Role of the motor system in language knowledge

Area of Science:

• Linguistics
• Neuroscience
• Cognitive Science

Background:

• Spoken languages exhibit systematic preferences for certain sound patterns over others.
• The underlying principles for these preferences are debated: abstract rules or motor production demands.

Purpose of the Study:

• To investigate whether syllable structure preferences in English speakers are driven by motor simulation or abstract linguistic knowledge.
• To determine if the motor cortex's involvement in speech perception is causally linked to linguistic structure computation.

Main Methods:

• Participants underwent transcranial magnetic stimulation (TMS) over the left orbicularis oris muscle representation.
• Sensitivity to syllable hierarchy was tested during TMS.
• Functional MRI (fMRI) was used to examine brain activity.

Main Results:

• Repetitive TMS pulses impaired global sensitivity to syllable number.
• fMRI confirmed the stimulated cortical site's sensitivity to the syllable hierarchy.
• Contrary to motor simulation hypotheses, ill-formed syllables engaged the lip sensorimotor area less and were least impaired by TMS.

Conclusions:

• Speech perception automatically triggers motor action, but this is not causally linked to linguistic structure computation.
• The language and motor systems are closely linked yet distinct.
• Language knowledge includes abstract, disembodied principles beyond motor optimization.