Permanent threshold shift associated with overamplification by hearing aids.

Humes and Jesteadt have proposed that the Modified Power Law (MPL) provides a means of predicting permanent threshold shift (PTS) due to noise exposure in subjects with preexisting sensorineural hearing loss. Data concerning PTS attributed to overamplification by hearing aids in 8 children with severe sensorineural hearing loss were used to evaluate the MPL hypothesis. The excessive amplification was partly due to use by the children of very high volume-control settings instead of mid-range volume-control settings. The PTS tended to be flat across frequency. Its course in time was a miniature version of the time course of PTS that would be induced by a similar noise exposure in a person with normal hearing. It began to occur soon after the start of hearing aid use and its rate of development was slower than that which would occur in a person with normal hearing. The growth of PTS could be predicted from the estimated real ear output levels of the children's hearing aids by means of the MPL combined with the logarithmic equation proposed by Kraak for predicting the effect of noise exposure on hearing.