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PubMed2001

Infants' sensitivity to broadband noise.

Infants have higher pure-tone thresholds than adults. One explanation is that infants do not adopt the frequency-selective listening strategy that adults use when detecting tones. In contrast to other models of infants' immature sensitivity, the listening strategy account predicts that infants will be more sensitive to broadband sounds, relative to adults. Infants 7-9 months old were tested in two experiments to examine their sensitivity to broadband noise. Unmasked and masked thresholds for a 1000-Hz tone and for broadband noise were estimated adaptively for infants and adults using an observer-based behavioral procedure. The difference between infants and adults in unmasked threshold were 14 and 7 dB for tones and noise, respectively. The difference between infants and adults in masked threshold were 10 and 5 dB for tones and noise, respectively. Psychometric functions for detection of broadband noise were also obtained from some infants and adults. Infants' psychometric functions were similar to those obtained in tone detection with shallower slopes and lower upper asymptotes than adults'. This suggests that the relative improvement in infants' threshold for broadband noise is not due to greater attentiveness to the noise. A model of infants' sound detection invoking inattentiveness, listening strategy, and an unspecified source of internal noise may account for the characteristics of the infant psychometric function.

Adolescent↗
PubMed2002

Noise in miniature microphones.

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.

Amplifiers, Electronic↗
PubMed2004

Sequential F0 comparisons between resolved and unresolved harmonics: no evidence for translation noise between two pitch mechanisms.

Carlyon and Shackleton [J. Acoust. Soc. Am. 95, 3541-3554 (1994)] suggested that fundamental-frequency (F0) discrimination performance between resolved and unresolved harmonics is limited by an internal "translation" noise between the outputs of two distinct F0 encoding mechanisms, in addition to the encoding noise associated with each mechanism. To test this hypothesis further, F0 difference limens (DLF0s) were measured in six normal-hearing listeners using sequentially presented groups of harmonics. The two groups of harmonics presented on each trial were bandpass filtered into the same or different spectral regions, in such a way that both groups contained mainly resolved harmonics, both groups contained only unresolved harmonics, or one group contained mainly resolved and the other only unresolved harmonics. Three spectral regions (low: 600-1150 Hz, mid: 1400-2500 Hz, or high: 3000-5250 Hz) and two nominal F0s (100 and 200 Hz) were used. The DLF0s measured in across-region conditions were well accounted for by a model assuming only two sources of internal noise: the encoding noise estimated on the basis of the within-region results plus a constant noise associated with F0 comparisons across different spectral regions, independent of resolvability. No evidence for an across-pitch-mechanism translation noise was found. A reexamination of previous evidence for the existence of such noise suggests that the present negative outcome is unlikely to be explained by insufficient measurement sensitivity or an unusually large across-region comparison noise in the present study. While the results do not rule out the possibility of two separate pitch mechanisms, they indicate that the F0s of sequentially presented resolved and unresolved harmonics can be compared internally at no or negligible extra cost.

Acoustic Stimulation↗
PubMed2005

Word recognition in noise at higher-than-normal levels: decreases in scores and increases in masking.

Under certain conditions, speech recognition in noise decreases above conversational levels when signal-to-noise ratio is held constant. The current study was undertaken to determine if nonlinear growth of masking and the subsequent reduction in "effective" signal-to-noise ratio accounts for this decline. Nine young adults with normal hearing listened to monosyllabic words at three levels in each of three levels of a masker shaped to match the speech spectrum. An additional low-level noise equated audibility by producing equivalent masked thresholds for all subjects. If word recognition was determined entirely by signal-to-noise ratio and was independent of overall speech and masker levels, scores at a given signal-to-noise ratio should remain constant with increasing level. Masked pure-tone thresholds measured in the speech-shaped maskers increased linearly with increasing masker level at lower frequencies but nonlinearly at higher frequencies, consistent with nonlinear growth of upward spread of masking that followed the peaks in the spectrum of the speech-shaped masker. Word recognition declined significantly with increasing level when signal-to-noise ratio was held constant which was attributed to nonlinear growth of masking and reduced "effective" signal-to-noise ratio at high speech-shaped masker levels, as indicated by audibility estimates based on the Articulation Index.

Adult↗
PubMed2005

Underwater temporary threshold shift in pinnipeds: effects of noise level and duration.

Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing.

Animals↗
PubMed2006

Auditory evoked potentials in females with high and low acceptance of background noise when listening to speech.

