Brain processes of loud speech and faking an accent as a window on motor speech planning/programming

Abstract

Numerous factors interfere with the successful transmission of messages during verbal conversations leading speakers to use different speech modes, i.e., specific prototypes of speech with unique phonatory and articulatory characteristics. Despite their omnipresence in verbal exchanges, no theoretical model in the speech production literature has provided a mechanistical account of the encoding processes underpinning speech in different modes. The present study thus aims to investigate how speech modes are planned/programmed relative to standard speech using the high temporal resolution provided by electroencephalography (EEG). 20 Participants uttered pseudowords in three different conditions-standard speech, speaking louder than usual and faking an English accent in French-during a delayed production task. Event-related potential (ERP) of standard speech was contrasted separately with the two others speech modes. Results indicate that speaking by adopting speech modes varying in articulatory and phonatory properties entails increased neural activity of the brain networks that are already involved in standard speech production. Especially, electrophysiological signatures of loud speech and faking an accent were both associated to differences in ERP responses relative to standard speech in a time period covering the last 200 msec preceding the vocal onset. This observation was coherent across waveform analysis (more extended differences in time and space for faking an accent), topographical dissimilarity analysis and microstates analysis (more extended for loud speech). The present findings highlight that different speech modes are encoded in the last 200 msec preceding their vocal production, possibly in a mode-specific way which will need further investigation.

Keywords: Amplitudes; EEG/ERP; Microstates; Source localization; Speech modes.