Biology subjects

Pylkkanen, L.

Publications and source records attributed to Pylkkanen, L..

8 recordsLinked to original sources

bioRxiv2024

Manipulating syntax without taxing working memory: MEG correlates of syntactic dependencies in a Verb-Second language

The neural basis of syntax is notoriously difficult to study without working memory and lexico-semantic confounds. To tackle these challenges, we presented syntactic dependencies in Danish two-word sentences using Rapid Parallel Visual Presentation (RPVP), eliminating the temporal delay between displaced elements and their base-generated positions. Our stimuli involved various dependencies as a function of syntactic frame (declarative, yes/no question) and verb argument structure (unergative, unaccusative, alternating unaccusative). Behaviour was facilitated and magnetoencephalography responses were increased for sentences compared to list-controls in left fronto-temporal regions (231-407ms; 506-622ms), largely replicating the Sentence Superiority Effect of prior RPVP studies. Each cluster showed sensitivity to syntactic frame, with the earlier one likely reflecting basic structure detection and the second syntactic movement. No effects of verb argument structure were obtained. The RPVP paradigms sensitivity to both the sentence-list contrast and to certain grammatical details highlights its value for probing the neurobiology of syntax.

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bioRxiv2022

Non-Local Conceptual Combination

It is uncontroversial that the syntax of an expression largely determines its meaning. For example, there is no way to interpret a sentence like "the blue hat has a white bow" as telling you that there is a white hat that has blue bow. But to what extent are the brains combinatory interpretive routines exclusively locked into the structures given by syntax? Consider another example: "The blue color of his hat is pretty." This sentence tells us that a color is pretty, that the color is blue and that the color belongs to a hat. What the syntax of this sentence does not give us is a combination of "blue" and "hat." But clearly, if we were to draw a picture of the meaning of this sentence, it would have a blue hat in it. We asked: upon encountering "hat" in this sentence, do our brains combine the features of "blue" with the features of "hat," despite the long distance between them and no direct syntactic relation? By using a known neural measure of conceptual combination in the left anterior temporal lobe, we obtained evidence using MEG that our brains appear to perform such a long-distance conceptual combination that does not track the syntax. Intriguingly, word (or rather concept) order affected the directionality of the effect. While the effect of concept order remains a topic for future work, our results overall suggest that the meaning composition system of language is likely richer than the combinatory steps predicted from syntactic structures.

neuroscience↗

bioRxiv2022

Global Motor Inhibition Precedes Stuttering Events

Research points to neurofunctional differences underlying fluent speech between stutterers and non-stutterers. Considerably less work has focused on processes that underlie stuttered vs. fluent speech. Additionally, most of this research has focused on speech motor processes despite contributions from cognitive processes that occur prior to the onset of stuttered speech. We used MEG to test the hypothesis that reactive inhibitory control is triggered prior to stuttered speech. Twenty-nine stutterers completed a delayed-response task that featured a cue (prior to a go cue) signaling the imminent requirement to produce a word that was either stuttered or fluent. Consistent with our hypothesis, we observed increased beta power in the R-preSMA -an area implicated in reactive inhibitory control- in response to the cue preceding stuttered vs. fluent productions. Beta power differences between stuttered and fluent trials correlated with stuttering severity and participants percentage of trials stuttered increased exponentially with beta power in the R-preSMA. Trial-by-trial beta power modulations in the R-preSMA following the cue predicted whether a trial would be stuttered or fluent. Stuttered trials were also associated with delayed speech onset suggesting an overall slowing or freezing of the speech motor system that may be a consequence of inhibitory control. Post-hoc analyses revealed that independently-generated anticipated words were associated with greater beta power and more stuttering than researcher-assisted anticipated words, pointing to a relationship between self-perceived likelihood of stuttering (i.e., anticipation) and inhibitory control. This work offers a neurocognitive account of stuttering by characterizing the cognitive processes that precede overt stuttering events.

