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PubMed1987

Sampling time effects on signal-to-noise and contrast-to-noise ratios in spin-echo MRI.

This work discusses the effect of sampling time on noise, signal-to-noise and contrast-to-noise ratios in magnetic resonance imaging. A simple imaging experiment is performed to demonstrate the effect of sampling time on noise, confirming theoretical expectations that doubling the sampling time while decreasing the read gradient strength by a factor of two reduces statistical noise to 1/square root 2 of its original level. This result suggests that sampling time should be maximized within the constraints of the pulse sequence: namely, that sampling time should be increased and read gradient strength decreased as TE is increased. Revised expressions for signal-to-noise and contrast-to-noise ratios are presented based on the assumption that sampling time increases linearly with echo delay time above a certain minimum TE value. The revised expressions are then used to derive new predictions of the interpulse delay times that maximize signal-to-noise and contrast-to-noise ratios in spin-echo imaging. It is demonstrated that sampling times are critical in determining whether T1-weighted or T2-weighted sequences produce superior tissue contrast in spin-echo imaging.

Image Enhancement↗
PubMed2006

Merits of PM noise measurement over noise figure: a study at microwave frequencies.

This paper primarily addresses the usefulness of phase-modulation (PM) noise measurements versus noise figure (NF) measurements in characterizing the merit of an amplifier. The residual broadband (white PM) noise is used as the basis for estimating the NF of an amplifier. We have observed experimentally that many amplifiers show an increase in the broadband noise of 1 to 5 dB as the signal level through the amplifier increases. This effect is linked to input power through the amplifier's nonlinear intermodulation distortion. Consequently, this effect is reduced as linearity is increased. We further conclude that, although NF is sometimes used as a selection criteria for an amplifier for low-level signal, NF yields no information about potentially important close-to-carrier 1/f noise of an amplifier nor broadband noise in the presence of a high-level signal, but a PM noise measurements does. We also have verified experimentally that the single-sideband PM noise floor of an amplifier due to thermal noise is -177 dBc/Hz, relative to a carrier input power of 0 dBm.

Journal Article↗
PubMed1978

[The effect of noise trauma on speech discrimination in silence and under influence of party noise (author's transl)].

Speech audiometry investigations were carried out in silence and under action of cocktail party noise in 44 soldiers. The testing subjects were grouped according to age and degree of noise lesion. The statistical evaluation of discrimination losses measured in silence and under acting party noise indicated that noise lesions induced considerable discrimination losses even in young subjects particularly under cocktail party noise conditions. Discrimination decreases significantly as the degree of noise trauma increases. In order to assess the real effect of the hearing loss caused by noise trauma upon speech discrimination, the tests of speech audiometry should be performed under noise conditions.

Adult↗
PubMed2003

Cochlear toughening, protection, and potentiation of noise-induced trauma by non-Gaussian noise.

An interrupted noise exposure of sufficient intensity, presented on a daily repeating cycle, produces a threshold shift (TS) following the first day of exposure. TSs measured on subsequent days of the exposure sequence have been shown to decrease relative to the initial TS. This reduction of TS, despite the continuing daily exposure regime, has been called a cochlear toughening effect and the exposures referred to as toughening exposures. Four groups of chinchillas were exposed to one of four different noises presented on an interrupted (6 h/day for 20 days) or noninterrupted (24 h/day for 5 days) schedule. The exposures had equivalent total energy, an overall level of 100 dB(A) SPL, and approximately the same flat, broadband long-term spectrum. The noises differed primarily in their temporal structures; two were Gaussian and two were non-Gausssian, nonstationary. Brainstem auditory evoked potentials were used to estimate hearing thresholds and surface preparation histology was used to determine sensory cell loss. The experimental results presented here show that: (1) Exposures to interrupted high-level, non-Gaussian signals produce a toughening effect comparable to that produced by an equivalent interrupted Gaussian noise. (2) Toughening, whether produced by Gaussian or non-Gaussian noise, results in reduced trauma compared to the equivalent uninterrupted noise, and (3) that both continuous and interrupted non-Gaussian exposures produce more trauma than do energy and spectrally equivalent Gaussian noises. Over the course of the 20-day exposure, the pattern of TS following each day's exposure could exhibit a variety of configurations. These results do not support the equal energy hypothesis as a unifying principal for estimating the potential of a noise exposure to produce hearing loss.

