An investigation of temporary threshold shift caused by hearing aid use

Temporary threshold shift (TTS) caused by hearing aid use was measured by Bekesy audiometry in a group of individuals with severe sensorineural hearing loss. The accuracy with which a mathematical model consisting of the Modified Power Law (MPL) (Humes & Jesteadt, 1991) combined with equations for predicting TTS in normal listeners (Mills, Gilbert, & Adkins, 1979) could predict the TTS was evaluated. When the exponent of the MPL was set to 0.15, the predicted TTS was significantly greater than the observed TTS at two out of six frequencies. When the exponent was increased to 0.20, there were no significant differences between the predictions and the observations. With this value of the exponent, the mathematical model was able to predict the observed TTS as accurately as it could be measured. The MPL was used to derive safety limits for TTS, and gain reduction was recommended as the best method of reducing TTS to the safety limits.