Loudness scaling revisited.

The present work was undertaken in an attempt to evaluate whether it is reasonable to expect that categorical loudness scaling can provide useful information for nonlinear hearing aid fitting. Normative data from seven scaling procedures show that the individual procedures relate the perceptual categories differently to sound level and with a substantial between-subject variance. Hearing-impaired data from four studies demonstrate that the inverse slope of the loudness function varies linearly with hearing loss and with a constant variance. In relation to hearing aid fitting, the slope can, in most cases, be predicted from the hearing loss with an accuracy within the range of a normal finetuning. For the fitting of nonlinear hearing aids, the statistical properties of both normal and impaired loudness functions are equally important. The present analysis strongly suggests that categorical loudness scaling cannot, in general, provide significant information for the fitting process.