The effect of stimulus intensity on neural envelope tracking

Area of Science:

• Neuroscience
• Auditory Processing
• Speech Perception

Background:

• Growing interest in neural speech processing, particularly in hearing-impaired individuals.
• Need to amplify speech for hearing-impaired listeners, raising questions about intensity's influence on neural tracking.
• Uncertainty regarding the impact of sound amplification on neural speech tracking.

Purpose of the Study:

• To investigate the influence of stimulus intensity on neural speech tracking.
• To determine if neural envelope tracking is robust to varying sound intensities.
• To assess the relationship between neural envelope tracking and speech intelligibility.

Main Methods:

• Recorded electroencephalogram (EEG) from 20 normal-hearing participants.
• Presented a narrated story at intensities ranging from 10 to 80 dB A.
• Analyzed neural tracking of the speech envelope using a linear decoder and temporal response functions (TRF), focusing on delta (0.5-4 Hz) and theta (4-8 Hz) bands.

Main Results:

• Neural envelope tracking demonstrated intensity dependence in both TRF and envelope reconstruction analyses.
• Envelope reconstruction proved robust to stimulus intensity when the decoder was trained and tested at the same intensity.
• TRF amplitudes and latencies were intensity-dependent; peak 1 amplitude increased, and peak 2 latency decreased with higher intensities. Delta band tracking correlated with speech intelligibility.

Conclusions:

• Neural envelope tracking is robust to stimulus intensity when using consistent training and testing intensities for the linear decoder.
• Intensity is unlikely to be a confounding factor when testing hearing-impaired individuals with amplified speech using this decoder approach.
• Delta band neural envelope tracking shows potential as an objective measure of speech intelligibility.