This study investigated factors that contribute to deficits of elderly listeners in recognizing speech that is degraded by temporal waveform distortion. Young and elderly listeners with normal hearing sensitivity and with mild-to-moderate, sloping sensorineural hearing losses were evaluated. Low-predictability (LP) sentences from the Revised Speech Perception in Noise test (R-SPIN) (Bilger, Nuetzel, Rabinowitz, & Rzeczkowski, 1984) were presented to subjects in undistorted form and in three forms of distortion: time compression, reverberation, and interruption. Percent-correct recognition scores indicated that age and hearing impairment contributed independently to deficits in recognizing all forms of temporally distorted speech. In addition, subjects’ auditory temporal processing abilities were assessed on duration discrimination and gap detection tasks. Canonical correlation procedures showed that some of the suprathreshold temporal processing measures, especially gap duration discrimination, contributed to the ability to recognize reverberant speech. The overall conclusion is that age-related factors other than peripheral hearing loss contribute to diminished speech recognition performance of elderly listeners.

This investigation examined age-related performance differences on a range of speech and nonspeech measures involving temporal manipulation of acoustic signals and variation of stimulus complexity. The goal was to identify a subset of temporally mediated measures that effectively distinguishes the performance patterns of younger and older listeners, with and without hearing loss. The nonspeech measures included duration discrimination for simple tones and gaps, duration discrimination for tones and gaps embedded within complex sequences, and discrimination of temporal order. The speech measures were undistorted speech, time-compressed speech, reverberant speech, and combined time-compressed + reverberant speech. All speech measures were presented both in quiet and in noise. Strong age effects were observed for the nonspeech measures, particularly in the more complex stimulus conditions. Additionally, age effects were observed for all time-compressed speech conditions and some reverberant speech conditions, in both quiet and noise. Effects of hearing loss were observed also for the speech measures only. Discriminant function analysis derived a formula, based on a subset of these measures, for classifying individuals according to temporal performance consistent with age and hearing loss categories. The most important measures to accomplish this goal involved conditions featuring temporal manipulations of complex speech and nonspeech signals.

The influence of selected cognitive factors on age-related changes in speech recognition was examined by measuring the effects of recall task, speech rate, and availability of contextual cues on recognition performance by young and elderly listeners. Stimuli were low and high context sentences from the R-SPIN test presented at normal and slowed speech rates in noise. Response modes were final word recall and sentence recall. The effects of hearing loss and age were examined by comparing performances of young and elderly listeners with normal hearing and young and elderly listeners with hearing loss. Listeners with hearing loss performed more poorly than listeners with normal hearing in nearly every condition. In addition, elderly listeners exhibited poorer performance than younger listeners on the sentence recall task, but not on the word recall task, indicating that added memory demands have a detrimental effect on elderly listeners' performance. Slowing of speech rate did not have a differential effect on performance of young and elderly listeners. All listeners performed well when stimulus contextual cues were available. Taken together, these results support the notion that the performance of elderly listeners with hearing loss is influenced by a combination of auditory processing factors, memory demands, and speech contextual information.

Temporal resolution, estimated by measuring the minimum detectable gap (delta t ms) separating two successive signals, was assessed in five normal-hearing and five cochlear-impaired listeners. The signals were octave-band noises (400-800 Hz, 800-1600 Hz, and 2000-4000 Hz) presented in a background of continuous, broadband notched noise that was applied to eliminate unwanted spectral cues. Temporal resolution in all listeners showed systematic improvement with an increase in octave-band center frequency. Resolution in the hearing-impaired subjects was significantly poorer than normal regardless of whether the comparisons were made at equal sound pressure level or at equal sensation level.

This study investigated age-related differences in sensitivity to temporal cues in modified natural speech sounds. Listeners included young noise-masked subjects, elderly normal-hearing subjects, and elderly hearing-impaired subjects. Four speech continua were presented to listeners, with stimuli from each continuum varying in a single temporal dimension. The acoustic cues varied in separate continua were voice-onset time, vowel duration, silence duration, and transition duration. In separate conditions, the listeners identified the word stimuli, discriminated two stimuli in a same-different paradigm, and discriminated two stimuli in a 3-interval, 2-alternative forced-choice procedure. Results showed age-related differences in the identification function crossover points for the continua that varied in silence duration and transition duration. All listeners demonstrated shorter difference limens (DLs) for the three-interval paradigm than the two-interval paradigm, with older hearing-impaired listeners showing larger DLs than the other listener groups for the silence duration cue. The findings support the general hypothesis that aging can influence the processing of specific temporal cues that are related to consonant manner distinctions.

Temporal gap resolution is measured with Békésy tracking procedure and filtered noise stimuli in the frequency range below 6000 Hz. Stimulus parameters include high-pass and low-pass cutoff frequency, band center frequency, bandwidth in a 2-oct range, and signal level in the low-to-moderate intensity range. The pattern of results indicates that gap resolution improves with an increase in stimulus frequency in a manner that can be described by a linear function with a slope of about 2 ms/oct. This relationship applies to signal levels greater than 25--30 dB SL. A linear trend also describes gap threshold as a function of the empirical critical bandwidth within the same frequency range. Implications of the results for simple functional models of temporal processing are examined.

Older people frequently show poorer recognition of rapid speech or time-compressed speech than younger listeners. The present investigation sought to determine if the age-related problem in recognition of time-compressed speech could be attributed primarily to a decline in the speed of information processing or to a decline in processing brief acoustic cues. The role of the availability of linguistic cues on recognition performance was examined also. Younger and older listeners with normal hearing and with hearing loss participated in the experiments. Stimuli were sentences, linguistic phrases, and strings of random words that were unmodified in duration or were time compressed with uniform time compression or with selective time compression of consonants, vowels, or pauses. Age effects were observed for recognition of unmodified random words, but not for sentences and linguistic phrases. Analysis of difference scores (unmodified speech versus time-compressed speech) showed age effects for time-compressed sentences and phrases. The forms of time compression that were notably difficult for older listeners were uniform time compression and selective time compression of consonants. Indeed, poor performance in recognizing uniformly time-compressed speech was attributed primarily to difficulty in recognizing speech that incorporated selective time compression of consonants. Hearing loss effects were observed also for most of the listening conditions, although these effects were independent of the aging effects. In general, the findings support the notion that the problems of older listeners in recognizing time-compressed speech are associated with difficulty in processing the brief, limited acoustic cues for consonants that are inherent in rapid speech.

This study examined auditory temporal sensitivity in young adult and elderly listeners using psychophysical tasks that measured duration discrimination. Listeners in the experiments were divided into groups of young and elderly subjects with normal hearing sensitivity and with mild-to-moderate sloping sensorineural hearing loss. Temporal thresholds in all tasks were measured with an adaptive forced-choice procedure using tonal stimuli centered at 500 Hz and 4000 Hz. Difference limens for duration were measured for tone bursts (250 msec reference duration) and for silent intervals between tone bursts (250 msec and 6.4 msec reference durations). Results showed that the elderly listeners exhibited diminished duration discrimination for both tones and silent intervals when the reference duration was 250 msec. Hearing loss did not affect these results. Discrimination of the brief temporal gap (6.4 msec) was influenced by age and hearing loss, but these effects were not consistent across all listeners. Effects of stimulus frequency were not evident for most of the duration discrimination conditions.