A comparison of threshold estimation methods in children 6-11 years of age.

Estimating detection threshold for auditory stimuli in children can be problematic because of lapses in attention and the time limits usually imposed by scheduling restrictions or fatigue. Data reported here were collected to compare the stability of threshold estimation procedures in testing children ages 6 to 11 in a three-alternative, forced-choice paradigm. Stimuli consisted of a 1-kHz tonal signal and a Gaussian noise masker, bandpass filtered between 500-2,000 Hz and presented at 25-dB spectrum level. The signal was either presented for 400 ms in the presence of a continuous masker (simultaneous masking) or for 10 ms just prior to a 400-ms masker (backward masking). For each masking paradigm the 79% correct threshold was assessed via each of three procedures: 3-down, 1-up adaptive staircase (Levitt), maximum likelihood estimation (MLE), and method of constant stimuli. Percent correct was measured at the end of the study for a signal 10 dB above the previously determined threshold in order to estimate the most appropriate psychometric function asymptote for fitting data collected via the method of constant stimuli. Both the MLE and Levitt procedures produced equally stable threshold estimates for both conditions and age groups. This was the case despite considerable variability in backward-masking thresholds.

Development of adult-like performance in backward, simultaneous, and forward masking.

Some researchers have argued that specific language impairment (SLI) is associated with deficits in processing certain temporal aspects of auditory stimuli. One recent study (Wright et al., 1997) suggests that backward masking in particular poses a problem for children with SLI, as compared to simultaneous or forward masking. Interpretation of this finding is complicated by the fact that very little is known about the development of normal, adult-like performance in these masking paradigms. The study reported here examined performance for children 5-11 years old on forward, simultaneous, and backward masking and compared their performance to that of adults. The data show a trend for improvement in performance with age in all three masking paradigms. There was no evidence for later or more gradual improvement in performance on the backward-masking paradigm. However, backward-masking thresholds were more variable than those in the other conditions and were subject to greater individual differences, even in the adult data set. Manipulation of masker bandwidth yielded no evidence for more adult-like performance in the child data with the wider bandwidth masker. Additional data collected on two naive adult observers show a marked improvement in backward-masking performance over time, suggesting that detection with these stimuli might be particularly subject to practice effects.

The effect of masker interaural time delay on the masking level difference in children with history of normal hearing or history of otitis media with effusion.

OBJECTIVE: To determine the relation between the masking level difference (MLD) and the interaural time delay of the stimulus in children with a history of normal hearing and with a history of otitis media with effusion (OME). DESIGN: MLDs for a 500 Hz pure tone presented in a 100 Hz-wide masking noise were determined as a function of the interaural delay of the masker (six interaural delays between -726 microsec and +998 microsec were examined). For the masker with zero interaural delay, the signal was presented either interaurally in-phase or 180 degrees out of phase. For the masker delay conditions, the signal was given the same interaural delay as the masker and then was inverted interaurally. All children had normal audiograms at the time of testing. Ten children had a history of normal hearing and seven children had a history of OME. RESULTS: Similar to what has been found previously in adults, children with a history of normal hearing showed the maximum MLD (approximately 16 dB) for an interaural time delay of 0 microsec, with the MLD decreasing as a function of interaural time delay (by as much as 4 to 5 dB for the extreme delays). Children with a history of OME had significantly smaller MLDs than normal for the three smallest interaural delays but did not differ significantly from normal at the three largest interaural delays. CONCLUSIONS: The form of the function relating masker interaural time delay to MLD magnitude is adult-like by age 6 yr. The function indicates a binaural advantage for the processing of sound near auditory midline. This advantage is less apparent in children having a history of OME.

The effect of otitis media with effusion on complex masking tasks in children.

