Relationship between Behavioral and Objective Measures of Sound Intensity in Normal-Hearing Listeners and Hearing-Aid Users: A Pilot Study

Abstract

Background: For hearing-impaired individuals, hearing aids are clinically fit according to subjective measures of threshold and loudness. The goal of this study was to evaluate objective measures of loudness perception that might benefit hearing aid fitting. Method: Seventeen adult hearing aid users and 17 normal-hearing adults participated in the study. Outcome measures including categorical loudness scaling, cortical auditory evoked potentials (CAEPs), and pupillometry. Stimuli were 1-kHz tone bursts presented at 40, 60, and 80 dBA. Results: Categorical loudness scaling showed that loudness significantly increased with intensity for all participants (p < 0.05). For CAEPs, high intensity was associated with greater P1, N1, and P2 peak amplitude for all listeners (p < 0.05); a significant but small effect of hearing aid amplification was observed. For all participants, pupillometry showed significant effects of high intensity on pupil dilation (p < 0.05); there was no significant effect of hearing aid amplification. A Focused Principal Component analysis revealed significant correlations between subjective loudness and some of the objective measures. Conclusion: The present data suggest that intensity had a significant impact on loudness perception, CAEPs, and pupil response. The correlations suggest that pupillometry and/or CAEPs may be useful in determining comfortable amplification for hearing aids.

Keywords: cortical auditory evoked potential; hearing aid; loudness perception; objective measures; pupillometry.

Figure 1

Pupillometry paradigm. Progression of the visual stimuli: first a white image was presented for 2 s, followed by a black image for 2 s, followed by a white image for 2 s, followed finally by a gray image, which remained present during the experimental run. A 1-kHz tone burst was presented at an interval of 20–30 s.

Figure 2

Boxplots of loudness ratings for 1-kHz tone bursts at 40, 60, or 80 dBA for the NH group, the HA group (aided), and the HA group (unaided). The boxes show the 25th and 75th percentiles, the error bars show the 10th and 90th percentiles, the filled circles show outliers, the horizontal lines show the median, and the white stars show the mean.

Figure 3

Mean CAEP responses recorded at Cz (top) or for GFP (bottom) with a 1-kHz tone burst presented at 40, 60, or 80 dBA for the NH group and the HA group (aided and unaided).

Figure 4

Peak pupil diameter as a function of time for mean NH group and the HA group (aided and unaided) after a tone burst at 1 kHz with 1 s length (grey shaded).

Figure 5

Boxplots of peak pupil diameter (top) and latency (bottom) in response to 1-kHz tone bursts at 40, 60, or 80 dBA for the NH for the NH group and the HA group with the HA on or off. The boxes show the 25th and 75th percentiles, the error bars show the 10th and 90th percentiles, the filled circles show outliers, the horizontal lines show the median, and the white stars show the mean.

Figure 6

Left panels: FPCA plots of between loudness perception and objective responses to stimuli for the NH and HA groups (HA on or off); the center represents the variable to explain (loudness) and explanatory variables (pupillometry and CAEPs). The circles represent Cz amplitude, the squares represent Cz latency, the up triangles represent GFP amplitude, the down triangles represent GFP latency, the stars represent pupil diameter, and the diamonds represent pupil latency. The green and yellow symbols represent positive and negative correlations between the dependent and explanatory variables, respectively. The explanatory variables within the red circle were significantly correlated with the dependent variable (p < 0.05). Right panels: Correlation matrices among the behavioral and objective measures. The bar to the right of the matrices shows the color coding for the correlation coefficients, ranging from −1 to 1. Within the matrices, the color and size of the circle represents the strength of correlation between two variables.