Spectral degradation and carrier sentences increase age-related temporal processing deficits in a cue-specific manner.

Advancing age is associated with decreased sensitivity to temporal cues in word segments, particularly when target words follow non-informative carrier sentences or are spectrally degraded (e.g., vocoded to simulate cochlear-implant stimulation). This study investigated whether age, carrier sentences, and spectral degradation interacted to cause undue difficulty in processing speech temporal cues. Younger and older adults with normal hearing performed phonemic categorization tasks on two continua: a Buy/Pie contrast with voice onset time changes for the word-initial stop and a Dish/Ditch contrast with silent interval changes preceding the word-final fricative. Target words were presented in isolation or after non-informative carrier sentences, and were unprocessed or degraded via sinewave vocoding (2, 4, and 8 channels). Older listeners exhibited reduced sensitivity to both temporal cues compared to younger listeners. For the Buy/Pie contrast, age, carrier sentence, and spectral degradation interacted such that the largest age effects were seen for unprocessed words in the carrier sentence condition. This pattern differed from the Dish/Ditch contrast, where reducing spectral resolution exaggerated age effects, but introducing carrier sentences largely left the patterns unchanged. These results suggest that certain temporal cues are particularly susceptible to aging when placed in sentences, likely contributing to the difficulties of older cochlear-implant users in everyday environments.

Semantic context and stimulus variability independently affect rapid adaptation to non-native English speech in young adults.

When speech is degraded or challenging to recognize, young adult listeners with normal hearing are able to quickly adapt, improving their recognition of the speech over a short period of time. This rapid adaptation is robust, but the factors influencing rate, magnitude, and generalization of improvement have not been fully described. Two factors of interest are lexico-semantic information and talker and accent variability; lexico-semantic information promotes perceptual learning for acoustically ambiguous speech, while talker and accent variability are beneficial for generalization of learning. In the present study, rate and magnitude of adaptation were measured for speech varying in level of semantic context, and in the type and number of talkers. Generalization of learning to an unfamiliar talker was also assessed. Results indicate that rate of rapid adaptation was slowed for semantically anomalous sentences, as compared to semantically intact or topic-grouped sentences; however, generalization was seen in the anomalous conditions. Magnitude of adaptation was greater for non-native as compared to native talker conditions, with no difference between single and multiple non-native talker conditions. These findings indicate that the previously documented benefit of lexical information in supporting rapid adaptation is not enhanced by the addition of supra-sentence context.

Effects of aging and hearing loss on perceptual and electrophysiological measures of pulse-rate discrimination.

Auditory temporal processing declines with age, leading to potential deleterious effects on communication. In young normal-hearing listeners, perceptual rate discrimination is rate limited around 300 Hz. It is not known whether this rate limitation is similar in older listeners with hearing loss. The purpose of this study was to investigate age- and hearing-loss-related rate limitations on perceptual rate discrimination, and age- and hearing-loss-related effects on neural representation of these stimuli. Younger normal-hearing, older normal-hearing, and older hearing-impaired listeners performed a pulse-rate discrimination task at rates of 100, 200, 300, and 400 Hz. Neural phase locking was assessed using the auditory steady-state response. Finally, a battery of non-auditory cognitive tests was administered. Younger listeners had better rate discrimination, higher phase locking, and higher cognitive scores compared to both groups of older listeners. Aging, but not hearing loss, diminished neural-rate encoding and perceptual performance; however, there was no relationship between the perceptual and neural measures. Higher cognitive scores were correlated with improved perceptual performance, but not with neural phase locking. This study shows that aging, rather than hearing loss, may be a stronger contributor to poorer temporal processing, and cognitive factors such as processing speed and inhibitory control may be related to these declines.

Younger and older adults show non-linear, stimulus-dependent performance during early stages of auditory training for non-native English.

