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Poster E54, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall

Microstate ERP analyses for detecting the articulation onset in speech production

Anne-Lise Jouen1, Monica Lancheros1, Marina Laganaro1;1Faculty of Psychology and Educational Science, University of Geneva

Despite the unresolved issues of brain signals ‘contamination by articulation-induced artifacts, the use of electroencephalography (EEG) to study overt speech production has increased substantially in the past 15 years (Ganushchak et al., 2011). The majority of EEG studies have used stimulus-aligned analysis to avoid possible artifacts during motor preparation/execution, hence targeting only the early encoding processes. As it well known that production latencies can vary considerably from one participant/trial to another, the alignment on the vocal response onset has become recently an extremely useful tool to target later stages of word production (Riès et al., 2013; Laganaro, 2014). Yet the response-aligned evoked potential (ERPs) raise another methodological issue: where to place the point of alignment of the ERPs (Fargier et al., 2018)? Indeed, the point of alignment -that would ideally be the onset of the articulatory movement- is generally measured by voice onset but articulation may start up to several hundred milliseconds prior to voice onset and depends on the properties of the phonemes (Rastle et al., 2005). The purpose of the present study was to determine if the articulatory onset can be detected from the EEG signal itself and thus identify neurally the existing gap between the vocal and articulatory onsets, in particular when their precise onset is unclear which is the case when speech stimuli start with voiceless stops (/p, t, k/,Ouyang et al., 2016). To this end, we recorded high density EEG in 25 healthy participants during a delayed production task of 224 monosyllabic pseudowords, consisting of complex consonant clusters (CCV/CCCV) beginning either with voiceless stops consonants (/p/, /t/, /k/) or with a fricative voiceless consonant (/s/) for which the vocal and articulatory onsets are closer. ERPs were aligned to the vocal onset, detected manually on the acoustic signal, and microstate analysis (spatio-temporal analysis, Michel & Koenig, 2018) was performed on the 300 ms preceding the vocal onset. Behavioral analysis on production latencies, identified by the vocal onset, revealed that the /s/-pseudowords were initiated approximatively 100 ms faster than the /p, t, k/-ones. However, the microstate ERP analyses invalidated this interpretation showing that the behavioral observations were due to the fact that articulatory and vocal onsets were not aligned similarly. Indeed, the spatio-temporal segmentation revealed a global topographic ERPs (maps) pattern similar in all onset conditions with the specific microstate, corresponding to the global distribution of scalp topography likely associated with articulation, shifted of about 100 ms for the /s/-pseudowords relative to the /p/, /t/, /k/. The fitting in the single epochs also revealed earlier onsets of the same microstate for labial and alveolar stops relative to velar /k/. These results show that articulatory onset had already begun about 100 ms before the vocal onset for the voiceless stops and suggest that ERP microstates can be used to target articulation onset, which may represent a complementary marker to electromyography (EMG), in particular for velar stops difficult to detect with facial EMG.

Themes: Language Production, Speech Motor Control
Method: Electrophysiology (MEG/EEG/ECOG)

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