OBJECTIVE: To determine whether there is a relationship between the presumed complexity of auditory processing and the time course of recovery of auditory function in children with a history of otitis media with effusion (OME). DESIGN: Longitudinal testing over a 1-year period following insertion of tympanostomy tubes in clinical and control groups. SUBJECTS: A total of 34 children with a history of OME were tested. Twenty-five were tested both just before the placement of tympanostomy tubes and on up to 3 separate occasions (1 month, 6 months, and 1 year) after the placement of the tubes. With subject attrition, there were 27, 16, and 10 listeners at the 1-month, 6-month, and 1-year tests, respectively. An age-matched control group of 29 children was tested. METHODS: The comodulation masking release (CMR) paradigm was used to measure the ability of the listener to detect a signal in a noise background composed of a simple (1 amplitude modulation pattern) or more complex (2 amplitude modulation patterns) masking background. RESULTS: Children with a history of OME had reduced masking release before and 1 month after insertion of tympanostomy tubes for both the simple and complex CMR tasks. After surgery, the CMR results for simple task was not significantly different from that in controls by 6 months, but CMR for the complex task remained significantly reduced even 1 year after surgery. CONCLUSION: Our results suggest a slower recovery of auditory function for more complex auditory tasks in children with a history of OME.

Signal detection and pitch ranking in conditions of masking release.

Masked threshold levels for signal detection or pitch ranking (low, middle, or high) were determined in conditions where one of three possible signal frequencies could be presented on a given trial of a three-interval forced-choice task. Thresholds were determined under conditions investigating binaural masking release (the masking-level difference, or MLD) and monaural masking release in modulated noise. It was assumed that part of the masking release in modulated noise was due to a within-channel analysis of information in the masker dips, and that part of the masking release was due to across-frequency analysis of temporal envelope information (comodulation masking release, or CMR). In the MLD experiment, the masker was a low-pass noise with a frequency cutoff of 1000 Hz. In the modulated-noise experiment, a broadband noise was square-wave amplitude modulated at a rate of 25 Hz and then digitally low-passed filtered at 1000 Hz. The results indicated that when the frequency separation between frequency components was relatively wide, masking release for pitch ranking was similar to that for signal detection. However, as the frequency separation between components narrowed, masking release for pitch ranking decreased. The results are consistent with an interpretation that information regarding signal frequency is relatively coarse under the conditions of masking release examined here.

Auditory development in complex tasks of comodulation masking release.

Experiments on listeners aged 5 years to adult were conducted to investigate the development of comodulation masking release (CMR) under conditions where auditory grouping could be affected either by the coherence of modulation pattern among noise bonds, or the temporal asynchrony among bands. The conditions examining CMR when two modulation patterns were present (each carried by a different set of noise bands) indicated a similar effect across all age groups. Here, CMR was substantial when the on-signal band (OSB) and six comodulated flanking bands (FBs) were presented, decreased when two bands having a second pattern of modulation were added, and then recovered partially when a further six bands that had the second modulation pattern were added. In conditions where there was a temporal asynchrony between the OSB and the FBs, the children typically showed smaller CMRs than the adults. In the case where the OSB preceded the FBs, adults typically showed CMR near zero when the temporal fringe was 50 ms or more. Children usually showed negative CMRs for such conditions. In the case where the FBs preceded the OSB, all age groups showed substantial CMRs, but the CMRs of adults were significantly larger than those of the children. The present results indicate that the effect of a second, independent modulation pattern on CMR is similar in children and adult listeners, but that CMR appears to be detrimentally affected more in children than in adults when there is a temporal asynchrony between the on-signal and flanking bands.

MLD in children: effects of signal and masker bandwidths.

The first aim of this study was to obtain a more detailed picture of the effect of masker bandwidth (20 Hz to 1000 Hz bandwidth) on the masking level difference (MLD) for a 500-Hz signal as a function of listener age. The results of the pure-tone signal experiment showed that the MLDs of older children differed from adults only for the narrowest masker bandwidth. In contrast, children younger than about 7 years of age tended to have smaller MLDs than adults at all but the widest masker bandwidth must be for MLDs of adult magnitude to be observed. One interpretation of this effect is that younger listeners require relatively great spectral dissimilarity (and, therefore perceptual dissimilarity) between the signal and masker in order to obtain MLDs of adult magnitude. The second aim of this study was to test this possibility by determining the MLD for noise signals in cases where the signal and masker bandwidths were the same. The results of this experiment showed that the MLDs of children were as large as those of adults when the signal/masker bandwidth was 320 Hz, but were smaller than those of adults when the signal/masker bandwidth was 20 Hz. This indicates that the factor limiting the MLD for narrowband noise in children is related more to the masker bandwidth than to the perceptual similarity between the signal and the masker.