Older adults often report difficulty understanding speech produced by non-native talkers. These listeners can achieve rapid adaptation to non-native speech, but few studies have assessed auditory training protocols to improve non-native speech recognition in older adults. In this study, a word-level training paradigm was employed, targeting improved recognition of Spanish-accented English. Younger and older adults were trained on Spanish-accented monosyllabic word pairs containing four phonemic contrasts (initial s/z, initial f/v, final b/p, final d/t) produced in English by multiple male native Spanish speakers. Listeners completed pre-testing, training, and post-testing over two sessions. Statistical methods, such as growth curve modeling and generalized additive mixed models, were employed to describe the patterns of rapid adaptation and how they varied between listener groups and phonemic contrasts. While the training protocol failed to elicit post-test improvements for recognition of Spanish-accented speech, examination of listeners' performance during the pre-testing period showed patterns of rapid adaptation that differed, depending on the nature of the phonemes to be learned and the listener group. Normal-hearing younger and older adults showed a faster rate of adaptation for non-native stimuli that were more nativelike in their productions, while older adults with hearing impairment did not realize this benefit.

The cafeteria study: Effects of facial masks, hearing protection, and real-world noise on speech recognition.

The objective of this study was to evaluate the impact of wearing various types of personal protective equipment on speech recognition in a real-world, noisy listening environment. Groups of four young, normal-hearing adults participated in a live version of the Modified Rhyme Test in a noisy public cafeteria with and without the use of a non-medical disposable facial mask or combat earplugs in two different modes. Speech recognition, response time, and subjective difficulty were measured per individual. In addition, the signal-to-noise ratio was estimated during the interval when the talker spoke the target word. Results showed that the listeners' speech recognition performance declined not only when the listener wore earplugs, but also when the talker wore earplugs. The measured signal-to-noise ratio significantly decreased when the talker wore earplugs, suggesting that occlusion may have caused the talkers to reduce their voice levels. Results also showed a decline in speech recognition performance when the talker wore a facial mask. Listeners rated all conditions in which talkers and listeners wore personal protective equipment as more difficult than the baseline condition. These data suggest that speech recognition in real-world listening environments can be impaired by personal protective equipment worn by both talkers and listeners.

Spectral-Temporal Trade-Off in Vocoded Sentence Recognition: Effects of Age, Hearing Thresholds, and Working Memory.

OBJECTIVES: Cochlear implant (CI) signal processing degrades the spectral components of speech. This requires CI users to rely primarily on temporal cues, specifically, amplitude modulations within the temporal envelope, to recognize speech. Auditory temporal processing ability for envelope modulations worsens with advancing age, which may put older CI users at a disadvantage compared with younger users. To evaluate how potential age-related limitations for processing temporal envelope modulations impact spectrally degraded sentence recognition, noise-vocoded sentences were presented to younger and older normal-hearing listeners in quiet. Envelope modulation rates were varied from 10 to 500 Hz by adjusting the low-pass filter cutoff frequency (LPF). The goal of this study was to evaluate if age impacts recognition of noise-vocoded speech and if this age-related limitation existed for a specific range of envelope modulation rates. DESIGN: Noise-vocoded sentence recognition in quiet was measured as a function of number of spectral channels (4, 6, 8, and 12 channels) and LPF (10, 20, 50, 75, 150, 375, and 500 Hz) in 15 younger normal-hearing listeners and 15 older near-normal-hearing listeners. Hearing thresholds and working memory were assessed to determine the extent to which these factors were related to recognition of noise-vocoded sentences. RESULTS: Younger listeners achieved significantly higher sentence recognition scores than older listeners overall. Performance improved in both groups as the number of spectral channels and LPF increased. As the number of spectral channels increased, the differences in sentence recognition scores between groups decreased. A spectral-temporal trade-off was observed in both groups in which performance in the 8- and 12-channel conditions plateaued with lower-frequency amplitude modulations compared with the 4- and 6-channel conditions. There was no interaction between age group and LPF, suggesting that both groups obtained similar improvements in performance with increasing LPF. The lack of an interaction between age and LPF may be due to the nature of the task of recognizing sentences in quiet. Audiometric thresholds were the only significant predictor of vocoded sentence recognition. Although performance on the working memory task declined with advancing age, working memory scores did not predict sentence recognition. CONCLUSIONS: Younger listeners outperformed older listeners for recognizing noise-vocoded sentences in quiet. The negative impact of age was reduced when ample spectral information was available. Age-related limitations for recognizing vocoded sentences were not affected by the temporal envelope modulation rate of the signal, but instead, appear to be related to a generalized task limitation or to reduced audibility of the signal.

