The silent threat: investigating sleep disturbances in hospitalized patients.

Sleep disruptions in the hospital setting can have adverse effects on patient safety and well-being, leading to complications like delirium and prolonged recovery. This study aimed to comprehensively assess the factors influencing sleep disturbances in hospital wards, with a comparison of the sleep quality of patients staying in single rooms to those in shared rooms. A mixed-methods approach was used to examine patient-reported sleep quality and sleep disruption factors, in conjunction with objective noise measurements, across seven inpatient wards at an acute tertiary public hospital in Sydney, Australia. The most disruptive factor to sleep in the hospital was noise, ranked as 'very disruptive' by 20% of patients, followed by acute health conditions (11%) and nursing interventions (10%). Patients in shared rooms experienced the most disturbed sleep, with 51% reporting 'poor' or 'very poor' sleep quality. In contrast, only 17% of the patients in single rooms reported the same. Notably, sound levels in shared rooms surpassed 100 dB, highlighting the potential for significant sleep disturbances in shared patient accommodation settings. The results of this study provide a comprehensive overview of the sleep-related challenges faced by patients in hospital, particularly those staying in shared rooms. The insights from this study offer guidance for targeted healthcare improvements to minimize disruptions and enhance the quality of sleep for hospitalized patients.

Effects of noise exposure on stress hormone changes during task performance in young Korean men: quasi-experimental study.

Numerous studies have suggested that noise exposure might be associated with changes in stress hormone levels. However, quantitative evidence for these effects in humans is rare and remains controversial. This study aimed to investigate the acute effects of exposure to noise and its different levels on stress hormone changes in task performance. Quasi-experimental noise exposure environment was established for 90 male university student volunteers in their twenties, and each was exposed to different noise levels during task performance. The stress hormones tested included cortisol, adrenocorticotropic hormone (ACTH), adrenaline, and noradrenaline. A one-way ANOVA was performed to investigate differences in hormone levels measured in the three groups according to the noise exposure levels (35, 45, or 75 dB). Analysis of covariance (ANCOVA) was used to adjust for confounding factors that might affect hormone levels. After adjusting for confounders, significant exposure-dependent differences were found in hormone levels in salivary cortisol, serum cortisol, serum ACTH, and serum adrenaline. The amount of hormonal increase in 75 dB exposure group compared to 35 or 45 dB groups was detected. Similar results were also seen in the rate of change analysis. Our findings indicate that short-term noise exposure during task performance elevates stress hormone levels. Further, the extent of stress hormone alterations varies with noise exposure levels. Changes in hormone levels are an objective measure that may be used to identify health effects and stress responses in various noise environments.

Perceptual Consequences of Cochlear Deafferentation in Humans.

Cochlear synaptopathy, a form of cochlear deafferentation, has been demonstrated in a number of animal species, including non-human primates. Both age and noise exposure contribute to synaptopathy in animal models, indicating that it may be a common type of auditory dysfunction in humans. Temporal bone and auditory physiological data suggest that age and occupational/military noise exposure also lead to synaptopathy in humans. The predicted perceptual consequences of synaptopathy include tinnitus, hyperacusis, and difficulty with speech-in-noise perception. However, confirming the perceptual impacts of this form of cochlear deafferentation presents a particular challenge because synaptopathy can only be confirmed through post-mortem temporal bone analysis and auditory perception is difficult to evaluate in animals. Animal data suggest that deafferentation leads to increased central gain, signs of tinnitus and abnormal loudness perception, and deficits in temporal processing and signal-in-noise detection. If equivalent changes occur in humans following deafferentation, this would be expected to increase the likelihood of developing tinnitus, hyperacusis, and difficulty with speech-in-noise perception. Physiological data from humans is consistent with the hypothesis that deafferentation is associated with increased central gain and a greater likelihood of tinnitus perception, while human data on the relationship between deafferentation and hyperacusis is extremely limited. Many human studies have investigated the relationship between physiological correlates of deafferentation and difficulty with speech-in-noise perception, with mixed findings. A non-linear relationship between deafferentation and speech perception may have contributed to the mixed results. When differences in sample characteristics and study measurements are considered, the findings may be more consistent.

Alpha9alpha10 knockout mice show altered physiological and behavioral responses to signals in masking noise.

