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PubMed2001

Active control of the volume acquisition noise in functional magnetic resonance imaging: method and psychoacoustical evaluation.

Functional magnetic resonance imaging (fMRI) provides a noninvasive tool for observing correlates of neural activity in the brain while a subject listens to sound. However, intense acoustic noise is generated in the process of capturing MR images. This noise stimulates the auditory nervous system, limiting the dynamic range available for displaying stimulus-driven activity. The noise is potentially damaging to hearing and is distracting for the subject. In an active noise control (ANC) system, a reference sample of a noise is processed to form a sound which adds destructively with the noise at the listener's ear. We describe an implementation of ANC in the electromagnetically hostile and physically compact MRI scanning environment. First, a prototype system was evaluated psychoacoustically in the laboratory, using the electrical drive to a noise-generating loudspeaker as the reference. This system produced 10-20 dB of subjective noise-reduction between 250 Hz and 1 kHz, and smaller amounts at higher frequencies. The system was modified to operate in a real MR scanner where the reference was obtained by recording the acoustic scanner noise. Objective reduction by 30-40 dB of the most intense component in scanner noises was realized between 500 Hz and 3500 Hz, and subjective reduction of 12 dB and 5 dB in tests at frequencies of 600 Hz and at 1.9 kHz, respectively. Although the benefit of ANC is limited by transmission paths to the cochlea other than air-conduction routes from the auditory meatus, ANC achieves worthwhile attenuation even in the frequency range of maximum bone conduction (1.5-2 kHz). ANC should, therefore, be generally useful during auditory fMRI.

Auditory Perception↗
PubMed1989

Binaural speech intelligibility in noise for hearing-impaired listeners.

The effect of head-induced interaural time delay (ITD) and interaural level differences (ILD) on binaural speech intelligibility in noise was studied for listeners with symmetrical and asymmetrical sensorineural hearing losses. The material, recorded with a KEMAR manikin in an anechoic room, consisted of speech, presented from the front (0 degree), and noise, presented at azimuths of 0 degree, 30 degrees, and 90 degrees. Derived noise signals, containing either only ITD or only ILD, were generated using a computer. For both groups of subjects, speech-reception thresholds (SRT) for sentences in noise were determined as a function of: (1) noise azimuth, (2) binaural cue, and (3) an interaural difference in overall presentation level, simulating the effect of a monaural hearing acid. Comparison of the mean results with corresponding data obtained previously from normal-hearing listeners shows that the hearing impaired have a 2.5 dB higher SRT in noise when both speech and noise are presented from the front, and 2.6-5.1 dB less binaural gain when the noise azimuth is changed from 0 degree to 90 degrees. The gain due to ILD varies among the hearing-impaired listeners between 0 dB and normal values of 7 dB or more. It depends on the high-frequency hearing loss at the side presented with the most favorable signal-to-noise (S/N) ratio. The gain due to ITD is nearly normal for the symmetrically impaired (4.2 dB, compared with 4.7 dB for the normal hearing), but only 2.5 dB in the case of asymmetrical impairment. When ITD is introduced in noise already containing ILD, the resulting gain is 2-2.5 dB for all groups. The only marked effect of the interaural difference in overall presentation level is a reduction of the gain due to ILD when the level at the ear with the better S/N ratio is decreased. This implies that an optimal monaural hearing aid (with a moderate gain) will hardly interfere with unmasking through ITD, while it may increase the gain due to ILD by preventing or diminishing threshold effects.

Adolescent↗
PubMed1993

Audiometric and histological differences between the effects of continuous and impulsive noise exposures.

An experiment was designed to determine if, for equal SPL and power spectrum, the effects on hearing of high-kurtosis noise exposures and a Gaussian noise exposure are different and the extent to which any differences measured in terms of audiometric and histological variables are frequency specific. Three groups of chinchillas with 10 animals/group were exposed for 5 days at 90 dB SPL to one of three types of noise, each with the same power spectrum. The impulsiveness, defined by the kurtosis, and the region of the spectrum from which the impulsive components of the noise were created differed for two of the noises, while the third was a continuous Gaussian noise. The results show that the most impulsive noise produced up to 20 dB greater permanent threshold shift at the high frequencies than did the Gaussian noise exposure. However, these audiometric results were difficult to reconcile with the pattern of sensory cell losses that showed statistically significant larger losses of outer hair cells for the impulsive exposure in the 0.25-kHz region. When the impacts in a high-kurtosis noise were created from the energy in the 1- through 6-kHz region of the spectrum, the audiometric profile of hearing loss was similar to that produced by the Gaussian noise; however, inner hair cell losses were significantly greater in the 4-kHz octave band region of the cochlea.

