Asymmetry of Auditory-Motor Speech Processing is Determined by Language Experience

Area of Science:

• Neuroscience
• Psycholinguistics
• Speech Processing

Background:

• Human brain exhibits asymmetric auditory speech processing, with left specialization for phonemes and right for prosody.
• Linguistic function, like tonal language pitch changes, can shift speech processing asymmetries.
• Motor system interactions with auditory processing in speech are not fully understood.

Purpose of the Study:

• Investigate how motor cortex contributions to auditory speech processing differ between speakers of tonal and non-tonal languages.
• Determine if language experience shapes the asymmetry of motor influences on speech sound discrimination.
• Examine the causal role of the speech motor cortex in auditory discrimination of phonemes and tones.

Main Methods:

• Utilized transcranial magnetic stimulation (TMS) to temporarily disrupt the left or right speech motor cortex.
• Employed electroencephalography (EEG) to measure mismatch negativity (MMN) responses.
• Assessed auditory discrimination of phoneme and tone changes in syllable sequences.

Main Results:

• Disruption of right motor cortex impaired tone change processing in non-tonal speakers; left motor cortex disruption impaired tone processing in tonal speakers.
• Left motor cortex disruption impaired phoneme change processing in both language groups.
• Motor cortex influence on auditory speech discrimination is modulated by the linguistic function of acoustic cues.

Conclusions:

• The functional role of acoustic cues in a listener's native language determines the asymmetry of motor cortex contributions to auditory speech processing.
• Lateralized top-down motor influences play a causal role in shaping speech processing asymmetries in the auditory system.
• Language experience significantly shapes neural processing of speech sounds.