Relating speech perception in noise to temporal-processing auditory capacities during childhood
Temporal cues (e.g., amplitude modulation, AM) play a crucial role in speech intelligibility for adults. How the ability to track these temporal cues develops and interacts with the development of speech perception is however unclear. Although aspects of AM processing appear to be mature as early as 3 months of age, children’ ability to detect AM continues to improve until 10 years of age. The present study explored whether the development of AM processing is related to sensory development or to changes in processing efficiency and how this ability relates to speech intelligibility in noise during childhood.
Eighty-three children with normal-hearing from 5 to 11 years and 22 young adults completed three 3IAFC adaptive tasks. The first psychophysical task assessed AM sensitivity using pure tone carriers and three modulation rates (4, 8, 32 Hz). A second task assessed susceptibility to AM masking by comparing AM detection thresholds at the same modulation rates using three carriers varying in their inherent AM fluctuations: tones, narrowband noises with small inherent AM fluctuations and noises with larger fluctuations. Finally, a third XAB task was designed to measure consonant identification thresholds in speech-shaped noise using fricative consonants contrasting on either place of articulation or voicing.
Results showed that between 5 and 11 years, AM detection thresholds improved and that susceptibility to AM masking slightly increased. However, the effects of AM rate and carrier were not associated with age, suggesting that sensory factors (tuning of AM filters, susceptibility to AM masking) are mature by 5 years. Increased AM masking with age result from worse thresholds with tone carriers at 5 years as if tone carriers were “noisier”.
These changes in AM sensitivity and masking during childhood may reflect a more efficient use of AM cues with age, due to a reduction in internal noise and/or optimization of decision strategies. Subsequent computational modelling indicated that a reduction in internal noise by a factor 10 better accounted for these developmental trends.
The development of temporal processing during childhood may be in terms of changes in processing efficiency. Finally, children’s consonant identification thresholds in noise decreased with age and were somewhat related to AM sensitivity. Thus, increased efficiency in AM detection may support better use of temporal information in speech during childhood.