neuroscience↗

bioRxiv2020

Modeling pronoun resolution in the brain

Human language processing involves not only combining word meanings in accordance with semantic and syntactic constraints, but also figuring out who and what is being referred to. Here we present a first study towards a mechanistic understanding of the neural basis for referential processing. Using both functional MRI and magnetoencephalography (MEG), we identified a consistent increase of activity in a network spanning the anterior and posterior left middle temporal gyrus and the angular gyrus for pronoun processing during naturalistic listening for both English and Chinese speakers. We then adopted a "reverse-engineering" approach to examine the cognitive processes underlying pronoun resolution. We evaluated the neural fit of three symbolic models that each formalizes a different strand of explanation for pronoun resolution in the cognitive and linguistic literature, as well as two deep neural network models with an LSTM or a Transformer architecture. Our results favor the memory-based symbolic model, suggesting a domain-general mechanism of pronoun resolution that resembles memory retrieval.

neuroscience↗

bioRxiv2020

Lists with and without syntax: A new approach to measuring the neural processing of syntax

In the neurobiology of language, a fundamental challenge is deconfounding syntax from semantics. Changes in syntactic structure usually correlate with changes in meaning. We approached this challenge from a new angle. We deployed word lists, which are usually the unstructured control in studies of syntax, as both the test and the control stimulus. Three-noun lists (lamps, dolls, guitars) were embedded in sentences (The eccentric man hoarded lamps, dolls, guitars...) and in longer lists (forks, pen, toilet, rodeo, graves, drums, mulch, lamps, dolls, guitars...). This allowed us to perfectly control both lexical characteristics and local combinatorics: the same words occurred in both conditions and in neither case did the list items locally compose into phrases (e.g. lamps and dolls do not form a phrase). But in one case, the list partakes in a syntactic tree, while in the other, it does not. Being embedded inside a syntactic tree increased source-localized MEG activity at ~250-300ms from word onset in the left inferior frontal cortex, at ~300-350ms in the left anterior temporal lobe and, most reliably, at ~330-400ms in left posterior temporal cortex. In contrast, effects of semantic association strength, which we also varied, localized in left temporo-parietal cortex, with high associations increasing activity at around 400ms. This dissociation offers a novel characterization of the structure vs. meaning contrast in the brain: The fronto-temporal network that is familiar from studies of sentence processing can be driven by the sheer presence of global sentence structure, while associative semantics has a more posterior neural signature. SIGNIFICANCE STATEMENTHuman languages all have a syntax, which both enables the infinitude of linguistic creativity and determines what is grammatical in a language. The neurobiology of syntactic processing has, however, been challenging to characterize despite decades of study. One reason is pure manipulations of syntax are difficult to design. The approach here offers a perfect control of two variables that are notoriously hard to keep constant when syntax is manipulated: word meaning and phrasal combinatorics. The same noun lists occurred inside longer lists and sentences, while semantic associations also varied. Our MEG results show that classic fronto-temporal language regions can be driven by sentence structure even when local semantic contributions are absent. In contrast, the left temporo-parietal junction tracks associative relationships.

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bioRxiv2019

Neural adaptation to accented speech: prefrontal cortex aids attunement in auditory cortices

