Neural and psychoacoustic insights into amplitude modulation processing and its link with speech perception in noise

Overview & Synopsis

Temporal modulations, especially amplitude modulations (AMs), play a fundamental role in speech perception in noisy envi- ronments, as highlighted by psychoacoustic research. However, the mechanisms underlying AM processing and its contribu- tion to speech perception in noise remain unclear. The present study combined both behavioral psychophysics and electroencephalography (EEG) measures to investigate AM processing and its relationship to the perception of consonants in noise for young adults with normal hearing. Participants completed psychoacoustic measures of AM sensitivity, i.e., detection thresholds for AM fluctuations at 8 Hz, and susceptibility to AM masking (the effect on AM detection thresholds of interfering AM fluctuations carried by a masker) at 8 Hz. In addition, participants underwent an EEG recording measuring the neural AM following response (AMFR, or envelope following response) for AM tones modulated at 8 or 40 Hz presented without mask- ing. Finally, they completed a consonant identification task in a stationary speech-shaped noise. Results showed a significant positive correlation between the signal-to-noise ratio of the AMFR recorded at 8 Hz and AM masking effects measured at the same rate. This finding is discussed in terms of both reduced selectivity of AM filters and elevated internal noise. Finally, no relationship between AM measures and consonant-in-noise perception was observed, suggesting that the mechanisms involved in AM processing may not fully capture the ability of adults with normal hearing to identify consonants in noisy backgrounds.