Animals↗
PubMed1979

Noise-induced hearing loss and the comprehension of speech in noise.

Subjects suffering from noise-induced hearing loss (NIHL) with or without hearing loss at 2 kHz were examined by speech audiometry with a three-digit test, bisyllabic and monosyllabic PB word lists in silence, and in USASI noise with a masking effect of 44 dB and 68 dB at 1 kHz. Subjects with up to 20 dB hearing loss at 2 kHz had almost the same speech comprehension in noise as normal hearing subjects. Subjects with hearing loss greater than 20 dB at 2 kHz had increasing discrimination loss at increasing noise levels. They also needed a signal-to-noise ratio better than normal-hearing persons would yield at the noise levels used. The evaluation of hearing disablement in occupational noise-included hearing loss should therefore be based for one-half on the results of speech audiometry in silence, and for the other half, in noise.

Adult↗
PubMed1987

Impulse noise and continuous noise of equivalent frequency spectrum and total sound energy.

It has been proposed that impulse noise and continuous noise affect the inner ear differently and investigations have found impulse noise to be harmful to both the inner hair cells and the outer hair cells. Scanning electron microscopy and non-standard methods for statistical analysis have facilitated the evaluation of different types of morphological changes after exposure to various kinds of noise. Morphological differences were compared in groups of guinea pigs exposed to either impulse noise or continuous noise of equivalent duration, spectral content and energy. Functionally, the groups also showed similar threshold elevations. In order to separate the two groups, subtle hair cell changes were recorded and evaluated either alone, in combination with each other or with hair cell loss. It was found that both the inner hair cells and the outer hair cells were affected differently by impulse noise than by continuous noise even though the auditory thresholds were similar.

Animals↗
PubMed2005

Extraction of overt verbal response from the acoustic noise in a functional magnetic resonance imaging scan by use of segmented active noise cancellation.

A method to extract the subject's overt verbal response from the obscuring acoustic noise in an fMRI scan is developed by applying active noise cancellation with a conventional MRI microphone. Since the EPI scanning and its accompanying acoustic noise in fMRI are repetitive, the acoustic noise in one time segment was used as a reference noise in suppressing the acoustic noise in subsequent segments. However, the acoustic noise from the scanner was affected by the subject's movements, so the reference noise was adaptively adjusted as the scanner's acoustic properties varied in time. This method was successfully applied to a cognitive fMRI experiment with overt verbal responses.

Acoustics↗
PubMed2006

Effects of noise-induced hearing loss at young age on voice onset time and gap-in-noise representations in adult cat primary auditory cortex.

Here we show that mild hearing loss induced by noise exposure in early age causes a decrease in neural temporal resolution when measured in adulthood. We investigated the effect of this chronic hearing loss on the representation of a voice onset time (VOT) and a gap-duration continuum in primary auditory cortex (AI) in cats, which were exposed at the age of 6 weeks to a 120-dB SPL, 5-kHz 1/3 octave noise band for 2 h. The resulting hearing loss measured using auditory brainstem responses and cortical multiunit thresholds at 4-6 months of age was 20-40 dB between 1 and 32 kHz. Multiple single-unit activity was recorded in seven noise-exposed cats and nine control cats related to the presentation of a/ba/-/pa/ continuum in which VOT was varied in 5-ms step from 0 to 70 ms. We also obtained data for noise bursts with gaps, of duration equal to the VOT, embedded in noise 5 ms after the onset. Both stimuli were presented at 65 dB SPL. Minimum VOT and early-gap duration were defined as the lowest value in which an on-response, significantly above the spontaneous activity, to both the leading and trailing noise bursts or vowel was obtained. The mild chronic noise-induced hearing loss increased the minimum detectable VOT and gap duration by 10 ms. We also analyzed the maximum firing rate (FRmax) and the latency of the responses as a function of VOT and gap duration and found a significant reduction in the FRmax to the trailing noise burst for gap durations above 50 ms. This suggests that mild hearing loss acquired in early age may affect cortical temporal processing in adulthood.

