Test-retest reliability of loudness scaling

Objective: Establish the test-retest reliability of loudness scaling using a bounded category rating method. Design: The individual loudness functions were investigated in three groups of listeners: seven normal-hearing listeners aged 18 to 35 yr, five normal-hearing listeners aged 57 to 84 yr, and five Listeners aged 54 to 82 yr with bilateral sloping sensorineural hearing loss. Test-retest reliability was investigated by determining the intralistener, between-session standard deviation. Results: The pattern of test-retest reliability was similar across all three groups. It improved as the intensity of the stimulus increased: 7 dB at the first quartile of the loudness function, and 3 dB at the third quartile. Two to four runs of the task appear to be sufficient to obtain a stable loudness function, and it was shown that an exponential function provided a better goodness of fit than a linear function (r(2): 0.99 compared with 0.94). Conclusions: Loudness scaling is a longer test than most conventional suprathreshold measures and requires special equipment. However, it has good test-retest reliability and provides more information on the loudness function that might be useful in the fitting of nonlinear hearing aids. The data show that an exponential function provides a good fit to the loudness growth data, and should probably be incorporated into fitting algorithms associated with loudness scaling.