The origin of the articulatory interference effect on speech perception

Carneiro, Sarah Pereira [UCL] Guérit, Charlie [UCL] Dutrieux, Charlotte [UCL] Vannuscorps, Gilles [UCL] et al.

How do we understand others when they are speaking? According to a motor hypothesis, speech perception is supported not only by the auditory system, but also by motor articulatory resources – those that we use to speak. This hypothesis is supported by the finding that behavioral (execution of silent articulatory movements) and rTMS (on articulators’ representation) interference with participants’ lip or tongue motor representations affects the perception of the corresponding (lip or tongue related) speech sounds. However, the execution of silent articulatory movements and rTMS applied on the premotor cortex also activate auditory/phonological representations, to which articulatory representations are connected in the service of speech motor control. Hence, the reported effects could be a by-product of the activation of auditory rather than motor representations. To discriminate these alternatives, we determined the minimal signal/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 movement (exp1) or a non-speech-related movement (exp2). Both lip movements mobilize lip motor representations, but only the speech-related movement activates auditory/phonological representations. Therefore, if the motor hypothesis is true, both types of lip movements should interfere with participants’ ability to discriminate specifically the bilabial/lingual syllables pair in comparison to the finger movement. In contrast with this prediction, only the speech-related lip movements (exp 1) interfered with speech perception. These findings force a reinterpretation of previous results claimed to support the motor hypothesis of speech perception.