Acoustic Stimulation↗
PubMed1995

The discrimination of samples of noise in monotic, diotic, and dichotic conditions.

Listeners' ability to discriminate between independent tokens of 800-Hz-wide bands of noise (centered at 1200 Hz) was measured in monaural, diotic, and several dichotic conditions. In a two-cue, two-alternative, temporal forced-choice task, listeners indicated whether the second or third interval contained a token of noise that was different from the sample of noise that was presented in each of the remaining three intervals. Samples of noise were selected on a trial-by-trial basis from a set of 50 independent noises for each hourly session. Six durations of noise, ranging from 10 to 328 ms, were utilized, and all were presented at an overall level of 79 dB. The baseline condition for comparisons of performance was a monaural presentation of the noises. As expected, discriminability improved when the baseline condition was presented diotically. The next best performance was obtained when the baseline stimuli was presented to both ears with the proviso that the noises were interaurally uncorrelated. Other dichotic conditions, all of which also utilized interaurally uncorrelated noises, produced performance that was worse than that obtained in the monaural condition. Large degradations in performance were observed when the left ear received a different sample of noise in each of the four intervals of a trial while the right ear continued to receive the baseline stimuli. This finding indicates that listeners were effectively unable to ignore the waveforms presented to one ear while performing a task which could be solved with the information presented to the other ear.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗
PubMed1999

Sound localization in noise in hearing-impaired listeners.

The present study assesses the ability of four listeners with high-frequency, bilateral symmetrical sensorineural hearing loss to localize and detect a broadband click train in the frontal-horizontal plane, in quiet and in the presence of a white noise. The speaker array and stimuli are identical to those described by Lorenzi et al. (in press). The results show that: (1) localization performance is only slightly poorer in hearing-impaired listeners than in normal-hearing listeners when noise is at 0 deg azimuth, (2) localization performance begins to decrease at higher signal-to-noise ratios for hearing-impaired listeners than for normal-hearing listeners when noise is at +/- 90 deg azimuth, and (3) the performance of hearing-impaired listeners is less consistent when noise is at +/- 90 deg azimuth than at 0 deg azimuth. The effects of a high-frequency hearing loss were also studied by measuring the ability of normal-hearing listeners to localize the low-pass filtered version of the clicks. The data reproduce the effects of noise on three out of the four hearing-impaired listeners when noise is at 0 deg azimuth. They reproduce the effects of noise on only two out of the four hearing-impaired listeners when noise is at +/- 90 deg azimuth. The additional effects of a low-frequency hearing loss were investigated by attenuating the low-pass filtered clicks and the noise by 20 dB. The results show that attenuation does not strongly affect localization accuracy for normal-hearing listeners. Measurements of the clicks' detectability indicate that the hearing-impaired listeners who show the poorest localization accuracy also show the poorest ability to detect the clicks. The inaudibility of high frequencies, "distortions," and reduced detectability of the signal are assumed to have caused the poorer-than-normal localization accuracy for hearing-impaired listeners.

Aged↗
PubMed2006

Road traffic noise and hypertension.

