Long Term Usage Of A Programmable, Two-Memory Hearing Aid

Gitte Keidser , Rebecca Stephens (Australian Hearing, VIC), and Catherine Bradfield (Australian Hearing, ACT).

National Acoustic Laboratories Annual Report 1996/97

Background
The efficacy of multiple memory hearing aids has mainly been investigated in controlled environments during laboratory experiments and short term field tests of a few weeks to a few months duration. Whereas such studies provide important information about the possible usage and benefit of multiple memory devices, two studies (Kuk, 1992; Keidser, 1994) suggest that they do not necessarily reflect long term usage and benefit of multiple memory hearing aids in everyday life.

Research Question
This study aimed at investigating the usage pattern of a multiple memory hearing aid during 12 months.

Procedure
Nineteen clients, with diverse hearing problems, were randomly selected from two Australian Hearing Services clinics to participate in the study. They were fitted with a remotely controlled, linear, single channel, two-memory hearing aid. All clients were fitted with the NAL response in one memory. The second memory contained a linear frequency response flatter or steeper than the NAL response. In some cases only one of the alternative responses could be fitted to the client. Otherwise, the choice was made based on a paired comparison test using a range of listening conditions. In all, ten clients were fitted with a flatter response, and nine clients were fitted with a steeper response in program two. After one month, four months and twelve months, the subjects were asked to fill in an evaluation form concerning the usage of the two frequency response characteristics. Of the 19 subjects, 5 dropped out before the end of 12 months due to illness, practical problems with the device, and change of hearing. Of the remaining 14 subjects, 11 completed the 12 months field test whereas 3 did not return the last evaluation form. If a client in the evaluation form clearly could identify different situations for which each of the two programs was preferred, it was concluded that this client was a multiple memory user.

Findings
The reports suggested that clients who showed a strong preference for one or two frequency responses during the first four months stood firm by their decision at the end of twelve months. On the other hand, clients who were inconsistent in their preference during the first four months reported usage of only one program at the end of twelve months. The findings suggest that long-term users of multiple memory devices may be predicted from the usage pattern within the four post-fitting months. Further, the reports showed that: 1) the NAL-response was the overall preferred response (with two exceptions), 2) the alternative frequency response was, on average, only used about 20% of the time at anytime during the test period, 3) the alternative frequency response was mainly reported to be beneficial in noisy environments and in crowds, and 4) the remote control was well received by all subjects because it enabled easier and more discreet adjustment of the hearing aid. Finally and unfortunately, those clients who could benefit from a multiple memory hearing aid on a long-term basis, were not identifiable, at the time of fitting, from audiometric or disability related data.

Significance
The study will assist in making the most effective use of multiple-memory hearing aids.

References
Keidser G. 1994. Selecting amplification for different listening conditions. Report No 61, The Acoustic Laboratory, The Technical University of Denmark. Pg:73-76.

Kuk FK. 1992. Evaluation of the efficacy of a multi-memory hearing aid. J.Am.Acad. Audiol 3:338-348.

Table
Multiple memory usage for the nine subjects who returned all three evaluation forms, after one, four, and twelve months.

Clients	1 Month	4 Months	12 Months
2 4 1 2	yes no yes no	yes no no yes	yes no no no