Recognition of Accented Speech by Cochlear-Implant Listeners: Benefit of Audiovisual Cues.

OBJECTIVES: When auditory and visual speech information are presented together, listeners obtain an audiovisual (AV) benefit or a speech understanding improvement compared with auditory-only (AO) or visual-only (VO) presentations. Cochlear-implant (CI) listeners, who receive degraded speech input and therefore understand speech using primarily temporal information, seem to readily use visual cues and can achieve a larger AV benefit than normal-hearing (NH) listeners. It is unclear, however, if the AV benefit remains relatively large for CI listeners when trying to understand foreign-accented speech when compared with unaccented speech. Accented speech can introduce changes to temporal auditory cues and visual cues, which could decrease the usefulness of AV information. Furthermore, we sought to determine if the AV benefit was relatively larger in CI compared with NH listeners for both unaccented and accented speech. DESIGN: AV benefit was investigated for unaccented and Spanish-accented speech by presenting English sentences in AO, VO, and AV conditions to 15 CI and 15 age- and performance-matched NH listeners. Performance matching between NH and CI listeners was achieved by varying the number of channels of a noise vocoder for the NH listeners. Because of the differences in age and hearing history of the CI listeners, the effects of listener-related variables on speech understanding performance and AV benefit were also examined. RESULTS: AV benefit was observed for both unaccented and accented conditions and for both CI and NH listeners. The two groups showed similar performance for the AO and AV conditions, and the normalized AV benefit was relatively smaller for the accented than the unaccented conditions. In the CI listeners, older age was associated with significantly poorer performance with the accented speaker compared with the unaccented speaker. The negative impact of age was somewhat reduced by a significant improvement in performance with access to AV information. CONCLUSIONS: When auditory speech information is degraded by CI sound processing, visual cues can be used to improve speech understanding, even in the presence of a Spanish accent. The AV benefit of the CI listeners closely matched that of the NH listeners presented with vocoded speech, which was unexpected given that CI listeners appear to rely more on visual information to communicate. This result is perhaps due to the one-to-one age and performance matching of the listeners. While aging decreased CI listener performance with the accented speaker, access to visual cues boosted performance and could partially overcome the age-related speech understanding deficits for the older CI listeners.

Objective Assessment of Speech Intelligibility in Crowded Public Spaces.

The objective of this study was to obtain a normative database of speech intelligibility data for young normal-hearing listeners communicating in public spaces. A total of 174 listeners participated in an interactive speech intelligibility task that required four-person groups to conduct a live version of the Modified Rhyme Test in noisy public spaces. The public spaces tested included a college library, a college cafeteria, a casual dining restaurant during lunch hour, and a crowded bar during happy hour. At the start of each trial, one of the participants was randomly selected as the talker, and a tablet computer was used to prompt them to say a word aloud from the Modified Rhyme Test. Then, the other three participants were required to select this word from one of six rhyming alternatives displayed on three other tablet computers. The tablet computers were also used to record the SPL at each listener location during and after the interval where the target talker was speaking. These SPL measurements were used to estimate the signal-to-noise ratio (SNR) in each trial of the experiment. As expected, the results show that speech intelligibility decreases, response time increases, and perceived difficulty increases as the background noise level increases. There was also a systematic decrease in SNR with increasing background noise, with SNR decreasing 0.44 dB for every 1 dB increase in ambient noise level above 60 dB. Overall, the results of this study have demonstrated how low-cost tablet computer-based data collection systems can be used to collect live-talker speech intelligibility data in real-world environments. We believe these techniques could be adapted for use in future studies focused on obtaining ecologically valid assessments of the effects of age, hearing impairment, amplification, and other factors on speech intelligibility performance in real-world environments.

Effect of Stimulation Rate on Speech Understanding in Older Cochlear-Implant Users.

