Background Noise Conditions Research Articles

Effects of a hearing aid noise management feature on user perception and performance under noise

This paper presents the effects of a hearing aid noise management feature on user perception and performance under noise. Hearing-impaired subjects were exposed twice to seven different noise signals which simulate common mechanical system noise, once with the noise management feature enabled and once disabled. The seven noise signals vary in terms of level and spectral quality, but are all within the range of background noise conditions found in commercial offices. Performance is gauged on three types of tests (math, verbal and typing), while subjective perception is measured via a subjective questionnaire. The results of this investigation will show if the hearing aid noise management feature reduces detrimental effects caused by background noise. Additionally, the data from hearing-impaired subjects are compared to those from normal-hearing persons to assess if significant differences are present between the two groups. If so, they may lead to the development of different standards for noise criteria levels in spaces designed for the hearing-impaired. [Work supported by a Univ. of Nebraska Layman Award and an ASHRAE Graduate Student Grant-in-Aid]

Misty picture: A unique experiment for the interpretation of the infrasound propagation from large explosive sources

In the framework of the Comprehensive Nuclear-Test-Ban Treaty, the International Monitoring System develops a 60 micro-barometric stations network. These stations, which records infrasound, detect various powerful natural and artificial sources like long range explosions, oceanic swell, and volcano eruptions. For data analysis, the CEA, in collaboration with the LMFA, develops specific methods based on measurements, data processing and numerical simulation. The Misty Picture experiment is a high explosive event (4685 Tons of ANFO) realized in 1987 in New Mexico (US). Infrasounds were recorded by 22 sensors until a distance of 1000 km in a quiet background noise condition. Multireflected tropospheric, stratospheric and thermospheric phases are detected. Signals recorded near the source (1 km away) and observed in the geometrical shadow zone (between 150 km and 250 km from the point source) are of particular interest. This reference experiment very well documented is used to improve our understanding of the atmospheric propagation of infrasound as well as to evaluate our models. Using various methods such as ray tracing, parabolic equation and finite differences, we investigate effects of the wind, atmospheric absorption, nonlinearity, refraction, (2D and 3D) and scattering by small atmospheric scales on observed phase kinds, their travel time and their waveform.

A new approach for the adaptation of HMMs to reverberation and background noise

Looking at practical application scenarios of speech recognition systems several distortion effects exist that have a major influence on the speech signal and can considerably deteriorate the recognition performance. So far, mainly the influence of stationary background noise and of unknown frequency characteristics has been studied. A further distortion effect is the hands-free speech input in a reverberant room environment. A new approach is presented to adapt the energy and spectral parameters of HMMs as well as their time derivatives to the modifications by the speech input in a reverberant environment. The only parameter, needed for the adaptation, is an estimate of the reverberation time. The usability of this adaptation technique is shown by presenting the improvements for a series of recognition experiments on reverberant speech data. The approach for adapting the time derivatives of the acoustic parameters can be applied in general for all different types of distortions and is not restricted to the case of a hands-free input. The use of a hands-free speech input comes along with the recording of any background noise that is present in the room. Thus there exists the need of combining the adaptation to reverberant conditions with the adaptation to background noise and unknown frequency characteristics. A combined adaptation scheme for all mentioned effects is presented in this paper. The adaptation is based on an estimation of the noise characteristics before the beginning of speech is detected. The estimation of the distortion parameters is based on signal processing techniques. The applicability is demonstrated by showing the improvements on artificially distorted data as well as on real recordings in rooms.

Timbre discrimination in normal-hearing and hearing-impaired listeners under different noise conditions

In an attempt to quantify differences in object separation and timbre discrimination between normal-hearing and hearing-impaired listeners with a moderate sensorineural hearing loss of two different configurations, psychoacoustic measurements were performed with a total of 50 listeners. The experiments determined just noticeable differences (JND) of timbre in normal-hearing and hearing-impaired subjects along continua of “morphed” musical instruments and investigated the variance of JND in silence and different background noise conditions and on different sound levels. The results show that timbre JNDs of subjects with a steep hearing loss are significantly higher than of normal-hearing subjects, both in silence and noise, whereas timbre JNDs of flat/diagonal hearing-impaired subjects are similar to JNDs of normal-hearing subjects for signal levels above 55 dB (plus appropriate amplification for hearing-impaired). In noise (SNR = + 10 dB) timbre JNDs of all subject groups are significantly higher than in silence. In the condition testing, transferability from silence to noise (i.e., the ability to imagine how the stimulus heard in silence would sound in noise), no significant JND differences across listener groups were found. The results can be explained by primary factors involved in sensorineural hearing loss and contradict the hypothesis that hearing-impaired people generally have more problems in object discrimination than normal-hearing people.

