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The Effect of Ultrasound Visual Feedback on Speech Processing ‒ An fNIRS Study
Poster Session E, Friday, October 2, 11:00 am - 1:00 pm, Wangari Maathai
Satu Saalasti1, Iida Aakko2, Petri Pulli1, Jaakko Kauramäki2, Riikka Möttönen2; 1University of Eastern Finland, 2University of Helsinki
Speech production is a highly complex motor act that requires precise coordination of articulators. It involves continuous integration of sensorimotor information for speech planning and articulation, while simultaneously relying on auditory feedback to monitor and adjust speech output. Real-time ultrasound visual feedback (UVF) of tongue movements has been shown to enhance the efficacy of speech disorder treatment, but the underlying neural mechanisms are unknown. Functional near-infrared spectroscopy (fNIRS) is particularly well suited for studying speech production because it is relatively robust to movement-related interference and can be used during UVF. The aim of the present study was to investigate cortical processing of UVF in bilateral frontotemporal speech processing networks. Participants were 27 right-handed neurotypical adults (24 females, 3 males; mean age = 23 years) with normal or corrected-to-normal vision and no history of hearing impairment. The experiment investigated the effect of real-time UVF of tongue movements during speech production in three counterbalanced conditions: speaking without UVF, speaking with UVF, and listening to speech. Participants’ speech was recorded using microphones and transmitted via an external audio interface (Focus rite) to in-ear headphones for real-time auditory feedback. In the listening condition, the auditory stimuli were presented via the same headphones from pre-recorded audio from speaking without UVF. A block design was used, with 25 s trials and variable inter-trial intervals of 15–26 s, resulting in a duration of 6 min for each block. Participants produced pseudowords while their hemodynamic responses were recorded using fNIRS (NIRx NIRSport 2) with 16 bilateral channels. Optode array was designed based on previous literature to cover frontotemporal speech-related areas. Preprocessing and first-level analyses with general linear models were conducted using the manufacturer-provided acquisition software, after which statistical analysis with linear mixed models were performed in RStudio. The results revealed that speech production conditions elicited increased HbO responses relative to listening across the frontotemporal speech processing areas. Channel-wise analyses showed increased responses in the inferior frontal gyrus, motor and premotor cortices, and auditory cortex. When UVF was available, hemodynamic responses were further increased specifically in superior fronto-parietal regions in both hemispheres in contrast to speech production without UVF. These findings suggest that real-time UVF activates the visual dorsal pathway and modulates functioning of frontotemporal speech processing network. Together, these results provide new evidence that visual feedback of articulatory movements modulates the neural processes underlying speech production and offer a preliminary explanation for the mechanisms by which UVF may enhance interventions for speech disorders.
Topic Areas: Speech Motor Control, Speech Perception