OBJECTIVES: Cochlear implants (CIs) are considered a safe and effective intervention for more severe degrees of hearing loss in adults of all ages. Although older CI users ≥65 years of age can obtain large benefits in speech understanding from a CI, there is a growing body of literature suggesting that older CI users may not perform as well as younger CI users. One reason for this potential age-related limitation could be that default CI stimulation settings are not optimal for older CI users. The goal of this study was to determine whether improvements in speech understanding were possible when CI users were programmed with nondefault stimulation rates and to determine whether lower-than-default stimulation rates improved older CI users' speech understanding. DESIGN: Sentence recognition was measured acutely using different stimulation rates in 37 CI users ranging in age from 22 to 87 years. Maps were created using rates of 500, 720, 900, and 1200 pulses per second (pps) for each subject. An additional map using a rate higher than 1200 pps was also created for individuals who used a higher rate in their clinical processors. Thus, the clinical rate of each subject was also tested, including non-default rates above 1200 pps for Cochlear users and higher rates consistent with the manufacturer defaults for subjects implanted with Advanced Bionics and Med-El devices. Speech understanding performance was evaluated at each stimulation rate using AzBio and Perceptually Robust English Sentence Test Open-set (PRESTO) sentence materials tested in quiet and in noise. RESULTS: For Cochlear-brand users, speech understanding performance using non-default rates was slightly poorer when compared with the default rate (900 pps). However, this effect was offset somewhat by age, in which older subjects were able to maintain comparable performance using a 500-pps map compared with the default rate map when listening to the more difficult PRESTO sentence material. Advanced Bionics and Med-El users showed modest improvements in their overall performance using 720 pps compared with the default rate (>1200 pps). On the individual-subject level, 10 subjects (11 ears) showed a significant effect of stimulation rate, with 8 of those ears performing best with a lower-than-default rate. CONCLUSIONS: Results suggest that default stimulation rates are likely sufficient for many CI users, but some CI users at any age can benefit from a lower-than-default rate. Future work that provides experience with novel rates in everyday life has the potential to identify more individuals whose performance could be improved with changes to stimulation rate.

Sentence perception in noise by hearing-aid users predicted by syllable-constituent perception and the use of context.

Masked sentence perception by hearing-aid users is strongly correlated with three variables: (1) the ability to hear phonetic details as estimated by the identification of syllable constituents in quiet or in noise; (2) the ability to use situational context that is extrinsic to the speech signal; and (3) the ability to use inherent context provided by the speech signal itself. This approach is called "the syllable-constituent, contextual theory of speech perception" and is supported by the performance of 57 hearing-aid users in the identification of 109 syllable constituents presented in a background of 12-talker babble and the identification of words in naturally spoken sentences presented in the same babble. A simple mathematical model, inspired in large part by Boothroyd and Nittrouer [(1988). J. Acoust. Soc. Am. 84, 101-114] and Fletcher [Allen (1996) J. Acoust. Soc. Am. 99, 1825-1834], predicts sentence perception from listeners' abilities to recognize isolated syllable constituents and to benefit from context. When the identification accuracy of syllable constituents is greater than about 55%, individual differences in context utilization play a minor role in determining the sentence scores. As syllable-constituent scores fall below 55%, individual differences in context utilization play an increasingly greater role in determining sentence scores. Implications for hearing-aid design goals and fitting procedures are discussed.

Effects of listener age and native language on perception of accented and unaccented sentences.

Degradations to auditory input have deleterious effects on speech recognition performance, especially by older listeners. Alterations to timing information in speech, such as occurs in rapid or foreign-accented speech, can be particularly difficult for older people to resolve. It is currently unclear how prior language experience modulates performance with temporally altered sentence-length speech utterances. The principal hypothesis is that prior experience with a foreign language affords an advantage for recognition of accented English when the talker and listener share the same native language, which may minimize age-related differences in performance with temporally altered speech. A secondary hypothesis is that native language experience with a syllable-timed language (Spanish) is advantageous for recognizing rapid English speech. Native speakers of English and Spanish completed speech recognition tasks with both accented and unaccented English sentences presented in various degrees of time compression (TC). Native English listeners showed higher or equivalent recognition of accented and unaccented English speech compared to native Spanish listeners in all TC conditions. Additionally, significant effects of aging were seen for native Spanish listeners on all tasks. Overall, the results did not support the hypotheses for a benefit of shared language experience for non-native speakers of English, particularly older native Spanish listeners.

