Word recognition for temporally and spectrally distorted materials: the effects of age and hearing loss

Transducer Variability in Speech-in-Noise Testing: Considerations Related to Stimulus Bandwidth

PURPOSE

Clinical audiologists typically assume that headphones and insert phones will produce comparable results when they are used to conduct speech-in-noise or other audiological tests; however, this may not always be the case. Here, we show that there are significant differences in the scores that previous studies have reported for headphone and insert-phone transducers on the Words-in-Noise (WIN) Test, and discuss the possibility that the variations in high-frequency output that are allowable under the speech source specifications of American National Standards Institute S3.6 might be contributing to transducer-dependent differences in performance for the WIN and other tests that are presented through the auxiliary input channels of clinical audiometers.

METHOD

A literature review was conducted to identify articles that reported WIN Test results for both listeners with normal hearing and with hearing impairment and specified the type of transducer (insert or TDH-50) used for the data collection.

RESULTS

Among the 19 included studies, participants with normal hearing using inserts exhibited systematically worse WIN Test scores compared to those using TDH-50 headphones, while participants with hearing loss showed comparable average scores across transducer types.

CONCLUSIONS

The results highlight the importance of considering transducer type when interpreting WIN Test outcomes, particularly when comparing to normative scores obtained from individuals with normal hearing. Although further research is needed to elucidate the underlying mechanisms driving differences in test performance across transducer types, these findings underscore the need for standardized test administration protocols and careful documentation of transducer type when administering speech-in-noise tests for clinical or research applications.

Non-linguistic auditory speech processing

OBJECTIVES

A method for testing auditory processing of non-linguistic speech-like stimuli was developed and evaluated.

DESIGN

Monosyllabic words were temporally reversed and distorted. Stimuli were matched for spectrum and level. Listeners discriminated between distorted and undistorted stimuli.

STUDY SAMPLE

Three groups were tested. The Normal group was comprised of 12 normal-hearing participants. The Senior group was comprised of 12 seniors. The Hearing Loss group was comprised of 12 participants with thresholds of at least 35 dB HL at one or more frequencies.

RESULTS

The Senior group scored lower than the Normal group, and the Hearing Loss group scored lower than the Senior group. Scores for forward compressed speech were slightly higher than backward compressed speech but the difference was not statistically significant. Retest scores were slightly higher than scores on the first test, but the difference was not statistically significant.

CONCLUSIONS

Large differences in discrimination of distorted speech were observed among the three groups. Age and hearing loss separately affected performance. The depressed performance of the Senior group may be a result of "hidden hearing loss" that is attributed to cochlear synaptopathy. The backward-distorted speech task may be a useful non-linguistic test of speech processing that is language independent.

Aging-Related Decline in Phonated and Whispered Speech Perception Not Compensated For by Increased Duration and Intensity: Evidence From Mandarin-Speaking Adult Listeners

PURPOSE

This study aimed to examine how aging and modifications of critical acoustic parameters may affect the perception of whispered speech as a degraded signal.

METHOD

Forty Mandarin-speaking adults were included in the study. Part 1 of the study compared the perception of Mandarin lexical tones, vowels, and syllables in older and younger adults in whispered versus phonated speech conditions. Parts 2 and 3 further examined how modification of duration and intensity cues contributed to the perceptual outcomes.

RESULTS

Perception of whispered tones was compromised in older and younger adults. Older adults identified lexical tones less accurately than their younger counterparts, particularly for phonated T2 and T3 and whispered T3. Aging also negatively affected the vowel identification of /i, u/ in the whispered condition. Syllable-level accuracy was largely dependent on the accuracy of lexical tones and vowels. Furthermore, reduced duration led to the decreased accuracy of phonated T3 and whispered T2 and T3 but increased accuracy of phonated T4. Reduced intensity lowered the recognition accuracy for phonated vowels /i, ɤ, o, y/ in older adults and /i, u/ in younger adults, and it also lowered the accuracy of whispered vowels /a, ɤ/ in older adults. Contrary to our expectation, increased duration and intensity did not improve older adults' speech perception in either phonated or whispered conditions.

CONCLUSIONS

The results suggest that aging adversely affected speech perception in both phonated and whispered conditions with more challenges in identifying whispered speech for older adults. While older adults' diminished performance may be potentially due to problems with processing the degraded temporal and spectral information of the target speech sounds, it cannot be simply compensated for by increasing the duration and intensity of the target sounds beyond the audible level.

