Age-Related Temporal Processing Deficits in Word Segments in Adult Cochlear-Implant Users

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.

Cochlear Implant Qualification in Noise Versus Quiet: Do Patients Demonstrate Similar Postoperative Benefits?

OBJECTIVE

To assess patient factors, audiometric performance, and patient-reported outcomes in cochlear implant (CI) patients who would not have qualified with in-quiet testing alone.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

METHODS

Adult CI recipients implanted between 2012 and 2022 were identified. Patients with preoperative AzBio Quiet > 60% in the implanted ear, requiring multitalker babble to qualify, comprised the in-noise qualifying (NQ) group. NQ postoperative performance was compared with the in-quiet qualifying (QQ) group using CNC, AzBio Quiet, and AzBio +5 dB signal-to-noise ratio. Speech, Spatial and Qualities of Hearing Scale (SSQ), Cochlear Implant Quality of Life scale (CIQOL-10), and daily device usage were also compared between the groups.

RESULTS

The QQ group (n = 771) and NQ group (n = 67) were similar in age and hearing loss duration. NQ had higher average preoperative and postoperative speech recognition scores. A larger proportion of QQ saw significant improvement in CNC and AzBio Quiet scores in the CI-only listening condition (eg, CI-only AzBio Quiet: 88% QQ vs 51% NQ, P < .001). Improvement in CI-only AzBio +5 dB and in all open set testing in the best-aided binaural listening condition was similar between groups (eg, Binaural AzBio Quiet 73% QQ vs 59% NQ, P = .345). Postoperative SSQ ratings, CIQOL scores, and device usage were also equivalent between both groups.

CONCLUSION

Patients who require in-noise testing to meet CI candidacy demonstrate similar improvements in best-aided speech perception and patient-reported outcomes as in-QQ, supporting the use of in-noise testing to determine CI qualification for borderline CI candidates.

Association of Aging and Cognition With Complex Speech Understanding in Cochlear-Implanted Adults: Use of a Modified National Institutes of Health (NIH) Toolbox Cognitive Assessment

Importance

The association between cognitive function and outcomes in cochlear implant (CI) users is not completely understood, partly because some cognitive tests are confounded by auditory status. It is important to determine appropriate cognitive tests to use in a cohort of CI recipients.

Objective

To provide proof-of-concept for using an adapted version of the National Institutes of Health (NIH) Toolbox Cognition Battery in a cohort of patients with CIs and to explore how hearing in noise with a CI is affected by cognitive status using the adapted test.

Design, Setting, and Participants

In this prognostic study, participants listened to sentences presented in a speech-shaped background noise. Cognitive tests consisted of 7 subtests of the NIH Toolbox Cognition Battery that were adapted for hearing impaired individuals by including written instructions and visual stimuli. Participants were prospectively recruited from and evaluated at a tertiary medical center. All participants had at least 6 months' experience with their CI.

Main Outcomes and Measures

The main outcomes were performance on the adapted cognitive test and a speech recognition in noise task.

Results

Participants were 20 adult perilingually or postlingually deafened CI users (50% male participants; median [range] age, 66 [26-80] years old). Performance on a sentence recognition in noise task was negatively associated with the chronological age of the listener (R2 = 0.29; β = 0.16; standard error, SE = 0.06; t = 2.63; 95% confidence interval, 0.03-0.27). Testing using the adapted version of the NIH Toolbox Cognition Battery revealed that a test of processing speed was also associated with performance, using a standardized score that accounted for contributions of other demographic factors (R2 = 0.28; 95% confidence interval, -0.42 to -0.05).

Conclusions and Relevance

In this prognostic study, older CI users showed poorer performance on a sentence-in-noise test compared with younger users. This poorer performance was correlated with a cognitive deficit in processing speed when cognitive function was assessed using a test battery adapted for participants with hearing loss. These results provide initial proof-of-concept results for using a standardized and adapted cognitive test battery in CI recipients.

