Individualized frequency importance functions for listeners with sensorineural hearing loss

Abstract

The Speech Intelligibility Index includes a series of frequency importance functions for calculating the estimated intelligibility of speech under various conditions. Until recently, techniques to derive frequency importance required averaging data over a group of listeners, thus hindering the ability to observe individual differences due to factors such as hearing loss. In the current study, the "random combination strategy" [Bosen and Chatterjee (2016). J. Acoust. Soc. Am. 140, 3718-3727] was used to derive frequency importance functions for individual hearing-impaired listeners, and normal-hearing participants for comparison. Functions were measured by filtering sentences to contain only random subsets of frequency bands on each trial, and regressing speech recognition against the presence or absence of bands across trials. Results show that the contribution of each band to speech recognition was inversely proportional to audiometric threshold in that frequency region, likely due to reduced audibility, even though stimuli were shaped to compensate for each individual's hearing loss. The results presented in this paper demonstrate that this method is sensitive to factors that alter the shape of frequency importance functions within individuals with hearing loss, which could be used to characterize the impact of audibility or other factors related to suprathreshold deficits or hearing aid processing strategies.

FIG. 1.

Normalized frequency importance functions for listeners with NH. Each frequency band is represented by a set of horizontal lines denoting the frequency range of that band, and the height of each band representing its importance (plotted on a log-odds scale and normalized by subtracting the mean band importance). Each color represents the frequency importance for an individual participant, and gray regions represent an estimated 95% range (mean +/- two standard deviations) for the group.

FIG. 2.

Normalized frequency importance functions for listeners with HI. Each vertical pair of panels represents an individual's frequency importance function and audiogram. Frequency importance is plotted for each individual in color on top of the 95% range from the NH group, for reference. Thresholds were plotted with blue Xs and red circles for the left and right ears, respectively, and the black line represents the mean threshold across ears.

FIG. 3.

Simple linear regression of individual frequency importance relative to NH mean frequency importance against mean interpolated audiometric threshold for each frequency band, for each listener with HI. Colors represent the same listeners as in Fig. 2.

FIG. 4.

Normalized frequency importance functions for listeners with NH in the spectrally shaped control experiment. The top panel shows frequency importance for seven subjects in this condition as separate bars, and the gray region represents the 95% range of results from NH listeners without spectral shaping shown in Fig. 1. The bottom panel shows the cross-ear average threshold for six listeners that we obtained audiograms from (thin lines), and the typical presbyacusis profile used to generate the spectral profile used to shape the stimuli (thick line).

FIG. 5.

Simple linear regression of individual frequency importance relative to the NH mean frequency importance (as in Fig. 3), plotted against the relative change in sensation level due to audiometric threshold and spectral shaping. Listeners with HI are represented by large points and solid lines in the top panel, and listeners with NH and spectrally shaped stimuli are represented by small points and broken lines in the bottom panel. Colors correspond to the same listeners in Figs. 3 and 4 for the respective groups.