Gap detection in school-age children and adults: effects of inherent envelope modulation and the availability of cues across frequency

Abstract

Purpose: The present study evaluated the effects of inherent envelope modulation and the availability of cues across frequency on behavioral gap detection with noise-band stimuli in school-age children.

Method: Listeners were 34 normal-hearing children (ages 5.2-15.6 years) and 12 normal-hearing adults (ages 18.5-28.8 years). Stimuli were continuous bands of noise centered on 2000 Hz, either 1000- or 25-Hz wide. In addition to Gaussian noise at these bandwidths, there were conditions using 25-Hz-wide noise bands modified to either accentuate or minimize inherent envelope modulation (staccato and low-fluctuation noise, respectively).

Results: Within the 25-Hz-wide conditions, adults' gap detection thresholds were highest in the staccato, lower in the Gaussian, and lowest in the low-fluctuation noise. Similar trends were evident in children's thresholds, although inherent envelope modulation had a smaller effect on children than on adults. Whereas adults' thresholds were comparable for the 1000-Hz-wide Gaussian and 25-Hz-wide low-fluctuation stimulus, children's performance converged on adults' performance at a younger age for the 1000-Hz-wide Gaussian stimulus.

Conclusions: Results are consistent with the idea that children are less susceptible to the disruptive effects of inherent envelope modulation than adults when detecting a gap in a narrow-band noise. Further, the ability to use spectrally distributed gap detection cues appears to mature relatively early in childhood.

Figure 1

Illustrations of the inherent envelope modulation characteristics of the four stimulus conditions at the output of a roex filter centered on 2000 Hz. The left column of panels shows the envelopes of 1-sec samples, plotted as a function of time. The right column of panels shows the envelope magnitude spectra of the full 10.7-sec samples. Values of W (fourth moment) and V (ratio of std and mean, in dB) appear to the far right of the right column of panels. Stimuli expected to produce the lowest thresholds (wide and low-fluctuation noise) appear in the bottom rows, whereas those expected to produce higher thresholds (Gaussian and staccato noise) appear in the top rows.

Figure 2

Gap detection thresholds for individual child listeners, plotted as a function of listener age. Circles show individual child listeners’ thresholds as a function of age, with shading indicating data where one or more threshold estimates were based on a psychometric function fits. Stars indicate the geometric mean of adult thresholds, and dotted lines indicate the 95% confidence interval around those means. Solid lines and the text in each panel indicate fits to child data.