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PubMed2006

Executive brain functions after exposure to nocturnal traffic noise: effects of task difficulty and sleep quality.

The after-effects of nocturnal traffic noise on cognitive performance and inhibitory brain activity were investigated. Twenty participants (18-30 years) performed an easy and a difficult visual Go/Nogo task with simultaneous EEG recording after a quiet night and then during three nights when aircraft noise was presented with equivalent noise levels of 39, 44, and 50 dBA, respectively, between 11 p.m. to 7 a.m. Based on subjective sleep quality rating, participants were separated into "good" versus "bad" sleepers. The performance and inhibition-related components (N2, P3) of event-related potentials were analysed. The N2 and P3 amplitudes were smaller and latencies were prolonged in the difficult than in the easy task. This effect was more pronounced for Nogo than for Go trials. The Nogo-P3 amplitude was smaller in Noise than in "Quiet" conditions in the difficult task only. In the difficult task, the Nogo-P3 latency was prolonged in bad sleepers than in good sleepers. The Nogo-P3 amplitude was reduced in Noise as compared to "Quiet" conditions in bad sleepers only. Sleep quality in bad sleepers worsened steadily with increasing noise levels. No effects of noise or subjective sleep quality on performance were found. Inhibitory processes appear to be selectively impaired after nocturnal noise exposure. The task difficulty and perceived sleep quality are important factors modulating noise effects. The results suggest that nocturnal traffic noise increase physiological costs for inhibitory functioning on the day even if no overt performance decrement is observed.

Action Potentials↗
PubMed1989

Plasma catecholamine and corticosterone responses to predictable and unpredictable noise stress in rats.

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) increases were determined in individual rats subjected to either 20 regularly or irregularly scheduled white-noise stimulations (4 min, 100 dBA). Blood was frequently sampled during the first and twentieth noise exposure, and during a reexposure after 24 hr. During the sampling periods, behavioral activities of the rats were recorded. The initial noise-induced CS release was partially reduced following the regular noise presentations. The increase after irregular presentations remained high. The difference in adrenocortical responsiveness between regular and irregular exposure persisted for 24 hr. The NA response to noise was partially attenuated following irregular administration of noise. However, regular exposure produced increased NA levels prior to noise presentation and a subsequent decrease during stimulation. After 24 hr, noise evoked an exaggerated initial NA release in the regular group. The noise-elicited rise in A was completely abolished after 20 noise presentations irrespective of whether these were applied regularly or irregularly. Reexposure after 24 hr evoked again a significant A response in both groups. No differences were observed in the habituation pattern of behavioral reactions among the regular and irregular groups. The results show that the sympathetic neural, adrenomedullary and adrenocortical systems differ in degree and speed of adaptation to intermittent stressful stimuli and in sensitivity to the predictability of stressors.

Animals↗
PubMed1992

Contrast sensitivity as a function of spatial frequency, viewing distance and eccentricity with and without spatial noise.

Using computer graphics and a two-alternative forced-choice method we measured threshold contrast as a function of viewing distance, spatial frequency, and eccentricity for gratings with and without added, white two-dimensional spatial noise. Our experiments showed that in spatial noise contrast sensitivity was independent of viewing distance as long as contrast sensitivity was lower with noise than without. With increasing spatial frequency (f) the grating area (A) was reduced in order to keep the relative grating size (Af2) constant. At all spatial frequencies the test gratings thus had the same amount of detail and contour. Noise spectral density was reduced in direct proportion to grating area in order to keep the physical signal-to-noise ratio constant. An increase in spatial frequency was thus accompanied with reductions in grating area and noise spectral density similar to those produced by a corresponding increase in viewing distance. In agreement, contrast detection in spatial noise was found to be independent of spatial frequency as long as contrast sensitivity was lower with noise than without. The effect of increasing eccentricity on visual performance can be compensated for by reducing the viewing distance (M-scaling). Hence, without M-scaling the effect of increasing eccentricity is similar to that of increasing viewing distance. In agreement, we found that contrast sensitivity in spatial noise was independent of eccentricity as long as contrast sensitivity was lower with noise than without.

