Predicting the loudness discomfort level from the acoustic reflex threshold and growth function

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The purpose of the present study was to evaluate the relationship between several measures of the acoustic reflex [acoustic reflex threshold (ART), dynamic range of the acoustic reflex growth function, the 50% point along the acoustic reflex growth function, and the maximum intensity value of the acoustic reflex growth function] and behavioral measurements of loudness [loudness discomfort level (LDL) and the loudness contour (LC)]. The underlying objective was to determine if any of these measures can be used to predict the LDL. A finding of a strong relationship between these measures could potentially assist in the creation of an objective method to measure LDLs, which may have implications for hearing aid fittings. Prior research in this area has yielded conflicting results. However, very few studies examined measures of loudness growth and the dynamic range of the acoustic reflex.

Twenty young adults ranging from 22-35 years of age (Mean age = 25.85, s.d. 3.07) with normal hearing participated in this study. Participants were required to provide a subjective loudness rating to warbled-tone stimuli in accordance with a categorical loudness scaling procedure adapted from Cox et al. (1997), as well as an LDL rating. Additionally, an ART was obtained from each participant, as defined by a 0.02 mmho change in admittance. Following identification of the ART, the acoustic reflex growth function was obtained by increasing the stimulus until the termination point. Experimental measures were obtained over two test sessions.

Results revealed no significant relationship between measures of the acoustic reflex and loudness. Analysis of test-retest measures revealed moderate to very high positive (0.70 - 0.92) correlations for the acoustic reflex and LDL measures over a period of 1 day to 2 weeks. Test-retest performance on the majority of loudness categories on the LC did not reveal stable results. Implications for these findings are that the ART cannot be used to reliably predict the LDL. Additionally, the LC may not be a reliable clinical measurement to assess loudness.