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PubMed1992

Effects of noise on blood pressure and vascular reactivities.

1. The present study investigated the effects of noise stress (100 dB, 1 kHz, 4 h/day, 6 days/week) on both systolic blood pressure and vascular reactivities in rats exposed to noise for 2 and 4 weeks. The systolic blood pressure was significantly increased after rats were exposed to noise for 4 weeks but not 2 weeks. 2. In isolated thoracic aortic rings, the responses to serotonin were enhanced in noise-treated rats while there were no changes in response to phenylephrine and high K+ between noise-treated and control rats. 3. The relaxant responses to endothelium-dependent vasodilators (A23187 and acetylcholine) in noise-treated rats were less than those in control rats. The vasodilator responses to acetylcholine were completely abolished by methylene blue or N omega-nitro-L-arginine. 4. Responses to the endothelium-independent vasodilator, nitroglycerin, were not significantly changed after rats were exposed to noise. 5. The enhanced response to vasoconstrictors and the attenuation to endothelium-dependent vasodilators may account for elevations in blood pressure during noise stress. This indicates that the elevation in blood pressure by noise stress may be partly due to the deterioration of endothelial function.

Animals↗
PubMed2004

Speech-in-noise perception in high-functioning individuals with autism or Asperger's syndrome.

BACKGROUND: High-functioning individuals with autism (HFA) or Asperger's syndrome (AS) commonly report difficulties understanding speech in situations where there is background speech or noise. The objective of this study was threefold: (1) to verify the validity of these reports; (2) to quantify the difficulties experienced; and (3) to propose possible mechanisms to explain the perceptual deficits described. METHOD: Speech-in-noise perception abilities were measured using speech reception thresholds (SRTs), defined as the speech-to-noise ratio (SNR) at which approximately 50% of the speech is correctly identified. SRTs were measured for 11 individuals with HFA/AS and 9 age/IQ-matched normal-hearing control subjects, using an adaptive procedure, in a non-reverberant sound-attenuating chamber. The speech materials were standardised lists of everyday sentences spoken by a British male speaker. The background sounds were: (1) a single female talker; (2) a steady speech-shaped noise; (3) a speech-shaped noise with temporal dips; (4) a steady speech-shaped noise with regularly spaced spectral dips; and (5) a speech-shaped noise with temporal and spectral dips. RESULTS: SRTs for the HFA/AS group were generally higher (worse) than those for the controls, across the five background sounds. A statistically significant difference in SRTs between the subject groups was found only for those background sounds that contained temporal or spectro-temporal dips. SRTs for the HFA/AS individuals were 2 to 3.5 dB higher than for the controls, equivalent to a substantial decrease in speech recognition. Expressed another way, the HFA/AS individuals required a higher SNR, whenever there were temporal dips in the background sound, to perform at the same level as the controls. CONCLUSIONS: The results suggest that the speech-in-noise perception difficulties experienced by individuals with autism may be due, in part, to a reduced ability to integrate information from glimpses present in the temporal dips in the noise.

Adult↗
PubMed2005

Effects of background noise on the human startle reflex and prepulse inhibition.

Three experiments investigated whether background noise modified the startle blink reflex and prepulse inhibition (PPI). In Experiment 1 background noise was about 28 (ambient), 40, and 60 dB; in Experiments 2 and 3 background noise was ambient and 60 dB. Prepulses were 70-dB tones (Experiments 1 and 3) or a tactile stimulus (Experiment 2). Startle-eliciting stimuli were 94-dB noise (Experiments 1 and 2) or an airpuff to the face (Experiment 3). Prepulses were presented at stimulus onset asynchronies of 30, 60, 120, 240, and 2000 ms relative to the startle-eliciting stimulus. Background noise of 60 dB had no effect on control reflexes, whereas 40-dB background noise increased control reflexes. Background noise decreased PPI, but only when an acoustic stimulus was used as prepulse. In sum, the findings show that background noise reduces the signal-to-noise ratio of acoustic prepulses and decreases their modulatory effect on the startle reflex.

Acoustic Stimulation↗
PubMed1969

Classification of inferior collicular neurones of bats in terms of responses to pure tones, FM sounds and noise bursts.