Relationship Between Domain-Specific Cognitive Function and Speech-in-Noise Performance in Older Adults: The Atherosclerosis Risk in Communities Hearing Pilot Study

Purpose The purpose of this study was to investigate associations between performance on a clinical speech-in-noise measure with a comprehensive neurocognitive battery of tests. Method A group of older adults (N = 250, M _age = 77 years, age range: 67.3-89.1 years) enrolled in the Atherosclerosis Risk in Communities Neurocognitive Study took part in the hearing pilot study (2013) that included testing for audiometric thresholds and speech-in-noise performance (Quick Speech-in-Noise Test; Killion, Niquette, Gudmundsen, Revit, & Banerjee, 2004). This research study analyzed the associations between domain-specific cognitive function and speech-in-noise performance after adjusting for hearing thresholds and other demographic and cardiovascular factors. Results Multivariable-adjusted associations were found between all cognitive domains and speech-in-noise performance in the full sample, but the observed associations varied when participants with varying levels of moderate to moderately severe hearing loss were excluded from the analysis. Conclusions The findings are discussed in terms considering the cognitive status of older adults in relation to their speech-in-noise performance during audiological evaluation and implications for aural rehabilitation.

Processing Mechanisms in Hearing-Impaired Listeners: Evidence from Reaction Times and Sentence Interpretation

OBJECTIVE

The authors aimed to determine whether hearing impairment affects sentence comprehension beyond phoneme or word recognition (i.e., on the sentence level), and to distinguish grammatically induced processing difficulties in structurally complex sentences from perceptual difficulties associated with listening to degraded speech. Effects of hearing impairment or speech in noise were expected to reflect hearer-specific speech recognition difficulties. Any additional processing time caused by the sustained perceptual challenges across the sentence may either be independent of or interact with top-down processing mechanisms associated with grammatical sentence structure.

DESIGN

Forty-nine participants listened to canonical subject-initial or noncanonical object-initial sentences that were presented either in quiet or in noise. Twenty-four participants had mild-to-moderate hearing impairment and received hearing-loss-specific amplification. Twenty-five participants were age-matched peers with normal hearing status. Reaction times were measured on-line at syntactically critical processing points as well as two control points to capture differences in processing mechanisms. An off-line comprehension task served as an additional indicator of sentence (mis)interpretation, and enforced syntactic processing.

RESULTS

The authors found general effects of hearing impairment and speech in noise that negatively affected perceptual processing, and an effect of word order, where complex grammar locally caused processing difficulties for the noncanonical sentence structure. Listeners with hearing impairment were hardly affected by noise at the beginning of the sentence, but were affected markedly toward the end of the sentence, indicating a sustained perceptual effect of speech recognition. Comprehension of sentences with noncanonical word order was negatively affected by degraded signals even after sentence presentation.

CONCLUSION

Hearing impairment adds perceptual processing load during sentence processing, but affects grammatical processing beyond the word level to the same degree as in normal hearing, with minor differences in processing mechanisms. The data contribute to our understanding of individual differences in speech perception and language understanding. The authors interpret their results within the ease of language understanding model.

Associations between speech understanding and auditory and visual tests of verbal working memory: effects of linguistic complexity, task, age, and hearing loss

Listeners with hearing loss commonly report having difficulty understanding speech, particularly in noisy environments. Their difficulties could be due to auditory and cognitive processing problems. Performance on speech-in-noise tests has been correlated with reading working memory span (RWMS), a measure often chosen to avoid the effects of hearing loss. If the goal is to assess the cognitive consequences of listeners’ auditory processing abilities, however, then listening working memory span (LWMS) could be a more informative measure. Some studies have examined the effects of different degrees and types of masking on working memory, but less is known about the demands placed on working memory depending on the linguistic complexity of the target speech or the task used to measure speech understanding in listeners with hearing loss. Compared to RWMS, LWMS measures using different speech targets and maskers may provide a more ecologically valid approach. To examine the contributions of RWMS and LWMS to speech understanding, we administered two working memory measures (a traditional RWMS measure and a new LWMS measure), and a battery of tests varying in the linguistic complexity of the speech materials, the presence of babble masking, and the task. Participants were a group of younger listeners with normal hearing and two groups of older listeners with hearing loss (n = 24 per group). There was a significant group difference and a wider range in performance on LWMS than on RWMS. There was a significant correlation between both working memory measures only for the oldest listeners with hearing loss. Notably, there were only few significant correlations among the working memory and speech understanding measures. These findings suggest that working memory measures reflect individual differences that are distinct from those tapped by these measures of speech understanding.

Speech-evoked ABR: Effects of age and simulated neural temporal jitter

The speech-evoked auditory brainstem response (sABR) provides a measure of encoding complex stimuli in the brainstem, and this study employed the sABR to better understand the role of neural temporal jitter in the response patterns from older adults. In experiment 1, sABR recordings were used to investigate age-related differences in periodicity encoding of the temporal envelope and fine structure components of the response to a /da/speech token. A group of younger and a group of older adults (n = 22 per group) participated. The results demonstrated reduced amplitude of the fundamental frequency and harmonic components in the spectral domain of the recorded response of the older listeners. In experiment 2, a model of neural temporal jitter was employed to simulate in a group of young adults (n = 22) the response patterns measured from older adults. A small group of older adults (n = 7) were also tested under the jitter simulation conditions. In the young adults, the results showed a systematic reduction in the response amplitude of the most robust response components as the degree of applied jitter increased. In contrast, the older adults did not demonstrate significant response reduction when tested under jitter conditions. The overall pattern of results suggests that older adults have reduced neural synchrony for encoding periodic, complex signals at the level of the brainstem, and that this reduced synchrony can be modeled by simulating neural jitter via disruption of the temporal waveform of the stimulus.