Controlling for spatial variability in single site recordings in an in vitro hippocampal preparation with a spontaneous rhythm

An important consideration in analyzing the time-frequency rhythms of hippocampal local field potentials is to what extent changes in time of a single site signal actually reflect spatial summation of two wholly separate signals. Signals observed could be the result of the spatial summation of different activities. For example, the duration of activities observed could be due to two shorter durations overlapping. More broadly, it is a source of concern if the hippocampal rhythms do not have well defined spatial properties (preferably fairly homogenous) since a single signal has no control for this variable. To that end, we examine the behaviour of a spontaneous hippocampal rhythm over time as it varies spatially within an intact whole hippocampus preparation. We also examine the response to a high frequency stimulation protocol of 80 Hz. Using four simultaneous rostral to caudal recordings of two to five minutes, we characterize this changing rhythmic activity according to clustered patterns of activity in its time-frequency distribution. Our data set consists of 40 extracellular recordings. The frequency distribution change in response to stimulation was observed. We calculate the spatial variance of the data for each unit of time. This allows us to link the time-frequency data to a level of spatial variance. The variance of the signal in time was defined to be the variance in the mean frequencies of the signal resultant from partitioning each time-frequency epoch into thirds. That is, a sliding 0.5 second temporal resolution was divided into thirds and the variance in the mean frequencies calculated. The change in the signal in time was then compared to the change in signal in space to determine whether there were any significant correlations. There is a distinct relationship between the variance among simultaneous rostral caudal recordings and the non-stationarity present in each of those spatially distinct recordings. The peak values nearly follow the y = -x line. Functional biological rhythms in the hippocampus are commonly both non-stationary and coherent, making this inverse relationship more intuitive. Consider that the hippocampal recording has two components, one of which is stationary background noise and one of which is the nonstationary signal of interest. Our finding, then, is that the noise is uncorrelated spatially and signal is correlated spatially. In this case, when the signal is low, the non-stationarity would be low and the spatial variance would be high. This is a very useful property for single site recordings because it means that the more physiologically interesting (nonstationary) the recording, the less we need to be concerned that spatial summation is a problem.

Effects of Redundancy Changes in Time and Frequency on Discriminating Monosyllabic Words(CVC) under Ipsilateral/Contralateral Background Noise Conditions

Effects of Redundancy Changes in Time and Frequency on Discriminating Monosyllabic Words(CVC) under Ipsilateral/Contralateral Background Noise Conditions

Auditory and nonauditory factors affecting speech reception in noise by older listeners

Speech reception thresholds (SRTs) for sentences were determined in stationary and modulated background noise for two age-matched groups of normal-hearing (N = 13) and hearing-impaired listeners (N = 21). Correlations were studied between the SRT in noise and measures of auditory and nonauditory performance, after which stepwise regression analyses were performed within both groups separately. Auditory measures included the pure-tone audiogram and tests of spectral and temporal acuity. Nonauditory factors were assessed by measuring the text reception threshold (TRT), a visual analogue of the SRT, in which partially masked sentences were adaptively presented. Results indicate that, for the normal-hearing group, the variance in speech reception is mainly associated with nonauditory factors, both in stationary and in modulated noise. For the hearing-impaired group, speech reception in stationary noise is mainly related to the audiogram, even when audibility effects are accounted for. In modulated noise, both auditory (temporal acuity) and nonauditory factors (TRT) contribute to explaining interindividual differences in speech reception. Age was not a significant factor in the results. It is concluded that, under some conditions, nonauditory factors are relevant for the perception of speech in noise. Further evaluation of nonauditory factors might enable adapting the expectations from auditory rehabilitation in clinical settings.

Predictive Measures of Directional Benefit Part 2: Verification of Different Approaches to Estimating Directional Benefit

