A speech envelope landmark for syllable encoding in human superior temporal gyrus

Area of Science:

• Neuroscience
• Speech Processing
• Auditory Neuroscience

Background:

• The amplitude envelope of speech is vital for comprehension, but its neural representation is debated.
• Understanding how the brain processes speech intensity modulations is key to deciphering auditory perception.

Purpose of the Study:

• To investigate the neural representation of the speech amplitude envelope in human auditory cortex.
• To identify specific cortical zones involved in processing envelope modulations.
• To determine the linguistic implications of neural envelope encoding.

Main Methods:

• High-density intracranial electroencephalography (iEEG) recordings during speech listening.
• Acoustic analysis of speech amplitude envelope features, specifically onset edges.
• Stimulation with synthesized amplitude-modulated tones to test neural responses.

Main Results:

• A distinct region in the middle superior temporal gyrus (STG) was identified as detecting acoustic onset edges.
• The timing of these onset edges correlates with syllabic nucleus onsets, and their slope with syllabic stress.
• Neural responses were stronger for steeper amplitude changes, indicating encoding of amplitude modulation rate, not absolute amplitude.

Conclusions:

• The STG plays a critical role in encoding the timing and magnitude of acoustic onset edges.
• This encoding mechanism in the STG is fundamental for perceiving the temporal structure of speech.
• Neural processing of amplitude envelope modulations by the STG supports speech comprehension.