Acceptable noise level (ANL) is a measure of a listener's acceptance of background noise when listening to speech. A consistent finding in research on ANL is large intersubject variability in the acceptance of background noise. This variability is not related to age, gender, hearing sensitivity, type of background noise, speech perception in noise performance, cochlear responses, or efferent activity of the medial olivocochlear pathway. In the present study, auditory evoked potentials were examined in 21 young females with normal hearing with low and high acceptance of background noise to determine whether differences in judgments of background noise are related to differences measured in aggregate physiological responses from the auditory nervous system. Group differences in the auditory brainstem response, auditory middle latency response, and cortical, auditory late latency response indicate that differences in more central regions of the nervous system account for, at least in part, the variability in listeners' willingness to accept background noise when listening to speech.

Adult↗
PubMed2006

Aircraft noise effects on sleep: application of the results of a large polysomnographic field study.

The Institute of Aerospace Medicine at the German Aerospace Center (DLR) investigated the influence of nocturnal aircraft noise on sleep in polysomnographic laboratory and field studies between 1999 and 2004. The results of the field studies were used by the Regional Council of Leipzig (Germany) for the establishment of a noise protection plan in the official approval process for the expansion of Leipzig/Halle airport. Methods and results of the DLR field study are described in detail. Special attention is given to the dose-response relationship between the maximum sound pressure level of an aircraft noise event and the probability to wake up, which was used to establish noise protection zones directly related to the effects of noise on sleep. These protection zones differ qualitatively and quantitatively from zones that are solely based on acoustical criteria. The noise protection plan for Leipzig/Halle airport is presented and substantiated: (1) on average, there should be less than one additional awakening induced by aircraft noise, (2) awakenings recalled in the morning should be avoided as much as possible, and (3) aircraft noise should interfere as little as possible with the process of falling asleep again. Issues concerned with the representativeness of the study sample are discussed.

Acoustics↗
PubMed2006

Identification of syllables in noise: electrophysiological and behavioral correlates.

This study was designed to characterize the effect of background noise on the identification of syllables using behavioral and electrophysiological measures. Twenty normal-hearing adults (18-30 years) performed an identification task in a two-alternative forced-choice paradigm. Stimuli consisted of naturally produced syllables [da] and [ga] embedded in white noise. The noise was initiated 1000 ms before the onset of the speech stimuli in order to separate the auditory event related potentials (AERP) response to noise onset from that to the speech. Syllables were presented in quiet and in five SNRs: +15, +3, 0, -3, and -6 dB. Results show that (1) performance accuracy, d', and reaction time were affected by the noise, more so for reaction time; (2) both N1 and P3 latency were prolonged as noise levels increased, more so for P3; (3) [ga] was better identified than [da], in all noise conditions; and (4) P3 latency was longer for [da] than for [ga] for SNR 0 through -6 dB, while N1 latency was longer for [ga] than for [da] in most listening conditions. In conclusion, the unique stimuli structure utilized in this study demonstrated the effects of noise on speech recognition at both the physical and the perceptual processing levels.

Acoustic Stimulation↗
PubMed1978

Threshold shifts in chinchillas exposed to octave bands of noise centered at 63 and 1000 Hz for three days(a).

Audiograms were obtained on eight binaural chinchillas trained on a shuttlebox avoidance procedure. Four of the animals were exposed to three successive levels of an octave band of noise centered at 63 Hz: 100 dB SPL (74 dBA), 110 dB SPL (84 dBA), and 120 dB SPL (94 dBA). The other four animals were also exposed to three successive levels of an octave band of noise centered at 1000 Hz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposure durations were 75 h. Little threshold shift (TS) resulted from the lower two exposure levels of the 63-Hz noise band. At the 120-dB exposure level, maximum TS of 43 dB occurred at 2000 Hz. Permanent threshold shifts (PTSs) of 16 dB at 2000 Hz and 11 dB at 1400 Hz were found. Exposure to the three levels of the 1000-Hz noise band produced TSs of 20, 45, and 61 dB at 1400 Hz. The 95-dB exposure level resulted in PTSs of 6 dB at 1400 Hz and 9 dB AT 2000 Hz. The major results were (1) high-frequency hearing loss to a low-frequency noise and (2) that noise bands matched within 1 dBA were not equally hazardous as dictated by damage-risk criteria. The 63-Hz noise band produced nearly twice as much PTS as the 1000-Hz noise band.

Acoustic Stimulation↗
PubMed1984

Growth rate of loudness, annoyance, and noisiness as a function of tone location within the noise spectrum.