Medial olivocochlear (MOC) efferents modulate outer hair cell motility through specialized nicotinic acetylcholine receptors to support encoding of signals in noise. Transgenic mice lacking the alpha9 subunits of these receptors (α9KOs) have normal hearing in quiet and noise, but lack classic cochlear suppression effects and show abnormal temporal, spectral, and spatial processing. Mice deficient for both the alpha9 and alpha10 receptor subunits (α9α10KOs) may exhibit more severe MOC-related phenotypes. Like α9KOs, α9α10KOs have normal auditory brainstem response (ABR) thresholds and weak MOC reflexes. Here, we further characterized auditory function in α9α10KO mice. Wild-type (WT) and α9α10KO mice had similar ABR thresholds and acoustic startle response amplitudes in quiet and noise, and similar frequency and intensity difference sensitivity. α9α10KO mice had larger ABR Wave I amplitudes than WTs in quiet and noise. Other ABR metrics of hearing-in-noise function yielded conflicting findings regarding α9α10KO susceptibility to masking effects. α9α10KO mice also had larger startle amplitudes in tone backgrounds than WTs. Overall, α9α10KO mice had grossly normal auditory function in quiet and noise, although their larger ABR amplitudes and hyperreactive startles suggest some auditory processing abnormalities. These findings contribute to the growing literature showing mixed effects of MOC dysfunction on hearing.

An Exploration of the Memory Performance in Older Adult Hearing Aid Users on the Integrated Digit-in-Noise Test.

This study aimed to preliminarily investigate the associations between performance on the integrated Digit-in-Noise Test (iDIN) and performance on measures of general cognition and working memory (WM). The study recruited 81 older adult hearing aid users between 60 and 95 years of age with bilateral moderate to severe hearing loss. The Chinese version of the Montreal Cognitive Assessment Basic (MoCA-BC) was used to screen older adults for mild cognitive impairment. Speech reception thresholds (SRTs) were measured using 2- to 5-digit sequences of the Mandarin iDIN. The differences in SRT between five-digit and two-digit sequences (SRT5-2), and between five-digit and three-digit sequences (SRT5-3), were used as indicators of memory performance. The results were compared to those from the Digit Span Test and Corsi Blocks Tapping Test, which evaluate WM and attention capacity. SRT5-2 and SRT5-3 demonstrated significant correlations with the three cognitive function tests (rs ranging from -.705 to -.528). Furthermore, SRT5-2 and SRT5-3 were significantly higher in participants who failed the MoCA-BC screening compared to those who passed. The findings show associations between performance on the iDIN and performance on memory tests. However, further validation and exploration are needed to fully establish its effectiveness and efficacy.

Frequency-dependent temporary threshold shifts in the Eastern painted turtle (Chrysemys picta picta).

Testudines are a highly threatened group facing an array of stressors, including alteration of their sensory environment. Underwater noise pollution has the potential to induce hearing loss and disrupt detection of biologically important acoustic cues and signals. To examine the conditions that induce temporary threshold shifts (TTS) in hearing in the freshwater Eastern painted turtle (Chrysemys picta picta), three individuals were exposed to band limited continuous white noise (50-1000 Hz) of varying durations and amplitudes (sound exposure levels ranged from 151 to 171 dB re 1 µPa2 s). Control and post-exposure auditory thresholds were measured and compared at 400 and 600 Hz using auditory evoked potential methods. TTS occurred in all individuals at both test frequencies, with shifts of 6.1-41.4 dB. While the numbers of TTS occurrences were equal between frequencies, greater shifts were observed at 600 Hz, a frequency of higher auditory sensitivity, compared to 400 Hz. The onset of TTS occurred at 154 dB re 1 µPa2 s for 600 Hz, compared to 158 dB re 1 µPa2 s at 400 Hz. The 400-Hz onset and patterns of TTS growth and recovery were similar to those observed in previously studied Trachemys scripta elegans, suggesting TTS may be comparable across Emydidae species.

Transcriptional-profile changes in the medial geniculate body after noise-induced tinnitus.