BACKGROUND: It has been suggested that noise exposure increases the risk of hypertension. Road traffic is the dominant source of community noise exposure. OBJECTIVE: To study the association between exposure to residential road traffic noise and hypertension in an urban municipality. METHODS: The study population comprised randomly selected subjects aged 19-80 years. A postal questionnaire provided information on individual characteristics, including diagnosis of hypertension. The response rate was 77%, resulting in a study population of 667 subjects. The outdoor equivalent traffic noise level (Leq 24 h) at the residence of each individual was determined using noise-dispersion models and manual noise assessments. The individual noise exposure was classified in units of 5 dB(A), from <45 dB(A) to >65 dB(A). RESULTS: The odds ratio (OR) for hypertension adjusted for age, smoking, occupational status and house type was 1.38 (95% confidence interval (CI) 1.06 to 1.80) per 5 dB(A) increase in noise exposure. The association seemed stronger among women (OR 1.71; 95% CI 1.17 to 2.50) and among those who had lived at the address for >10 years (OR 1.93; 95% CI 1.29 to 2.83). Analyses of categorical exposure variables suggested an exposure-response relationship. The strongest association between exposure to traffic noise and hypertension was found among those with the least expected misclassification of true individual exposure, as indicated by not having triple-glazed windows, living in an old house and having the bedroom window facing a street (OR 2.47; 95% CI 1.38 to 4.43). CONCLUSION: The results of our study suggest an association between exposure to residential road traffic noise and hypertension.

Adult↗
PubMed1997

Hormonal status and the neuroendocrine response to a novel heterotypic stressor involving subchronic noise exposure.

Despite a number of studies on noise-induced health effects, it is still unclear to what extent different neuroendocrine pathways are affected by noise exposure. Male Wistar rats were housed in sound-attenuated rooms isolated for noise from outside. Three groups of chronically cannulated rats were exposed to either background noise (+/-64 dB) only or irregular experimental white noise (90 dB, 2-22 kHz). Two protocols, with approximately the same total amount of noise but with different densities, were used: protocol N1 (180 min random noise per day for 18 days) or protocol N2 (540 min random noise per day for 8 days). Basal levels of circulating hormones (ACTH, corticosterone, prolactin and catecholamines) and plasma glucose were measured. In control animals, no significant changes in any of these parameters were observed over 18 days. Except for plasma prolactin, N1 did not induce a significant elevation in basal hormonal levels. N2 however induced significant elevation in basal prolactin, corticosterone and noradrenaline levels. At the end of the exposure period, all animals were subjected to a novel heterotypic stressor (restraint stress) to monitor differences in neuroendocrine activation (ACTH, corticosterone and prolactin). Compared to nonexposed control animals, N1 animals showed a normal ACTH and an enhanced corticosterone response, whereas N2 animals showed an increased ACTH but a normal corticosterone response. The prolactin response of both N1 and N2 animals was significantly decreased. Adrenal cell suspension experiments revealed that in noise-exposed rats both basal- and ACTH-stimulated corticosterone production were significantly increased as compared to control animals. These results indicate that chronic noise exposure at mild intensities induces subtle but significant changes in hormonal regulation.

Adrenal Glands↗
PubMed2002

The association between noise exposure and blood pressure and ischemic heart disease: a meta-analysis.

It has been suggested that noise exposure is associated with blood pressure changes and ischemic heart disease risk, but epidemiologic evidence is still limited. Furthermore, most reviews investigating these relations were not carried out in a systematic way, which makes them more prone to bias. We conducted a meta-analysis of 43 epidemiologic studies published between 1970 and 1999 that investigate the relation between noise exposure (both occupational and community) and blood pressure and/or ischemic heart disease (International Classification of Diseases, Ninth Revision, codes 410-414). We studied a wide range of effects, from blood pressure changes to a myocardial infarction. With respect to the association between noise exposure and blood pressure, small blood pressure differences were evident. Our meta-analysis showed a significant association for both occupational noise exposure and air traffic noise exposure and hypertension: We estimated relative risks per 5 dB(A) noise increase of 1.14 (1.01-1.29) and 1.26 (1.14-1.39), respectively. Air traffic noise exposure was positively associated with the consultation of a general practitioner or specialist, the use of cardiovascular medicines, and angina pectoris. In cross-sectional studies, road traffic noise exposure increases the risk of myocardial infarction and total ischemic heart disease. Although we can conclude that noise exposure can contribute to the prevalence of cardiovascular disease, the evidence for a relation between noise exposure and ischemic heart disease is still inconclusive because of the limitations in exposure characterization, adjustment for important confounders, and the occurrence of publication bias.

Adolescent↗
PubMed1996

Effects of earplugs on catecholamine and cortisol excretion in noise-exposed textile workers.

