The evaluation of CROS aids with the unilateral listener

The CROS hearing aid, originally designed to assist persons with one normal and one unaidable ear, has according to most reports been of most value when the better ear also requires amplification. The most common complaint from normal-hearing users has been excess noise and masking via the aid. While the problem is obviously complex, one of the major factors, that of in the ear performance, has not been adequately analysed. The amount of gain provided by the CROS system, which is closely related to excess noise and masking, is usually not evaluated. A method of evaluation which reflects the change in CROS-aided threshold values, rather than the more usual above-threshold performance is presented. This procedure, based on masked sound field thresholds, has a number of advantages. An example, using six cases, is presented to illustrate the method and its results.