1. Single unit activity in the inferior colliculus of bats was studied with pure tones, FM (frequency-modulated) sounds and noise bursts which are the most basic three components of the complex sounds produced by many different animals including man. Neurones were divided into three groups, (i) ;generalized' units responding to all three elements, (ii) ;deaf' units responding to two out of the three and (iii) ;specialized' units responding to only one of the three. Each of these was divided into three subgroups.2. Three subgroups of generalized units were called ;symmetrical', ;asymmetrical' and ;upper-threshold' units. The symmetrical unit had a wide excitatory area and responded to any sounds which had components falling in this area. The asymmetrical unit had a narrow excitatory area abutting on a large inhibitory one and showed different responses to FM sounds depending on the directions of frequency sweep. The upper-threshold unit had not only an excitatory area, but also an inhibitory one. The neurone failed to respond to strong sounds, i.e. these showed upper thresholds.3. Three subgroups of deaf units were called ;pure tone-deaf', ;FM-deaf' and ;noise-deaf' units. The pure tone-deaf unit did not respond to any pure tones but did respond to FM sounds and noise bursts. The noise-deaf unit did not respond to noise bursts but did respond to pure and FM tone pulses. An FM-deaf unit has not yet been confirmed.4. Three subgroups of specialized units were called ;pure tone-specialized', ;FM-specialized' and ;noise-specialized' units which responded exclusively to either pure tones, FM sounds or noise bursts, respectively. In the FM- and noise-specialized units, pure tone pulses caused only inhibitory processes.5. About 95% of neurones studied showed phasic on-responses to sound stimuli and almost no spontaneous discharges. Only a small percent of neurones showed spontaneous discharges higher than a few impulses per second. Response patterns of some of these neurones changed with frequency, intensity, duration and repetition rate of sound stimuli. These neurones responded to any of pure tones, FM sounds and noise bursts.6. All neurones except the symmetrical ones had inhibitory areas, in which sounds inhibited responses to excitatory ones when these are delivered simultaneously. Therefore the structure in complex sounds is very important in the excitation of these neurones.

Animals↗
PubMed1996

Relationship of firing intervals of human motor units to the trajectory of post-spike after-hyperpolarization and synaptic noise.

1. Interspike interval distributions from human motor units of a variety of muscles were analysed to assess the role of synaptic noise in excitation. The time course of the underlying post-spike after-hyperpolarization (AHP) was deduced by applying a specially developed transform to the interval data. Different firing rates were studied both by varying the firing voluntarily, and by selecting subpopulations of spikes for a given firing rate from long recordings with slight variations in frequency. 2. At low firing rates the interval histograms had an exponential tail. Thus at long intervals, the motoneurone was randomly excited by noise and its post-spike AHP was complete. This contrasts with the firing produced by intracellular current injection in the cat, when the membrane potential increases linearly until threshold is reached. The interval histogram was therefore analysed with the aid of a model of synaptic excitation to deduce the mean 'trajectory' of membrane voltage in the last part of the interspike interval. 3. The computer model, described in the Appendix, was used to determine the effect of the mean level of membrane potential on the probability of a spike being excited, per unit time, during an on-going interspike interval. All variables were treated as voltages, with synaptic noise simulated by time-smoothed Gaussian noise. This enabled an interval distribution to be transformed into a segment of the underlying trajectory of the membrane potential; the potential was expressed in terms of the noise amplitude and the spike threshold. 4. At low firing rates, the equilibrium value of the membrane voltage trajectory lay well below threshold; the deviation typically corresponded to the standard deviation of the noise or more. The noise standard deviation was estimated to be about 2 mV. 5. With increasing mean firing rate, the near-threshold portion of the trajectory obtainable from the histogram occurred earlier, was steeper and rose to a higher level. Trajectories for different firing rates fell on the same curve after shifting them vertically by varying amounts. The curve was taken to represent the AHP of the motoneurone and was closely exponential. The shift of the trajectory gave its mean synaptic drive. The duration of the AHP varied between units and was longer than average for units from soleus muscle. 6. Further modelling showed that summation of noise with the AHP can explain the well-known changes in discharge variability that occur as firing rate increases. 7. It is concluded that synaptic noise plays a major role in the excitation of tonically firing human motoneurones and that the noiseless motoneurone with a linear trajectory provides an inadequate model for the conscious human. This is of interest in relation to various standard measures of human motor unit activity such as short-term synchronization.

Action Potentials↗
PubMed2000

A software model to estimate zones of impact on marine mammals around anthropogenic noise.

Anthropogenic noise impacts marine mammals in a variety of ways. In order to estimate over which ranges this happens, we first need to understand the propagation of noise through the ocean away from the noise source, and, second, understand the relationship between received noise levels and impact thresholds. A software package combining both aspects is presented. (1) A sound propagation model based on ray theory was developed to calculate received noise levels as a function of range, depth, and frequency. (2) Current knowledge of noise impact thresholds for marine mammals was gathered and included in software routines predicting zones of impact on marine mammals around industrial underwater noise sources. As input parameters, this software package requires the source level and spectrum of the noise of interest; physical oceanography data about the local ocean environment such as bathymetry, bottom and surface loss data, and sound speed profiles; and bioacoustical information about the target species in the form of an audiogram, critical auditory bandwidths, spectra of typical animal vocalizations, reported sound levels of disturbance, and criteria for hearing damage. As output, the software produces data files and plots of the zones of audibility, masking, disturbance, and potential hearing damage around a noise source.