To investigate physiological and psychological effects of industrial noise, a survey was performed on 50 female workers exposed to machinery noise [93-100 dB(A)] (noise group) and 25 female workers in less-noisy environments [71-75 dB(A)] (control group) in a textile factory in Vietnam. Urine was collected for analysis of catecholamines and cortisol. The subjects were also asked to fill out a questionnaire. Each subject was examined over 2 working days. The workers in the noise group were asked to put earplugs in their ears during the working hours of the 2nd day. On the 1st day without earplugs, urinary excretion of catecholamines in the noise group were greater than those in the control group. Cortisol in urine showed a similar tendency. Differences in catecholamine excretion between the noise group and the control group decreased on the 2nd day when the earplugs were used for attenuation of noise level in the noise group. Frequency of subjective fatigue symptoms was lower on the 2nd day than that on the 1st day in noise group, while the control group showed almost no day-difference. The results indicate that the catecholamine response to noise in workers was reduced through the use of earplugs.

Adult↗
PubMed1990

Effects of different noises on speech discrimination by the elderly.

Elderly people often complain of difficulty in speech discrimination, especially in noise environments. The effects of 4 competing noises on sentence intelligibility were evaluated: speech noise, cocktail party noise, traffic noise and continuous discourse. A comparison was made between young and old normally hearing subjects and young and old hearing-impaired subjects with similar audiograms. The old people with normal hearing had slightly reduced discrimination compared to the young during competing speech noise and cocktail noise. Discrimination in the hearing-impaired elderly was also significantly worse than in the young people with normals hearing, during competing cocktail party noise, traffic noise and continuous discourse. The young hearing-impaired had results between young normal-hearing subjects and old hearing-impaired, except for continuous discourse. Thus the effects of age on speech discrimination in noise are subtle, becoming more pronounced in the presence of hearing loss. Age-related changes in primary speech discrimination were particularly evident during competing continuous discourse.

Adult↗
PubMedDate not supplied

Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality.

In this study, we measured the effects of a digital hearing aid on speech recognition or reception in noise for two noise reduction concepts: active noise reduction by speech-sensitive processing (SSP) and improved directionality by a dual- or so-called twin-microphone system (TMS). This was conducted in a well-controlled clinical field trial in 16 hearing-aid users, using a single-blind crossover design. The hearing aid fitting was controlled by insertion gain measurements and measurements with loudness scaling. This study combined laboratory experiments with three consecutive field trials of 4 weeks each. We used performance measurements (speech recognition tests in background noise), paired comparisons, and self-report measurements (questionnaires). The speech recognition or reception tests were performed before and after each field trial, the paired comparisons were performed in weeks 4 and 12, and the questionnaires were administered after each field trial. For all subjects, results were obtained for three different settings: no noise reduction, SSP alone, and TMS alone. In the last week, we also performed speech recognition or reception tests in background noise with both noise reduction concepts combined. Three types of results have been reported: "objective" results from the critical signal to noise ratios for speech recognition or reception in different background noises for different settings and "subjective" results: paired comparisons and questionnaires. The subjective scores show the same trend as the objective scores. The effects of TMS were clearly positive, especially for the speech reception threshold tests and for the paired comparisons. The effects of SSP were much smaller but showed significant benefits with respect to aversiveness and speech perception or reception in noise for specific acoustical environments. There was no extra benefit from the combined effect of SSP and TMS relative to TMS alone.

Adult↗
PubMedDate not supplied

The effect of broad-band noise on the binaural interaction components of human auditory brainstem-evoked potentials.