Age-Related Differences in the Processing of Temporal Envelope and Spectral Cues in a Speech Segment.

OBJECTIVES: As people age, they experience reduced temporal processing abilities. This results in poorer ability to understand speech, particularly for degraded input signals. Cochlear implants (CIs) convey speech information via the temporal envelopes of a spectrally degraded input signal. Because there is an increasing number of older CI users, there is a need to understand how temporal processing changes with age. Therefore, the goal of this study was to quantify age-related reduction in temporal processing abilities when attempting to discriminate words based on temporal envelope information from spectrally degraded signals. DESIGN: Younger normal-hearing (YNH) and older normal-hearing (ONH) participants were presented a continuum of speech tokens that varied in silence duration between phonemes (0 to 60 ms in 10-ms steps), and were asked to identify whether the stimulus was perceived more as the word "dish" or "ditch." Stimuli were vocoded using tonal carriers. The number of channels (1, 2, 4, 8, 16, and unprocessed) and temporal envelope low-pass filter cutoff frequency (50 and 400 Hz) were systematically varied. RESULTS: For the unprocessed conditions, the YNH participants perceived the word ditch for smaller silence durations than the ONH participants, indicating that aging affects temporal processing abilities. There was no difference in performance between the unprocessed and 16-channel, 400-Hz vocoded stimuli. Decreasing the number of spectral channels caused decreased ability to distinguish dish and ditch. Decreasing the envelope cutoff frequency also caused decreased ability to distinguish dish and ditch. The overall pattern of results revealed that reductions in spectral and temporal information had a relatively larger effect on the ONH participants compared with the YNH participants. CONCLUSIONS: Aging reduces the ability to utilize brief temporal cues in speech segments. Reducing spectral information-as occurs in a channel vocoder and in CI speech processing strategies-forces participants to use temporal envelope information; however, older participants are less capable of utilizing this information. These results suggest that providing as much spectral and temporal speech information as possible would benefit older CI users relatively more than younger CI users. In addition, the present findings help set expectations of clinical outcomes for speech understanding performance by adult CI users as a function of age.

Adaptation to novel foreign-accented speech and retention of benefit following training: Influence of aging and hearing loss.

Adaptation to speech with a foreign accent is possible through prior exposure to talkers with that same accent. For young listeners with normal hearing, short term, accent-independent adaptation to a novel foreign accent is also facilitated through exposure training with multiple foreign accents. In the present study, accent-independent adaptation is examined in younger and older listeners with normal hearing and older listeners with hearing loss. Retention of training benefit is additionally explored. Stimuli for testing and training were HINT sentences recorded by talkers with nine distinctly different accents. Following two training sessions, all listener groups showed a similar increase in speech perception for a novel foreign accent. While no group retained this benefit at one week post-training, results of a secondary reaction time task revealed a decrease in reaction time following training, suggesting reduced listening effort. Examination of listeners' cognitive skills reveals a positive relationship between working memory and speech recognition ability. The present findings indicate that, while this no-feedback training paradigm for foreign-accented English is successful in promoting short term adaptation for listeners, this paradigm is not sufficient in facilitation of perceptual learning with lasting benefits for younger or older listeners.

The effect of visual distraction on auditory-visual speech perception by younger and older listeners.

Visual distractions are present in real-world listening environments, such as conversing in a crowded restaurant. This study examined the impact of visual distractors on younger and older adults' ability to understand auditory-visual (AV) speech in noise. AV speech stimuli were presented with one competing talker and with three different types of visual distractors. SNR50 thresholds for both listener groups were affected by visual distraction; the poorest performance for both groups was the AV + Video condition, and differences across groups were noted for some conditions. These findings suggest that older adults may be more susceptible to irrelevant auditory and visual competition in a real-world environment.

