Comparison of three procedures for initial fitting of compression hearing aids. II. Experienced users, fitted unilaterally.

This paper is the second in a series comparing three procedures for the initial fitting of multichannel compression hearing aids. The first paper reported the results for a group of 10 experienced hearing aid users fitted bilaterally. This paper reports the results for a different group of 10 experienced hearing aid users fitted unilaterally. The three procedures were: (1) CAMEQ, which aims to amplify speech so as to give equal loudness per critical band over the frequency range 500-5000 Hz, and to give similar overall loudness to normal over a wide range of speech levels; (2) CAMREST, which aims to amplify speech so as to restore normal specific loudness patterns, over a wide range of speech levels; and (3) DSL [i/o], which aims to map the dynamic range of normal-hearing people into the reduced dynamic range of hearing-impaired people, with full restoration of audibility. Each subject was fitted with one Danalogic 163D digital hearing aid, using each of the three fitting procedures in turn; the order was counter-balanced across subjects. Prescribed insertion gains for 55 and 80 dB SPL input levels were verified using real-ear measurements. Immediately after fitting with a given procedure, and 1 week after fitting. the gains were adjusted, when required, by the minimum amount necessary to achieve acceptable fittings. On average, the adjustments were smallest for the CAMREST procedure, slightly larger for the CAMEQ procedure, and largest of all for DSL [i/o]. For the DSL [i/o] the gain changes were mostly negative, especially for high frequencies and the higher input level. After these gain adjustments, users wore the aids for at least 3 weeks before speech reception thresholds (SRTs) for sentences in quiet and in steady and fluctuating background noise were measured. The APHAB questionnaire was also administered. The hearing aids were then refitted with the next procedure. SRTs and APHAB scores did not differ significantly between the three procedures. We conclude that the CAMEQ and CAMREST procedures provide a more appropriate initial fitting than DSL [i/o] for unilaterally experienced hearing aid wearers. Comparison with our earlier study based on bilateral fittings suggests that the preferred gains are similar for unilateral and bilateral fittings.