Influence of talker and accent variability on rapid adaptation and generalization to non-native accented speech in younger and older adults.

Introduction: Listeners can rapidly adapt to English speech produced by non-native speakers of English with unfamiliar accents. Prior work has shown that the type and number of talkers contained within a stimulus set may impact rate and magnitude of learning, as well as any generalization of learning. However, findings across the literature have been inconsistent, with relatively little study of these effects in populations of older listeners. Methods: In this study, adaptation and generalization to unfamiliar talkers with familiar and unfamiliar accents are studied in younger normal-hearing adults and older adults with and without hearing loss. Rate and magnitude of adaptation are modelled using both generalized linear mixed effects regression and generalized additive mixed effects modelling. Results: Rate and magnitude of adaptation were not impacted by increasing the number of talkers and/or varying the consistency of non-native English accents across talkers. Increasing the number of talkers did strengthen generalization of learning for a talker with a familiar non-native accent, but not for an unfamiliar accent. Aging alone did not diminish adaptation or generalization. Discussion: These findings support prior evidence of a limited benefit for talker variability in facilitating generalization of learning for non-native accented speech, and extend the findings to older adults.

Hemispheric processing of affective and linguistic intonation contours in normal subjects.

In a previous study of the comprehension of linguistic prosody in brain-damaged subjects, S. R. Grant and W. O. Dingwall (1984. The role of the right hemisphere in processing linguistic prosody, presentation at the Academy of Aphasia, 1984) demonstrated that the right hemisphere (RH) of nonaphasic patients plays a prominent role in the processing of stress and intonation. The present study examines laterality for affective and linguistic prosody using the dichotic listening paradigm. Both types of prosody elicited a significant left ear advantage. This advantage was more pronounced for affective than for linguistic prosody. These findings strongly support previously documented evidence of RH involvement in the processing of affective prosody (R. G. Ley & M. P. Bryden, 1982. A dissociation of right and left hemispheric effects for recognizing emotional tone and verbal content, Brain and Cognition, 1, 3-9). They also provide support for the previously mentioned demonstration of RH involvement in the processing of linguistic intonation (S. Blumstein & W. E. Cooper, 1974. Hemispheric processing of intonation contours, Cortex, 10, 146-158; Grant & Dingwall, 1984).

Selected cognitive factors and speech recognition performance among young and elderly listeners.

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.

Profile of auditory temporal processing in older 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.

Sources of age-related recognition difficulty for time-compressed speech.

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.

Auditory temporal order perception in younger and older adults.

This investigation examined the abilities of younger and older listeners to discriminate and identify temporal order of sounds presented in tonal sequences. It was hypothesized that older listeners would exhibit greater difficulty than younger listeners on both temporal processing tasks, particularly for complex stimulus patterns. It was also anticipated that tone order discrimination would be easier than tone order identification for all listeners. Listeners were younger and older adults with either normal hearing or mild-to-moderate sensorineural hearing losses. Stimuli were temporally contiguous three-tone sequences within a 1/3 octave frequency range centered at 4000 Hz. For the discrimination task, listeners discerned differences between standard and comparison stimulus sequences that varied in tonal temporal order. For the identification task, listeners identified tone order of a single sequence using labels of relative pitch. Older listeners performed more poorly than younger listeners on the discrimination task for the more complex pitch patterns and on the identification task for faster stimulus presentation rates. The results also showed that order discrimination is easier than order identification for all listeners. The effects of hearing loss on the ordering tasks were minimal.

Frequency and temporal resolution in elderly listeners with good and poor word recognition.

There is a subgroup of elderly listeners with hearing loss who can be characterized by exceptionally poor speech understanding. This study examined the hypothesis that the poor speech-understanding performance of some elderly listeners is associated with disproportionate deficits in temporal resolution and frequency resolution, especially for complex signals. Temporal resolution, as measured by gap detection, and frequency resolution, as measured by the critical ratio, were examined in older listeners with normal hearing, older listeners with hearing loss and good speech-recognition performance, and older listeners with hearing loss and poor speech-recognition performance. Listener performance was evaluated for simple and complex stimuli and for tasks of added complexity. In addition, syllable recognition was assessed in quiet and noise. The principal findings were that older listeners with hearing loss and poor word-recognition performance did not perform differently from older listeners with hearing loss and good word recognition on the temporal resolution measures nor on the spectral resolution measures for relatively simple stimuli. However, frequency resolution was compromised for listeners with poor word-recognition abilities when targets were presented in the context of complex signals. Group differences observed for syllable recognition in quiet were eliminated in the noise condition. Taken together, the findings support the hypothesis that unusual deficits in word-recognition performance among elderly listeners were associated with poor spectral resolution for complex signals.