Interaural asymmetry of dynamic range: Abnormal fusion, bilateral interference, and shifts in attention

Speech information in the better ear interferes with the poorer ear in patients with bilateral cochlear implants (BiCIs) who have large asymmetries in speech intelligibility between ears. The goal of the present study was to assess how each ear impacts, and whether one dominates, speech perception using simulated CI processing in older and younger normal-hearing (ONH and YNH) listeners. Dynamic range (DR) was manipulated symmetrically or asymmetrically across spectral bands in a vocoder. We hypothesized that if abnormal integration of speech information occurs with asymmetrical speech understanding, listeners would demonstrate an atypical preference in accuracy when reporting speech presented to the better ear and fusion of speech between the ears (i.e., an increased number of one-word responses when two words were presented). Results from three speech conditions showed that: (1) When the same word was presented to both ears, speech identification accuracy decreased if one or both ears decreased in DR, but listeners usually reported hearing one word. (2) When two words with different vowels were presented to both ears, speech identification accuracy and percentage of two-word responses decreased consistently as DR decreased in one or both ears. (3) When two rhyming words (e.g., bed and led) previously shown to phonologically fuse between ears (e.g., bled) were presented, listeners instead demonstrated interference as DR decreased. The word responded in (2) and (3) came from the right (symmetric) or better (asymmetric) ear, especially in (3) and for ONH listeners in (2). These results suggest that the ear with poorer dynamic range is downweighted by the auditory system, resulting in abnormal fusion and interference, especially for older listeners.

Open-Set Phoneme Recognition Performance With Varied Temporal Cues in Younger and Older Cochlear Implant Users

PURPOSE

The goal of this study was to investigate the effect of age on phoneme recognition performance in which the stimuli varied in the amount of temporal information available in the signal. Chronological age is increasingly recognized as a factor that can limit the amount of benefit an individual can receive from a cochlear implant (CI). Central auditory temporal processing deficits in older listeners may contribute to the performance gap between younger and older CI users on recognition of phonemes varying in temporal cues.

METHOD

Phoneme recognition was measured at three stimulation rates (500, 900, and 1800 pulses per second) and two envelope modulation frequencies (50 Hz and unfiltered) in 20 CI participants ranging in age from 27 to 85 years. Speech stimuli were multiple word pairs differing in temporal contrasts and were presented via direct stimulation of the electrode array using an eight-channel continuous interleaved sampling strategy. Phoneme recognition performance was evaluated at each stimulation rate condition using both envelope modulation frequencies.

RESULTS

Duration of deafness was the strongest subject-level predictor of phoneme recognition, with participants with longer durations of deafness having poorer performance overall. Chronological age did not predict performance for any stimulus condition. Additionally, duration of deafness interacted with envelope filtering. Participants with shorter durations of deafness were able to take advantage of higher frequency envelope modulations, while participants with longer durations of deafness were not.

CONCLUSIONS

Age did not significantly predict phoneme recognition performance. In contrast, longer durations of deafness were associated with a reduced ability to utilize available temporal information within the signal to improve phoneme recognition performance.

Stimulus context affects the phonemic categorization of temporally based word contrasts in adult cochlear-implant users

Cochlear-implant (CI) users rely heavily on temporal envelope cues for speech understanding. This study examined whether their sensitivity to temporal cues in word segments is affected when the words are preceded by non-informative carrier sentences. Thirteen adult CI users performed phonemic categorization tasks that present primarily temporally based word contrasts: Buy-Pie contrast with word-initial stop of varying voice-onset time (VOT), and Dish-Ditch contrast with varying silent intervals preceding the word-final fricative. These words were presented in isolation or were preceded by carrier stimuli including a sentence, a sentence-envelope-modulated noise, or an unmodulated speech-shaped noise. While participants were able to categorize both word contrasts, stimulus context effects were observed primarily for the Buy-Pie contrast, such that participants reported more "Buy" responses for words with longer VOTs in conditions with carrier stimuli than in isolation. The two non-speech carrier stimuli yielded similar or even greater context effects than sentences. The context effects disappeared when target words were delayed from the carrier stimuli for ≥75 ms. These results suggest that stimulus contexts affect auditory temporal processing in CI users but the context effects appear to be cue-specific. The context effects may be governed by general auditory processes, not those specific to speech processing.