In this investigation, the relation between various directivity measures and subject performance with directional microphone hearing aids was determined. Test devices included first- and second-order directional microphones. Recordings of sentences and noise (Hearing in Noise Test, HINT) were made through each test device in simple, complex, and anisotropic background noise conditions. Twenty-six subjects, with normal hearing, were administered the HINT test recordings and directional benefit was computed. These measures were correlated to theoretical, free-field, and Knowles Electronic Manikin for Acoustic Research (KEMAR) directivity index (DI) values, as well as front-to-back ratios (FBR), in situ signal-to-noise ratios (SNR), and a newly proposed Db SNR, wherein a predictive value of the SNR improvement is calculated as a function of the noise source incidence. The different predictive scores showed high correlation to the measured directional benefit scores in the complex (diffuse-like) background noise condition (r = 0.89 to 0.97, p < 0.05) but not across all background noise conditions (r = 0.45 to 0.97, p < 0.05). The Db SNR approach and the in situ SNR measures provided excellent prediction of subject performance in all background noise conditions (0.85 to 0.97, p < 0.05). None of the predictive measures could account for the effects of reverberation on the speech signal (r = 0.35 to 0.40, p < 0.05). For environments that included a discrete number of noise sources, the in situ SNR and Db SNR estimates were most predictive of subject performance. No predictive approach was indicative of the directional benefit achieved when the speech was also subjected to reverberation (temporal distortion). This finding has implications for real-world estimates of directional benefit.

Effects of exposure duration and type of task on subjective performance and perception in noise

The influences of exposure time and the types of tasks on human perception and task performance have been investigated under a variety of noise conditions with differing level, spectral content, and behavior over time. Ten test subjects each completed 38 hours of testing over multiple days. Subjects were exposed to each of six background noise conditions over 20, 40, 80, and 240 minute trials. During the trials, subjects completed three types of performance tasks (typing, grammatical reasoning, and math tests) and answered questions about their perception of the indoor environment. Results indicate that the different exposure lengths used in this study did not have a significant effect on performance scores. Some influence of exposure time on subjective perception was observed, however; shorter time lengths combined with back to back exposures led to greater differentiation in perception. Significant differences in task performance between the different noise conditions were not observed, but differences in perception were found. Additionally, task performance was related to subjective perception; if subjects perceived the noise to be more tonal, they performed worse on all tasks. The performance results were not always negatively influenced by unfavorable quality perceptions, though. For example, as subjects perceived noise to be more roaring in this study, their typing scores decreased but reasoning and math scores improved.

Perception and performance of hearing-impaired versus normal-hearing persons under noise

Examining the effects of mechanical system noise on worker performance and perception for normal‐hearing persons has been an area of previous research; this study extends this research area to include hearing‐impaired subjects. The goal is to determine if persons with hearing impairments respond similarly to seven different mechanical system background noise conditions as persons with normal hearing. The seven noise signals vary in terms of level and spectral quality, but are all within the range of background noise conditions found in commercial offices. Performance is gauged on three types of tests (math, verbal and typing), while subjective perception is measured via a subjective questionnaire. The results of this investigation will show if significant differences are present between the two groups, and if so, they may lead to the development of different standards for noise criteria levels in spaces designed for the hearing‐impaired. [Work supported by a Univ. of Nebraska Layman Award and an ASHRAE Graduate Student Grant‐in‐Aid.]

Parametric speech codec for representing synthetic speech in the presence of background noise

A system and method are provided for processing audio and speech signals using a pitch and voicing dependent spectral estimation algorithm (voicing algorithm) to accurately represent voiced speech, unvoiced speech, and mixed speech in the presence of background noise, and background noise with a single model. The present invention also modifies the synthesis model based on an estimate of the current input signal to improve the perceptual quality of the speech and background noise under a variety of input conditions. The present invention also improves the voicing dependent spectral estimation algorithm robustness by introducing the use of a Multi-Layer Neural Network in the estimation process. The voicing dependent spectral estimation algorithm provides an accurate and robust estimate of the voicing probability under a variety of background noise conditions. This is essential to providing high quality intelligible speech in the presence of background noise.

Effects of Increasing Sound Pressure Level on Lip and Jaw Movement Parameters and Consistency in Young Adults

Examination of movement parameters and consistency has been used to infer underlying neural control of movement. However, there has been no systematic investigation of whether the way individuals are asked (or cued) to increase loudness alters articulation. This study examined whether different cues to elicit louder speech induce different lip and jaw movement parameters or consistency. Thirty healthy young adults produced two sentences (a) at comfortable loudness, (b) while targeting 10 dB SPL above comfortable loudness on a sound level meter, (c) at twice their perceived comfortable loudness, and (d) while multitalker noise was played in the background. Lip and jaw kinematics and acoustic measurements were taken. Each of the loud conditions resulted in a similar amount of SPL increase, about 10 dB. Speech rate was slower in the background noise condition. Changes to movement parameters and consistency (relative to comfortable) were different in the targeting condition as compared to the other loud conditions. The cues elicited different task demands, and therefore, different movement patterns were used by the speakers to achieve the target of increased loudness. Based on these results, cueing should be considered when eliciting increased vocal loudness in both clinical and research situations.

