Foreign Language Acquisition in Adolescent Cochlear Implant Users.

OBJECTIVES: This study explores to what degree adolescent cochlear implant (CI) users can learn a foreign language in a school setting similar to their normal-hearing (NH) peers despite the degraded auditory input. DESIGN: A group of native Dutch adolescent CI users (age range 13 to 17 years) learning English as a foreign language at secondary school and a group of NH controls (age range 12 to 15 years) were assessed on their Dutch and English language skills using various language tasks that either relied on the processing of auditory information (i.e., listening task) or on the processing of orthographic information (i.e., reading and/or gap-fill task). The test battery also included various auditory and cognitive tasks to assess whether the auditory and cognitive functioning of the learners could explain the potential variation in language skills. RESULTS: Results showed that adolescent CI users can learn English as a foreign language, as the English language skills of the CI users and their NH peers were comparable when assessed with reading or gap-fill tasks. However, the performance of the adolescent CI users was lower for English listening tasks. This discrepancy between task performance was not observed in their native language Dutch. The auditory tasks confirmed that the adolescent CI users had coarser temporal and spectral resolution than their NH peers, supporting the notion that the difference in foreign language listening skills may be due to a difference in auditory functioning. No differences in the cognitive functioning of the CI users and their NH peers were found that could explain the variation in the foreign language listening tasks. CONCLUSIONS: In short, acquiring a foreign language with degraded auditory input appears to affect foreign language listening skills, yet does not appear to impact foreign language skills when assessed with tasks that rely on the processing of orthographic information. CI users could take advantage of orthographic information to facilitate foreign language acquisition and potentially support the development of listening-based foreign language skills.

Meta-Analysis on the Identification of Linguistic and Emotional Prosody in Cochlear Implant Users and Vocoder Simulations.

OBJECTIVES: This study quantitatively assesses how cochlear implants (CIs) and vocoder simulations of CIs influence the identification of linguistic and emotional prosody in nontonal languages. By means of meta-analysis, it was explored how accurately CI users and normal-hearing (NH) listeners of vocoder simulations (henceforth: simulation listeners) identify prosody compared with NH listeners of unprocessed speech (henceforth: NH listeners), whether this effect of electric hearing differs between CI users and simulation listeners, and whether the effect of electric hearing is influenced by the type of prosody that listeners identify or by the availability of specific cues in the speech signal. DESIGN: Records were found by searching the PubMed Central, Web of Science, Scopus, Science Direct, and PsycINFO databases (January 2018) using the search terms "cochlear implant prosody" and "vocoder prosody." Records (published in English) were included that reported results of experimental studies comparing CI users' and/or simulation listeners' identification of linguistic and/or emotional prosody in nontonal languages to that of NH listeners (all ages included). Studies that met the inclusion criteria were subjected to a multilevel random-effects meta-analysis. RESULTS: Sixty-four studies reported in 28 records were included in the meta-analysis. The analysis indicated that CI users and simulation listeners were less accurate in correctly identifying linguistic and emotional prosody compared with NH listeners, that the identification of emotional prosody was more strongly compromised by the electric hearing speech signal than linguistic prosody was, and that the low quality of transmission of fundamental frequency (f0) through the electric hearing speech signal was the main cause of compromised prosody identification in CI users and simulation listeners. Moreover, results indicated that the accuracy with which CI users and simulation listeners identified linguistic and emotional prosody was comparable, suggesting that vocoder simulations with carefully selected parameters can provide a good estimate of how prosody may be identified by CI users. CONCLUSIONS: The meta-analysis revealed a robust negative effect of electric hearing, where CIs and vocoder simulations had a similar negative influence on the identification of linguistic and emotional prosody, which seemed mainly due to inadequate transmission of f0 cues through the degraded electric hearing speech signal of CIs and vocoder simulations.

Effects of Additional Low-Pass-Filtered Speech on Listening Effort for Noise-Band-Vocoded Speech in Quiet and in Noise.

