by a predictable, unpredictable, or incongruent target word for later recall. We observed a predictability benefit to memory, with predictable words remembered better than unpredictable words. In Experiment 2, participants performed the same task with electroencephalography (EEG) while undergoing event-related TMS over posterior LIFC using a protocol known to disrupt speech production, or over the right hemisphere homologue as an active control site. Under control stimulation, predictable words were better recalled than unpredictable words, replicating Experiment 1. This predictability benefit to memory was eliminated under LIFC stimulation. Moreover, while an a priori ROI-based analysis did not yield evidence for a reduction in the N400 predictability effect, mass-univariate analyses did suggest that the N400 predictability effect was reduced in spatial and temporal extent under LIFC stimulation. Collectively, these results provide causal evidence that the LIFC is recruited for prediction during silent reading, consistent with prediction-through-production accounts.

Ventral premotor cortex encodes task relevant features during eye and head movements

Visual exploration of the environment is achieved through gaze shifts or coordinated movements of the eyes and the head. The kinematics and contributions of each component can be decoupled to fit the context of the required behavior, such as redirecting the visual axis without moving the head or rotating the head without changing the line of sight. A neural controller of these effectors, therefore, must show code relating to multiple muscle groups, and it must also differentiate its code based on context. In this study we tested whether the ventral premotor cortex (PMv) in monkey exhibits a population code relating to various features of eye and head movements. We constructed three different behavioral tasks or contexts, each with four variables to explore whether PMv modulates its activity in accordance with these factors. We found that task related population code in PMv differentiates between all task related features and conclude that PMv carries information about task relevant features during eye and head movements. Furthermore, this code represents both lower-level (effector and movement direction) and higher-level (context) information.

Neurophysiological and functional neuroanatomical coding of statistical and deterministic rule information during sequence learning

Humans are capable of acquiring multiple types of information presented in the same information stream. It has been suggested that at least two parallel learning processes are important during learning of sequential patterns-statistical learning and rule-based learning. Yet, the neurophysiological underpinnings of these parallel learning processes are not fully understood. To differentiate between the simultaneous mechanisms at the single trial level, we apply a temporal EEG signal decomposition approach together with sLORETA source localization method to delineate whether distinct statistical and rule-based learning codes can be distinguished in EEG data and can be related to distinct functional neuroanatomical structures. We demonstrate that concomitant but distinct aspects of information coded in the N2 time window play a role in these mechanisms: mismatch detection and response control underlie statistical learning and rule-based learning, respectively, albeit with different levels of time-sensitivity. Moreover, the effects of the two learning mechanisms in the different temporally decomposed clusters of neural activity also differed from each other in neural sources. Importantly, the right inferior frontal cortex (BA44) was specifically implicated in visuomotor statistical learning, confirming its role in the acquisition of transitional probabilities. In contrast, visuomotor rule-based learning was associated with the prefrontal gyrus (BA6). The results show how simultaneous learning mechanisms operate at the neurophysiological level and are orchestrated by distinct prefrontal cortical areas. The current findings deepen our understanding on the mechanisms of how humans are capable of learning multiple types of information from the same stimulus stream in a parallel fashion.

Implicit learning of artificial grammatical structures after inferior frontal cortex lesions

OBJECTIVE

Previous research associated the left inferior frontal cortex with implicit structure learning. The present study tested patients with lesions encompassing the left inferior frontal gyrus (LIFG; including Brodmann areas 44 and 45) to further investigate this cognitive function, notably by using non-verbal material, implicit investigation methods, and by enhancing potential remaining function via dynamic attending. Patients and healthy matched controls were exposed to an artificial pitch grammar in an implicit learning paradigm to circumvent the potential influence of impaired language processing.

METHODS

Patients and healthy controls listened to pitch sequences generated within a finite-state grammar (exposure phase) and then performed a categorization task on new pitch sequences (test phase). Participants were not informed about the underlying grammar in either the exposure phase or the test phase. Furthermore, the pitch structures were presented in a highly regular temporal context as the beneficial impact of temporal regularity (e.g. meter) in learning and perception has been previously reported. Based on the Dynamic Attending Theory (DAT), we hypothesized that a temporally regular context helps developing temporal expectations that, in turn, facilitate event perception, and thus benefit artificial grammar learning.

RESULTS

Electroencephalography results suggest preserved artificial grammar learning of pitch structures in patients and healthy controls. For both groups, analyses of event-related potentials revealed a larger early negativity (100-200 msec post-stimulus onset) in response to ungrammatical than grammatical pitch sequence events.

CONCLUSIONS

These findings suggest that (i) the LIFG does not play an exclusive role in the implicit learning of artificial pitch grammars, and (ii) the use of non-verbal material and an implicit task reveals cognitive capacities that remain intact despite lesions to the LIFG. These results provide grounds for training and rehabilitation, that is, learning of non-verbal grammars that may impact the relearning of verbal grammars.

