3.4. Evaluation with modulated interferer
3.4.2. Results
2 kHz, and 3 kHz for the mid frequency component, and 4 kHz, 6 kHz, and 8 kHz for the high frequency component.
Statistical Analysis
The statistical significance of the measured effects was analysed by means of an ANOVA of the observed SRTs, which was performed separately for normal-hearing and hearing-impaired subjects. The significance level was always 5 %. The parameters for the ANOVA of the normal-hearing subjects’ data were the room condition, the spatial setup, and the noise type. Post-hoc comparisons of single parameter values were performed with Bonferroni corrections for multiple comparison. For the hearing-impaired subjects, the groups given in Table 3.3 were included as an additional parameter.
3.4. Evaluation with modulated interferer
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FIG. 3.2. SRTs of the normal hearing (NH) subjects, observed (filled symbols, dashed lines) and predicted (open symbols, solid lines) data. The observed SRTs are shown as mean with interindividual standard deviations. The panels are arranged in columns per room and rows per noise type. The data for stationary noise is replotted (dotted lines) in the respective panels for babble and single talker noise for comparison.
but it is non-significant between babble noise and stationary noise. With increasing reverberation time, the difference between the SRTs for S0N0 in single-talker noise and stationary noise decreases and becomes non-significant in the church condition, i.e. the effect of noise modulation is reduced by the reverberation. The difference between the SRTs for S0N0 in babble noise and stationary noise are never significant in any room.
FIG. 3.3. (right page) Observed SRTs of individual hearing-impaired subjects (small filled symbols), corresponding individual predicted SRTs (open symbols), and mean and standard deviation of the normal hearing subjects’ observed SRTs (large filled circles and dotted lines).
The panels are arranged in columns per room and rows per noise type. The symbols of the hearing-impaired subjects correspond with their group in Tab. 3.3 (I: circle, II: left-pointing triangles, III: square, IV: diamonds, V: right-pointing triangle).
The effect of noise source location, that is the difference between SRTs in the S0N0
condition and the other conditions, differs between noise types and is largest for the babble noise and the S0N105 situations. It decreases generally between the anechoic room condition and all other three rooms, but no clear dependence on reverberation time is seen in the non-anechoic rooms on the effect of noise source location.
Hearing-Impaired Subjects
Figure 3.3 shows the individual observed SRTs of the hearing-impaired (HI) subjects (small filled symbols) and the mean observed SRTs of the normal-hearing subjects (large filled circles and dashed lines with interindividual standard deviation). A general trend of higher SRTs with increasing severity of the hearing loss (i.e., increasing group number) can be found, but the intra-group variance is in the same order of magnitude as the inter-group variance so that a larger number of subjects per group would be necessary in order to find significant correlations between subject group and results.
In the anechoic/S0N0 condition, the SRTs are not more than 3 dB higher than the SRTs of the normal-hearing subjects for most HI subjects. But for the other interferer locations, the difference in SRT relative to the S0N0 condition is considerably smaller than for normal-hearing subjects for some of the HI subjects, especially in anechoic conditions and stationary noise. In contrast to the stationary noise, both modulated
3.4. Evaluation with modulated interferer
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FIG. 3.4. Scatter plots of the observed SRTs versus the predicted SRTs. Mean normal-hearing data are denoted with filled circles and lines for minimum and maximum individual SRTs, individual hearing-impaired data are denoted with open symbols. All parameter combinations are included in the plots. Each panel contains the data for one noise type. The symbols of the hearing-impaired subjects correspond with their group in Tab. 3.3 (I: circle, II: left-pointing triangles, III: square, IV: diamonds, V: right-pointing triangle).
noises, babble and single-talker, differentiate more between the individual HI subjects, which can be seen especially in anechoic conditions and single-talker noise. This is in line with the findings of Wagener and Brand (2006). Strong reverberation, like in the church conditions, reduces the noise modulation depth and thus this differentiating effect.
Model Predictions
Figure 3.2 shows the predicted SRTs for the NH subjects (open circles, solid lines).
Error bars are not shown, because there is no difference in the model predictions between individual NH subjects despite small differences in the audiograms of the NH subjects. The prediction error (i.e., the absolute difference between predicted and observed SRTs) is very small for the anechoic room condition and stationary
3.4. Evaluation with modulated interferer
and single-talker noise types. The predictions for the babble noise exhibit an overall prediction error and the predicted SRTs are always too low. Additionally, there is a room-dependent prediction error in all situations and for all noise types. The effect of spatial unmasking is nevertheless predicted quite well by the model, if the room-and noise-type-dependent prediction error is removed, that is if the predicted SRTs are shifted to match the S0N0 condition in each panel separately. Possible reasons for these prediction errors are discussed below.
Figure 3.3 shows the individual predicted SRTs for the HI subjects (open symbols).
The general trend of higher SRTs with increasing severity of the hearing loss is reflected in the predictions. In anechoic conditions, the absolute predicted SRTs are very close to the observed SRTs, but especially in the church conditions, there is a large difference between predicted and observed SRTs, an indication for particular detriment in strong reverberation not included in the model predictions, which are only based on the audiogram.
Figure 3.4 shows scatter plots of the observed SRTs versus the predicted SRTs. Filled symbols denote mean NH data, minimum and maximum of individual NH data are denoted by the error bars, and open symbols denote individual HI data. The symbols of the hearing-impaired subjects correspond with their group in Tab. 3.3 (I: circle, II: left-pointing triangles, III: square, IV: diamonds, V: right-pointing triangle). The noise-type-dependent prediction error can be observed as a parallel shift of the data points away from the unity line. There is a remaining variance in the HI data which can not be explained by the model so far, shown by the spread of data points around the unity line. This variance is slightly larger than the residual variance of the NH data that is not related with the pure tone audiogram.
In Table 3.4, the correlation coefficients for different subsets of the data are
summa-TABLE 3.4. Correlation coefficients between predicted and observed SRTs for different subsets of the data. For “Mean NH”, the normal-hearing data was averaged across subjects before calculation of the correlation.
all noise types stationary babble single-talker
All subjects 0.88 0.80 0.92 0.93
Mean NH 0.88 0.86 0.92 0.96
Individual NH 0.84 0.80 0.86 0.91
Individual HI 0.72 0.59 0.77 0.80
rized. They correspond with the scatter plots in Figure 3.4. The leftmost column in Table 3.4 combines all plots.