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Investigating brain dynamics of Motor Speech Encoding through speech modes
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Poster A68 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Bryan Sanders1, Monica Lancheros1, Marion Bourqui1, Marina Laganaro; 1University of Geneva
Humans have mastered their control over speech production throughout centuries to overcome signal transmission obstacles and to communicate effectively in various settings. Despite its prevalence in everyday life, speech modes (loud speech (LS) and whispered speech (WS) for instance), which are specific types of modulated speech, have received little interest in the neuropsycholinguistic scientific community. Even the Direction Into Velocities of Articulators (DIVA) model (Guenther, 1995), which accounts for most speech production mechanisms, does not clearly clarify which processes underly the modulation of speech (Tourville & Guenther, 2011). Here, we will investigate whether specific speech modes and standard speech (SS) share the same processes or if modulated speech require additional processes relative to normally phonated utterances. We will use two speech modes (WS and LS) to investigate the processes underlying speech modulation. WS is characterized by the absence of vibration of vocal folds (Tsunoda et al., 2011) resulting in reduced intelligibility and perceptibility (Zhang, 2012). WS is the speech mode which involves the most distinct behavioral and phonatory pattern in comparison to SS (Kelly & Hansen, 2021). By contrast, LS consists in increasing vocal loudness, without necessarily improving the intelligibility of the message conveyed (Whitfield et al., 2021). Utterances are usually considered loud when intensity is approximately 10 dB higher than SS utterances (Huber & Chandrasekaran, 2006). This change in intensity leads to modified articulatory pattern and increased effort (Schulman, 1989). Here we present two studies in which behavioral (vocal onset latencies) and electrophysiological signature of these speech modes is investigated through a delayed production task. In the WS study, 24 participants produced pseudo-words in the WS and SS conditions; in the LS study, 24 different participants produced the same pseudo-words in the LS and SS conditions across 8 experimental blocks alternating between the speech modes. Event-related potentials (ERPs) were extracted aligned to the vocal onset of speech backwards (response-locked) to study motor speech encoding processes across speech modes. Waveform amplitudes and microstates analyses have been performed to compare across conditions. In the WS study, participants had overall good accuracies (over 93%) in both speech conditions, but with 16 ms longer initialization latencies for WS. For the LS study, LS utterances were produced 29 ms faster than SS utterances with a similar accuracy across conditions (over 94%). Differences in waveform amplitudes and in the global dissimilarity index appeared in both studies, but in different time windows (300 ms before the vocal onset for WS and closer to the vocal onset for LS). In both cases, the microstate analyses indicate a shift of the same topographic maps in these time-windows. The results show that brain activity in the period preceding articulation indeed differs between speech modes. The microstates analyses indicate that the differences do not seem to be due to additional processes but rather a different distribution of the same brain activations. Unexpectedly, the differences occur in different time windows depending on the speech mode, a result which will need to be further investigated using other speech modes or other analyses.
Topic Areas: Speech Motor Control, Language Production