Modern digital hearing aids use advanced signal processing schemes. Because these schemes are new and precise details are often confidential, generic fitting procedures for them are not currently available. In daily practice the fitting of these new processing schemes is therefore strongly dependent on the experience of the audiologist.
One of the HearCom activities taking place at the Amsterdam Medical Centre (AMC) is the development of a novel and generic fitting procedure for the adjustment of aids that does not depend on knowledge of the signal processing used by a particular aid. The new method takes into account the preference of the hearing-aid user. The user has to compare carefully selected pairs of different hearing-aid settings, and to choose the one that sounds better. The user's preferences are interpreted by a set of mathematical rules (known as a simplex optimization) that efficiently chooses aid settings for the next comparison, and eventually finds the optimal hearing-aid setting.
The novel aspect of our approach is to ensure that the pairs of sounds presented to the listener can be distinguished and that every quality judgement collected is thus meaningful.
The method involves two steps. The first step is a discrimination task: Three sounds are presented one of which differs from the other two. The listener must choose the sound that differs ('odd-ball paradigm'). If listener does not hear the difference, the second step will be skipped. If the difference is detected, the listener is then asked if the selected sound sample is preferred over the other two: “Did you prefer this sound sample? Yes, No, Equal”.
The figure shows the computer screen that is presented to the participants