Acoustic Stimulation↗
PubMed1999

Susceptibility of the noise-toughened auditory system to noise-induced trauma.

The auditory system 'toughened' by an interrupted noise exposure has been shown in several reports, to be less affected by (or protected from) a subsequent high level noise exposure. A group of chinchillas (n = 12) was exposed to an interrupted noise at 95 dB SPL, 0.5 kHz octave band, 6 h/day for 10 days. Threshold shifts measured over the 10 day exposure showed that the animals responded by either (1) developing a large toughening effect (i.e., thresholds after day 10 of the exposure were considerably better than at the end of day 1) (n = 5) or (2) not showing any toughening, instead thresholds continued to get worse over the course of the exposure (n = 7). After a 5 day interval, during which thresholds of all the animals returned to normal, they, along with a control group (n = 10) not exposed to the interrupted noise, were exposed to an asymptotic threshold shift producing traumatic noise (127 dB peak SPL narrow band impact, 1 kHz center frequency, 24 h/day for 5 days). Auditory evoked potential audiometry and surface preparation histology showed that there were no statistically significant differences in the response of any of the above groups to the traumatic noise. The interrupted noise exposure, whether it produced a toughening or not, did not provide any protection from a subsequent high-level noise.

Animals↗
PubMed1997

The use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: some initial results.

MRI scanning generates high levels of acoustic noise that cannot only pose a safety hazard, but also impair communication between staff and patient. In this article we present active noise control (ANC) techniques that introduce antiphase noise to destructively interfere with the MRI noise and with the aim of producing a zone of quiet around the patient's ears. Using noise recorded from a 1.0 Tesla midfield MR scanner the acoustic noise generated by three standard MR imaging sequences was replayed to a real time two channel ANC system. The results obtained show a useful attenuation of low-frequency periodic acoustic noise components. Therefore, in combination with standard passive ear protection, this suggests that MR generated acoustic noise can be effectively attenuated at both low and high frequencies leading to improved patient comfort.

Acoustics↗
PubMed2002

Cancellation of simulated environmental noise as a tool for measuring vocal performance during noise exposure.

It can be difficult for the voice clinician to observe or measure how a patient uses his voice in a noisy environment. We consider here a novel method for obtaining this information in the laboratory. Worksite noise and filtered white noise were reproduced over high-fidelity loudspeakers. In this noise, 11 subjects read an instructional text of 1.5 to 2 minutes duration, as if addressing a group of people. Using channel estimation techniques, the site noise was suppressed from the recording, and the voice signal alone was recovered. The attainable noise rejection is limited only by the precision of the experimental setup, which includes the need for the subject to remain still so as not to perturb the estimated acoustic channel. This feasibility study, with 7 female and 4 male subjects, showed that small displacements of the speaker's body, even breathing, impose a practical limit on the attainable noise rejection. The noise rejection was typically 30 dB and maximally 40 dB down over the entire voice spectrum. Recordings thus processed were clean enough to permit voice analysis with the long-time average spectrum and the computerized phonetogram. The effects of site noise on voice sound pressure level, fundamental frequency, long-term average spectrum centroid, phonetogram area, and phonation time were much as expected, but with some interesting differences between females and males.

Acoustic Stimulation↗
PubMed2006

Comparison of performance on the hearing in noise test using directional microphones and digital noise reduction algorithms.

PURPOSE: Difficulty understanding speech in background noise is one of the most common complaints of hearing aid users. In modern hearing aids, directional microphones (d-mics) are considered the method of choice in improving signal-to-noise ratio, with demonstrated improvement in speech-perception-in-noise tasks. On the other hand, digital noise reduction (DNR) algorithms, in commercially available products, are considered to provide comfort but not significant assistance in improving speech perception in noise. In practice, these 2 technologies are often used in conjunction, but few studies have evaluated their interaction and the resultant effect on speech perception in noise. The purpose of this study was to evaluate the effect on speech performance of using d-mics and DNR in isolation as well as in conjunction in the presence of background noise. METHOD: This study evaluates the performance of 16 experienced adult hearing aid users on the Hearing in Noise Test when each technology was activated independently and then simultaneously in 4 commercially available hearing aids. RESULT: Approximately 50% of our participants performed better with both d-mics and DNR activated in conjunction, while the other 50% performed best in the d-mic-only condition. When considering statistically significant differences in performance only, a reduction or improvement in performance was observed in 17% and 14% of the conditions, respectively. CONCLUSION: A direction for further research would be to identify predictive variables that could help the audiologist determine an individual's preference a priori.

