Speech recognition for school-age children and adults tested in multi-tone vs multi-noise-band maskers

Children's syntactic parsing and sentence comprehension with a degraded auditory signal

During sentence comprehension, young children anticipate syntactic structures using early-arriving words and have difficulties revising incorrect predictions using late-arriving words. However, nearly all work to date has focused on syntactic parsing in idealized speech environments, and little is known about how children's strategies for predicting and revising meanings are affected by signal degradation. This study compares comprehension of active and passive sentences in natural and vocoded speech. In a word-interpretation task, 5-year-olds inferred the meanings of novel words in sentences that (1) encouraged agent-first predictions (e.g., The blicket is eating the seal implies The blicket is the agent), (2) required revising predictions (e.g., The blicket is eaten by the seal implies The blicket is the theme), or (3) weakened predictions by placing familiar nouns in sentence-initial position (e.g., The seal is eating/eaten by the blicket). When novel words promoted agent-first predictions, children misinterpreted passives as actives, and errors increased with vocoded compared to natural speech. However, when familiar words were sentence-initial that weakened agent-first predictions, children accurately interpreted passives, with no signal-degradation effects. This demonstrates that signal quality interacts with interpretive processes during sentence comprehension, and the impacts of speech degradation are greatest when late-arriving information conflicts with predictions.

Development of temporal auditory processing in childhood: Changes in efficiency rather than temporal-modulation selectivity

The ability to detect amplitude modulation (AM) is essential to distinguish the spectro-temporal features of speech from those of a competing masker. Previous work shows that AM sensitivity improves until 10 years of age. This may relate to the development of sensory factors (tuning of AM filters, susceptibility to AM masking) or to changes in processing efficiency (reduction in internal noise, optimization of decision strategies). To disentangle these hypotheses, three groups of children (5-11 years) and one of young adults completed psychophysical tasks measuring thresholds for detecting sinusoidal AM (with a rate of 4, 8, or 32 Hz) applied to carriers whose inherent modulations exerted different amounts of AM masking. 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 are mature by 5 years. Subsequent modelling indicated that reducing internal noise by a factor 10 accounted for the observed developmental trends. Finally, children's consonant identification thresholds in noise related to some extent to AM sensitivity. Increased efficiency in AM detection may support better use of temporal information in speech during childhood.

Amplitude modulation detection and modulation masking in school-age children and adults

Two experiments were performed to better understand on- and off-frequency modulation masking in normal-hearing school-age children and adults. Experiment 1 estimated thresholds for detecting 16-, 64- or 256-Hz sinusoidal amplitude modulation (AM) imposed on a 4300-Hz pure tone. Thresholds tended to improve with age, with larger developmental effects for 64- and 256-Hz AM than 16-Hz AM. Detection of 16-Hz AM was also measured with a 1000-Hz off-frequency masker tone carrying 16-Hz AM. Off-frequency modulation masking was larger for younger than older children and adults when the masker was gated with the target, but not when the masker was continuous. Experiment 2 measured detection of 16- or 64-Hz sinusoidal AM carried on a bandpass noise with and without additional on-frequency masker AM. Children and adults demonstrated modulation masking with similar tuning to modulation rate. Rate-dependent age effects for AM detection on a pure-tone carrier are consistent with maturation of temporal resolution, an effect that may be obscured by modulation masking for noise carriers. Children were more susceptible than adults to off-frequency modulation masking for gated stimuli, consistent with maturation in the ability to listen selectively in frequency, but the children were not more susceptible to on-frequency modulation masking than adults.