Tinnitus is a disturbing condition defined as the occurrence of acoustic hallucinations with no actual sound. Although the mechanisms underlying tinnitus have been explored extensively, the pathophysiology of the disease is not completely understood. Moreover, genes and potential treatment targets related to auditory hallucinations remain unknown. In this study, we examined transcriptional-profile changes in the medial geniculate body after noise-induced tinnitus in rats by performing RNA sequencing and validated differentially expressed genes via quantitative polymerase chain reaction analysis. The rat model of tinnitus was established by analyzing startle behavior based on gap-pre-pulse inhibition of acoustic startles. We identified 87 differently expressed genes, of which 40 were upregulated and 47 were downregulated. Pathway-enrichment analysis revealed that the differentially enriched genes in the tinnitus group were associated with pathway terms, such as coronavirus disease COVID-19, neuroactive ligand-receptor interaction. Protein-protein-interaction networks were established, and two hub genes (Rpl7a and AC136661.1) were identified among the selected genes. Further studies focusing on targeting and modulating these genes are required for developing potential treatments for noise-induced tinnitus in patients.

A single dose of AC102 restores hearing in a guinea pig model of noise-induced hearing loss to almost prenoise levels.

Although sudden sensorineural hearing loss (SSNHL) is a serious condition, there are currently no approved drugs for its treatment. Nevertheless, there is a growing understanding that the cochlear pathologies that underlie SSNHL include apoptotic death of sensory outer hair cells (OHCs) as well as loss of ribbon synapses connecting sensory inner hair cells (IHCs) and neurites of the auditory nerve, designated synaptopathy. Noise-induced hearing loss (NIHL) is a common subtype of SSNHL and is widely used to model hearing loss preclinically. Here, we demonstrate that a single interventive application of a small pyridoindole molecule (AC102) into the middle ear restored auditory function almost to prenoise levels in a guinea pig model of NIHL. AC102 prevented noise-triggered loss of OHCs and reduced IHC synaptopathy suggesting a role of AC102 in reconnecting auditory neurons to their sensory target cells. Notably, AC102 exerted its therapeutic properties over a wide frequency range. Such strong improvements in hearing have not previously been demonstrated for other therapeutic agents. In vitro experiments of a neuronal damage model revealed that AC102 protected cells from apoptosis and promoted neurite growth. These effects may be explained by increased production of adenosine triphosphate, indicating improved mitochondrial function, and reduced levels of reactive-oxygen species which prevents the apoptotic processes responsible for OHC death. This action profile of AC102 might be causal for the observed hearing recovery in in vivo models.

(Why) Do Transparent Hearing Devices Impair Speech Perception in Collocated Noise?

Hearing aids and other hearing devices should provide the user with a benefit, for example, compensate for effects of a hearing loss or cancel undesired sounds. However, wearing hearing devices can also have negative effects on perception, previously demonstrated mostly for spatial hearing, sound quality and the perception of the own voice. When hearing devices are set to transparency, that is, provide no gain and resemble open-ear listening as well as possible, these side effects can be studied in isolation. In the present work, we conducted a series of experiments that are concerned with the effect of transparent hearing devices on speech perception in a collocated speech-in-noise task. In such a situation, listening through a hearing device is not expected to have any negative effect, since both speech and noise undergo identical processing, such that the signal-to-noise ratio at ear is not altered and spatial effects are irrelevant. However, we found a consistent hearing device disadvantage for speech intelligibility and similar trends for rated listening effort. Several hypotheses for the possible origin for this disadvantage were tested by including several different devices, gain settings and stimulus levels. While effects of self-noise and nonlinear distortions were ruled out, the exact reason for a hearing device disadvantage on speech perception is still unclear. However, a significant relation to auditory model predictions demonstrate that the speech intelligibility disadvantage is related to sound quality, and is most probably caused by insufficient equalization, artifacts of frequency-dependent signal processing and processing delays.

Application of Noise Reduction Earplugs in Patients undergoing Total Knee Arthroplasty: A Retrospective Study.

