The Spatio-Temporal Dynamics of Phoneme Encoding in Aging and Aphasia.

Area of Science:

• Neuroscience
• Psycholinguistics
• Speech and Language Processing

Background:

• Successful language comprehension relies on dynamic neural encoding of speech sounds (phonemes).
• The neural dynamics of speech encoding may be altered in individuals with language disorders like aphasia.

Purpose of the Study:

• To investigate alterations in neural dynamics of speech encoding in individuals with post-stroke aphasia compared to healthy controls.
• To examine the duration, speed, and spatial location of phonetic feature encoding during naturalistic language processing.

Main Methods:

• Electroencephalography (EEG) recordings from 39 individuals with aphasia and 24 healthy older adults during 25 minutes of story listening.
• Estimation of phonetic feature encoding duration, neural pattern evolution speed, and spatial encoding over EEG sensors.

Main Results:

• Phonetic features are robustly encoded in healthy older adults' EEG responses.
• Individuals with aphasia exhibited significantly decreased phonetic encoding, particularly over left-lateralized electrodes, after initial processing.
• Healthy controls, unlike those with aphasia, extended phonetic feature encoding when word identity was uncertain, crucial for comprehension.

Conclusions:

• Aphasia is associated with impaired maintenance of lower-order phonetic information necessary for lexical recognition.
• This study highlights altered speech processing mechanisms in aphasia and provides insights into healthy aging and neurotypical language processing.