Auditory memory for random time patterns in cochlear implant listeners

Learning about new sounds is essential for cochlear-implant and normal-hearing listeners alike, with the additional challenge for implant listeners that spectral resolution is severely degraded. Here, a task measuring the rapid learning of slow or fast stochastic temporal sequences [Kang, Agus, and Pressnitzer (2017). J. Acoust. Soc. Am. 142, 2219-2232] was performed by cochlear-implant (N = 10) and normal-hearing (N = 9) listeners, using electric or acoustic pulse sequences, respectively. Rapid perceptual learning was observed for both groups, with highly similar characteristics. Moreover, for cochlear-implant listeners, an additional condition tested ultra-fast electric pulse sequences that would be impossible to represent temporally when presented acoustically. This condition also demonstrated learning. Overall, the results suggest that cochlear-implant listeners have access to the neural plasticity mechanisms needed for the rapid perceptual learning of complex temporal sequences.

Aging Effects on Cortical Responses to Tones and Speech in Adult Cochlear-Implant Users

Age-related declines in auditory temporal processing contribute to speech understanding difficulties of older adults. These temporal processing deficits have been established primarily among acoustic-hearing listeners, but the peripheral and central contributions are difficult to separate. This study recorded cortical auditory evoked potentials from younger to middle-aged (< 65 years) and older (≥ 65 years) cochlear-implant (CI) listeners to assess age-related changes in temporal processing, where cochlear processing is bypassed in this population. Aging effects were compared to age-matched normal-hearing (NH) listeners. Advancing age was associated with prolonged P2 latencies in both CI and NH listeners in response to a 1000-Hz tone or a syllable /da/, and with prolonged N1 latencies in CI listeners in response to the syllable. Advancing age was associated with larger N1 amplitudes in NH listeners. These age-related changes in latency and amplitude were independent of stimulus presentation rate. Further, CI listeners exhibited prolonged N1 and P2 latencies and smaller P2 amplitudes than NH listeners. Thus, aging appears to degrade some aspects of auditory temporal processing when peripheral-cochlear contributions are largely removed, suggesting that changes beyond the cochlea may contribute to age-related temporal processing deficits.

Head Shadow, Summation, and Squelch in Bilateral Cochlear-Implant Users With Linked Automatic Gain Controls

Speech understanding in noise is poorer in bilateral cochlear-implant (BICI) users compared to normal-hearing counterparts. Independent automatic gain controls (AGCs) may contribute to this because adjusting processor gain independently can reduce interaural level differences that BICI listeners rely on for bilateral benefits. Bilaterally linked AGCs may improve bilateral benefits by increasing the magnitude of interaural level differences. The effects of linked AGCs on bilateral benefits (summation, head shadow, and squelch) were measured in nine BICI users. Speech understanding for a target talker at 0° masked by a single talker at 0°, 90°, or −90° azimuth was assessed under headphones with sentences at five target-to-masker ratios. Research processors were used to manipulate AGC type (independent or linked) and test ear (left, right, or both). Sentence recall was measured in quiet to quantify individual interaural asymmetry in functional performance. The results showed that AGC type did not significantly change performance or bilateral benefits. Interaural functional asymmetries, however, interacted with ear such that greater summation and squelch benefit occurred when there was larger functional asymmetry, and interacted with interferer location such that smaller head shadow benefit occurred when there was larger functional asymmetry. The larger benefits for those with larger asymmetry were driven by improvements from adding a better-performing ear, rather than a true binaural-hearing benefit. In summary, linked AGCs did not significantly change bilateral benefits in cases of speech-on-speech masking with a single-talker masker, but there was also no strong detriment across a range of target-to-masker ratios, within a small and diverse BICI listener population.