OBJECTIVES: Residual acoustic hearing in electric-acoustic stimulation (EAS) can benefit cochlear implant (CI) users in increased sound quality, speech intelligibility, and improved tolerance to noise. The goal of this study was to investigate whether the low-pass-filtered acoustic speech in simulated EAS can provide the additional benefit of reducing listening effort for the spectrotemporally degraded signal of noise-band-vocoded speech. DESIGN: Listening effort was investigated using a dual-task paradigm as a behavioral measure, and the NASA Task Load indeX as a subjective self-report measure. The primary task of the dual-task paradigm was identification of sentences presented in three experiments at three fixed intelligibility levels: at near-ceiling, 50%, and 79% intelligibility, achieved by manipulating the presence and level of speech-shaped noise in the background. Listening effort for the primary intelligibility task was reflected in the performance on the secondary, visual response time task. Experimental speech processing conditions included monaural or binaural vocoder, with added low-pass-filtered speech (to simulate EAS) or without (to simulate CI). RESULTS: In Experiment 1, in quiet with intelligibility near-ceiling, additional low-pass-filtered speech reduced listening effort compared with binaural vocoder, in line with our expectations, although not compared with monaural vocoder. In Experiments 2 and 3, for speech in noise, added low-pass-filtered speech allowed the desired intelligibility levels to be reached at less favorable speech-to-noise ratios, as expected. It is interesting that this came without the cost of increased listening effort usually associated with poor speech-to-noise ratios; at 50% intelligibility, even a reduction in listening effort on top of the increased tolerance to noise was observed. The NASA Task Load indeX did not capture these differences. CONCLUSIONS: The dual-task results provide partial evidence for a potential decrease in listening effort as a result of adding low-frequency acoustic speech to noise-band-vocoded speech. Whether these findings translate to CI users with residual acoustic hearing will need to be addressed in future research because the quality and frequency range of low-frequency acoustic sound available to listeners with hearing loss may differ from our idealized simulations, and additional factors, such as advanced age and varying etiology, may also play a role.

Does Signal Degradation Affect Top-Down Processing of Speech?

Speech perception is formed based on both the acoustic signal and listeners' knowledge of the world and semantic context. Access to semantic information can facilitate interpretation of degraded speech, such as speech in background noise or the speech signal transmitted via cochlear implants (CIs). This paper focuses on the latter, and investigates the time course of understanding words, and how sentential context reduces listeners' dependency on the acoustic signal for natural and degraded speech via an acoustic CI simulation.In an eye-tracking experiment we combined recordings of listeners' gaze fixations with pupillometry, to capture effects of semantic information on both the time course and effort of speech processing. Normal-hearing listeners were presented with sentences with or without a semantically constraining verb (e.g., crawl) preceding the target (baby), and their ocular responses were recorded to four pictures, including the target, a phonological (bay) competitor and a semantic (worm) and an unrelated distractor.The results show that in natural speech, listeners' gazes reflect their uptake of acoustic information, and integration of preceding semantic context. Degradation of the signal leads to a later disambiguation of phonologically similar words, and to a delay in integration of semantic information. Complementary to this, the pupil dilation data show that early semantic integration reduces the effort in disambiguating phonologically similar words. Processing degraded speech comes with increased effort due to the impoverished nature of the signal. Delayed integration of semantic information further constrains listeners' ability to compensate for inaudible signals.

Validation of a simple response-time measure of listening effort.

This study compares two response-time measures of listening effort that can be combined with a clinical speech test for a more comprehensive evaluation of total listening experience; verbal response times to auditory stimuli (RT(aud)) and response times to a visual task (RTs(vis)) in a dual-task paradigm. The listening task was presented in five masker conditions; no noise, and two types of noise at two fixed intelligibility levels. Both the RTs(aud) and RTs(vis) showed effects of noise. However, only RTs(aud) showed an effect of intelligibility. Because of its simplicity in implementation, RTs(aud) may be a useful effort measure for clinical applications.

