Language and Brain Rhythms

Project Information

LaBRhythms

Grant agreement ID: 843088

DOI

10.3030/843088

Project closed

EC signature date 23 April 2019

Start date 1 September 2019

End date 10 July 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 184 707,84

EU contribution

€ 184 707,84

Coordinated by

INSTITUT NATIONAL DE LA SANTE ET DE LA RECHERCHE MEDICALE
France

Periodic Reporting for period 1 - LaBRhythms (Language and Brain Rhythms)

Reporting period: 2019-09-01 to 2021-08-31

Summary of the context and overall objectives of the project

The temporal fluctuations of speech are crucial acoustic anchors that enable the segmentation of the speech stream into words and syllables. Hence, the processing of speech temporal properties has a crucial influence on language comprehension. However, the brain mechanisms and structures that encode speech rhythms remain unknown. The overarching objective of this research project was to investigate to which extent neural oscillations are instrumental for the processing of speech rhythms.

In particular we addressed the following questions:
1) Are neural oscillations able to tune to the temporal statistics of language? Are they robust to the temporal variability that is naturally present in speech?
2) Is neural oscillatory activity reflecting comprehension of the speech signal?
3) Are the neural oscillatory mechanisms observed during speech listening speech-specific?

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In a first experiment, we investigated whether temporal predictions auding auditory listening are robust to temporal variability, which that are naturally present in many auditory signals such as speech and music. We tested whether temporal expectations can be formed in no-fully predictable context, and how the temporal variability of sensory contexts affects perception. Participants were asked to discriminate a target deviant sound embedded in sound sequences. Auditory discrimination performance progressively declined as the temporal variability of the sound sequence increased. Altogether, these results suggests that temporal predictions can be set up quickly based on the temporal statistics of past sensory events, and are robust to a certain amount of temporal variability. This data was presented at two conferences (Cutting EEG 2021, Biomag 2022), and the article is in preparation.

Second, we tested the influence of neural oscillations on speech comprehension, by manipulating oscillations with continuous transcranial alternating current stimulation (tACS) above the auditory cortices. We show an effect of tACS frequency on the perception of ambiguous words, suggesting that neural oscillations causally influence word comprehension. Results were published in Journal of Cognitive Neuroscience. We further tested the link between neural entrainment and linguistic processing in a Cocktail party setting (i.e. in the presence of multiple speakers). Listening to speech is difficult in noisy environments, and is even harder when the interfering noise consists of intelligible speech as compared to unintelligible sounds. We asked whether neural oscillations tracking the attended speech reflects its comprehension, and/or the comprehension of the distracting speech signal. In this magnetoencephalography (MEG) experiment, the low-frequency neural oscillations followed less the dynamics of target speech, when the target was less intelligible. The results were published in Current Research in Neurobiology, and presented at the Rhythm Workshop (Lyon, 2022)

Third, we directly dissociated the contribution of neural oscillations in the processing of speech acoustic cues from that related to linguistic processing. We examined the neural changes associated with the comprehension of acoustically degraded speech using MEG. Significant changes in neural oscillations were observed in relation to the acoustic degradation of speech. However, we failed to find a direct effect of speech comprehension on the neural oscillatory response. This suggests that acoustics greatly influence the neural oscillatory response to speech signals. These results were presented at the conference Biomag (2022), a preprint has been published on BioRxiv.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results of the project provide crucial insights on the brain mechanisms underlying the processing of the complex temporal structure of speech. They first show that the brain is able to follow the complex temporal structure of speech, and is able to predict auditory information that is regular but contains – like speech – some amount of temporal variability. It also shows that neural oscillatory activity seems to reflect temporal processing mechanisms that influence speech perception and comprehension, but do not necessarily reflect speech-specific processing.

This project bridges the gap between diverging views in linguistics and neuroscience. The complex temporal structure of speech is known to constrain speech comprehension, but the processing of speech rhythms is not clearly understood from a neurophysiological standpoint. On the other hand, research in neurophysiology suggests that neural oscillations provide a mechanism for speech temporal processing; yet, this has only been tested with either artificially rhythmic speech and/or without considering that speech is not a pure periodic signal. This project thus provides an overarching view on the neural mechanisms behind temporal predictions in speech processing. By investigating the role of neural oscillations in speech processing, it will also provide more understanding of the neural origins of specific language disorders. Beyond language processing, the results will give insight on the processing of temporal information that could generalize across sensory modalities.