Aged↗
PubMed1998

Noise-induced hearing loss in young adults: the role of personal listening devices and other sources of leisure noise.

CONCEPT: No consensus exists regarding the magnitude of the risk of noise-induced hearing loss (NIHL) associated with leisure noise, in particular, personal listening devices in young adults. OBJECTIVE: Examine the magnitude of hearing loss associated with personal listening devices and other sources of leisure noise in causing NIHL in young adults. STUDY DESIGN: Prospective auditory testing of college student volunteers with retrospective history exposure to home stereos, personal listening devices, firearms, and other sources of recreational noise. METHODS: Subjects underwent audiologic examination consisting of estimation of pure-tone thresholds, speech reception thresholds, and word recognition at 45 dB HL. RESULTS: Fifty subjects aged 18 to 30 years were tested. All hearing thresholds of all subjects (save one-a unilateral 30 dB HL threshold at 6 kHz) were normal, (i.e., 25 dB HL or better). A 10 dB threshold elevation (notch) in either ear at 3 to 6 kHz as compared with neighboring frequencies was noted in 11 (22%) subjects and an unequivocal notch (15 dB or greater) in either ear was noted in 14 (28%) of subjects. The presence or absence of any notch (small or large) did not correlate with any single or cumulative source of noise exposure. No difference in pure-tone threshold, speech reception threshold, or speech discrimination was found among subjects when segregated by noise exposure level. CONCLUSION: The majority of young users of personal listening devices are at low risk for substantive NIHL. Interpretation of the significance of these findings in relation to noise exposure must be made with caution. NIHL is an additive process and even subtle deficits may contribute to unequivocal hearing loss with continued exposure. The low prevalence of measurable deficits in this study group may not exclude more substantive deficits in other populations with greater exposures. Continued education of young people about the risk to hearing from recreational noise exposure is warranted.

Adolescent↗
PubMed1997

Word recognition in continuous noise, interrupted noise, and in quiet by normal-hearing listeners at two sensation levels.

The effect of presentation level on word recognition performance-intensity functions in continuous and interrupted broadband noise and in quiet was explored. Normal-hearing participants were tested at 30 and 50 dB sensation levels (SLs). Performance-intensity functions in both noises were determined at signal-to-noise ratios (S/Ns) of 10, 5, 0, -5, -10, -15, and -20 dB. There was no effect of SL presentation on word recognition performance in quiet (p = 0.136). A significant main effect was observed for S/N in both continuous and interrupted broadband noise conditions (p < 0.0001). Performance increased with increases in S/N regardless of the competing noise condition. A significant main effect for SL presentation was only observed in the interrupted noise condition (p = 0.0019). That is, performance was higher for the 50 SL for the interrupted noise condition only. It is suggested that the observed difference in performance in interrupted noise at different SLs offers additional evidence for level-dependent, temporal masking phenomena.

Hearing↗
PubMed2005

Noise level in different places of Dhaka Metropolitan City (DMC) and noise-induced hearing loss (NIHL) in Dhaka City dwellers.