Animals↗
PubMed2003

Acoustic communication in two freshwater gobies: ambient noise and short-range propagation in shallow streams.

Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra were measured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200-500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations.

Acoustics↗
PubMed2003

Active local control of propeller-aircraft run-up noise.

Engine run-ups are part of the regular maintenance schedule at Vancouver International Airport. The noise generated by the run-ups propagates into neighboring communities, disturbing the residents. Active noise control is a potentially cost-effective alternative to passive methods, such as enclosures. Propeller aircraft generate low-frequency tonal noise that is highly compatible with active control. This paper presents a preliminary investigation of the feasibility and effectiveness of controlling run-up noise from propeller aircraft using local active control. Computer simulations for different configurations of multi-channel active-noise-control systems, aimed at reducing run-up noise in adjacent residential areas using a local-control strategy, were performed. These were based on an optimal configuration of a single-channel control system studied previously. The variations of the attenuation and amplification zones with the number of control channels, and with source/control-system geometry, were studied. Here, the aircraft was modeled using one or two sources, with monopole or multipole radiation patterns. Both free-field and half-space conditions were considered: for the configurations studied, results were similar in the two cases. In both cases, large triangular quiet zones, with local attenuations of 10 dB or more, were obtained when nine or more control channels were used. Increases of noise were predicted outside of these areas, but these were minimized as more control channels were employed. By combining predicted attenuations with measured noise spectra, noise levels after implementation of an active control system were estimated.

Aircraft↗
PubMed2004

Formant discrimination in noise for isolated vowels.

Formant discrimination for isolated vowels presented in noise was investigated for normal-hearing listeners. Discrimination thresholds for F1 and F2, for the seven American English vowels /i, I, epsilon, ae, [symbol see text], a, u/, were measured under two types of noise, long-term speech-shaped noise (LTSS) and multitalker babble, and also under quiet listening conditions. Signal-to-noise ratios (SNR) varied from -4 to +4 dB in steps of 2 dB. All three factors, formant frequency, signal-to-noise ratio, and noise type, had significant effects on vowel formant discrimination. Significant interactions among the three factors showed that threshold-frequency functions depended on SNR and noise type. The thresholds at the lowest levels of SNR were highly elevated by a factor of about 3 compared to those in quiet. The masking functions (threshold vs SNR) were well described by a negative exponential over F1 and F2 for both LTSS and babble noise. Speech-shaped noise was a slightly more effective masker than multitalker babble, presumably reflecting small benefits (1.5 dB) due to the temporal variation of the babble.

Acoustic Stimulation↗
PubMed2005

A Speech Intelligibility Index-based approach to predict the speech reception threshold for sentences in fluctuating noise for normal-hearing listeners.

The SII model in its present form (ANSI S3.5-1997, American National Standards Institute, New York) can accurately describe intelligibility for speech in stationary noise but fails to do so for nonstationary noise maskers. Here, an extension to the SII model is proposed with the aim to predict the speech intelligibility in both stationary and fluctuating noise. The basic principle of the present approach is that both speech and noise signal are partitioned into small time frames. Within each time frame the conventional SII is determined, yielding the speech information available to the listener at that time frame. Next, the SII values of these time frames are averaged, resulting in the SII for that particular condition. Using speech reception threshold (SRT) data from the literature, the extension to the present SII model can give a good account for SRTs in stationary noise, fluctuating speech noise, interrupted noise, and multiple-talker noise. The predictions for sinusoidally intensity modulated (SIM) noise and real speech or speech-like maskers are better than with the original SII model, but are still not accurate. For the latter type of maskers, informational masking may play a role.

Attention↗
PubMed2006

Effects of directional microphone and adaptive multichannel noise reduction algorithm on cochlear implant performance.