Speech is a complex and ambiguous acoustic signal that varies significantly within and across speakers. A prevalent and ubiquitous example of such variation is accented speech, to which humans adapt extremely rapidly. The goal of this study is to uncover the neurobiological bases of the attunement process that enables such fluent comprehension. Twenty-four native English participants listened to words spoken by an unaccented "canonical" American talker and two "accented" talkers, and performed a word-picture matching task, while magnetoencephalography (MEG) was recorded. Accented speech was created by including systematic phonological substitutions within the word (e.g. [s] [->] [sh]). Activity in the auditory cortex (superior temporal gyrus) was greater for accented speech, but, critically, this was not attenuated by exposure. By contrast, prefrontal regions showed an interaction between the presence of an accent and amount of exposure: while activity decreased for canonical speech over time, responses to accented speech remained consistently elevated. Grainger causality analyses further revealed that prefrontal responses serve to modulate activity in auditory regions, suggesting the recruitment of top-down processing to decode accented signal. In sum, our results show that accented speech does not elicit the same prefrontal reduction in amplitude over time that unaccented speech does, and points to a dynamic exchange of information between the prefrontal and auditory cortices in order to recalculate phonetic classification and subsequent identification of lexical items. Significance statementHuman ability to adapt to different peoples idiosyncratic pronunciations is a hallmark of speech comprehension. This study aims to address whether adaptation to speakers accents manifests itself at the perceptual level (i.e. through adaptation of low-level neural responses in the auditory cortex) or at the post-perceptual level (i.e. higher-order regions correcting the sensory signal received from auditory cortex). Our results support the post-perceptual hypothesis: we found that responses in auditory cortex emitted an error-like signal that was invariant to exposure; whereas responses in the prefrontal cortex were modulated by exposure. These findings provide initial insight into accent adaptation, and illuminate the computational stages supporting speech comprehension more generally.

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bioRxiv2019

Understanding requires tracking: noise and knowledge interact in bilingual comprehension

Understanding speech in noise is a fundamental challenge for speech comprehension. This perceptual demand is amplified in a second language: it is a common experience in bars, train stations, and other noisy environments that degraded signal quality severely compromises second language comprehension. Through a novel design, paired with a carefully selected participant profile, we independently assessed signal-driven and knowledge-driven contributions to the brain bases of first versus second language processing. We were able to dissociate the neural processes driven by the speech signal from the processes that come from speakers knowledge of their first versus second languages. The neurophysiological data show that in combination with impaired access to top-down linguistic information in the second language, the locus of bilinguals difficulty in understanding second language speech in noisy conditions arises from a failure to successfully perform a basic, low-level process: cortical entrainment to speech signals above the syllabic level. Significance statementOver half of the worlds population is multilingual. Although proficiency in a second language improves over time, even to the point of reaching native-like proficiency, one persistent difficulty is understanding a second language in noisy environments (e.g. in crowds, train stations, etc.). We examined this processing impairment using a novel frequency-tagging paradigm with magnetoencephalography (MEG). We found that the reason underlying bilinguals difficulty in understanding second language speech in noisy conditions is induced by a failure to neurally track the operations reflecting structure (i.e., phrase) building.

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bioRxiv2018

Lexical Access in Comprehension vs. Production: Spatiotemporal Localization of Semantic Facilitation and Interference

Humans understand words faster when they are preceded by semantically related words. This facilitation is thought to result from spreading activation between words with similar meanings. Interestingly, in language production, semantic relatedness often has the opposite effect: in object naming for example, a related prior word delays the naming time of the current object. This could be due to competition during conceptual search or later interference at the motor preparation stage. However, no study has systematically compared the facilitory and inhibitory effects and thus their neurobiological relationship is unknown. We contrasted maximally parallel production and comprehension tasks during magnetoencephalography and found that in comprehension (specifically word reading), semantic relatedness modulated activity in the left middle STG at 180-335ms, consistent with prior findings on the spatiotemporal localization of lexical access. In contrast, a semantic interference pattern for the production task (object naming) occurred in a post-lexical time-window at 395-485ms in left posterior insular cortex, consistent with post-lexical motor preparation. Thus, our data show that semantic priming during comprehension and interference during production are not two sides of the same coin but rather they clearly dissociate in space and time, consistent with a lexical account for comprehension and a post-lexical one for production.\n\nSignificance statementThe processing of semantically related words has been a central tool for understanding the organization of the mental lexicon. One striking observation is that semantic relatedness tends to be facilitory in comprehension but inhibitory in language production, perhaps because only production involves a conceptual search through semantically related candidates. The neurobiology of this contrast is not understood. Our magnetoencephalography results demonstrate that the facilitory pattern is first observed in classic left temporal lexical access regions at ~200ms, whereas the inhibitory pattern occurs later and in the insular cortex. These findings show that the two effects do not co-localize in space or time and suggest that the inhibitory effects in production stem from a late motor preparation stage.

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