Effects of source-to-listener distance and masking on perception of cochlear implant processed speech in reverberant rooms

Speech Intelligibility and Spatial Release From Masking Improvements Using Spatial Noise Reduction Algorithms in Bimodal Cochlear Implant Users

This study investigated the speech intelligibility benefit of using two different spatial noise reduction algorithms in cochlear implant (CI) users who use a hearing aid (HA) on the contralateral side (bimodal CI users). The study controlled for head movements by using head-related impulse responses to simulate a realistic cafeteria scenario and controlled for HA and CI manufacturer differences by using the master hearing aid platform (MHA) to apply both hearing loss compensation and the noise reduction algorithms (beamformers). Ten bimodal CI users with moderate to severe hearing loss contralateral to their CI participated in the study, and data from nine listeners were included in the data analysis. The beamformers evaluated were the adaptive differential microphones (ADM) implemented independently on each side of the listener and the (binaurally implemented) minimum variance distortionless response (MVDR). For frontal speech and stationary noise from either left or right, an improvement (reduction) of the speech reception threshold of 5.4 dB and 5.5 dB was observed using the ADM, and 6.4 dB and 7.0 dB using the MVDR, respectively. As expected, no improvement was observed for either algorithm for colocated speech and noise. In a 20-talker babble noise scenario, the benefit observed was 3.5 dB for ADM and 7.5 dB for MVDR. The binaural MVDR algorithm outperformed the bilaterally applied monaural ADM. These results encourage the use of beamformer algorithms such as the ADM and MVDR by bimodal CI users in everyday life scenarios.

Effect of noise and reverberation on speech intelligibility for cochlear implant recipients in realistic sound environments

Previous studies have suggested a strong effect of reverberation on speech intelligibility (SI) in cochlear implant (CI) recipients. In many of them, different reverberation conditions were obtained by altering the acoustic absorption of a single room, thereby omitting the effect of the room volume. In addition, studies that have investigated the combined effects of reverberation and noise on SI have overlooked the effect of reverberation on the modulation of the noise. In the present study, SI was measured unilaterally in 12 CI recipients in quiet and in noise using a three-dimensional loudspeaker array. Target speech was convolved with room impulse responses (RIRs) recorded at three talker-to-listener distances in five physical rooms with distinct reverberation times. Noise consisted of four two-talker dialogues convolved with RIRs measured at fixed positions around the listener. Results in quiet suggest that a significant drop in SI occurs mainly at long talker-to-listener distances, and small reverberant rooms affect SI the most. In noise, the most detrimental type of noise is anechoic as it is the most modulated. Overall, the results suggest that at fixed signal-to-noise ratios the effects of noise and reverberation are smallest at short distances in large rooms or in small rooms with some reverberation.

Effect of wireless remote microphone application on speech discrimination in noise in children with cochlear implants

OBJECTIVES

Although cochlear implantation has significantly contributed to the speech perception of cochlear implant (CI) users, these individuals still have significant difficulty in understanding speech, especially in noisy environments and keeping track of the target speaker in the presence of speech sounds of others. This study was aimed to evaluate the effect of wireless Remote Microphones (RM) on speech discrimination scores in noise in child CI users.

MATERIALS AND METHODS

Twenty children with unilateral cochlear implantation were enrolled in this study with mean ± SD age of 5.8 ± 0.83 years who have undergone CI for at least one year. Speech discrimination scores in noise were assessed using the Words-in-Noise (WIN) test at a constant signal-to-noise ratio (SNR) of 0 dB, in the presence and absence of a wireless RM. Three loudspeakers were placed at a distance of 1 m in front of the child to present the speech and babble noise. The wireless microphone was placed on a base with a height equivalent to the height of the middle speech loudspeaker at a distance of 30 cm from it.

FINDINGS

The mean speech discrimination score in noise in the absence of wireless RM in all children was obtained 34% (6.8 words out of 20 words), with minimum and maximum of 15% and 50% words. Findings revealed the mean speech discrimination score in noise in the presence of wireless RMs is equivalent to 65% (13 words out of 20 words), with the minimum and maximum scores of 35% and 95%, respectively. The result showed that speech discrimination scores in noise improved in the presence of wireless RM.

CONCLUSION

The significant improvement was observed in speech discrimination in noise in all cochlear implanted children when the wireless RM was used, as compared to the absence of a wireless RM, which suggests the usefulness of this hearing aid accessory in CI users.

