Psychoacoustic abilities of subjects with unilateral and bilateral cochlear hearing impairments and their relationship to the ability to understand speech.

This paper is concerned with deficits in the ability to distinguish sounds, which accompany hearing loss of cochlear origin, and with the relationship of those deficits to the ability to understand speech in quiet and in background noise. Nine subjects with moderate unilateral cochlear hearing loss and 6 with moderate bilateral cochlear hearing loss took part in a series of psychoacoustic and speech perception tests. The impaired ears showed deficits in several of the psychoacoustic tests, including: detection of temporal gaps in bands of noise; frequency discrimination of pure tones; frequency discrimination of complex tones; and frequency selectivity as measured by the masking of tones by notched noise. The impaired ears showed near-normal performance in the detection of changes in intensity and for detecting temporal gaps in sinusoidal signals. Speech reception thresholds (SRTs--defined as the level of speech required for 50% intelligibility) were measured both in quiet and in speech-shaped noise, and were invariably higher for the impaired than for the normal ears. Correlational analysis, principal-components analysis and multiple-regression analysis were used to explore the relationships between the psychoacoustic measures and the SRTs. The results suggest that SRTs in quiet are determined primarily by absolute thresholds as measured by the pure-tone audiogram. SRTs in noise are related more to supra-threshold discrimination abilities, such as the detection of temporal gaps in noise and the frequency discrimination of pure and complex tones, and to age. Possible clinical applications of the results are briefly discussed.