Adult↗
PubMed1985

Some neural mechanisms in the cat's auditory cortex underlying sensitivity to combined tone and wide-spectrum noise stimuli.

In the auditory cortex of nitrous oxide-anesthetized, muscle-relaxed cats, single neurons were studied for their responsiveness to pure tones that were mixed acoustically with simultaneously gated wide-spectrum noise bursts presented using a calibrated sealed stimulating system. The intensities of both the tone and the noise were systematically varied, with a view to ascertaining the sensitivity of cortical cells to a characteristic frequency tone delivered in the presence of a noise mask. Neurons for which wide-spectrum noise provided a net excitatory influence typically displayed a 'strong-signal capture' effect; that is, the cell's responses were dominated by whichever of the two elements of the combined stimulus was the more effective when tested separately. These cells generally had monotonic tone rate intensity functions. Most of the cells that were suppressed by the noise displayed nonmonotonic pure tone rate intensity functions. When nonmonotonic cells were studied with the combined stimulus, the noise was found to produce an intensity-dependent suppression of their tone-evoked responses that could not be overcome by elevating the tone intensity. In contrast, for the minority of monotonic neurons whose tone-evoked responses were suppressed by noise, that suppression could be overcome by raising the tone intensity. None of the cells in the sample responded in a sustained fashion to continuous noise. In each of 11 cases examined, the effect of a continuous noise mask was to elevate tone thresholds and to prolong latent periods for tones; the magnitude of both of these effects depended on the intensity of the continuous noise mask.

Animals↗
PubMed2004

Deleterious effects of an environmental noise on sleep and contribution of its physical components in a rat model.

Sleep disturbances induced by environmental noise (EN) exposure are now well admitted. However, many contradictory conclusions and discrepancies have been reported, resulting from uncontrolled human factors or the use of artificial noises (pure tone). Thus, the development of an animal model appears to be a useful strategy for determining whether EN is deleterious to sleep. The aims of this study were: (i) to confirm the effects of noise on sleep in a rat model; and (ii) to determine the most deleterious physical component of noise regarding sleep structure. For this purpose, rats were exposed during 24 h either to EN or to artificial broad-band noises [either continuous broad-band noise (CBBN) or intermittent broad-band noise (IBBN)]. All the noises decrease both slow wave sleep (SWS) and paradoxical sleep (PS) amounts during the first hours of exposure. However, CBBN acts indirectly on PS through a reduction of SWS bout duration, whereas IBBN and EN disturb directly and more strongly both SWS and PS. Finally, EN fragments SWS and decreases PS amount during the dark period, whereas IBBN only fragments PS. These results demonstrate the validity and suitability of a rodent model for studying the effects of noise on sleep and definitively show that sleep is disturbed by EN exposure. Two physical factors seem to be implicated: the intermittency and the frequency spectrum of the noise events, which both induce long-lasting sleep disturbances. An additive effect of frequency spectrum to intermittency tends to abolish all possible adaptations to EN exposure. Since sleep is involved in cognitive processes, such disturbances could lead to cognitive deficits.

Animals↗
PubMed2005

The effect of different noise types on the speech and non-speech elicited mismatch negativity.

The effect of different types of real-life noise on the central auditory processing of speech and non-speech sounds was evaluated by the means of mismatch negativity and behavioral responses. Subjects (19-34 years old; 6 males, 4 females) were presented, in separate conditions, with either speech or non-speech stimuli of approximately equal complexity in five background conditions: babble noise, industrial noise, traffic noise, wide band noise, and silent condition. Whereas there were no effects of stimuli or noise on the behavioral responses, the MMN results revealed that speech and non-speech sounds are processed differently both in silent and noisy conditions. Speech processing was more affected than non-speech processing in all noise conditions. Moreover, different noise types had a differential effect on the pre-attentive discrimination, as reflected in MMN, on speech and non-speech sounds. Babble and industrial noises dramatically reduced the MMN amplitudes for both stimulus types, while traffic noise affected only speech stimuli.

