Effect of digital noise-reduction processing on subcortical speech encoding and relationship to behavioral outcomes

Area of Science:

• Neuroscience
• Audiology
• Speech Processing

Background:

• Perceptual benefits of digital noise reduction (NR) vary significantly across individuals.
• Individual differences in noise tolerance and sensitivity to NR-induced distortions are not well understood physiologically.
• The subcortical encoding of speech in the auditory pathway is a potential area for investigating these individual differences.

Purpose of the Study:

• To develop objective measures of speech encoding in the ascending auditory pathway.
• To assess if these measures can predict individual noise tolerance and sensitivity to NR-processed speech.
• To explore the physiological basis of individual variability in the benefits of NR.

Main Methods:

• Utilized speech-evoked brainstem responses (sEBRs) to the syllable /da/ as objective measures.
• Analyzed sEBRs for sensitivity to added noise and NR processing.
• Quantified NR effects using response-to-response correlation metrics and spectral amplitude ratios for consonant and vowel portions, respectively.
• Examined the correlation between fundamental frequency (f0) amplitude ratios and behavioral accuracy with NR.

Main Results:

• Speech-evoked brainstem responses were sensitive to both noise addition and NR processing.
• NR effects on consonant and vowel encoding were robustly quantified.
• f0 amplitude ratios between conditions showed a significant correlation with behavioral accuracy in NR conditions.
• These findings indicate that brainstem responses can objectively reflect NR effects on speech encoding.

Conclusions:

• Investigating NR effects on bottom-up speech encoding using brainstem measures is feasible.
• Individual subcortical encoding of NR-processed speech may predict individual behavioral outcomes.
• Brainstem response metrics offer a promising avenue for understanding individual differences in NR effectiveness.