Effect of Chronological Age on Pulse Rate Discrimination in Adult Cochlear-Implant Users

Cochlear-implant (CI) users rely heavily on temporal envelope cues to understand speech. Temporal processing abilities may decline with advancing age in adult CI users. This study investigated the effect of age on the ability to discriminate changes in pulse rate. Twenty CI users aged 23 to 80 years participated in a rate discrimination task. They attempted to discriminate a 35% rate increase from baseline rates of 100, 200, 300, 400, or 500 pulses per second. The stimuli were electrical pulse trains delivered to a single electrode via direct stimulation to an apical (Electrode 20), a middle (Electrode 12), or a basal location (Electrode 4). Electrically evoked compound action potential amplitude growth functions were recorded at each of those electrodes as an estimate of peripheral neural survival. Results showed that temporal pulse rate discrimination performance declined with advancing age at higher stimulation rates (e.g., 500 pulses per second) when compared with lower rates. The age-related changes in temporal pulse rate discrimination at higher stimulation rates persisted after statistical analysis to account for the estimated peripheral contributions from electrically evoked compound action potential amplitude growth functions. These results indicate the potential contributions of central factors to the limitations in temporal pulse rate discrimination ability associated with aging in CI users.

Access to semantic cues does not lead to perceptual restoration of interrupted speech in cochlear-implant users

Cochlear-implant (CI) users experience less success in understanding speech in noisy, real-world listening environments than normal-hearing (NH) listeners. Perceptual restoration is one method NH listeners use to repair noise-interrupted speech. Whereas previous work has reported that CI users can use perceptual restoration in certain cases, they failed to do so under listening conditions in which NH listeners can successfully restore. Providing increased opportunities to use top-down linguistic knowledge is one possible method to increase perceptual restoration use in CI users. This work tested perceptual restoration abilities in 18 CI users and varied whether a semantic cue (presented visually) was available prior to the target sentence (presented auditorily). Results showed that whereas access to a semantic cue generally improved performance with interrupted speech, CI users failed to perceptually restore speech regardless of the semantic cue availability. The lack of restoration in this population directly contradicts previous work in this field and raises questions of whether restoration is possible in CI users. One reason for speech-in-noise understanding difficulty in CI users could be that they are unable to use tools like restoration to process noise-interrupted speech effectively.

Impact of Aging and the Electrode-to-Neural Interface on Temporal Processing Ability in Cochlear-Implant Users: Gap Detection Thresholds

Accurate processing of temporal information is critical to understanding speech through a cochlear implant (CI). This has potential implications for the growing population of CI users who are ≥65 years of age because of age-related auditory temporal processing deficits. The goal of this study was to measure temporal processing ability in a gap detection task in younger, middle-aged, and older CI users and to determine the relative contributions of chronological age and peripheral neural survival to performance. Single-electrode gap detection thresholds (GDTs) were measured using direct stimulation at five electrode locations and three electrical stimulation rates. The relationship between peripheral status (e.g., electrode-to-neural interface) and GDTs was assessed by the slope of the electrically evoked compound action potential (ECAP) amplitude growth function. Results showed that ECAP slope was the strongest subject-level predictor of GDTs. Steeper ECAP slopes, which are partially indicative of better peripheral function, were associated with better GDTs in younger participants. However, ECAP slope significantly interacted with stimulation rate and age, suggesting that ECAP slopes were not predictive of GDTs in middle-aged and older participants at some stimulation rates. ECAP slope was also related to age, with middle-aged and older participants exhibiting relatively shallow slopes and smaller ranges of slopes compared with younger participants. This pattern of ECAP results limited the evaluation of the independent effects of aging per se and peripheral status on temporal processing ability.