Auditory temporal processing in elderly listeners.

This paper examines the hypothesis that auditory temporal processing is impaired in elderly listeners. Several recent psychoacoustic studies are reviewed that describe various aspects of temporal processing that appear to be influenced by aging. The temporal phenomena range from measures of temporal resolution and duration discrimination to sequential processing of complex stimulus patterns. For many of the research findings, age-related deficits on temporal performance measures are unaffected by the presence of presbyacusic hearing loss. Additionally, the consequences of aging on auditory temporal processing appear to be correlated with the complexity of stimulation and the difficulty of the listening tasks.

Auditory duration discrimination in young and elderly listeners with normal hearing.

This study investigated the effects of age on two parameters of auditory temporal processing: auditory duration discrimination and the backward interference of auditory duration discrimination. Young and elderly listeners with normal hearing sensitivity participated. In experiment I, the just-noticeable difference (JND) in duration between a standard 1000-Hz tone of 40 msec and a comparison tone of longer duration was evaluated using a three-interval forced-choice task. In experiment II, the duration discrimination paradigm was presented with a tonal masker following the tonal stimulus at three delay times: 80 msec, 240 msec, and 720 msec. Age effects were observed on the duration discrimination task with interference but not on the initial duration discrimination task without interference. These results suggest that the time required to process the duration characteristics of acoustic stimuli is prolonged in elderly listeners.

Risk factors related to age-associated hearing loss in the speech frequencies.

This paper examines the relationship between several risk factors and the development of age-associated hearing loss in the speech frequencies. Hearing loss is defined as an average threshold level of 30 dB HL or greater at the frequencies of 0.5, 1, 2, and 3 kHz. Hearing thresholds from 0.5 to 8 kHz using a pulse-tone tracking procedure were collected on participants of the Baltimore Longitudinal study of Aging since 1965. A proportional hazards regression model was used to study the relationship between several risk factors that have previously been found to be associated with numerous health-related outcomes and the length of follow-up time until the occurrence of unilateral or bilateral hearing loss in a screened group of 531 men. Risk factors considered are age, blood pressure, and alcohol and cigarette consumption. After controlling for age, only systolic blood pressure showed a significant relationship with hearing loss in the speech frequencies (p < .05). Since blood pressure is a modifiable risk factor, these results suggest that preventing hypertension might contribute to an effective program for the prevention of apparent age-associated hearing loss.

Effects of aging on response criteria in speech-recognition tasks.

This study examined whether young and elderly listeners exhibit different response criteria on speech-recognition tasks. Young and elderly listeners with normal hearing and with matched mild hearing losses were evaluated on Northwestern University Test No. 6 (Tillman & Carhart, 1966) and the California Consonant Test (Owens & Schubert, 1977) presented at 80 dB SPL and 95 dB SPL. The level of the multitalker babble background was adjusted individually to the signal-to-babble ratio at which the listener achieved 50% criterion performance. Significant differences between the performances of young and elderly listeners were observed on the response bias measure (B) but not on the percent-correct or sensitivity [P(A)] measures. Elderly listeners exhibited less cautious response criteria than did younger listeners. The implications of these results to communication strategies of elderly listeners are discussed.

Recognition of digitized CV syllables in multitalker babble.

Nonsense syllable recognition by 10 normal-hearing listeners was assessed in quiet and three levels of multitalker babble. Stimuli were 19 consonants paired with /a/, /i/, and /u/ in a CV format. Performance measures included total syllable recognition, consonant feature-class recognition, and consonant feature errors. Results of each analysis were strongly affected by vowel coarticulation and noise level. However, a distinctive pattern of performance in the babble was observed. Comparisons are made between this pattern and those obtained previously in other types of noise backgrounds. Implications for clinical evaluation and auditory training are discussed.

Recognition of natural and time/intensity altered CVs by young and elderly subjects with normal hearing.

The purpose of this study was to evaluate the efficiency of three acoustic modifications derived from clear speech for improving consonant recognition by young and elderly normal-hearing subjects. Percent-correct nonsense syllable recognition was measured for four stimulus sets: unmodified stimuli; stimuli with consonant duration increased by 100%; stimuli with consonant-vowel ratio increased by 10 dB; and stimuli with both consonant duration and consonant-vowel ratio increased. Analyses of overall nonsense syllable recognition, consonant feature recognition, and consonant confusion patterns demonstrated that the consonant-vowel ratio increase modification produced better performance than the other acoustic modifications by both subject groups. However, elderly subjects exhibited poorer performance than young subjects in most conditions. These results and their implications are discussed.