Acoustic Stimulation↗
PubMed2006

Does erythropoietin augment noise induced hearing loss?

Noise-induced hearing loss may result from excessive release of glutamate, nitrogen oxide and reactive oxygen species. The effects of these factors on the inner ear may potentially be prevented or reduced by erythropoietin (EPO), as indicated by previously demonstrated neuro-protective effects of EPO upon damage to the central nervous system and the retina. This paper reports three separate trials, conducted to investigate the hypothesis that noise-induced hearing loss is prevented or reduced by erythropoietin. The trials employed three different modes of drug application, different administration time windows and different rodent species. In trial 1, guinea pigs were exposed to 110dB SPL, 4-20kHz wide band noise (WBN) for 8h. EPO was administered to the round window membrane 24h after noise exposure, either sustained by pump for a week or by single dose middle ear instillation. In trial 2, rats were exposed to 105dB SPL, 4-20kHz WBN for 8h. EPO was administered by single dose middle ear instillation 1 or 14h after noise exposure. In trial 3, rats were exposed to 105dB SPL, 4-20kHz WBN for 8 or 3x8h. EPO was injected intraperitoneally 1h before noise exposure. Oto-acoustic emissions and auditory brainstem responses (at 16kHz) were recorded before and after noise exposure in all trials. The noise exposure induced a hearing loss in all animals. In trial 1, no recovery and no improvement of hearing occurred in any treatment group. In trial 2 and 3, a partial hearing recovery was seen. However, the hearing loss of the EPO treated animals was significantly worse than controls in trial 2. In trial 3, the hearing of the EPO treated animals exposed for 3x8h was significantly worse than controls. Thus, surprisingly, the results from 2 of the 3 present trials indicate that erythropoietin may in fact augment noise-induced hearing loss. This is contradictory to the beneficial effect of EPO reported by the vast majority of studies on stressed neural tissues. EPO administration may alter the blood flow dynamics of the cochlear vascular bed during or after noise exposure, by a potential induction of vasoconstriction. This may be the cause of the surprising findings.

Animals↗
PubMed2005

Acrylonitrile potentiates hearing loss and cochlear damage induced by moderate noise exposure in rats.

The diversity of chemical and drugs that can potentiate noise-induced hearing loss (NIHL) has impeded efforts to predict such interactions. We have hypothesized that chemical contaminants that disrupt intrinsic antioxidant defenses hold significant risk for potentiating NIHL. If this is true, then acrylonitrile (ACN) would be expected to potentiate NIHL. ACN, one of the 50 most commonly used chemicals in the United States, is metabolized via two pathways that are likely to disrupt intrinsic reactive oxygen species (ROS) buffering systems: (1) it conjugates glutathione, depleting this important antioxidant rapidly; (2) a second pathway involves the formation of cyanide, which can inhibit superoxide dismutase. We hypothesized that moderate noise exposure, that does not produce permanent hearing loss by itself, could initiate oxidative stress and that ACN could render the inner ear more sensitive to noise by disrupting intrinsic antioxidant defenses. Temporary and persistent effects of ACN alone (50 mg/kg, sc 5 days), noise alone (95 or 97 dB octave band noise, 4 h/day for 5 days), or ACN in combination with noise were determined using distortion product otoacoustic emissions (DPOAEs) and compound action potential (CAP) amplitudes. Histopathological damage to hair cells resulting from these treatments was also investigated using surface preparations of the organ of Corti. Individually, neither ACN nor noise exposures caused any permanent hearing or hair cell loss; only a reversible temporary threshold shift was measured in noise-exposed animals. However, when given in combination, ACN and noise induced permanent threshold shifts (13-16 dB between 7 and 40 kHz) and a decrease in DPOAE amplitudes (up to 25 dB at 19 kHz), as well as significant outer hair cell (OHC) loss (up to 20% in the first row between 13 and 47 kHz). This investigation demonstrates that ACN can potentiate NIHL at noise levels that are realistic in terms of human exposure, and that the OHCs are the main target of toxicity. While the exact mechanism is unknown, the results are consistent with the hypothesis of ROS involvement in NIHL at moderate levels.

