The execution of silent articulatory lip or tongue movements is known to affect the perception of corresponding (lip or tongue related) speech sounds. This finding is often considered as a piece of evidence that speech perception is supported by motor articulatory resources (the motor interpretation). However, the execution of silent articulatory movements involves not only the motor system, but also the auditory/phonological system, to which articulatory representations are connected in the service of speech motor control. Hence, the reported effect could be a by-product of the activation of auditory rather than motor representations (the auditory interpretation). The aim of the two experiments reported here was to discriminate these two hypotheses. To do so, we tested the effect of the execution of both speech-related and non-speech-related lip movements on the perception of lip-related and non-lip-related speech sounds. Both lip movements mobilize lip motor representations, but only the speech-related movement activates auditory/phonological representations. Thus, the central question was whether only speech-related lip movements (in line with the auditory interpretation) or both types of lip movements (in line with the motor interpretation) would affect the perception of lip-related speech sounds beyond the effect of control conditions. We determined the minimal signal/white noise ratio at which participants could discriminate two pairs of syllables (bilabial/lingual and lingual/lingual) while performing a repetitive movement of the finger or one of two lip movements: a speech-related lip movement (experiment 1: open & close the lips) or a non-speech-related lip movement (experiment 2: protrusion & retrusion of the lips). The results of frequentists and Bayesian statistical analyses indicated that in comparison to the execution of finger movements, the execution of speech-related lip movements interfered significantly more with the perception of lip-related than non-lip-related speech sounds. There was no such disproportionate effect when participants executed non-speech-related lip movements. Therefore, these findings are in line with the auditory interpretation and invite revision of previous results claimed to support the motor interpretation.
Carneiro, S., Guérit, C., Dutrieux, C., Vannuscorps, G., & et al. (2023). The effect of articulatory suppression on speech perception originates from phonological rather than motor interference. International Convention of Psychological Science, Brussels, Belgium. https://hdl.handle.net/2078.5/29808