Inhibition of articulation muscles during listening and reading: a matter of intention to speak out loud

The articulation of speech sounds is often contingent on the intention to subsequently produce other sounds (co-articulation). Thus, intended acts affect the way current acts are executed. We show that the intention to subsequently repeat a short sentence, overtly or covertly, significantly modulated articulatory muscle activity already during speech perception or reading (input interval) and when delaying response (i.e., prior to production). Young adults were instructed to read (whole sentences or word-by-word) or listen to recordings of sentences to be repeated afterwards, either covertly or overtly. Surface electromyography (sEMG) recordings showed different patterns of articulatory muscle modulation in the two articulatory muscles measured - orbicularis oris inferior (OOI) and sternohyoid (STH). In the OOI, activity increased relative to baseline during speech perception or reading in both intended output conditions (overt and covert); in the STH, articulatory muscle activity decreased, during the input intervals, in both intended output conditions. However, the modulations in EMG activity were contingent on the intention to subsequently repeat the input overtly or covertly, so that activation in the OOI, and inhibition in the STH, were significantly more pronounced when overt responses were intended. Input modality was also a factor; immediately before overt responses, activity in the OOI muscle increased for listening and word-by-word reading, but not in reading whole sentences. The current results suggest that speech perception and articulation interact already during the input phase, listening or reading, reflecting the intended responses. However, this interaction may differentially affect facial-articulatory and laryngeal control mechanisms of speech production.