BACKGROUND: Patients undergoing total knee arthroplasty (TKA) need to tolerate the effects of noise. MATERIALS AND METHODS: This study retrospectively analyzed the clinical data of 167 TKA patients at The Affiliated Hospital of Southwest Medical University from April 2019 to April 2021. A total of 154 patients who met inclusion criteria were divided into the conventional noise reduction management group (CMG) and the noise reduction earplug group (EPG), following different management schemes. The CMG received routine noise reduction management after surgery, while the EPG used noise reduction earplugs based on the CMG. The clinical indexes of the two groups were compared. RESULTS: In this study, 79 patients were included in the CMG, and 75 patients were included in the EPG. The results showed that the Pittsburgh Sleep Quality Index (PSQI) scores of both groups 2 weeks after surgery were significantly lower than those before management (ZEPG = 5.995, ZCMG = 4.109, all P < 0.001), and the EPG exhibited a significantly lower PSQI score than the CMG (Z = -2.442, P < 0.05). Two weeks after surgery, the EPG had significantly lower levels of systolic blood pressure (ZSBP = -4.303) and diastolic blood pressure (ZDBP = -3.115), as well as lower scores on the Hospital Anxiety and Depression Scale-Anxiety (HADS-A; ZHADS-A = -7.140) and Hospital Anxiety and Depression Scale-Depression (HADS-D; ZHADS-D = -4.545) compared to the CMG (all P < 0.05). In addition, no significant correlation existed between the duration of wearing earplugs and the HADS-A and HADS-D scores (r = -0.201, r = -0.002, P > 0.05). CONCLUSION: Noise reduction earplugs can improve sleep quality and regulate negative emotions of patients undergoing TKA treatment through a complex mechanism involving noise, which is beneficial to the prognosis of the disease.

Synaptic ribbon dynamics after noise exposure in the hearing cochlea.

Moderate noise exposure induces cochlear synaptopathy, the loss of afferent ribbon synapses between cochlear hair cells and spiral ganglion neurons, which is associated with functional hearing decline. Prior studies have demonstrated noise-induced changes in the distribution and number of synaptic components, but the dynamic changes that occur after noise exposure have not been directly visualized. Here, we describe a live imaging model using RIBEYE-tagRFP to enable direct observation of pre-synaptic ribbons in mature hearing mouse cochleae after synaptopathic noise exposure. Ribbon number does not change, but noise induces an increase in ribbon volume as well as movement suggesting unanchoring from synaptic tethers. A subgroup of basal ribbons displays concerted motion towards the cochlear nucleus with subsequent migration back to the cell membrane after noise cessation. Understanding the immediate dynamics of synaptic damage after noise exposure may facilitate identification of specific target pathways to treat cochlear synaptopathy.

Comparison between perceived and felt emotions in the soundscape evaluation of urban open spacesa).

In the current study on soundscape, the distinction between felt emotion and perceived emotion in soundscape measurement has not been addressed as much as that in music studies. This research was conducted to investigate perceived and felt emotions associated with soundscape evaluation in urban open spaces through a laboratory audio-visual experiment using photographs and binaural recordings of 16 urban open locations across Harbin, China. In total, 46 participants were required to assess both the "perceived emotion" and "felt emotion" of the soundscapes using a questionnaire (in Chinese). First, five felt emotions and seven perceived emotions associated with the soundscape were identified, among which the dominant factors were enjoyment and excitement for felt emotions and comfortable and festive for perceived emotions. Second, when comparing perceived and felt emotions, the holistic soundscape descriptor "preference" is more suitable for predicting through felt emotion, while the holistic soundscape descriptor "appropriateness" is more suitable for predicting through perceived emotion. Third, preference is a more stringent soundscape descriptor than appropriateness, indicating a higher level of requirement in its definition. Meanwhile, preference is a more emotional soundscape descriptor than appropriateness. It may be inferred that for evaluating soundscapes, the more emotional the descriptor, the greater its stringency.

On the Feasibility of Using Behavioral Listening Effort Test Methods to Evaluate Auditory Performance in Cochlear Implant Users.

Realistic outcome measures that reflect everyday hearing challenges are needed to assess hearing aid and cochlear implant (CI) fitting. Literature suggests that listening effort measures may be more sensitive to differences between hearing-device settings than established speech intelligibility measures when speech intelligibility is near maximum. Which method provides the most effective measurement of listening effort for this purpose is currently unclear. This study aimed to investigate the feasibility of two tests for measuring changes in listening effort in CI users due to signal-to-noise ratio (SNR) differences, as would arise from different hearing-device settings. By comparing the effect size of SNR differences on listening effort measures with test-retest differences, the study evaluated the suitability of these tests for clinical use. Nineteen CI users underwent two listening effort tests at two SNRs (+4 and +8 dB relative to individuals' 50% speech perception threshold). We employed dual-task paradigms-a sentence-final word identification and recall test (SWIRT) and a sentence verification test (SVT)-to assess listening effort at these two SNRs. Our results show a significant difference in listening effort between the SNRs for both test methods, although the effect size was comparable to the test-retest difference, and the sensitivity was not superior to speech intelligibility measures. Thus, the implementations of SVT and SWIRT used in this study are not suitable for clinical use to measure listening effort differences of this magnitude in individual CI users. However, they can be used in research involving CI users to analyze group data.