Lexical Stress Identification in Cochlear Implant-Simulated Speech by Non-Native Listeners.

This study investigates whether a presumed difference in the perceptibility of cues to lexical stress in spectro-temporally degraded simulated cochlear implant (CI) speech affects how listeners weight these cues during a lexical stress identification task, specifically in their non-native language. Previous research suggests that in English, listeners predominantly rely on a reduction in vowel quality as a cue to lexical stress. In Dutch, changes in the fundamental frequency (F0) contour seem to have a greater functional weight than the vowel quality contrast. Generally, non-native listeners use the cue-weighting strategies from their native language in the non-native language. Moreover, few studies have suggested that these cues to lexical stress are differently perceptible in spectro-temporally degraded electric hearing, as CI users appear to make more effective use of changes in vowel quality than of changes in the F0 contour as cues to linguistic phenomena. In this study, native Dutch learners of English identified stressed syllables in CI-simulated and non-CI-simulated Dutch and English words that contained changes in the F0 contour and vowel quality as cues to lexical stress. The results indicate that neither the cue-weighting strategies in the native language nor in the non-native language are influenced by the perceptibility of cues in the spectro-temporally degraded speech signal. These results are in contrast to our expectations based on previous research and support the idea that cue weighting is a flexible and transferable process.

Prosodic Focus Interpretation in Spectrotemporally Degraded Speech by Non-Native Listeners.

PURPOSE: This study assesses how spectrotemporal degradations that can occur in the sound transmission of a cochlear implant (CI) may influence the ability of non-native listeners to recognize the intended meaning of utterances based on the position of the prosodically focused word. Previous research suggests that perceptual accuracy and listening effort are negatively affected by CI processing (or CI simulations) or when the speech is presented in a non-native language, in a number of tasks and circumstances. How these two factors interact to affect prosodic focus interpretation, however, remains unclear. METHOD: In an online experiment, normal-hearing (NH) adolescent and adult native Dutch learners of English and a small control group of NH native English adolescents listened to CI-simulated (eight-channel noise-band vocoded) and non-CI-simulated English sentences differing in prosodically marked focus. For assessing perceptual accuracy, listeners had to indicate which of four possible context questions the speaker answered. For assessing listening effort, a dual-task paradigm was used with a secondary free recall task. RESULTS: The results indicated that prosodic focus interpretation was significantly less accurate in the CI-simulated condition compared with the non-CI-simulated condition but that listening effort was not increased. Moreover, there was no interaction between the influence of the degraded CI-simulated speech signal and listening groups in either their perceptual accuracy or listening effort. CONCLUSION: Non-native listeners are not more strongly affected by spectrotemporal degradations than native listeners, and less proficient non-native listeners are not more strongly affected by these degradations than more proficient non-native listeners.

Working-Memory, Alpha-Theta Oscillations and Musical Training in Older Age: Research Perspectives for Speech-on-speech Perception.

During the normal course of aging, perception of speech-on-speech or "cocktail party" speech and use of working memory (WM) abilities change. Musical training, which is a complex activity that integrates multiple sensory modalities and higher-order cognitive functions, reportedly benefits both WM performance and speech-on-speech perception in older adults. This mini-review explores the relationship between musical training, WM and speech-on-speech perception in older age (> 65 years) through the lens of the Ease of Language Understanding (ELU) model. Linking neural-oscillation literature associating speech-on-speech perception and WM with alpha-theta oscillatory activity, we propose that two stages of speech-on-speech processing in the ELU are underpinned by WM-related alpha-theta oscillatory activity, and that effects of musical training on speech-on-speech perception may be reflected in these frequency bands among older adults.

Objective measures of listening effort: effects of background noise and noise reduction.