Impact of room acoustic parameters on speech and music perception among participants with cochlear implants

OBJECTIVES

Besides numerous other factors, listening experience with cochlear implants is substantially impaired by room acoustics. Even for persons without hearing impairment, the perception of auditory scenes, for example, concerning speech intelligibility, acoustic quality or audibility, is considerably influenced by room acoustics. For CI users, complex listening environments are usually associated with heavy losses. The aim of the present study was to determine room acoustic criteria that particularly influence speech pleasantness for CI users.

DESIGN

Accordingly, speech material of the Oldenburg Sentence Test (Oldenburger Satztest, OLSA) as well as basic music material (major and minor triads) were auralized using the software Auratorium which allows auralization of simulated rooms. The constructed rooms for speech stimuli were based on the standard DIN 18041:2016-03 concerning acoustic quality in rooms, the binding standard referred to by room acoustic consultants in Germany, which also includes specifications for inclusive applications in schools. For the music perception tests, two typical concert halls of different sizes were modelled. The auralized test stimuli were unilaterally presented to 10 CI users via their auxiliary input as well as to 18 participants with typical hearing via headphones (control group). Speech pleasantness was evaluated using modified MUSHRA tests. Concerning music perception, chord discrimination was tested using paired comparisons.

RESULTS

A strong preference of small source to listener distances by CI users was found, but no significant preference for room acoustic attenuation which exceeded the recommended for inclusive applications in schools. The analyses of the energy-time-structures suggested that a dense concentration of early reflections makes a beneficial impact on CI listeners' pleasantness ratings. Music materials were distinguished more consistently without any room acoustic impact, while any room acoustic impact led to performance close to chance level. This effect is probably due to spectral smearing effects caused by reverberation.

CONCLUSIONS

These results suggest that in terms of pleasantness of speech, for CI-users, source-to-listener distance is the more influential parameter than room attenuation which goes beyond the German standard recommendation. Reflections from which CI users can benefit seem to occur much earlier than those from which NH listeners benefit. Future studies on chord discrimination concerning room acoustics are needed.

Auditory Environment Across the Life Span of Cochlear Implant Users: Insights From Data Logging

PURPOSE

We describe the natural auditory environment of people with cochlear implants (CIs), how it changes across the life span, and how it varies between individuals.

METHOD

We performed a retrospective cross-sectional analysis of Cochlear Nucleus 6 CI sound-processor data logs. The logs were obtained from 1,501 people with CIs (ages 0-96 years). They covered over 2.4 million hr of implant use and indicated how much time the CI users had spent in various acoustical environments. We investigated exposure to spoken language, noise, music, and quiet, and analyzed variation between age groups, users, and countries.

RESULTS

CI users spent a substantial part of their daily life in noisy environments. As a consequence, most speech was presented in background noise. We found significant differences between age groups for all auditory scenes. Yet even within the same age group and country, variability between individuals was substantial.

CONCLUSIONS

Regardless of their age, people with CIs face challenging acoustical environments in their daily life. Our results underline the importance of supporting them with assistive listening technology. Moreover, we found large differences between individuals' auditory diets that might contribute to differences in rehabilitation outcomes. Their causes and effects should be investigated further.

Evaluation of a spectral subtraction strategy to suppress reverberant energy in cochlear implant devices

The smearing effects of room reverberation can significantly impair the ability of cochlear implant (CI) listeners to understand speech. To ameliorate the effects of reverberation, current dereverberation algorithms focus on recovering the direct sound from the reverberated signal by inverse filtering the reverberation process. This contribution describes and evaluates a spectral subtraction (SS) strategy capable of suppressing late reflections. Late reflections are the most detrimental to speech intelligibility by CI listeners as reverberation increases. By tackling only the late part of reflections, it is shown that users of CI devices can benefit from the proposed strategy even in highly reverberant rooms. The proposed strategy is also compared against an ideal reverberant (binary) masking approach. Speech intelligibility results indicate that the proposed SS solution is able to suppress additive reverberant energy to a degree comparable to that achieved by an ideal binary mask. The added advantage is that the SS strategy proposed in this work can allow for a potentially real-time implementation in clinical CI processors.

Inferences and metaphoric comprehension in unilaterally implanted children with adequate formal oral language performance

OBJECTIVES

To assess skills in inferences during conversations and in metaphors comprehension of unilaterally cochlear implanted children with adequate abilities at the formal language tests, comparing them with well-matched hearing peers; to verify the influence of age of implantation on overall skills.

