Motor cortex maps articulatory features of speech sounds

TLDR

Speech perception has traditionally been linked to superior temporal lobe activation, yet models suggest articulatory feature knowledge of phonemes also plays a key role in comprehension. The study aimed to investigate whether specific motor circuits are engaged during speech perception by presenting syllables that involve lip or tongue movements. Event‑related fMRI was employed while subjects listened to lip‑ and tongue‑produced syllables, with nonlinguistic noise as control, and localizer scans required silent articulation and isolated lip or tongue movements. Listening to lip‑ or tongue‑related phonemes activated superior temporal cortex and, importantly, distinct precentral gyrus motor areas in a somatotopic pattern, demonstrating that motor circuits linked to articulatory features are recruited during speech perception.

Abstract

The processing of spoken language has been attributed to areas in the superior temporal lobe, where speech stimuli elicit the greatest activation. However, neurobiological and psycholinguistic models have long postulated that knowledge about the articulatory features of individual phonemes has an important role in their perception and in speech comprehension. To probe the possible involvement of specific motor circuits in the speech-perception process, we used event-related functional MRI and presented experimental subjects with spoken syllables, including [p] and [t] sounds, which are produced by movements of the lips or tongue, respectively. Physically similar nonlinguistic signal-correlated noise patterns were used as control stimuli. In localizer experiments, subjects had to silently articulate the same syllables and, in a second task, move their lips or tongue. Speech perception most strongly activated superior temporal cortex. Crucially, however, distinct motor regions in the precentral gyrus sparked by articulatory movements of the lips and tongue were also differentially activated in a somatotopic manner when subjects listened to the lip- or tongue-related phonemes. This sound-related somatotopic activation in precentral gyrus shows that, during speech perception, specific motor circuits are recruited that reflect phonetic distinctive features of the speech sounds encountered, thus providing direct neuroimaging support for specific links between the phonological mechanisms for speech perception and production.