Acrylonitrile↗
PubMed2002

Effects of predictable and unpredictable intermittent noise on spatial learning in rats.

The effects of predictable (periodic) and unpredictable (aperiodic) intermittent noise of moderate intensity (68 dB) on the learning of a complex T-maze by genetically defined rats were investigated. In Experiment 1, three groups (n=8) of rats learned a multiple T-maze, one group under control conditions, one group with predictable intermittent noise and one group with unpredictable intermittent noise. Results showed a profound effect of noise on learning and behavioural scores. Noise-exposed animals made less errors, finished their trials sooner and explored less. There was no difference between predictable and unpredictable noise. Further tests, during which formerly noise-exposed groups learned a new route under control conditions (Experiment 2) or the former controls learned a new route with noise (Experiment 3), suggest that the effects of noise on learning were caused by an effect of noise on memory formation and/or retrieval, rather than by long-term shifts in behavioural strategies.

Analysis of Variance↗
PubMed2001

Free radical generation in the cochlea during combined exposure to noise and carbon monoxide: an electrophysiological and an EPR study.

Ototoxicity following combined exposure to noise and carbon monoxide (CO) is known to result in more severe permanent threshold shifts than exposure to noise alone. We have previously demonstrated that such potentiation of noise-induced auditory impairment by CO can be prevented by the administration of a nitrone spin-trapping agent. Although such protection implicates injury via free radical pathways, drug-induced protection does not provide direct evidence for the presence of free radicals in the cochlea. The objective of this study was to demonstrate the actual presence of nitrone spin adducts in the cochlea following simultaneous exposure to noise and CO. Using electrophysiological end-points, the protective effects of the nitrone spin-trapping agent alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) were assessed following combined exposure of adult male Long Evans hooded rats to noise and CO. In addition, an ex-vivo evaluation of POBN spin adducts was done by electron paramagnetic resonance spectroscopy (EPR). The noise used was octave band noise with center frequency 13.6 kHz at 100 dB(Lin) for a duration of 2 h. The level of CO used was 1200 ppm. Electrophysiological results demonstrate that POBN protects against combined exposure to noise plus CO. The EPR study demonstrates POBN spin adducts in the cochleae of animals exposed to noise plus CO. Therefore, this study provides evidence to the hypothesis that ototoxicity due to noise plus CO exposure is mediated via free radicals.

Animals↗
PubMed2003

Effects of alpha-tocopherol on noise-induced hearing loss in guinea pigs.

Preventing noise-induced hearing loss (NIHL) by antioxidants is based on the hypothesis that generation of reactive oxygen species is one of the causes of NIHL. alpha-Tocopherol is a naturally occurring antioxidant with no noticeable side effects. In this study, we attempted to protect guinea pigs from developing NIHL by administering alpha-tocopherol. Pigmented male guinea pigs were exposed to a noise (4 kHz octave band, 100 dB SPL), 8 h/day for 3 days consecutively. alpha-Tocopherol (10 mg/kg or 50 mg/kg daily) was given by intraperitoneal injection from 3 days before through 3 days after the noise exposure. Auditory evoked brainstem response (ABR) thresholds at 2, 4 and 8 kHz were recorded prior to the experiment, immediately post-noise, 2 and 8 days post-noise. On day 8 post-noise, after the ABR recording, guinea pigs were decapitated and the cochleae were removed for cochlear surface preparations and scanning electron microscope (SEM) study. ABR threshold shifts of groups receiving alpha-tocopherol were significantly smaller than those of groups not receiving alpha-tocopherol at all frequencies and all time points tested except that of group 3 at 8 kHz 8 days post-noise. No hair cell loss was seen on the surface preparations, but stereocilia loss was found by SEM study. The noise-induced stereocilia loss was significantly decreased by alpha-tocopherol. These results indicate that alpha-tocopherol can attenuate the noise-induced cochlear damage. Further investigations on the preventive effect of alpha-tocopherol on NIHL in noise-exposed workers are necessary.

