Role of the motor system in language knowledge

Individualized white matter connectivity of the articulatory pathway: An ultra-high field study

In current sensorimotor theories pertaining to speech perception, there is a notable emphasis on the involvement of the articulatory-motor system in the processing of speech sounds. Using ultra-high field diffusion-weighted imaging at 7 Tesla, we visualized the white matter tracts connected to areas activated during a simple speech-sound production task in 18 healthy right-handed adults. Regions of interest for white matter tractography were individually determined through 7T functional MRI (fMRI) analyses, based on activations during silent vocalization tasks. These precentral seed regions, activated during the silent production of a lip-vowel sound, demonstrated anatomical connectivity with posterior superior temporal gyrus areas linked to the auditory perception of phonetic sounds. Our study provides a macrostructural foundation for understanding connections in speech production and underscores the central role of the articulatory motor system in speech perception. These findings highlight the value of ultra-high field 7T MR acquisition in unraveling the neural underpinnings of speech.

Phonetic categorization relies on motor simulation, but combinatorial phonological computations are abstract

To identify a spoken word (e.g., dog), people must categorize the speech steam onto distinct units (e.g., contrast dog/fog,) and extract their combinatorial structure (e.g., distinguish dog/god). However, the mechanisms that support these two core functions are not fully understood. Here, we explore this question using transcranial magnetic stimulation (TMS). We show that speech categorization engages the motor system, as stimulating the lip motor area has opposite effects on labial (ba/pa)- and coronal (da/ta) sounds. In contrast, the combinatorial computation of syllable structure engages Broca's area, as its stimulation disrupts sensitivity to syllable structure (compared to motor stimulation). We conclude that the two ingredients of language-categorization and combination-are distinct functions in human brains.

Neural evidence suggests phonological acceptability judgments reflect similarity, not constraint evaluation

Acceptability judgments are a primary source of evidence in formal linguistic research. Within the generative linguistic tradition, these judgments are attributed to evaluation of novel forms based on implicit knowledge of rules or constraints governing well-formedness. In the domain of phonological acceptability judgments, other factors including ease of articulation and similarity to known forms have been hypothesized to influence evaluation. We used data-driven neural techniques to identify the relative contributions of these factors. Granger causality analysis of magnetic resonance imaging (MRI)-constrained magnetoencephalography (MEG) and electroencephalography (EEG) data revealed patterns of interaction between brain regions that support explicit judgments of the phonological acceptability of spoken nonwords. Comparisons of data obtained with nonwords that varied in terms of onset consonant cluster attestation and acceptability revealed different cortical regions and effective connectivity patterns associated with phonological acceptability judgments. Attested forms produced stronger influences of brain regions implicated in lexical representation and sensorimotor simulation on acoustic-phonetic regions, whereas unattested forms produced stronger influence of phonological control mechanisms on acoustic-phonetic processing. Unacceptable forms produced widespread patterns of interaction consistent with attempted search or repair. Together, these results suggest that speakers' phonological acceptability judgments reflect lexical and sensorimotor factors.

Modeling Sonority in Terms of Pitch Intelligibility With the Nucleus Attraction Principle

Sonority is a fundamental notion in phonetics and phonology, central to many descriptions of the syllable and various useful predictions in phonotactics. Although widely accepted, sonority lacks a clear basis in speech articulation or perception, given that traditional formal principles in linguistic theory are often exclusively based on discrete units in symbolic representation and are typically not designed to be compatible with auditory perception, sensorimotor control, or general cognitive capacities. In addition, traditional sonority principles also exhibit systematic gaps in empirical coverage. Against this backdrop, we propose the incorporation of symbol-based and signal-based models to adequately account for sonority in a complementary manner. We claim that sonority is primarily a perceptual phenomenon related to pitch, driving the optimization of syllables as pitch-bearing units in all language systems. We suggest a measurable acoustic correlate for sonority in terms of periodic energy, and we provide a novel principle that can account for syllabic well-formedness, the nucleus attraction principle (NAP). We present perception experiments that test our two NAP-based models against four traditional sonority models, and we use a Bayesian data analysis approach to test and compare them. Our symbolic NAP model outperforms all the other models we test, while our continuous bottom-up NAP model is at second place, along with the best performing traditional models. We interpret the results as providing strong support for our proposals: (i) the designation of periodic energy as the acoustic correlate of sonority; (ii) the incorporation of continuous entities in phonological models of perception; and (iii) the dual-model strategy that separately analyzes symbol-based top-down processes and signal-based bottom-up processes in speech perception.

Is Phonology Embodied? Evidence from Mechanical Stimulation

Across languages, certain syllables are systematically preferred to others (e.g., plaf > ptaf). Here, we examine whether these preferences arise from motor simulation. In the simulation account, ill-formed syllables (e.g., ptaf) are disliked because their motor plans are harder to simulate. Four experiments compared sensitivity to the syllable structure of labial- vs. corona-initial speech stimuli (e.g., plaf > pnaf > ptaf vs. traf > tmaf > tpaf); meanwhile, participants (English vs. Russian speakers) lightly bit on their lips or tongues. Results suggested that the perception of these stimuli was selectively modulated by motor stimulation (e.g., stimulating the tongue differentially affected sensitivity to labial vs. coronal stimuli). Remarkably, stimulation did not affect sensitivity to syllable structure. This dissociation suggests that some (e.g., phonetic) aspects of speech perception are reliant on motor simulation, hence, embodied; others (e.g., phonology), however, are possibly abstract. These conclusions speak to the role of embodiment in the language system, and the separation between phonology and phonetics, specifically.

Is markedness a confused concept?