Three-channel Lissajous trajectories (3-CLTs) of binaural interaction components (BI) of auditory brainstem potentials (ABEPs) were derived from 13 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaurally evoked responses to clicks. ABEPs were recorded in response to 65 dB nHL, alternating-polarity clicks, presented at a rate of 11/s. The procedure was repeated with clicks alone as well as with clicks with broad-band masking noise. Noise was presented at 25 and 45 dB nHL, producing a signal-to-noise ratio of +40 and +20 dB, respectively. All BI 3-CLTs included 6 planar segments (labeled BdI, BdII, BdIII, BeI, BeII and Bf) whose apex latencies, except Bf, increased with increasing noise level above 25 dB nHL, and whose durations, sizes, shapes and orientations did not change across noise levels. There were also significant increases in peak latencies of the BI from single channels vertex-mastoid and vertex-neck with increasing noise level. No significant change was found in the trajectory amplitude of apices, with the exception of apices BdIII and Bf whose amplitudes increased with increasing noise level. We suggest that the paradoxical increase in BI amplitude with masking noise may reflect a binaural enhancement of the effect of noise. The effects observed indicate that, whereas the response to clicks displays occlusion, the response to noise displays spatial facilitation at the brainstem level.

Adolescent↗
PubMed1987

Self-noise problems in hearing aids.

A study has been carried out to determine the extent to which the self-noise of a hearing aid constitutes a problem for aid users. A survey of hearing aid users was carried out followed by a laboratory study. None of the 75 hearing aid users seen during the survey complained of being troubled by self-noise and none of the subjects investigated at the Institute of Sound and Vibration Research was able to hear any self-noise at normal aid settings when listened for in a sound proofed room. Tests confirmed that aid noise becomes audible only when the noise level in any 1/3 octave band rises above the threshold for a pure tone at the centre of that band, and typical equivalent input noise levels indicate that audible self-noise is caused by gain being applied over a frequency band where the aid user has negligible or no hearing loss, as is likely in the case of persons with 'ski-slope' hearing loss. It is suggested that anyone else complaining of problems with self-noise is probably mistaking external background noise for self-noise of the aid.

Adult↗
PubMed1993

Frequency analysis of the contralateral suppression of evoked otoacoustic emissions by narrow-band noise.

The influence of noise bandwidth on the contralateral masking of click-evoked otoacoustic emissions was investigated by recording emissions from 20 normal subjects with contralateral narrow-band noise, with wide-band noise and without contralateral noise for comparison. Narrow-band noise of five different centre frequencies and three different bandwidths per frequency was used at intensities of 40 and 60 dB SL. Analysis of the emissions showed that the 40-dB SL contralateral noise did not produce a significant amount of suppression. The suppression produced by 60-dB SL noise was spread throughout the frequency range of the emissions, with limited frequency specificity. There was some evidence that the amount of suppression increases with the bandwidth of the noise, particularly for noises centred on 1 and 2 kHz; the wide-band noise produced much greater suppression than any of the narrow bands. There was a large amount of inter-subject variation, which could not be explained by differences in the absolute level of the emissions. One subject with a total unilateral hearing loss in the contralateral ear was also tested, and gave no significant suppression.

Acoustic Stimulation↗
PubMed1994

[A study on speech intelligibility in traffic noise].

In studying speech intelligibility in traffic noise, I was able to reproduce a sound field with considerable reality by reproducing both speech and traffic noises by the speaker method using a CD. As a result, the following conclusions were reached. 1) The influence of noise on speech intelligibility is similar for the single syllable and adult disyllable in normal persons. 2) The influence of the kinds of noises and changes with time in the sound pressure level on the intelligibility of the single syllable does not easily manifest itself in patients with sensorineural hearing loss. 3) The speech intelligibility depends largely on the blocking effect of the mid-high frequency components of the noise in both normal persons and patients with sensorineural hearing loss. 4) The intelligibility of the second sound of the adult disyllable is good in both normal persons and patients with sensorineural hearing loss. Furthermore, normal persons can understand a significant disyllable word to some extent by means of "uncertain understanding" even when they cannot hear each vowel and consonant clearly. 5) The intelligibility of the vowel is good in both normal persons and patients with sensorineural hearing loss. 6) As for the intelligibility classified by consonant in normal persons, the intelligibility of the nasal sounds (m, n) and voiced consonants (b, d, g, r, z) becomes low in the case of the S/N ratio being poor. 7) In patients with sensorineural hearing loss, the intelligibility of the bulldozer noise was the lowest, followed by motorway noise among the noises applied. The frequency spectrum distribution of the former consisted mainly of mid-high frequencies of 1 kHz or more. A serrated change with an amplitude of about 6 dB, 2 Hz was noted at the sound pressure level. A sine wave-like change with an amplitude of about 7 dB, 1 Hz was recognized at the sound pressure level of the latter. These are considered to be factors which account for a decline in intelligibility. The present study is part of an experiment I conducted at a sound field using TY-89. The results of this experiment suggest that the frequency spectrum intelligibility of noise as well as time-dependent changes in the sound pressure level of the noise exert an influence on communication disruption in patients with sensorineural hearing loss.