METHODS

The study was designed as a matched case-control study. 31 deaf children, unilateral cochlear implant users, with normal linguistic competence at formal language tests were compared with 31 normal hearing matched peers. Inferences and metaphor comprehension skills were assessed through the Implicit Meaning Comprehension, Situations and Metaphors subtests of the Italian Standardized Battery of "Pragmatic Language Skills MEDEA". Differences between patient and control groups were tested by the Mann-Whitney U test. Correlations between age at implantation and time of implant use with each subtest were investigated by the Spearman rank correlation coefficient.

RESULTS

No significant differences between the two groups were found in inferencing skills (p=0.24 and p=0.011 respectively for Situations and Implicit Meaning Comprehension). Regarding figurative language, unilaterally cochlear implanted children performed significantly below their normal hearing peers in Verbal Metaphor comprehension (p=0.001). Performances were related to age at implantation, but not with time of implant use.

CONCLUSIONS

Unilaterally cochlear implanted children with normal language level showed responses similar to NH children in discourse inferences, but not in figurative language comprehension. Metaphors still remains a challenge for unilateral implant users and above all when they have not any reference, as demonstrated by the significant difference in verbal rather than figurative metaphors comprehension. Older age at implantation was related to worse performance for all items. These aspects, until now less investigated, had to receive more attention to deeply understand specific mechanisms involved and possible effects of different levels of figurative language complexity (presence or absence of contextual input, degree of transparency and syntactic frozenness). New insight is needed to orient programs in early intervention settings in considering and adequately responding to all these complex communicative need of children with hearing loss.

Análise do ruído e intervenção fonoaudiológica em ambiente escolar: rede privada e pública de ensino regular

Objetivo : mensurar os níveis de ruído, durante o ano letivo, em duas salas de aula do 1º ano do Ensino Fundamental, sendo uma da rede privada de ensino e outra da rede pública, frequentadas por alunos deficientes auditivos usuários de implante coclear; analisar se os níveis de ruídos encontrados estão de acordo com a Norma Brasileira, NBR 10.152 da ABNT (1990), e discutir com a equipe escolar estratégias que minimizem o impacto do ruído, na aprendizagem dos alunos deficientes auditivos.Métodos : foram realizadas oito mensurações do nível de ruído, empregando um dosímetro, modelo 1444, em cada sala de aula, sendo uma sala da rede privada e outra da rede pública de ensino. Concomitantemente às mensurações de ruído, foram feitas reuniões com os professores e gestores.Resultados : verificou-se que os níveis de ruído presente na rede pública variaram entre 74,3 e 79 dB (A) e que, na rede privada, os níveis de ruído variaram entre 76,1 e 80,9 dB (A). Também foram realizadas 8 reuniões em cada escola.Conclusão : diante dos dados, notaram-se elevados índices de ruído em ambiente escolar, não ocorrendo diferenças estatísticas entre as redes pública e privada de ensino regular. Com relação às reuniões mensais, foi possível observar que os educadores adotaram estratégias que auxiliam a comunicação no ambiente escolar. É evidente a necessidade da aquisição de recurso tecnológico de acessibilidade para alunos deficientes auditivos que utilizam a comunicação oral, o sistema de frequência modulada.

Use of amplitude modulation cues recovered from frequency modulation for cochlear implant users when original speech cues are severely degraded

Won et al. (J Acoust Soc Am 132:1113-1119, 2012) reported that cochlear implant (CI) speech processors generate amplitude-modulation (AM) cues recovered from broadband speech frequency modulation (FM) and that CI users can use these cues for speech identification in quiet. The present study was designed to extend this finding for a wide range of listening conditions, where the original speech cues were severely degraded by manipulating either the acoustic signals or the speech processor. The manipulation of the acoustic signals included the presentation of background noise, simulation of reverberation, and amplitude compression. The manipulation of the speech processor included changing the input dynamic range and the number of channels. For each of these conditions, multiple levels of speech degradation were tested. Speech identification was measured for CI users and compared for stimuli having both AM and FM information (intact condition) or FM information only (FM condition). Each manipulation degraded speech identification performance for both intact and FM conditions. Performance for the intact and FM conditions became similar for stimuli having the most severe degradations. Identification performance generally overlapped for the intact and FM conditions. Moreover, identification performance for the FM condition was better than chance performance even at the maximum level of distortion. Finally, significant correlations were found between speech identification scores for the intact and FM conditions. Altogether, these results suggest that despite poor frequency selectivity, CI users can make efficient use of AM cues recovered from speech FM in difficult listening situations.