PURPOSE: This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. METHOD: To address this, the hypothesis tested here is that the positive effects of NR might be to reduce cognitive effort directed toward speech reception, making it available for other tasks. Normal-hearing individuals participated in 2 dual-task experiments, in which 1 task was to report sentences or words in noise set to various signal-to-noise ratios. Secondary tasks involved either holding words in short-term memory or responding in a complex visual reaction-time task. RESULTS: At low values of signal-to-noise ratio, although NR had no positive effect on speech reception thresholds, it led to better performance on the word-memory task and quicker responses in visual reaction times. CONCLUSIONS: Results from both dual tasks support the hypothesis that NR reduces listening effort and frees up cognitive resources for other tasks. Future hearing aid research should incorporate objective measurements of cognitive benefits.

Auditory stream segregation with cochlear implants: A preliminary report.

Auditory stream segregation was measured in cochlear implant (CI) listeners using a subjective "Yes-No" task in which listeners indicated whether a sequence of stimuli was perceived as two separate streams or not. Stimuli were brief, 50-ms pulse trains A and B, presented in an A_B_A_A_B_A... sequence, with 50 ms in between consecutive stimuli. All stimuli were carefully loudness-balanced prior to the experiments. The cochlear electrode location of A was fixed, while the location of B was varied systematically. Measures of electrode discrimination and subjective perceptual difference were also included for comparison. There was strong intersubject variation in the pattern of results. One of the participants participated in a second series of experiments, the results of which indicated that he was able to perceptually segregate stimuli that were different in cochlear electrode location, as well as stimuli that were different in temporal envelope. Although preliminary, these results suggest that it is possible for some cochlear implant listeners to perceptually segregate stimuli based on differences in cochlear location as well as temporal envelope.

The effects of acute tryptophan depletion on speech and behavioural mimicry in individuals at familial risk for depression.

Major depressive disorder (MDD) has been associated with abnormalities in speech and behavioural mimicry. These abnormalities may contribute to the impairments in interpersonal functioning that are often seen in MDD patients. MDD has also been associated with disturbances in the brain serotonin system, but the extent to which serotonin regulates speech and behavioural mimicry remains unclear. In a randomized, double-blind, crossover study, we induced acute tryptophan depletion (ATD) in individuals with or without a family history of MDD. Five hours afterwards, participants engaged in two behavioural-mimicry experiments in which speech and behaviour were recorded. ATD reduced the time participants waited before speaking, which might indicate increased impulsivity. However, ATD did not significantly alter speech otherwise, nor did it affect mimicry. This suggests that a brief lowering of brain serotonin has limited effects on verbal and non-verbal social behaviour. The null findings may be due to low test sensitivity, but they otherwise suggest that low serotonin has little effect on social interaction quality in never-depressed individuals. It remains possible that recovered MDD patients are more strongly affected.

Listening effort with cochlear implant simulations.

PURPOSE: Fitting a cochlear implant (CI) for optimal speech perception does not necessarily optimize listening effort. This study aimed to show that listening effort may change between CI processing conditions for which speech intelligibility remains constant. METHOD: Nineteen normal-hearing participants listened to CI simulations with varying numbers of spectral channels. A dual-task paradigm combining an intelligibility task with either a linguistic or nonlinguistic visual response-time (RT) task measured intelligibility and listening effort. The simultaneously performed tasks compete for limited cognitive resources; changes in effort associated with the intelligibility task are reflected in changes in RT on the visual task. A separate self-report scale provided a subjective measure of listening effort. RESULTS: All measures showed significant improvements with increasing spectral resolution up to 6 channels. However, only the RT measure of listening effort continued improving up to 8 channels. The effects were stronger for RTs recorded during listening than for RTs recorded between listening. CONCLUSION: The results suggest that listening effort decreases with increased spectral resolution. Moreover, these improvements are best reflected in objective measures of listening effort, such as RTs on a secondary task, rather than intelligibility scores or subjective effort measures.