Animals↗
PubMed1995

A CQI approach to the investigation of noise levels within the intensive care unit environment.

In February 1991, the Intensive Care Unit (ICU) at Liverpool Hospital was extended and relocated to a larger area. It soon became apparent that noise levels within the newly renovated unit were particularly worrying to patients, staff and relatives. A Continuous Quality Improvement (CQI) group was formed to investigate, and develop measures to reduce these noise levels. Through the implementation of various CQI tools a study plan was developed to investigate the noise problem. The study plan included: a patient, relative and staff questionnaire; a literature search; identification of levels of noise using a sound level meter; contracting a noise consultant to visit and review the ICU environment. The results of the CQI investigations revealed that there was an inappropriately high level of noise in the ICU. Several key contributing factors were also identified. These findings provided the basis for several positive measures to be undertaken including: the installation of sound absorbing ceilings; removal of rubbish bin lids; revision of the telephone ringing system; revision of the mobile x-ray machine; prioritisation of audible machine alarms; education of staff in noise level awareness; The application of the Continuous Quality Improvement (CQI) process to the noise problem facilitated the exploration of the source of noise, the effects on staff and patients, and ways to reduce noise levels in the intensive care environment.

Health Facility Environment↗
PubMed2002

A comparison of the effects of broadband masking noise on the auditory brainstem response in young and older adults.

We examined the effects of ipsilateral-direct, continuous, broadband noise on auditory brainstem response (ABR) wave I and V latencies and amplitudes in young adult versus older adult humans. It was hypothesized that age might influence the effects of masking noise on ABR peak latencies and/or amplitudes, given the frequent complaint of older persons' ability to process speech in background noise. Young adults had hearing thresholds of 20 dB HL or better for the octave frequencies from 250 to 8,000 Hz. A subset of older study participants had thresholds of 20 dB HL or better across frequency, but others had thresholds up to 45 dB HL. All data were collected and analyzed with a Nicolet Bravo. An electrode was placed on the tympanic membrane (as well as on high forehead and contralateral mastoid), and a click level of 115 dB pSPL was used to maximize wave I amplitude. Masker conditions included a no-noise control and noise levels ranging from 20 to 70 dB effective masking, in 10 dB steps. With increasing noise level, both age groups showed minimal changes in wave I latency, but substantial increases in wave V latency and I-V interval. Peak amplitudes decreased with increasing noise level. Mean amplitudes were smaller for the older group, most notably for wave I. Mean peak latencies were greater in the older group, but the I-V interval was similar across age groups, as was the change in peak latencies and I-V interval across noise level. ABR parameters for the older adults with hearing meeting the 20-dB HL criterion at all frequencies (older-better) were compared to those who didn't meet this criterion (older-worse). Mean wave I latency was greater and wave V latency and I-V interval were smaller for the older-worse group at all noise levels. Mean wave I and V amplitudes were similar for the older-better and older-worse groups. In participants with normal or near-normal hearing, ABR changes with increasing age included small latency increases and a substantial reduction in wave I amplitude. The effects of ipsilateral-direct masking noise on the click-evoked ABR are similar for young and older adults.

Adult↗
PubMed1991

Notched-noise measures of frequency selectivity in adults and children using fixed-masker-level and fixed-signal-level presentation.