The relation between overall perceived magnitude (loudness, annoyance, and noisiness) of noise-tone complexes and the location of the tone within the spectrum was investigated by absolute magnitude estimation (AME). Single tones at 250, 1000, 2000, and 3000 Hz were added to low-and high-pass noises. In contrast to noisiness, loudness and annoyance growth behavior depends on the relationship between the frequency of the added tone and the spectral shape of the noise. Tones centered in noise produce nonmonotonic loudness and annoyance growth functions; those added to the skirt produce power functions. The measured exponents are invariant across tone-to-noise ratio when the tones are positioned within the spectrum, but not when they are added to the skirt. Moreover, for complexes at approximately the same overall SPL, the tone's position determines the functional relationship between loudness (or annoyance) and tone-to-noise ratio. Although a tone correction for annoyance is warranted for certain noise-tone configurations, none of the proposed calculation procedures considers all the variables relevant to perceived annoyance of tonal components. To a large extent, complex auditory interactions generated by the simultaneous presentation of noise and tone can account for the observed effects.

Acoustic Stimulation↗
PubMed1985

Effects of flanking noise bands on the rate of growth of loudness of tones in normal and recruiting ears.

Five subjects with unilateral cochlear hearing impairments and three normally hearing subjects made loudness matches between tones presented alternately to two ears, as a function of the intensity of the tone in the impaired ear (or the left ear of the normal subjects). The impaired ears showed recruitment; the rate of growth of loudness with increasing intensity was more rapid in the impaired ear than the normal ear. Presenting the tone in the impaired ear with two noise bands on either side of the tone frequency, at a fixed signal-to-noise ratio, did not abolish the recruitment. This suggests that recruitment is not caused by an abnormally rapid spread of excitation in the peripheral auditory system. At low signal-to-noise ratios, a continuous background noise reduced the loudness of the tone more than a noise gated with the tone, suggesting that the continuous noise induces adaptation to the tone. The noise had a greater effect on the loudness of the tone in normal ears than in impaired ears. It is possible that the loudness reduction of the tone in noise is mediated by suppression; suppression is weak or absent in impaired ears, and so the loudness reduction is smaller.

Aged↗
PubMed1985

Pitch shift of pure and complex tones induced by masking noise.

Psychoacoustic experiments were performed to measure the pitch-shift effects of pure and complex tones resulting from the addition of a masking noise to the tonal stimuli. Harmonic residue tones with either two or three harmonics and a fundamental frequency of 200 Hz were chosen as test tones. The pitch shifts of virtual and spectral pitches of the residue tones were measured as a function of the intensity of a low-pass noise with 600-Hz cutoff frequency. The SPL of this noise varied between 30 and 70 dB. In another experiment, the pitch shifts of single pure tones corresponding to the frequencies and SPLs of the harmonics of the residue tones were measured using the same masking noise. The results from five subjects for the harmonic residue tones show only a weak dependence of pitch shift on masking noise intensity. This dependence exists for both spectral and virtual pitches. In the case of single pure tones, pitch shift depends more distinctly on noise intensity. Pitch shifts of up to 5% were found in the range of noise intensity investigated. The magnitude of pitch shift shows pronounced interindividual differences, but the direction of the shift effect is always the same. In all cases pitch increases with higher masking noise levels.

Adult↗
PubMed1987

The effect of broadband noise on the human brain-stem auditory evoked response. III. Anatomic locus.

The effects of broadband noise on the brain-stem auditory evoked response (BAER) are reported for two experiments. Experiment 1 used a high-pass subtractive-masking technique and covaried derived bandwidth and continuous broadband noise level. Comparison of responses to half-octave wide derived bands in the presence of within-band noise showed that wave V latency changes were greater than could be explained on the basis of shifts in the cochlear region responsible for generating the response. The magnitude of within-band noise-induced wave V latency shift was independent of the frequency separation of the masker cutoffs. In experiment 2 the effects of noise level and rate on waves I, III, and V of the BAER were evaluated. Peak latencies increased and peak amplitudes decreased with increasing noise level and rate. Higher noise levels and rates produced an increased central (I-V) conduction time in which the wave III-V increase was greater than the wave I-III increase. Together, these results are most consistent with the hypothesis that a nonplace, central auditory mechanism produces most of the noise-induced latency shifts in normal-hearing adults.

Adult↗
PubMed1987

The effect of intermittent noise on vigilance performance.

