Using an adaptive strategy, the effects of mild sensorineural hearing loss and adult listeners' chronological age on speech recognition in babble were evaluated. The signal-to-babble ratio required to achieve 50% recognition was measured for three speech materials presented at soft to loud conversational speech levels. Four groups of subjects were tested: (1) normal-hearing listeners less than 44 years of age, (2) subjects less than 44 years old with mild sensorineural hearing loss and excellent speech recognition in quiet, (3) normal-hearing listeners greater than 65 with normal hearing, and (4) subjects greater than 65 years old with mild hearing loss and excellent performance in quiet. Groups 1 and 3, and groups 2 and 4 were matched on the basis of pure-tone thresholds, and thresholds for each of the three speech materials presented in quiet. In addition, groups 1 and 2 were similar in terms of mean age and age range, as were groups 3 and 4. Differences in performance in noise as a function of age were observed for both normal-hearing and hearing-impaired listeners despite equivalent performance in quiet. Subjects with mild hearing loss performed significantly worse than their normal-hearing counterparts. These results and their implications are discussed.

Previous investigations have established that, under identical test conditions, hearing-impaired listeners have more difficulty than normal-hearing listeners understanding speech in noise. Using an adaptive strategy, the effect of mild sensorineural hearing loss on speech recognition in babble was evaluated and the extent of the interaction of mild hearing loss with adult listeners' chronological age was examined. The signal-to-babble ratio required to achieve 50% recognition was measured for three speech materials presented at 56, 72, and 88 dB SPL; likewise, performance without babble was measured. Four sets of subjects (N = 18, each set) were tested: normal-hearing listeners <44 and >65 years of age, and hearing-impaired subjects <44 and >65 years. Subjects were selected so that age-group audiograms were closely matched. For results in babble, a consistent and statistically significant difference was demonstrated between the groups differentiated by age and by hearing loss, while only the latter effect was present in the absence of babble. Significant differences in articulation indices (AIs) between the two age groups were found for results in babble only, while no differences in AIs were seen between the two hearing loss groups under either listening condition. [Work supported by NINCDS.]

The terminology used in studies documenting changes in auditory performance following fitting of hearing aids has been diverse. Definitions for the auditory deprivation effect and auditory acclimatization are offered as a first step in rationalization. Two statements summarize current knowledge concerning auditory deprivation effects and auditory acclimatization, as well as considering the potential implications for research, field trial and clinical practice applications. Potential areas for future research are identified.

The effect of amplitude-modulated (AM) noise on speech recognition in listeners with normal and impaired hearing was investigated in two experiments. In the first experiment, nonsense syllables were presented in high-pass steady-state or AM noise to determine whether the release from masking in AM noise relative to steady-state noise was significantly different between normal-hearing and hearing-impaired subjects when the two groups listened under equivalent masker conditions. The normal-hearing subjects were tested in the experimental noise under two conditions: (a) in a spectrally shaped broadband noise that produced pure tone thresholds equivalent to those of the hearing-impaired subjects, and (b) without the spectrally shaped broadband noise. The release from masking in AM noise was significantly greater for the normal-hearing group than for either the hearing-impaired or masked normal-hearing groups. In the second experiment, normal-hearing and hearing-impaired subjects identified nonsense syllables in isolation and target words in sentences in steady-state or AM noise adjusted to approximate the spectral shape and gain of a hearing aid prescription. The release from masking was significantly less for the subjects with impaired hearing. These data suggest that hearingimpaired listeners obtain less release from masking in AM noise than do normal-hearing listeners even when both the speech and noise are presented at levels that are above threshold over much of the speech frequency range.

A series of five experiments was conducted to investigate the effects of spatial separation of speakers on the intelligibility of spondaic and PB words in noise and the identification of synthetic sentences in noise and competing message. Conditions in which the spatial location of the speakers produced interaural time differences ranked highest in intelligibility. The rank order of other conditions was dependent on the S/N ratio at the monaural near ear. Separations of only 10° between the speech and noise sources resulted in measurable changes in intelligibility. The binaural intelligibility scores were enhanced substantially over the monaural near ear results during conditions where an interaural time difference was present. This result was observed more effectively when spondaic words or sentences were used rather than PB words. The implications of this result were related to the interaural time difference and the frequency range of the critical information in the primary message. Although the initial experiments were facilitated by recording through an artificial head, almost identical results were obtained in the final experiment when subjects were tested in the sound field.