Neural Decoding of the Speech Envelope: Effects of Intelligibility and Spectral Degradation

Area of Science:

• Neuroscience
• Auditory Perception
• Signal Processing

Background:

• Endogenous neural activity synchronizes with speech features during perception.
• Electroencephalography (EEG) enables decoding of speech-brain coupling.
• Objective measures of auditory encoding are crucial for audiological applications, especially with cochlear implants.

Purpose of the Study:

• To investigate neural decoding of the speech envelope under spectral degradation using EEG.
• To differentiate sensory encoding from higher-order processing by comparing intelligible and non-intelligible speech.
• To assess the potential clinical utility of neural decoding for audiological applications.

Main Methods:

• EEG data were collected from 38 acoustically hearing listeners (18-35 years old) exposed to vocoded speech.
• Intelligible (English) and non-intelligible (Dutch) stimuli were used to dissociate linguistic content.
• Subject-specific and group decoders were trained to reconstruct the speech envelope; statistical significance was tested using permutation testing.

Main Results:

• Speech envelope reconstruction accuracy did not differ based on spectral resolution.
• Intelligible speech generally yielded higher decoding accuracy.
• While robust decoding was observed, significant participant variability suggests limitations for individual clinical differentiation of spectral degradation and intelligibility.

Conclusions:

• Neural decoding of speech-brain coupling is feasible but influenced by speech intelligibility.
• Participant variability in decoding accuracy may hinder direct clinical application for assessing spectral degradation.
• Further research is needed to refine neural decoding methods for audiological use.