[Mechanism of noise induced hidden hearing loss based on proteomics].

Objective: To explore the mechanism of noise-induced hidden hearing loss by proteomics. Methods: In October 2022, 64 SPF male C57BL/6J mice were divided into control group and noise exposure group with 32 mice in each group according to random sampling method. The noise exposure group was exposed to 100 dB sound pressure level, 2000-16000 Hz broadband noise for 2 h, and the mouse hidden hearing loss model was established. Auditory brainstem response (ABR) was used to test the change of hearing threshold of mice on the 7th day after noise exposure, the damage of basal membrane hair cells was observed by immunofluorescence, and the differentially expressed proteins in the inner ear of mice in each group were identified and analyzed by 4D-Label-free quantitative proteomics, and verified by Western blotting. The results were statistically analyzed by ANOVA and t test. Results: On the 7th day after noise exposure, there was no significant difference in hearing threshold between the control group and the noise exposure group at click and 8000 Hz acoustic stimulation (P>0.05) . The hearing threshold in the noise exposure group was significantly higher than that in the control group under 16000 Hz acoustic stimulation (P<0.05) . Confocal immunofluorescence showed that the basal membrane hair cells of cochlear tissue in noise exposure group were arranged neatly, but the relative expression of C-terminal binding protein 2 antibody of presynaptic membrane in middle gyrus and basal gyrus was significantly lower than that in control group (P<0.05) . GO enrichment analysis showed that the functions of differentially expressed proteins were mainly concentrated in membrane potential regulation, ligand-gated channel activity, and ligand-gated ion channel activity. KEGG pathway enrichment analysis showed that differentially expressed proteins were significantly enriched in phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt) signaling pathway, NOD-like receptor signaling pathway, calcium signaling pathway, etc. Western blotting showed that the expression of inositol 1, 4, 5-trisphosphate receptor 3 (Itpr3) was increased and the expression of solute carrier family 38 member 2 (Slc38a2) was decreased in the noise exposure group (P<0.05) . Conclusion: Through proteomic analysis, screening and verification of the differential expression proteins Itpr3 and Slc38a2 in the constructed mouse noise-induced hidden hearing loss model, the glutaminergic synaptic related pathways represented by Itpr3 and Slc38a2 may be involved in the occurrence of hidden hearing loss.

Sources of Sound Exposure in Pediatric Critical Care.

BACKGROUND: Sound levels in the pediatric intensive care unit (PICU) are often above recommended levels, but few researchers have identified the sound sources contributing to high levels. OBJECTIVES: To identify sources of PICU sound exposure. METHODS: This was a secondary analysis of continuous bedside video and dosimeter data (n = 220.7 hours). A reliable coding scheme developed to identify sound sources in the adult ICU was modified for pediatrics. Proportions of sound sources were compared between times of high (≥45 dB) and low (<45 dB) sound, during day (7 AM to 6:59 PM) and night (7 PM to 6:59 AM) shifts, and during sound peaks (≥70 dB). RESULTS: Overall, family vocalizations (38% of observation time, n = 83.9 hours), clinician vocalizations (32%, n = 70.6 hours), and child nonverbal vocalizations (29.4%, n = 64.9 hours) were the main human sound sources. Media sounds (57.7%, n = 127.3 hours), general activity (40.7%, n = 89.8 hours), and medical equipment (31.3%, n = 69.1 hours) were the main environmental sound sources. Media sounds occurred in more than half of video hours. Child nonverbal (71.6%, n = 10.2 hours) and family vocalizations (63.2%, n = 9 hours) were highly prevalent during sound peaks. General activity (32.1%, n = 33.2 hours), clinician vocalizations (22.5%, n = 23.3 hours), and medical equipment sounds (20.6, n = 21.3 hours) were prevalent during night shifts. CONCLUSIONS: Clinicians should partner with families to limit nighttime PICU noise pollution. Large-scale studies using this reliable coding scheme are needed to understand the PICU sound environment.