Recognition of asynchronous auditory-visual speech by younger and older listeners: A preliminary study.

This study examined the effects of age and hearing loss on recognition of speech presented when the auditory and visual speech information was misaligned in time (i.e., asynchronous). Prior research suggests that older listeners are less sensitive than younger listeners in detecting the presence of asynchronous speech for auditory-lead conditions, but recognition of speech in auditory-lead conditions has not yet been examined. Recognition performance was assessed for sentences and words presented in the auditory-visual modalities with varying degrees of auditory lead and lag. Detection of auditory-visual asynchrony for sentences was assessed to verify that listeners detected these asynchronies. The listeners were younger and older normal-hearing adults and older hearing-impaired adults. Older listeners (regardless of hearing status) exhibited a significant decline in performance in auditory-lead conditions relative to visual lead, unlike younger listeners whose recognition performance was relatively stable across asynchronies. Recognition performance was not correlated with asynchrony detection. However, one of the two cognitive measures assessed, processing speed, was identified in multiple regression analyses as contributing significantly to the variance in auditory-visual speech recognition scores. The findings indicate that, particularly in auditory-lead conditions, listener age has an impact on the ability to recognize asynchronous auditory-visual speech signals.

Syllable-constituent perception by hearing-aid users: Common factors in quiet and noise.

The abilities of 59 adult hearing-aid users to hear phonetic details were assessed by measuring their abilities to identify syllable constituents in quiet and in differing levels of noise (12-talker babble) while wearing their aids. The set of sounds consisted of 109 frequently occurring syllable constituents (45 onsets, 28 nuclei, and 36 codas) spoken in varied phonetic contexts by eight talkers. In nominal quiet, a speech-to-noise ratio (SNR) of 40 dB, scores of individual listeners ranged from about 23% to 85% correct. Averaged over the range of SNRs commonly encountered in noisy situations, scores of individual listeners ranged from about 10% to 71% correct. The scores in quiet and in noise were very strongly correlated, R = 0.96. This high correlation implies that common factors play primary roles in the perception of phonetic details in quiet and in noise. Otherwise said, hearing-aid users' problems perceiving phonetic details in noise appear to be tied to their problems perceiving phonetic details in quiet and vice versa.

Effects of Age and Working Memory Capacity on Speech Recognition Performance in Noise Among Listeners With Normal Hearing.

OBJECTIVES: This study aimed to determine if younger and older listeners with normal hearing who differ on working memory span perform differently on speech recognition tests in noise. Older adults typically exhibit poorer speech recognition scores in noise than younger adults, which is attributed primarily to poorer hearing sensitivity and more limited working memory capacity in older than younger adults. Previous studies typically tested older listeners with poorer hearing sensitivity and shorter working memory spans than younger listeners, making it difficult to discern the importance of working memory capacity on speech recognition. This investigation controlled for hearing sensitivity and compared speech recognition performance in noise by younger and older listeners who were subdivided into high and low working memory groups. Performance patterns were compared for different speech materials to assess whether or not the effect of working memory capacity varies with the demands of the specific speech test. The authors hypothesized that (1) normal-hearing listeners with low working memory span would exhibit poorer speech recognition performance in noise than those with high working memory span; (2) older listeners with normal hearing would show poorer speech recognition scores than younger listeners with normal hearing, when the two age groups were matched for working memory span; and (3) an interaction between age and working memory would be observed for speech materials that provide contextual cues. DESIGN: Twenty-eight older (61 to 75 years) and 25 younger (18 to 25 years) normal-hearing listeners were assigned to groups based on age and working memory status. Northwestern University Auditory Test No. 6 words and Institute of Electrical and Electronics Engineers sentences were presented in noise using an adaptive procedure to measure the signal-to-noise ratio corresponding to 50% correct performance. Cognitive ability was evaluated with two tests of working memory (Listening Span Test and Reading Span Test) and two tests of processing speed (Paced Auditory Serial Addition Test and The Letter Digit Substitution Test). RESULTS: Significant effects of age and working memory capacity were observed on the speech recognition measures in noise, but these effects were mediated somewhat by the speech signal. Specifically, main effects of age and working memory were revealed for both words and sentences, but the interaction between the two was significant for sentences only. For these materials, effects of age were observed for listeners in the low working memory groups only. Although all cognitive measures were significantly correlated with speech recognition in noise, working memory span was the most important variable accounting for speech recognition performance. CONCLUSIONS: The results indicate that older adults with high working memory capacity are able to capitalize on contextual cues and perform as well as young listeners with high working memory capacity for sentence recognition. The data also suggest that listeners with normal hearing and low working memory capacity are less able to adapt to distortion of speech signals caused by background noise, which requires the allocation of more processing resources to earlier processing stages. These results indicate that both younger and older adults with low working memory capacity and normal hearing are at a disadvantage for recognizing speech in noise.