Is there a prediction network? Meta-analytic evidence for a cortical-subcortical network likely subserving prediction

Predictive coding is an increasingly influential and ambitious concept in neuroscience viewing the brain as a 'hypothesis testing machine' that constantly strives to minimize prediction error, the gap between its predictions and the actual sensory input. Despite the invaluable contribution of this framework to the formulation of brain function, its neuroanatomical foundations have not been fully defined. To address this gap, we conducted activation likelihood estimation (ALE) meta-analysis of 39 neuroimaging studies of three functional domains (action perception, language and music) inherently involving prediction. The ALE analysis revealed a widely distributed brain network encompassing regions within the inferior and middle frontal gyri, anterior insula, premotor cortex, pre-supplementary motor area, temporoparietal junction, striatum, thalamus/subthalamus and the cerebellum. This network is proposed to subserve domain-general prediction and its relevance to motor control, attention, implicit learning and social cognition is discussed in light of the predictive coding scheme. Better understanding of the presented network may help advance treatments of neuropsychiatric conditions related to aberrant prediction processing and promote cognitive enhancement in healthy individuals.

Evidence for we-representations during joint action planning

Do people engaged in joint action form action plans that specify joint outcomes at the group level? EEG was recorded from pairs of participants who performed coordinated actions that could result in different postural configurations. To isolate individual and joint action planning processes, a pre-cue specified in advance the individual actions and/or the joint configuration. Participants had 1200 ms to prepare their actions. Then a Go cue specified all action parameters and participants performed a synchronized action as quickly as possible. Action onsets were shorter when the pre-cue specified the joint configuration, regardless of whether individual action was also specified. EEG analyses showed that specifying joint action parameters in advance reduced ambiguity in a structured joint action plan (reflected in the decrease of the amplitude of the P600) and helped with representing action goals and interpersonal coordination patterns in sensorimotor brain areas (reflected in increased alpha/mu suppression and CNV amplitudes). These results provide clear evidence that joint action is driven not only by action plans that specify individual contributions, but also by action plans that specify joint action outcomes at the group level.

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People form individual and group-level representations during joint action planning.

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Information about joint configuration benefits task performance.

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Information about joint configuration reduces ambiguity in joint task representation.

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Evidence for predictive “we-representations” in the sensorimotor system.

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“We-representations” may be formed independently of “I” and “You” representations.

Artificial grammar learning in vascular and progressive non-fluent aphasias

Patients with non-fluent aphasias display impairments of expressive and receptive grammar. This has been attributed to deficits in processing configurational and hierarchical sequencing relationships. This hypothesis had not been formally tested. It was also controversial whether impairments are specific to language, or reflect domain general deficits in processing structured auditory sequences. Here we used an artificial grammar learning paradigm to compare the abilities of controls to participants with agrammatic aphasia of two different aetiologies: stroke and frontotemporal dementia. Ten patients with non-fluent variant primary progressive aphasia (nfvPPA), 12 with non-fluent aphasia due to stroke, and 11 controls implicitly learned a novel mixed-complexity artificial grammar designed to assess processing of increasingly complex sequencing relationships. We compared response profiles for otherwise identical sequences of speech tokens (nonsense words) and tone sweeps. In all three groups the ability to detect grammatical violations varied with sequence complexity, with performance improving over time and being better for adjacent than non-adjacent relationships. Patients performed less well than controls overall, and this was related more strongly to aphasia severity than to aetiology. All groups improved with practice and performed well at a control task of detecting oddball nonwords. Crucially, group differences did not interact with sequence complexity, demonstrating that aphasic patients were not disproportionately impaired on complex structures. Hierarchical cluster analysis revealed that response patterns were very similar across all three groups, but very different between the nonsense word and tone tasks, despite identical artificial grammar structures. Overall, we demonstrate that agrammatic aphasics of two different aetiologies are not disproportionately impaired on complex sequencing relationships, and that the learning of phonological and non-linguistic sequences occurs independently. The similarity of profiles of discriminatory abilities and rule learning across groups suggests that insights from previous studies of implicit sequence learning in vascular aphasia are likely to prove applicable in nfvPPA.

Conserved Sequence Processing in Primate Frontal Cortex

An important aspect of animal perception and cognition is learning to recognize relationships between environmental events that predict others in time, a form of relational knowledge that can be assessed using sequence-learning paradigms. Humans are exquisitely sensitive to sequencing relationships, and their combinatorial capacities, most saliently in the domain of language, are unparalleled. Recent comparative research in human and nonhuman primates has obtained behavioral and neuroimaging evidence for evolutionarily conserved substrates involved in sequence processing. The findings carry implications for the origins of domain-general capacities underlying core language functions in humans. Here, we synthesize this research into a 'ventrodorsal gradient' model, where frontal cortex engagement along this axis depends on sequencing complexity, mapping onto the sequencing capacities of different species.