Although cochlear implant (CI) users have enjoyed good speech recognition in quiet, they still have difficulties understanding speech in noise. We conducted three experiments to determine whether a directional microphone and an adaptive multichannel noise reduction algorithm could enhance CI performance in noise and whether Speech Transmission Index (STI) can be used to predict CI performance in various acoustic and signal processing conditions. In Experiment I, CI users listened to speech in noise processed by 4 hearing aid settings: omni-directional microphone, omni-directional microphone plus noise reduction, directional microphone, and directional microphone plus noise reduction. The directional microphone significantly improved speech recognition in noise. Both directional microphone and noise reduction algorithm improved overall preference. In Experiment II, normal hearing individuals listened to the recorded speech produced by 4- or 8-channel CI simulations. The 8-channel simulation yielded similar speech recognition results as in Experiment I, whereas the 4-channel simulation produced no significant difference among the 4 settings. In Experiment III, we examined the relationship between STIs and speech recognition. The results suggested that STI could predict actual and simulated CI speech intelligibility with acoustic degradation and the directional microphone, but not the noise reduction algorithm. Implications for intelligibility enhancement are discussed.

Adult↗
PubMed1978

Growth function for human response to large-amplitude impulse noise.

The U. S. Environmental Protection Agency has proposed the use of C-weighted day/night level for the assessment of impulse noise such as the noise resulting from sonic boom, blast noise (artillery, armor, demolition, etc.) and other large-amplitude impulse sources. One remaining question pertaining to the use of C-weighting has been the growth function for human response to impulse noise. This question arises because work by Kryter and by Young using peak values and/or small amplitudes exhibited growth functions of 6--7dB for a doubling of annoyance, while the growth function for human response to common sources (planes, vehicles, etc.) increases by about 10 dB for a doubling of annoyance. Kyter's and Young's data are reanalyzed herein by using C-weighting and by including only large-amplitude data. This reanalysis results in a growth function for human response to impulse noise which increases by about 10 dB for a doubling of annoyance. This equality of growth function between common A-weighted noise and C-weighted impulse noise further supports the use of C-weighted day/night level for assessment of sonic boom, blast noise, or other large-amplitude impulse noises having similar spectral content.

Humans↗
PubMed1979

Temporary threshold shifts in humans exposed to octave bands of noise for 16 to 24 hours.

Groups of human subjects were exposed in a diffuse sound field for 16--24 h to an octave-band noise centered at 4, 2, 1, or 0.5 kHz. Sound-pressure levels were varied on different exposure occasions. At specified times during an exposure, the subject was removed from the noise, auditory sensitivity was measured, and the subject was returned to the noise. Temporary threshold shifts (TTS) increased for about 8 h and then reached a plateau or asymptote. The relation between TTS and exposure duration can be described by a simple exponential function with a time constant of 2.1 h. In the frequency region of greatest loss, threshold shifts at asymptote increased about 1.7 dB for every 1 dB increase in the level of the noise above a critical level. Critical levels were empirically estimated to be 74.0 dB SPL at 4 kHz. 78 dB at 2 kHz, and 82 dB at 1 and 0.5 kHz. Except for the noise centered at 4.0 kHz, threshold shifts were maximal about 1/2 octave above the center frequency of the noise. A smaller second maximum was observed also at 7.0 kHz for the noise centered at 2.0 kHz, at 6.0 kHz for the noise centered at 1.0 kHz, and at 5.5 kHz for the noise centered at 0.5 kHz. After termination of the exposure, recovery to within 5 dB of pre-exposure thresholds was achieved within 24 h or less. Recovery can be described by a simple exponential function with a time constant of 7.1 h. The frequency contour defined by critical levels matches almost exactly the frequency contour defined by the E-weighting network.

Adult↗
PubMed1980

Effects of noise on some autonomic system activities.

Experiments were conducted on the effects of various expected noise conditions upon autonomic system activity in men during rest and work (bicycle ergometer). Skin temperature and heart rate were not appreciably, if at all, affected by any of the noises. Wide-band, predominantly low-frequency noise, at a level of 92 dB, A-weighted, generally caused a decrease in pulse amplitude (indicative of constriction of peripheral blood vessels) during either work or rest, whereas an equally intense one-third octave band of random noise, center frequency of 3150 Hz, had no appreciable effect on pulse amplitude. Repeated exposures to the wide-band noise showed some adaptation or habituation of the pulse amplitude response during conditions of either work or rest. The results were the same for fast rise time (impulsive) bursts of wide-band noise as for bursts with slow, gradual onsets. Rapid interruptions of wide-band noise caused less of a decrease in average pulse amplitude than did uninterrupted noise. It is suggested that constriction of peripheral blood vessels in response to expected intense low-frequency or wide-band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.

Adaptation, Physiological↗
PubMed1982

Loudness, annoyance, and noisiness produced by single-tone-noise complexes.