Age effects in discrimination of intervals within accented tone sequences differing in accent type and sequence presentation rate.

The study measured listener sensitivity to increments in the duration of one or two target silent intervals embedded within unaccented tone sequences and sequences that featured a single accented component. The baseline unaccented sequences consisted of six 1000-Hz 40-ms tone bursts that were separated equally by silent intervals to establish a slower tone sequence rate, with tonal inter-onset intervals (IOIs) set to 200 ms, or a faster rate with tonal IOIs set to 100 ms. Stimulus accent was created by doubling the baseline duration of a single sequence component, either the second tone burst (tonal accent), or the second tonal IOI (interval accent). Duration difference limens for increments of the target interval(s) were measured adaptively by varying a single inter-tone silent interval or co-varying two successive inter-tone silent intervals; target intervals occurred at the third, or third and fourth, sequence locations. Listeners included younger normal-hearing adults and groups of older listeners with and without hearing loss. Discrimination for the two older groups was equivalent and poorer than that of the younger listeners, especially for the faster accented sequences. Discrimination was best for stimuli with two successive target intervals, indicating that target repetition within accented sequences acts to improve listener temporal sensitivity.

Perception of contrastive bi-syllabic lexical stress in unaccented and accented words by younger and older listeners.

This study examined the ability of older and younger listeners to perceive contrastive syllable stress in unaccented and Spanish-accented cognate bi-syllabic English words. Younger listeners with normal hearing, older listeners with normal hearing, and older listeners with hearing impairment judged recordings of words that contrasted in stress that conveyed a noun or verb form (e.g., CONduct/conDUCT), using two paradigms differing in the amount of semantic support. The stimuli were spoken by four speakers: one native English speaker and three Spanish-accented speakers (one moderately and two mildly accented). The results indicate that all listeners showed the lowest accuracy scores in responding to the most heavily accented speaker and the highest accuracy in judging the productions of the native English speaker. The two older groups showed lower accuracy in judging contrastive lexical stress than the younger group, especially for verbs produced by the most accented speaker. This general pattern of performance was observed in the two experimental paradigms, although performance was generally lower in the paradigm without semantic support. The findings suggest that age-related difficulty in adjusting to deviations in contrastive bi-syllabic lexical stress produced with a Spanish accent may be an important factor limiting perception of accented English by older people.

Age effects in discrimination of intervals within rhythmic tone sequences.

This study measured listener sensitivity to increments of a target inter-onset interval (IOI) embedded within tone sequences that featured different rhythmic patterns. The sequences consisted of six 50-ms 1000-Hz tone bursts separated by silent intervals that were adjusted to create different timing patterns. Control sequences were isochronous, with all tonal IOIs fixed at either 200 or 400 ms, while other patterns featured combinations of the two IOIs arranged to create different sequential tonal groupings. Duration difference limens in milliseconds for increments of a single sequence IOI were measured adaptively by adjusting the duration of an inter-tone silent interval. Specific target IOIs within sequences differed across discrimination conditions. Listeners included younger normal-hearing adults and groups of older adults with and without hearing loss. Discrimination performance measured for each of the older groups of listeners was observed to be equivalent, with each group exhibiting significantly poorer discrimination performance than the younger listeners in each sequence condition. Additionally, the specific influence of variable rhythmic grouping on temporal sensitivity was found to be greatest among older listeners.