Three experiments were performed to examine the development of frequency selectivity and to attempt to separate peripheral versus central contributions to frequency selectivity. In Experiment 1, frequency selectivity was examined in 4-year-old children, 6-year-old children, and adults, using a fixed-masker-level, notched-noise masking method. Thresholds were determined in a no-notch condition and in conditions in which the notchwidth was 0.3 times the center frequency (0.3 x fc) or 0.6 x fc. The results for the adults and 6-year-olds were similar, but the notched-noise functions of the 4-year-old listeners were relatively shallow. These results were consistent with an interpretation that frequency selectivity is relatively poor in 4-year-old listeners; however, the results of the 4-year-old listeners might also be accounted for in terms of poor processing efficiency. For example, the children may require a relatively high level of signal-related excitation in order for detection to occur. If the growth of excitation is steeper in the no-notch condition than in notched-noise conditions, then thresholds in the notched-noise conditions might be elevated because of poor processing efficiency rather than poor frequency selectivity. This interpretation is consonant with past data showing that the growth of loudness of partially masked signals steepens as a function of increasing masker level: The masker level at the output of the auditory filter centered on the signal frequency would be less for the notched-noise masker than for the masker having no notch. In Experiment 2 the growth of loudness was examined for three adult listeners in the no-notch condition and the 0.6 x fc notched noise. Results showed a steeper growth of loudness in the no-notch case. In Experiment 3, a notched-noise measure of frequency selectivity was used in which the signal level was fixed at 15 dB SL and the masker level was varied adaptively. In this method the noise level at the output of the auditory filter centered on the signal should theoretically be constant over the different notch conditions. Adult and 4-year-old listeners were tested. The notched-noise functions were similar between the adult and 4-year-old listeners. This result supports an interpretation that the shallow notched-noise, fixed-masker-level functions of 4-year-old children may be due to poor processing efficiency rather than to poor peripheral frequency selectivity.

Adult↗
PubMed2004

Masking and scrambling in the auditory thalamus of awake rats by Gaussian and modulated noises.

This paper provides a look at how modulated broad-band noises modulate the thalamic response evoked by brief probe sounds in the awake animal. We demonstrate that noise not only attenuates the response to probe sounds (masking) but also changes the temporal response pattern (scrambling). Two brief probe sounds, a Gaussian noise burst and a brief sinusoidal tone, were presented in silence and in three ongoing noises. The three noises were targeted at activating the auditory system in qualitatively distinct ways. Dynamic ripple noise, containing many random tone-like elements, is targeted at those parts of the auditory system that respond well to tones. International Collegium of Rehabilitative Audiology noise, comprised of the sum of several simultaneous streams of Schroeder-phase speech, is targeted at those parts of the auditory system that respond well to modulated sounds but lack a well defined response to tones. Gaussian noise is targeted at those parts of the auditory system that respond to acoustic energy regardless of modulation. All noises both attenuated and decreased the precise temporal repeatability of the onset response to probe sounds. In addition, the modulated noises induced context-specific changes in the temporal pattern of the response to probe sounds. Scrambling of the temporal response pattern may be a direct neural correlate of the unfortunate experience of being able to hear, but not understand, speech sounds in noisy environments.

Acoustic Stimulation↗
PubMedDate not supplied

Effects of lead and noise exposures on hearing ability.

Lead and noise, via different mechanisms, may damage hearing ability, and, in some cases, cause severe and irreversible damage. To explore possible independent and synergistic effects of lead and noise on auditory function, the authors conducted a cross-sectional study in two lead-battery manufacturing factories. Lead and noise were the two most common sources of occupational exposures in the factories. Blood lead level, ambient lead concentration, noise exposure level, and hearing thresholds of 339 lead-battery workers-including clerical and managerial staffs-were measured. The authors obtained demographics and working histories via an interview-based structured questionnaire. A total of 220 lead-battery workers were exposed to high levels of lead and noise; their average blood lead concentration was 56.9 microg/dl, and their average noise exposure level was 86.0 dBALeq. Multivariate analysis, in which possible risk factors of hearing ability were considered, demonstrated a significant correlation between a high, long-term lead exposure index (defined by duration of employment and ambient lead concentration) and decreased hearing ability. In contrast, such a correlation between short-term lead exposure (defined by blood lead level) and hearing ability was not significant. Furthermore, neither noise exposure level alone nor the interaction between noise exposure level and short- or long-term lead exposure was correlated significantly with hearing ability. The present study raises an important, but typically ignored, issue: lead exposure might precipitate a more severe auditory than noise-exposure effect. The preservation of workers' hearing ability requires that preventive measures be taken against noise exposure, which is as essential as measures taken against lead exposure.