An fMRI study of implicit language learning in developmental language impairment

Individuals with developmental language impairment can show deficits into adulthood. This suggests that neural networks related to their language do not normalize with time. We examined the ability of 16 adults with and without impaired language to learn individual words in an unfamiliar language. Adults with impaired language were able to segment individual words from running speech, but needed more time to do so than their normal-language peers. ICA analysis of fMRI data indicated that adults with language impairment activate a neural network that is comparable to that of adults with normal language. However, a regional analysis indicated relative hyperactivation of a collection of regions associated with language processing. These results are discussed with reference to the Statistical Learning Framework and the sub-skills thought to relate to word segmentation.

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Adults with developmental language impairment were imaged during a word segmentation task in an unfamiliar natural language.

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Impaired adults learned to identify individual words, although it took them longer than their typical language peers.

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The impaired group used the same learning network as the typical group, arguing against recruitment of additional regions.

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Hyper-activation in language regions characterized the impaired group, unless performance was equated between groups.

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This suggests that hyper-activation for the impaired group reflects greater effort by learners at earlier stages of learning.

Implicit structured sequence learning: an fMRI study of the structural mere-exposure effect

In this event-related fMRI study we investigated the effect of 5 days of implicit acquisition on preference classification by means of an artificial grammar learning (AGL) paradigm based on the structural mere-exposure effect and preference classification using a simple right-linear unification grammar. This allowed us to investigate implicit AGL in a proper learning design by including baseline measurements prior to grammar exposure. After 5 days of implicit acquisition, the fMRI results showed activations in a network of brain regions including the inferior frontal (centered on BA 44/45) and the medial prefrontal regions (centered on BA 8/32). Importantly, and central to this study, the inclusion of a naive preference fMRI baseline measurement allowed us to conclude that these fMRI findings were the intrinsic outcomes of the learning process itself and not a reflection of a preexisting functionality recruited during classification, independent of acquisition. Support for the implicit nature of the knowledge utilized during preference classification on day 5 come from the fact that the basal ganglia, associated with implicit procedural learning, were activated during classification, while the medial temporal lobe system, associated with explicit declarative memory, was consistently deactivated. Thus, preference classification in combination with structural mere-exposure can be used to investigate structural sequence processing (syntax) in unsupervised AGL paradigms with proper learning designs.

Generating predictions: lesion evidence on the role of left inferior frontal cortex in rapid syntactic analysis

A well-documented phenomenon in event-related electroencephalography (EEG) and magnetoencephalography (MEG) studies on language processing is that syntactic violations of different types elicit negativities as early as 100 msec after the violation point. Recently, these responses have been associated with activations in or very close to sensory cortices, suggesting the involvement of basic sensory mechanisms in the detection of syntactic violations. The present study investigated whether intact auditory cortices and adjacent temporal regions are sufficient to generate early syntactic negativities in the auditory event-related potential (ERP). We tested ten clinically non-aphasic patients with left inferior frontal lesions, but intact temporal cortices in a passive auditory ERP paradigm that had reliably elicited early negativities in response to violations of subject-verb agreement and word category in the past. Subject-verb agreement violations failed to elicit early grammaticality effects in these patients, whereas a group of ten age-matched controls showed a reliable early negativity. This finding supports the idea that sensory aspects of syntactic analysis as reflected in early syntactic negativities critically depend on top-down predictions generated by the left inferior frontal cortex. In contrast, word category violations elicited a small, marginally significant early negativity both in controls and patients, suggesting an additional involvement of temporal regions in early phrase structure processing. In an additional auditory oddball experiment patients showed a regular P300, but no N2b component in response to deviant tones, indicating that their deficit in generating sensory predictions extends beyond the language domain.

Does it really matter? Separating the effects of musical training on syntax acquisition

The possible transfer of musical expertise to the acquisition of syntactical structures in first and second language has emerged recently as an intriguing topic in the research of cognitive processes. However, it is unlikely that the benefits of musical training extend equally to the acquisition of all syntactical structures. As cognitive transfer presumably requires overlapping processing components and brain regions involved in these processing components, one can surmise that transfer between musical ability and syntax acquisition would be limited to structural elements that are shared between the two. We propose that musical expertise transfers only to the processing of recursive long-distance dependencies inherent in hierarchical syntactic structures. In this study, we taught fifty-six participants with widely varying degrees of musical expertise the artificial language BROCANTO, which allows the direct comparison of long-distance and local dependencies. We found that the quantity of musical training (measured in accumulated hours of practice and instruction) explained unique variance in performance in the long-distance dependency condition only. These data suggest that musical training facilitates the acquisition specifically of hierarchical syntactic structures.

Toward a neural basis of music perception - a review and updated model

Music perception involves acoustic analysis, auditory memory, auditory scene analysis, processing of interval relations, of musical syntax and semantics, and activation of (pre)motor representations of actions. Moreover, music perception potentially elicits emotions, thus giving rise to the modulation of emotional effector systems such as the subjective feeling system, the autonomic nervous system, the hormonal, and the immune system. Building on a previous article (Koelsch and Siebel, 2005), this review presents an updated model of music perception and its neural correlates. The article describes processes involved in music perception, and reports EEG and fMRI studies that inform about the time course of these processes, as well as about where in the brain these processes might be located.