A cross sectional, exploratory study was designed at "National Center for Hearing and Speech for Children" (NCHSC), Dhaka, Bangladesh, from May 2001 to June 2002, with a view to determine the average noise level in different places of Dhaka Metropolitan City (DMC), and also aiming at evaluating the extent of Noise-induced Hearing Loss (NIHL) in different groups of city dwellers and finally a base line information. A total of 32 places in DMC were selected randomly. The highest noise level recorded 104 dB at Sayedabad bus terminal and the lowest 68 dB in Banani and Baridhara residential area. In silent zone of DMC, average noise level was 79 dB, in residential zone 72 dB, in commercial zone 90 dB, and in mixed zone average noise level was recorded at 91 dB. Measured noise levels were more than acceptable and permissible levels in all places of DMC. A total of 312 persons aged between 15-45 years (mean age- 24.64 years) were enrolled for the study as per inclusion criteria. Gender-wise male were 211(67.62%) and female were 101(32.57%). Profession-wise Automobile drivers were 57(18.26 %), Garment workers 58(18.55 %), City dwellers 72(23.07%), Students 72(23.07%), Traffic polices 12(3.85%), Hawkers and Road side shopkeepers were 41(13.1%). Definite noise notch (>25dB) at 4KHz observed in 33(10.58%) audiogram of persons under study. Automobile drivers, Traffic polices, Road side hawkers and Shop keepers, Garment workers are mostly affected were 17.54%, 16.4%, 12.09% and 12.06% respectively. A total of 201 persons (64.42%) were not aware of their hearing impairment, 244(78%) of the person had poor level of knowledge regarding bad effects of noise on health and about protective means available. Amongst persons (33) found to have NIHL did not use any protective device.

Adult↗
PubMed2007

Are investigators aware of environmental noise in animal facilities and that this noise may affect experimental data?

Control of environmental factors, such as noise, in animal facilities is important to ensure that research animals respond consistently to experimental procedures and that experimental results are not confounded by outside influences. A survey of personnel involved with animal facilities (173 respondents) showed that almost all agreed with this statement. However, 48% thought that one or more environmental factors in their facilities could be stressing the animals, and a majority of respondents reported generation of audible noise from people (72% of respondents), fans (61%), and squeaky carts (56%). The presence of these noises was correlated with the perception of noise as a problem because of its psychologic and physiologic effects on the animals. The amount of time respondents spent in the facilities was strongly correlated with their perception of noise as a problem, with veterinarians spending the most time and perceiving the most problems, and professors and assistant/ associate professors spending the least and perceiving the fewest. Therefore, they may lack key knowledge that can affect their research goals. In addition, because faculty are the least aware of noise as a potential problem but are primarily responsible for designing experiments, research involving animals may be confounded by noise as an unknown variable. This effect may lead to unnecessary numbers of animals being required to achieve statistical significance and possibly to erroneous interpretation of results. On the basis of the findings of this survey, we present recommendations for improving the environment, particularly for decreasing the noise level, in animal facilities.

Animal Welfare↗
PubMed1983

Information integration and the identification of stimulus noise and criterial noise in absolute judgment.

Two main classes of theories have been proposed regarding range effects in unidimensional absolute-identification tasks. One class posits that as range is increased, criterial noise increases but stimulus noise remains constant. Another class posits increasing stimulus noise but constant criterial noise. In this study, an effort is made to help decide this issue. Multiple observations are used in several absolute-identification tasks of varying range. A stimulus integration model is proposed in which averaging takes place over stimulus internal representations, thereby reducing stimulus variance; on the other hand, it is assumed that criterial variance is unaffected by the number of observations. The model allows one to identify the relative amounts of stimulus noise and criterial noise inherent in observers' recognition judgments. The model yields good fits to data in several experiments, and it is concluded that both stimulus noise and criterial noise increase as range in the absolute-identification task is increased.

Adolescent↗
PubMed2001

Additive noise in noise-induced nonequilibrium transitions.

We study different nonlinear systems which possess noise-induced nonequlibrium transitions and shed light on the role of additive noise in these effects. We find that the influence of additive noise can be very nontrivial: it can induce first- and second-order phase transitions, can change properties of on-off intermittency, or stabilize oscillations. For the Swift-Hohenberg coupling, that is a paradigm in the study of pattern formation, we show that additive noise can cause the formation of ordered spatial patterns in distributed systems. We show also the effect of doubly stochastic resonance, which differs from stochastic resonance, because the influence of noise is twofold: multiplicative noise and coupling induce a bistability of a system, and additive noise changes a response of this noise-induced structure to the periodic driving. Despite the close similarity, we point out several important distinctions between conventional stochastic resonance and doubly stochastic resonance. Finally, we discuss open questions and possible experimental implementations. (c) 2001 American Institute of Physics.

Journal Article↗