Adult↗
PubMed1999

The effect of earplugs on sleep measures during exposure to simulated intensive care unit noise.

BACKGROUND: Sleep deprivation may contribute to impaired immune function, ventilatory compromise, disrupted thermoregulation, and delirium. Noise levels in intensive care units may be related to disturbed sleep patterns, but noise reduction has not been tested in this setting. OBJECTIVE: To measure the effect of a noise reduction intervention on the sleep of healthy subjects exposed to simulated intensive care unit noise. METHODS: After digital audiotape recording of noise and development of the noise reduction intervention, 5 nocturnal 8-hour periods of sleep were measured in 6 paid, healthy volunteers at 7-day intervals in a sleep disorders center. Polysomnographic data were collected by experienced sleep disorders technicians and scored by certified raters. After the first 3 quiet nights, earplugs were randomly assigned to be worn on the fourth and fifth nights during exposure to the recorded noise. Sound pressure levels were measured during all 5 nights. RESULTS: Sleep architecture and sound measurements on quiet nights did not differ significantly. Sound levels were significantly lower on quiet nights than on noise nights. Exposure to the noise increased the number of awakenings, percentage of stage 2 sleep, and rapid eye movement latency and decreased time asleep, sleep maintenance efficiency index, and percentage of rapid eye movement sleep. Earplugs worn during exposure to the noise produced a significant decrease in rapid eye movement latency and an increase in the percentage of rapid eye movement sleep. CONCLUSION: The results provide a reasonable basis for testing the effects of earplugs on the sleep of critically ill subjects.

Adult↗
PubMed2004

[Noise reduction at an emergency intensive care unit of medical center in southern Taiwan].

This project was the result of numerous complaints from patients and their families about high levels of human and mechanical noise inside the emergency intensive care unit (EICU) of a major medical center in southern Taiwan. Other complaints were made by members of the medical staff, who claimed that they could not hear the alarms built into medical equipment. The project entailed a data inventory, analysis, and the identification of noise sources. Maximum mechanical noise level was measured at 79.6 dBA. After classifying noise sources as non-mechanical or mechanical, we established a list of objectives and used 13 approaches to achieve them. As a result, average reduction in mechanical noise volume was 11.72 dBA (14.47%) and in non-mechanical noise volume 10.5 dBA (14.0%). Still, we were only successful in protecting 50% of all EICU patients from noise disturbance levels according to the guidelines established in the Noise Prevention Act that is used in the United States. We therefore recommend that noise monitoring systems be added in order to increase the percentage of EICU patients who are protected from unnecessary noise.

Emergency Medical Services↗
PubMed1992

[Impact noise and hearing. A study from audiometry screening in noisy occupational environments].

The hearing loss of 46,776 subjects exposed to hazardous impact or continuous noise was measured: 11% were exposed to impact noise (10.3% in men, 12.7% in women). Impact noise causes less hearing loss than continuous noise up to a noise emission level (NIL) of 115 dB(A). This result is still compatible with the concept of equivalent continuous A-weighted sound pressure level (LA,eq) and seems to be caused by the protective effect of the stapedius muscle. However, at emission levels higher than 115 dB(A), not covered by ISO 1999 prognosis, impact noise becomes more detrimental. This could be the effect of mechanical damage to the organ of Corti, as observed in animal experiments at sound pressure levels exceeding 114 dB(A). A diminishing protective function of the stapedius muscle could explain the more serious hearing impairment after long exposure to impact noise compared with shorter exposures to an equal dose. Since the hearing loss caused by impact or continuous noise is clearly different in the highest NIL ranges, safety criteria for impact noise should be revised. The NIL defined by Burns and Robinson underestimates the effect of the exposure time for impact noise.

Adolescent↗