Adult↗
PubMedDate not supplied

Occupational noise exposure and blood pressure: longitudinal and cross-sectional observations in a group of underground miners.

The question of an association between occupational noise exposure and blood pressure has important public health implications. The harmful effects of hypertension are well known, and noise is considered the most pervasive of all occupational exposures. Most previous studies have looked cross-sectionally at blood pressure and noise exposures in workers. The present study examined historic medical and personnel records of 2,197 white male South African miners. At approximately 3-y intervals, the job title, diastolic and systolic blood pressures, height, weight, and use of medication for hypertension were recorded. Noise levels were estimated, based on noise measurements of individual jobs and work areas. In the cross-sectional analyses, multiple linear regression was used with blood pressure as the dependent variable; age, body mass index (BMI), and noise exposure were the independent variables. Longitudinal analyses were performed for those miners who had observations at four or more time periods, by calculating regression coefficients for individuals for blood pressure and noise, controlling for age and BMI. Additional longitudinal analyses compared blood pressure changes between two points in time for individual miners with changes in noise exposure, controlling for changes in age and BMI. The results of the cross-sectional and longitudinal analyses indicated no association between blood pressure and noise exposure. On the basis of these results, it does not appear that occupational noise exposure has an effect on blood pressure. Inconsistencies in the literature and shortcomings in the present study indicate that additional study is needed.

Adult↗
PubMed2001

Effects of slow- and fast-acting compression on the detection of gaps in narrow bands of noise.

The inherent amplitude fluctuations in narrow bands of noise may limit the ability to detect gaps in the noise; 'dips' in the noise may be confused with the gap to be detected. For people with cochlear hearing loss, loudness recruitment may effectively magnify the fluctuations and this could partly account for the reduced ability to detect gaps in noise bands that is usually found for such people. Previously, we tested these ideas by processing the envelopes of noise bands to alter the amount of envelope fluctuation. We showed that instantaneous compression, implemented via processing of the Hilbert envelope, led to smaller (that is, better) gap detection thresholds for subjects with cochlear hearing loss. In the present experiment, we determined whether fast-acting compression of the type sometimes used in hearing aids could also lead to improved gap detection. A behind-the-ear (BTE) digital hearing aid was programmed to implement multi-band compression, either fast-acting or slow-acting (control condition). A reference condition using unaided listening was also used. Stimuli were delivered via an earphone placed over the hearing aid. Overall stimulus levels at the output of the hearing aid were similar across conditions. Thresholds for detecting gaps in noise bands centred at 4 kHz were measured as a function of noise bandwidth (10-500 Hz). To prevent the detection of spectral changes introduced by the gap, stimuli were presented in a broad-band background noise. Three normally hearing subjects and three subjects with bilateral cochlear hearing loss were tested. Gap thresholds varied non-monotonically with noise bandwidth, being maximal around 50 Hz. Gap thresholds were generally higher for the hearing-impaired than for the normally hearing subjects. For the latter, gap thresholds were similar for the three conditions. For the hearing-impaired subjects, gap thresholds were similar for the unaided condition and the condition using slow compression. However, fast compression led to smaller gap thresholds, especially for noise bandwidths up to 50 Hz. The results show that fast compression can improve the ability of hearing-impaired subjects to detect gaps in sounds with slowly fluctuating envelopes.

Adult↗