It is well known that, across languages, certain phonological features are more frequent than others. But whether these facts reflect abstract universal markedness constraints or functional pressures (auditory and articulatory difficulties and lexical frequency) is unknown. Romani, Galuzzi, Guariglia, and Goslin (2017) report that the putative markedness of phonological features captures their order of acquisition and their propensity to elicit errors in patients with an apraxia of speech (but not in phonological aphasia). The authors believe these results challenge the existence of abstract markedness constraints. They also raise some concerns about the explanatory utility of the markedness hypothesis. This commentary demonstrates that markedness is not inherently vague or vacuous nor is it falsified by Romani et al.'s empirical findings. As such, these results leave wide open the possibility that some phonological markedness constraints are abstract.

The Basis of the Syllable Hierarchy: Articulatory Pressures or Universal Phonological Constraints?

Across languages, certain syllable types are systematically preferred to others (e.g., [Formula: see text] lbif, where [Formula: see text] indicates a preference). Previous research has shown that these preferences are active in the brains of individual speakers, they are evident even when none of these syllable types exists in participants' language, and even when the stimuli are presented in print. These results suggest that the syllable hierarchy cannot be reduced to either lexical or auditory/phonetic pressures. Here, we examine whether the syllable hierarchy is due to articulatory pressures. According to the motor embodiment view, the perception of a linguistic stimulus requires simulating its production; dispreferred syllables (e.g., lbif) are universally disliked because their production is harder to simulate. To address this possibility, we assessed syllable preferences while articulation was mechanically suppressed. Our four experiments each found significant effects of suppression. Remarkably, people remained sensitive to the syllable hierarchy regardless of suppression. Specifically, results with auditory materials (Experiments 1-2) showed strong effects of syllable structure irrespective of suppression. Moreover, syllable structure uniquely accounted for listeners' behavior even when controlling for several phonetic characteristics of our auditory materials. Results with printed stimuli (Experiments 3-4) were more complex, as participants in these experiments relied on both phonological and graphemic information. Nonetheless, readers were sensitive to most of the syllable hierarchy (e.g., [Formula: see text]), and these preferences emerged when articulation was suppressed, and even when the statistical properties of our materials were controlled via a regression analysis. Together, these findings indicate that speakers possess broad grammatical preferences that are irreducible to either sensory or motor factors.

On the Origins of Phonology

Why do humans drink and drive but fail to rdink and rdive? Here, I suggest that these regularities could reflect abstract phonological principles that are active in the minds and brains of all speakers. In support of this hypothesis, I show that (a) people converge on the same phonological preferences (e.g., dra over rda) even when the relevant structures (e.g., dra, rda) are unattested in their language and that (b) such behavior is inexplicable by purely sensorimotor pressures or experience with similar syllables. Further support for the distinction between phonology and the sensorimotor system is presented by their dissociation in dyslexia, on the one hand, and the transfer of phonological knowledge from speech to sign, on the other. A detailed analysis of the phonological system can elucidate the functional architecture of the typical mind/brain and the etiology of speech and language disorders.

Universal Restrictions on Syllable Structure: Evidence From Mandarin Chinese

Across languages, certain onset clusters are systematically preferred (e.g., [Formula: see text], "[Formula: see text]" indicates preference), and speakers extend these preferences even to onsets that are unattested in their language. All such demonstrations, however, come from cluster-rich languages, so the observed preferences could reflect not universal linguistic restrictions but lexical analogy. To address this possibility, here, we turn to Mandarin Chinese-a cluster-poor language. We reasoned that, if people are sensitive to the onset hierarchy, then they should repair ill-formed onsets as better-formed ones [Formula: see text]-the worse formed the onset, the more likely its repair, hence, its misidentification. Results were consistent with this hypothesis, and they obtained irrespective of participants' experience with their second language (English). Nonetheless, the effect of syllable structure was strongly modulated by phonetic cues and task demands. These findings suggest that speakers might share broad phonological restrictions, but phonetic factors play a major role in their detection.

Commentary: "An Evaluation of Universal Grammar and the Phonological Mind"-UG Is Still a Viable Hypothesis

Everett (2016b) criticizes The Phonological Mind thesis (Berent, 2013a,b) on logical, methodological and empirical grounds. Most of Everett’s concerns are directed toward the hypothesis that the phonological grammar is constrained by universal grammatical (UG) principles. Contrary to Everett’s logical challenges, here I show that the UG hypothesis is readily falsifiable, that universality is not inconsistent with innateness (Everett’s arguments to the contrary are rooted in a basic confusion of the UG phenotype and the genotype), and that its empirical evaluation does not require a full evolutionary account of language. A detailed analysis of one case study, the syllable hierarchy, presents a specific demonstration that people have knowledge of putatively universal principles that are unattested in their language and these principles are most likely linguistic in nature. Whether Universal Grammar exists remains unknown, but Everett’s arguments hardly undermine the viability of this hypothesis.

Exploring the Neural Representation of Novel Words Learned through Enactment in a Word Recognition Task

Vocabulary learning in a second language is enhanced if learners enrich the learning experience with self-performed iconic gestures. This learning strategy is called enactment. Here we explore how enacted words are functionally represented in the brain and which brain regions contribute to enhance retention. After an enactment training lasting 4 days, participants performed a word recognition task in the functional Magnetic Resonance Imaging (fMRI) scanner. Data analysis suggests the participation of different and partially intertwined networks that are engaged in higher cognitive processes, i.e., enhanced attention and word recognition. Also, an experience-related network seems to map word representation. Besides core language regions, this latter network includes sensory and motor cortices, the basal ganglia, and the cerebellum. On the basis of its complexity and the involvement of the motor system, this sensorimotor network might explain superior retention for enactment.