Phoneme feature perception in noise by normal-hearing and hearing-impaired subjects.

The purpose of this investigation was to determine whether normal-hearing and hearing-impaired listeners perceive phoneme features differently in noise and to determine whether phoneme perception changes as a function of signal-to-noise ratio (S/N). Consonant-vowel recognition by normal-hearing and hearing-impaired listeners was assessed in quiet and in three noise conditions. Analysis of total percent correct recognition scores revealed significant effects of hearing status, S/N, and vowel context. Patterns of phoneme errors were analyzed by INDSCAL. Derived consonant features that accounted for phoneme errors by both subject groups were similar to ones reported by other investigators. However, weightings associated with the individual features varied with changes in noise condition. Although hearing-impaired listeners exhibited poorer overall nonsense syllable recognition scores in noise than normal-hearing listeners, no specific set of features emerged from the multidimensional scaling procedures that could uniquely account for this performance deficit.

Consonant recognition and confusion patterns among elderly hearing-impaired subjects.

This study investigated whether unique consonant recognition and confusion patterns are associated with hearing loss among elderly listeners. Subjects were all greater than 65 years, and had normal hearing, or gradually or sharply sloping sensorineural hearing losses. Recognition of 19 consonants, paired with each of three vowels in a CV format, was assessed at two speech levels in a background of babble (+6 dB signal-to-babble ratio). Analyses of percent correct scores for overall nonsense syllable performance and for consonants according to place, manner, and voicing categories generally revealed better performance by the normal-hearing subjects than by the hearing-impaired subjects. However, individual differences scaling analysis of consonant confusions failed to retrieve speech perception patterns that were unique to listener group. These results tentatively suggest that the presence and configuration of hearing loss among elderly listeners may affect the level of performance but not the specific pattern of performance.

Age-related differences in speech recognition performance as a function of test format and paradigm.

This study assessed speech recognition performance by young and elderly listeners with normal hearing and mild sensorineural hearing loss on a variety of speech recognition tasks. The tasks varied in terms of presence of noise, stimulus presentation level, test format, and test paradigm. The purpose was to identify a set of test conditions which is sensitive for revealing the effects of age, independent of hearing loss. The results showed that young and elderly listeners usually did not exhibit significant performance differences in quiet or fixed-noise conditions. However, an age effect was observed consistently for all conditions involving an adaptive noise paradigm. These findings imply that the important variables to consider for revealing effects of age are the use of noise coupled with an adaptive paradigm.

Effects of acoustic modification on consonant recognition by elderly hearing-impaired subjects.

In a recent study [S. Gordon-Salant, J. Acoust. Soc. Am. 80, 1599-1607 (1986)], young and elderly normal-hearing listeners demonstrated significant improvements in consonant-vowel (CV) recognition with acoustic modification of the speech signal incorporating increments in the consonant-vowel ratio (CVR). Acoustic modification of consonant duration failed to enhance performance. The present study investigated whether consonant recognition deficits of elderly hearing-impaired listeners would be reduced by these acoustic modifications, as well as by increases in speech level. Performance of elderly hearing-impaired listeners with gradually sloping and sharply sloping sensorineural hearing losses was compared to performance of elderly normal-threshold listeners (reported previously) for recognition of a variety of nonsense syllable stimuli. These stimuli included unmodified CVs, CVs with increases in CVR, CVs with increases in consonant duration, and CVs with increases in both CVR and consonant duration. Stimuli were presented at each of two speech levels with a background of noise. Results obtained from the hearing-impaired listeners agreed with those observed previously from normal-hearing listeners. Differences in performance between the three subject groups as a function of level were observed also.

Effects of reducing low-frequency amplification on consonant perception in quiet and noise.

The aim of this study was to assess the effect of low-frequency amplification on speech recognition performance by hearing-impaired listeners. Consonant identification performance by subjects with flat hearing losses and high-frequency hearing losses was assessed in three different hearing aid conditions, in quiet and noise. The experimental hearing aids all provided extra high-frequency amplification but differed in the amount of low-frequency amplification. The results showed that listeners with flat hearing losses benefited by low-frequency amplification, whereas subjects with high-frequency hearing losses exhibited deteriorating scores in conditions with greatest low-frequency amplification. Analyses of phonetic feature perception and individual consonant recognition scores revealed subtle interactions between hearing loss configuration and amplification contour.