Consonant recognition performance was examined in 18 subjects listening in quiet and speech noise with linear and nonlinear hearing aids. Subjects were divided into three groups by audiometric configuration: flat, moderately sloping, and sharply sloping. Nonlinear amplification schemes included adaptive high-pass filtering (Argosy's Manhattan II, experimentally modified; MANe), MANe circuitry followed by expansion (EXP), and infinite amplitude clipping (IAC). Consonant-to-vowel ratios (CVRs) were calculated for syllables processed through each hearing aid. Performance with the IAC was significantly poorer than with the other amplifiers across audiograms in noise. Intersubject variability in performance was high, even within audiogram groups. High-frequency phonemes were more often audible with the EXP than with the other hearing aids for subjects with moderately and severely sloping audiograms. Output CVRs increased for some phonemes with a nonlinear hearing aid versus linear, but recognition of individual phonemes did not correlate significantly with CVR.
Previous research has reported reduced otoacoustic emission amplitude as a function of age. In each study, however, interpretation of findings was confounded by age-related hearing loss. The present study was designed to re-evaluate the contribution of age and peripheral hearing loss on the prevalence and amplitude of distortion-product otoacoustic emissions (DPOAEs) by controlling for degree of peripheral hearing loss. Twenty subjects were divided into four age ranges. All subjects in each group had 15 dB HL or better thresholds from 0.25 through 8 kHz and normal immittance findings. DPOAE audiograms recorded at three intensity levels and input/output functions recorded at six discrete frequencies showed no significant differences in amplitude or noise level between age groups. Findings indicate that when the degree of peripheral hearing loss is adequately controlled, there is no direct effect of advanced age on DPOAE measures. Clinical implications are discussed.