An experiment was conducted to determine the effect of the level of predictability of intermittent noise on performance on a visual vigilance task. Under a quiet condition and three intermittent noise conditions, subjects (Ss) carried out a 55-min task where they were required to detect a change in the brightness of one element of a visual display. The results indicated that Ss were less sensitive, less accurate, and more prone to response failures during intermittent noise, although responses were faster under noise conditions. Measures of response bias and response certainty were not significantly affected by the presentation of noise. Variation in the level of predictability of the noise affected only the accuracy of response measure during the final quarter of the vigilance task, with the group receiving the least predictable noise performing significantly worse than the other three groups. The results are discussed in relation to theories of noise and performance.

Adult↗
PubMed1994

Effect of masker level on overshoot in running- and frozen-noise maskers.

Masked thresholds were measured with running- and frozen-noise maskers. The 5-kHz signal was 2 ms in duration. The masker was low-pass noise (20 Hz-10 kHz); its total duration was 300 ms. The overall level of the masker was 30, 50, or 70 dB SPL. The onset of the signal was delayed by 0, 3, 8, 18, 198, or 278 ms relative to the onset of the masker. In all frozen-noise measurements, the signal was added to the same fine structure of the noise. Overshoot in frozen noise was measured for two starting phases of the signal that led to a 10-dB difference for large signal-onset delays. In all three configurations (running noise and frozen noise with two different signal phases) masker level had a similar influence on overshoot. At the intermediate masker level (50 dB SPL), a significant amount of overshoot (up to 15 dB) was observed in all three conditions. At the low and the high masker levels, overshoot was very much reduced, and even became negative in most conditions for the 30-dB-SPL masker. For the 50-dB frozen-noise masker, the total variation of thresholds with signal phase was 8 to 11 dB for long signal-onset delays, but only 3 to 6 dB for short delays. For the low- and high-level maskers, where only a small overshoot was observed, the threshold variation with phase for a signal at masker onset was the same as that for the long-delay condition. An explanation for the variation of signal detectability with masker level is proposed that refers explicitly to the compressive input-output characteristic of the basilar membrane at intermediate levels.

Adult↗
PubMed1995

Classification of background noises for hearing-aid applications.

A background-noise classification procedure is being developed for hearing-aid applications, wherein the hearing-aid response would be adjusted in response to changes in the noise environment. The classification procedure is based on measuring four signal features giving the fluctuations of the signal envelope and the mean frequency and low- and high-frequency slopes of the average spectrum. A more complicated procedure, based on determining the envelope modulation spectra in auditory critical bands, was also investigated and was found to offer no advantages over the simpler procedure. The accuracy of the classification procedure was determined for eleven everyday background noises under optimal conditions where the training and test noise sequences were different portions of the same short noise recording. A cluster analysis was used to determine the similarities among the feature vectors for the noises, and when the noises are grouped into a reduced number of clusters the noise-classification accuracy using the four features exceeds 90%.

Cluster Analysis↗
PubMed1996

Gap detection for pairs of noise bands: effects of stimulus level and frequency separation.

Temporal gap detection was determined for single 20-Hz-wide noise bands having various center frequencies, and for simultaneously present pairs of noise bands where the spectral separation between center frequencies was varied. in most conditions, each noise band was present 30 dB above its detection threshold, but in some conditions, each noise band was presented 15 dB above its detection threshold. The results for single noise bands indicated that the gap threshold did not vary significantly across center frequency. Gap detection was significantly better for pairs of noise bands than for single noise bands. The improvement in gap detection when two noise bands were presented instead of one was greater at the 15-dB presentation level than at the 30-dB level. In the case where pairs of bands were presented, there was no effect of the spectral separation between bands, even though the spectral separation was varied over a range of 5 oct. Spectral integration for gap detection may be limited only by the audibility curve.

Adult↗
PubMed1997

A psychoacoustic model for the noise masking of plosive bursts.

A model for predicting the masked thresholds of the voiceless plosive bursts /k,t,p/ in background noise is proposed. Because plosive bursts are brief, are generated by a noise source, and have different spectral characteristics, the modeling approach accounts for duration, center frequency, and signal bandwidth. Noise-in-noise masking experiments are conducted using a broadband masker and bandpass noise signals of varying bandwidth (100-5483 Hz), duration (10-300 ms), and center frequency (0.4-4 kHz). Data from these experiments are used to parametrize an auditory filter model in which the effective bandwidth and the signal-to-noise ratio at threshold for each filter are duration dependent. The duration-dependent filter model is then used to predict the thresholds of synthetic and naturally spoken plosive bursts in background noise. Finally, results from pilot notched-noise experiments are presented which support duration-dependent frequency selectivity.

Adult↗