Reverberation suppression in cochlear implants using a blind channel-selection strategy

Reverberation severely degrades speech intelligibility for cochlear implant (CI) users. The ideal reverberant mask (IRM), a binary mask for reverberation suppression which is computed using signal-to-reverberant ratio, was found to yield substantial intelligibility gains for CI users even in highly reverberant environments (e.g., T60 = 1.0 s). Motivated by the intelligibility improvements obtained from IRM, a monaural blind channel-selection criterion for reverberation suppression is proposed. The proposed channel-selection strategy is blind, meaning that prior knowledge of neither the room impulse response nor the anechoic signal is required. By the use of a residual signal obtained from linear prediction analysis of the reverberant signal, the residual-to-reverberant ratio (RRR) of individual frequency channels was employed as the channel-selection criterion. In each frame, the channels with RRR less than an adaptive threshold were retained while the rest were zeroed out. Performance of the proposed strategy was evaluated via intelligibility listening tests conducted with CI users in simulated rooms with two reverberation times of 0.6 and 0.8 s. The results indicate significant intelligibility improvements in both reverberant conditions (over 30 and 40 percentage points in T60 = 0.6 and 0.8 s, respectively). The improvement is comparable to that obtained with the IRM strategy.

The combined effects of reverberation and noise on speech intelligibility by cochlear implant listeners

OBJECTIVE

The purpose of this study is to assess the individual effect of reverberation and noise, as well as their combined effect, on speech intelligibility by cochlear implant (CI) users.

DESIGN

Sentence stimuli corrupted by reverberation, noise, and reverberation + noise are presented to 11 CI listeners for word identification. They are tested in two reverberation conditions (T60 = 0.6 s, 0.8 s), two noise conditions (SNR = 5 dB, 10 dB), and four reverberation + noise conditions.

STUDY SAMPLE

Eleven CI users participated.

RESULTS

Results indicated that reverberation degrades speech intelligibility to a greater extent than additive noise (speech-shaped noise), at least for the SNR levels tested. The combined effects were greater than those introduced by either reverberation or noise alone.

CONCLUSIONS

The effect of reverberation on speech intelligibility by CI users was found to be larger than that by noise. The results from the present study highlight the importance of testing CI users in reverberant conditions, since testing in noise-alone conditions might underestimate the difficulties they experience in their daily lives where reverberation and noise often coexist.

The impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners (L)

The purpose of this study is to determine the relative impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners. Sentences were presented in two conditions wherein reverberant consonant segments were replaced with clean consonants, and in another condition wherein reverberant vowel segments were replaced with clean vowels. The underlying assumption is that self-masking effects would dominate in the first condition, whereas overlap-masking effects would dominate in the second condition. Results indicated that the degradation of speech intelligibility in reverberant conditions is caused primarily by self-masking effects that give rise to flattened formant transitions.

A channel-selection criterion for suppressing reverberation in cochlear implants

Little is known about the extent to which reverberation affects speech intelligibility by cochlear implant (CI) listeners. Experiment 1 assessed CI users' performance using Institute of Electrical and Electronics Engineers (IEEE) sentences corrupted with varying degrees of reverberation. Reverberation times of 0.30, 0.60, 0.80, and 1.0 s were used. Results indicated that for all subjects tested, speech intelligibility decreased exponentially with an increase in reverberation time. A decaying-exponential model provided an excellent fit to the data. Experiment 2 evaluated (offline) a speech coding strategy for reverberation suppression using a channel-selection criterion based on the signal-to-reverberant ratio (SRR) of individual frequency channels. The SRR reflects implicitly the ratio of the energies of the signal originating from the early (and direct) reflections and the signal originating from the late reflections. Channels with SRR larger than a preset threshold were selected, while channels with SRR smaller than the threshold were zeroed out. Results in a highly reverberant scenario indicated that the proposed strategy led to substantial gains (over 60 percentage points) in speech intelligibility over the subjects' daily strategy. Further analysis indicated that the proposed channel-selection criterion reduces the temporal envelope smearing effects introduced by reverberation and also diminishes the self-masking effects responsible for flattened formants.