Effects of age on melody and timbre perception in simulations of electro-acoustic and cochlear-implant hearing

OBJECTIVES

Recent evidence suggests that age might affect the ability of listeners to process fundamental frequency cues in speech, and that this difficulty might impact the ability of older listeners to use and combine envelope and fine structure cues available in simulations of electro-acoustic and cochlear-implant hearing. The purpose of this article is to examine whether this difficulty extends to music. Specially, this study focuses on whether older listeners have a decreased ability to use and combine different types of cues in the perception of melody and timbre.

DESIGN

A group of older listeners with normal to near-normal hearing and a group of younger listeners with normal hearing participated in the melody and timbre recognition tasks of the University of Washington Clinical Assessment of Music Perception test. The recognition tasks were completed for five different processing conditions: (1) an unprocessed condition; (2) an eight-channel vocoding condition that simulated a traditional cochlear implant and contained temporal envelope cues; (3) a simulation of electro-acoustic stimulation (sEAS) that included a low-pass acoustic component and high-pass vocoded portion, and which provided fine structure and envelope cues; (4) a condition that included only the low-pass acoustic portion of the sEAS; and (5) a condition that included only the high-frequency vocoded portion of the sEAS stimulus.

RESULTS

Melody recognition was excellent for both younger and older listeners in the conditions containing the unprocessed stimuli, the full sEAS stimuli, and the low-pass sEAS stimuli. Melody recognition was significantly worse in the cochlear-implant simulation condition, especially for the older group of listeners. Performance on the timbre task was highest for the unprocessed condition, and progressively decreased for the sEAS and cochlear-implant simulation conditions. Compared with younger listeners, older listeners had significantly poorer timbre recognition for all processing conditions. For melody recognition, the unprocessed low-frequency portion of the sEAS stimulus was the primary factor determining improved performance in the sEAS condition compared with the cochlear-implant simulation. For timbre recognition, both the unprocessed low-frequency and high-frequency vocoded portions of the sEAS stimulus contributed to sEAS improvement in the younger group. In contrast, most listeners in the older group were not able to take advantage of the high-frequency vocoded portion of the sEAS stimulus for timbre recognition.

CONCLUSIONS

The results of this simulation study support the idea that older listeners will have diminished timbre and melody perception in traditional cochlear-implant listening due to degraded envelope processing. The findings also suggest that music perception by older listeners with cochlear implants will be improved with the addition of low-frequency residual hearing. However, these improvements might not be comparable for all dimensions of music perception. That is, more improvement might be evident for tasks that rely primarily on the low-frequency portion of the electro-acoustic stimulus (e.g., melody recognition), and less improvement might be evident in situations that require across-frequency integration of cues (e.g., timbre perception).

Working memory affects older adults' use of context in spoken-word recognition

Many older listeners report difficulties in understanding speech in noisy situations. Working memory and other cognitive skills may modulate older listeners' ability to use context information to alleviate the effects of noise on spoken-word recognition. In the present study, we investigated whether verbal working memory predicts older adults' ability to immediately use context information in the recognition of words embedded in sentences, presented in different listening conditions. In a phoneme-monitoring task, older adults were asked to detect as fast and as accurately as possible target phonemes in sentences spoken by a target speaker. Target speech was presented without noise, with fluctuating speech-shaped noise, or with competing speech from a single distractor speaker. The gradient measure of contextual probability (derived from a separate offline rating study) affected the speed of recognition. Contextual facilitation was modulated by older listeners' verbal working memory (measured with a backward digit span task) and age across listening conditions. Working memory and age, as well as hearing loss, were also the most consistent predictors of overall listening performance. Older listeners' immediate benefit from context in spoken-word recognition thus relates to their ability to keep and update a semantic representation of the sentence content in working memory.

Speech Comprehension Training and Auditory and Cognitive Processing in Older Adults

Purpose

To provide a brief history of speech comprehension training systems and an overview of research on auditory and cognitive aging as background to recommendations for future directions for rehabilitation.

Method

Two distinct domains were reviewed: one concerning technological and the other concerning psychological aspects of training. Historical trends and advances in these 2 domains were interrelated to highlight converging trends and directions for future practice.

Results

Over the last century, technological advances have influenced both the design of hearing aids and training systems. Initially, training focused on children and those with severe loss for whom amplification was insufficient. Now the focus has shifted to older adults with relatively little loss but difficulties listening in noise. Evidence of brain plasticity from auditory and cognitive neuroscience provides new insights into how to facilitate perceptual (re-)learning by older adults.

Conclusions

There is a new imperative to complement training to increase bottom-up processing of the signal with more ecologically valid training to boost top-down information processing based on knowledge of language and the world. Advances in digital technologies enable the development of increasingly sophisticated training systems incorporating complex meaningful materials such as music, audiovisual interactive displays, and conversation.