Focusing on Positive Listening Experiences Improves Speech Intelligibility in Experienced Hearing Aid Users.

Negativity bias is a cognitive bias that results in negative events being perceptually more salient than positive ones. For hearing care, this means that hearing aid benefits can potentially be overshadowed by adverse experiences. Research has shown that sustaining focus on positive experiences has the potential to mitigate negativity bias. The purpose of the current study was to investigate whether a positive focus (PF) intervention can improve speech-in-noise abilities for experienced hearing aid users. Thirty participants were randomly allocated to a control or PF group (N = 2 × 15). Prior to hearing aid fitting, all participants filled out the short form of the Speech, Spatial and Qualities of Hearing scale (SSQ12) based on their own hearing aids. At the first visit, they were fitted with study hearing aids, and speech-in-noise testing was performed. Both groups then wore the study hearing aids for two weeks and sent daily text messages reporting hours of hearing aid use to an experimenter. In addition, the PF group was instructed to focus on positive listening experiences and to also report them in the daily text messages. After the 2-week trial, all participants filled out the SSQ12 questionnaire based on the study hearing aids and completed the speech-in-noise testing again. Speech-in-noise performance and SSQ12 Qualities score were improved for the PF group but not for the control group. This finding indicates that the PF intervention can improve subjective and objective hearing aid benefits.

Pre- and postnatal noise directly impairs avian development, with fitness consequences.

Noise pollution is expanding at an unprecedented rate and is increasingly associated with impaired reproduction and development across taxa. However, whether noise sound waves are intrinsically harmful for developing young-or merely disturb parents-and the fitness consequences of early exposure remain unknown. Here, by only manipulating the offspring, we show that sole exposure to noise in early life in zebra finches has fitness consequences and causes embryonic death during exposure. Exposure to pre- and postnatal traffic noise cumulatively impaired nestling growth and physiology and aggravated telomere shortening across life stages until adulthood. Consistent with a long-term somatic impact, early life noise exposure, especially prenatally, decreased individual offspring production throughout adulthood. Our findings suggest that the effects of noise pollution are more pervasive than previously realized.

From the perspective of perceptual speech quality: The robustness of frequency bands to noise.

Speech quality is one of the main foci of speech-related research, where it is frequently studied with speech intelligibility, another essential measurement. Band-level perceptual speech intelligibility, however, has been studied frequently, whereas speech quality has not been thoroughly analyzed. In this paper, a Multiple Stimuli With Hidden Reference and Anchor (MUSHRA) inspired approach was proposed to study the individual robustness of frequency bands to noise with perceptual speech quality as the measure. Speech signals were filtered into thirty-two frequency bands with compromising real-world noise employed at different signal-to-noise ratios. Robustness to noise indices of individual frequency bands was calculated based on the human-rated perceptual quality scores assigned to the reconstructed noisy speech signals. Trends in the results suggest the mid-frequency region appeared less robust to noise in terms of perceptual speech quality. These findings suggest future research aiming at improving speech quality should pay more attention to the mid-frequency region of the speech signals accordingly.

Effects of training length on adaptation to noise-vocoded speech.

Listeners show rapid perceptual learning of acoustically degraded speech, though the amount of exposure required to maximize speech adaptation is unspecified. The current work used a single-session design to examine the length of auditory training on perceptual learning for normal hearing listeners exposed to eight-channel noise-vocoded speech. Participants completed short, medium, or long training using a two-alternative forced choice sentence identification task with feedback. To assess learning and generalization, a 40-trial pre-test and post-test transcription task was administered using trained and novel sentences. Training results showed all groups performed near ceiling with no reliable differences. For test data, we evaluated changes in transcription accuracy using separate linear mixed models for trained or novel sentences. In both models, we observed a significant improvement in transcription at post-test relative to pre-test. Critically, the three training groups did not differ in the magnitude of improvement following training. Subsequent Bayes factors analysis evaluating the test by group interaction provided strong evidence in support of the null hypothesis. For these stimuli and procedure, results suggest increased training does not necessarily maximize learning outcomes; both passive and trained experience likely supported adaptation. Findings may contribute to rehabilitation recommendations for listeners adapting to degraded speech signals.