Browsing by Author "Kujala, Jan, Dr., Aalto University, Department of Neuroscience and Biomedical Engineering, Finland"

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  • Neurophysiological correlates of producing and perceiving natural connected speech
    (2018) Alexandrou, Anna Maria
     School of Science | Doctoral dissertation (article-based)
    Spoken language is an essential part of our every-day lives. Despite being one of the most prominent human behaviors, little is known about the cortical substrates supporting the perception and production of continuous, connected speech. This doctoral dissertation aimed to fill this gap through an extensive experimental paradigm consisting of both natural speech production and speech perception tasks. There was a special emphasis on speech rhythm which is tied to speaking rate. Cortical signals were measured with magnetoencephalography. Electromyographic and acoustic signals were recorded during the speech production tasks. Study I aimed to quantify speech rhythm using a multimodal spectral approach in the form of coherence between electromyographic and acoustic signals. This multimodal approach was compared to a unimodal approach, which involves spectral analysis of electromyographic and acoustic signals in isolation. As opposed to a unimodal analysis, a multimodal analysis was shown to successfully reveal the shared periodic components in the two signals. This suggests that coherence metrics are especially useful in quantifying rhythm in the inherently complex natural speech. Study II investigated the cortical correlates of natural speech production and perception. Modulations in band-limited cortical signal power were examined in response to variations in three fundamental speech-related features: the amount of linguistic content present in an utterance, speaking rate and social relevance. The resulting spatiospectral patterns revealed that the right hemisphere is markedly involved in natural speech processing and, particularly, that processing of socially relevant speech engages the right temporo-parietal junction. Notably, natural speech production and perception were found to extensively overlap in both hemispheres. Study III examined, using audio-MEG coherence, the cortical tracking of global rhythmic structure and local, transient variations in speaking rate in perceived natural, connected speech. It was found that cortical tracking of perceived natural, connected speech extends beyond the previously reported emphasis on the temporal regions and also engages higher-order cortical regions. Furthermore, the observed audio-MEG coherence patterns revealed two spatially and functionally distinct components of cortical tuning: evolutionary tuning to global rhythmic structure, and predictive tuning that is driven by local changes in speaking rate. This doctoral dissertation presents novel methodological tools for characterizing rhythm in natural speech. It also contributes to an emerging view on cortical speech processing that is not confined to traditional left-hemispheric cortical regions and offers an insight into the functional role of speech rhythm in speech comprehension.
  • Rhythmic cortical dynamics in production of speech and hand motor sequences
    (2019) Saarinen, Timo
     School of Science | Doctoral dissertation (article-based)
    Human behaviors, such as speech or object handling, rely on movement sequences. Production of these meaningful movement patterns is supported by concurrent motor and cognitive processes,which presumably involve both local and distributed dynamics in the large-scale cortical networks. This Thesis examined the electrophysiological dynamics underlying sequential motor production in the human cortex. The focus of the Thesis was on rhythmic activity, a signaling feature often associated with neurocognitive processing, and on the question of how rhythmic cortical dynamics link with themotor and cognitive aspects of sequence production and modulate for different types of sequences. Magnetoencephalography (MEG) was used to record cortical population activity during motor performance, while muscle signals were tracked with electromyography (EMG). The first two studies of the Thesis examined the relationship between local rhythmicity in the sensorimotor cortex and speech articulation. The role of the primary sensorimotor region insequence production has remained unresolved. Here, inherent rhythmic activity (~20 Hz) of this region indicated sensitivity for organizing oromotor gestures into sequences (PI). Furthermore, coherent signaling between the sensorimotor cortex and lip muscle was enhanced at the preferredrate (~2–3 Hz) of articulatory production (PII). In the latter two studies, Dynamic Imaging of Coherent Sources (DICS) analysis method wasused to explore interactions between regions when cognitive-motor sequences were produced in object manipulation and handwriting tasks. Coherent rhythmic activity between regions has been viewed as a mechanism for distributed neurocognitive processing. Here, task-sensitive corticocortical (6–20 Hz) coherence was shown to reconfigure to support object manipulation: theleft-lateralized frontoparietal connectivity in simple object handling extended to cover bothhemispheres and temporo-occipital cortices when performance required visuospatial reasoning(PIII). In the context of handwriting, corticocortical phase synchrony highlighted functional elements that were sensitive to variation in complexity and linguistic content of the task: regular handwriting enhanced (~2–5/13–24 Hz) synchrony among central and frontoparietal regions linked with hand coordination and working memory, whereas separate (~7–10 Hz) synchrony within the temporo-occipital system associated with audiovisual language processing emerged specifically to support a kinetically simplified version of the writing task (PIV). In conclusion, the Thesis suggests that the primary sensorimotor cortex functionally reflectssequence-related information in speech production and shows behaviorally optimized coupling with the articulatory muscles. Interregional coherence seems to serve as a mechanism of engaging the task-relevant neurocognitive systems, and phase-coupling further coordinates processing of distinct aspects of cognitive-motor performance.