Single tones centered within the noise spectrum were added to three different broadband spectra: flat, low pass, and high pass. Judgments of overall loudness, annoyance, and noisiness (perceived magnitude) were obtained by absolute magnitude estimation (AME) supplemented by loudness matching. The data were evaluated to determine how the overall SPL of the noise-tone complex, and tone-to-noise ratio effect judged perceived magnitude. In addition, the relationship among the tree judged attributes was assessed. Results obtained with the different noise spectra show that the growth of perceived magnitude is a nonmonotonic function of the overall SPL of the noise-tone complex. More summation between tone and noise was found for relatively small tone-to-noise ratios (+5, +10, +15 dB), as measured in 1/3-octave bands, than for relatively large tone-to-noise ratios (+20 dV and greater). Data analysis suggests that the extent of the increments and decrements in perceived magnitude depends on the absolute loudness of the component stimuli, the interaction between a specific tone frequency and noise spectrum, and the attribute judged. An attempt is made to quantify the observed effects and to relate them to the published results of other investigators.

Acoustics↗
PubMed1982

Threshold of degradation for frequency-distributed band-limited noise in continuous speech.

Two series of perceptual experiments have been conducted to investigate the level of noise that acts as a threshold of degradation (TOD) when band-limited noise is added to speech such that the noise is either constrained to lie in one subband of the entire speech band or separately introduced into all subbands. In all cases the within-band signal-to-noise ratio is maintained invariant with time to model the encoding of subbands with the aid of adaptive quantizers. Below 1000 Hz, the TOD for 500 Hz wide bands is found to drop with frequency at roughly half the rate of the speech drop. Above 1000 Hz, the TOD for noise in individual subbands in only 10 dB and does not vary significantly with frequency. When noise is introduced simultaneously into all bands, the TOD is some 5 dB lower than when the noise is introduced into one band alone. Additional subdivision of the frequency bands for independent encoding, so as to increase the noise at TOD and thereby reduce the required SNR, is particularly effective at the lower speech frequencies, because it allows one to take advantage of both the rapidly dropping speech spectrum as well as the time incoherence of the speech energy variations within the various bands. The perceptual tolerance appears guided by the extent to which the noise can be masked by the speech energy present. Encoding techniques that take better advantage of this factor are likely to lead to transmission efficiencies while maintaining excellent speech quality.

Auditory Threshold↗
PubMed1983

The intelligibility of sentences in quiet and in noise in aged listeners.

The monaural speech-reception threshold (SRT) for sentences was investigated in quiet and under four noise conditions for 80 male subjects (age 60-90) and 30 female subjects (age 71-89). The noise levels used were 28, 43, 58, and 73 dBA. The noise had the long-term average spectrum of speech. It is shown that a model developed by Plomp [J. Acoust. Soc. Am. 63, 533-549 (1978)], which interprets any hearing loss for speech (SHL) as a combination of a loss of class A (attenuation of both speech and noise) and a loss of class D (distortion of the sound signals), enables one to make an accurate description of the SRT values measured. Fitting this model, for each individual, to the SRT data yielded values for SHL in quiet (= A + D) and in noise (= D). These individual SHL values were studied in relation to one another and in relation to such parameters as the pure-tone average (PTA), the Fletcher Index (FI), and the increment in intelligibility score per dB near SRT. It was found that (1) subjects with the same SHL in quiet may differ considerably in their SHL in noise; (2) for an individual, PTA and FI are inaccurate measures for predicting SHL in quiet and in noise, and (3) the higher an individual's SHL in noise, the lower is the increase per dB of the intelligibility score for sentences in noise.

Adult↗
PubMed1984

Noise-induced hearing loss as influenced by other agents and by some physical characteristics of the individual.

The interaction of noise with a variety of other agents and with some physical characteristics of the individual to produce noise-induced hearing loss is reviewed critically. The review is restricted, for the most part, to publications since 1970. Other agents interacting with steady-state noise that are reviewed here include: (1) ototoxic drugs (kanamycin, neomycin, ethacrynic acid, furosemide, and salicylates), (2) impulse noise, and (3) whole-body vibration. Physical characteristics of the individual that are reviewed are: (1) age, (2) presence of previous hearing loss from prior noise exposure, (3) eye color, and (4) race. Suggestions for future research in this general area are also made. Some of these suggestions are as follows: (1) to extend studies of the interaction of steady-state noise with impulse noise, salicylates, and whole-body vibration to encompass a broader range of exposure conditions, including exposure conditions typically encountered by the worker, (2) to develop an animal model of presbycusis to explore the interactions of noise-induced hearing loss and presbycusis, and (3) to explore the potential interactions resulting from concurrent exposure to multiple agents, such as impulse noise and ototoxic drugs, in younger, more susceptible animals.

Acoustic Stimulation↗