Double-pass consistency for amplitude- and frequency-modulation detection in normal-hearing listeners

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

Temporal modulations, especially amplitude modulations (AMs), play a fundamental role in speech perception in noisy environments, as highlighted by psychoacoustic research. However, the mechanisms underlying AM processing and its contribution 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 masking. 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.NEW & NOTEWORTHY Results showed a significant correlation between the amplitude modulation (AM) following response (AMFR) and AM masking effect. Participants who are more susceptible to AM masking exhibit higher neural tracking of AM at the same fluctuation rate (8 Hz). This result might be explained both in terms of reduced selectivity of AM filters and elevated internal noise. Our results also showed no relationship between AM measures and consonant-in-noise perception, indicating that AM sensitivity mechanisms do not fully explain speech-in-noise perception skills in young normal-hearing adults.

Reduced processing efficiency impacts auditory detection of amplitude modulation in children: Evidence from an experimental and modeling study

Auditory detection of the Amplitude Modulation (AM) of sounds, crucial for speech perception, improves until 10 years of age. This protracted development may not only be explained by sensory maturation, but also by improvements in processing efficiency: the ability to make efficient use of available sensory information. This hypothesis was tested behaviorally on 86 6-to-9-year-olds and 15 adults using AM-detection tasks assessing absolute sensitivity, masking, and response consistency in the AM domain. Absolute sensitivity was estimated by the detection thresholds of a sinusoidal AM applied to a pure-tone carrier; AM masking was estimated as the elevation of AM-detection thresholds produced when replacing the pure-tone carrier by a narrowband noise; response consistency was estimated using a double-pass paradigm where the same set of stimuli was presented twice. Results showed that AM sensitivity improved from childhood to adulthood, but did not change between 6 and 9 years. AM masking did not change with age, suggesting that the selectivity of perceptual AM filters was adult-like by 6 years. However, response consistency increased developmentally, supporting the hypothesis of reduced processing efficiency in early childhood. At the group level, double-pass data of children and adults were well simulated by a model of the human auditory system assuming a higher level of internal noise for children. At the individual level, for both children and adults, double-pass data were better simulated when assuming a sub-optimal decision strategy in addition to differences in internal noise. In conclusion, processing efficiency for AM detection is reduced in childhood. Moreover, worse AM detection was linked to both systematic and stochastic inefficiencies, in both children and adults.