Speech recognition in normal hearing and sensorineural hearing loss as a function of the number of spectral channels

Speech recognition by normal-hearing listeners improves as a function of the number of spectral channels when tested with a noiseband vocoder simulating cochlear implant signal processing. Speech recognition by the best cochlear implant users, however, saturates around eight channels and does not improve when more electrodes are activated, presumably due to reduced frequency selectivity caused by channel interactions. Listeners with sensorineural hearing loss may also have reduced frequency selectivity due to cochlear damage and the resulting reduction in the nonlinear cochlear mechanisms. The present study investigates whether such a limitation in spectral information transmission would be observed with hearing-impaired listeners, similar to implant users. To test the hypothesis, hearing-impaired subjects were selected from a population of patients with moderate hearing loss of cochlear origin, where the frequency selectivity would be expected to be poorer compared to normal hearing. Hearing-impaired subjects were tested for vowel and consonant recognition in steady-state background noise of varying levels using a noiseband vocoder and as a function of the number of spectral channels. For comparison, normal-hearing subjects were tested with the same stimuli at different presentation levels. In quiet and low background noise, performance by normal-hearing and hearing-impaired subjects was similar. In higher background noise, performance by hearing-impaired subjects saturated around eight channels, while performance by normal-hearing subjects continued to increase up to 12-16 channels with vowels, and 10-12 channels with consonants. A similar trend was observed for most of the presentation levels at which the normal-hearing subjects were tested. Therefore, it is unlikely that the effects observed with hearing-impaired subjects were due to insufficient audibility or high presentation levels. Consequently, the results with hearing-impaired subjects were similar to previous results obtained with implant users, but only for background noise conditions.

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

Several noise criteria methods commonly used in architectural acoustics have been quantitatively related to noise perception and task performance under a variety of ventilation systems-induced background noise conditions. Noise criteria, balanced noise criteria, room criteria, room criteria mark II, and A-weighted equivalent sound pressure level were examined. The first phase of the project included noise conditions controlled to be non-time-varying and nontonal, with neutral, rumbly, roaring, or hissy characteristics. An intermediate study examined exposure time length and types of performance tasks used. The final phase included noise conditions containing various levels of discrete tones from 120 to 595 Hz. Under each noise, subjects completed performance tasks and perception questionnaires. Results indicate task performance was significantly affected by perception of noise, but this relationship was not fully demonstrated by the criteria systems analyzed. The five criteria were generally well suited in describing subjective loudness perception, but some discrepancies in criteria spectral quality ratings and subjective perception existed. Finally, perception of annoyance changed based on the frequency and prominence of tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Modifications to the existing criteria are recommended.

Analysis of parameter effects on sound energy decay in coupled volume systems

Several noise criteria methods commonly used in architectural acoustics have been quantitatively related to noise perception and task performance under a variety of ventilation systems-induced background noise conditions. Noise criteria, balanced noise criteria, room criteria, room criteria mark II, and A-weighted equivalent sound pressure level were examined. The first phase of the project included noise conditions controlled to be non-time-varying and nontonal, with neutral, rumbly, roaring, or hissy characteristics. An intermediate study examined exposure time length and types of performance tasks used. The final phase included noise conditions containing various levels of discrete tones from 120 to 595 Hz. Under each noise, subjects completed performance tasks and perception questionnaires. Results indicate task performance was significantly affected by perception of noise, but this relationship was not fully demonstrated by the criteria systems analyzed. The five criteria were generally well suited in describing subjective loudness perception, but some discrepancies in criteria spectral quality ratings and subjective perception existed. Finally, perception of annoyance changed based on the frequency and prominence of tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Modifications to the existing criteria are recommended.

Investigations of indoor noise criteria systems based on human perception and task performance

Several noise criteria methods commonly used in architectural acoustics have been quantitatively related to noise perception and task performance under a variety of ventilation systems-induced background noise conditions. Noise criteria, balanced noise criteria, room criteria, room criteria mark II, and A-weighted equivalent sound pressure level were examined. The first phase of the project included noise conditions controlled to be non-time-varying and nontonal, with neutral, rumbly, roaring, or hissy characteristics. An intermediate study examined exposure time length and types of performance tasks used. The final phase included noise conditions containing various levels of discrete tones from 120 to 595 Hz. Under each noise, subjects completed performance tasks and perception questionnaires. Results indicate task performance was significantly affected by perception of noise, but this relationship was not fully demonstrated by the criteria systems analyzed. The five criteria were generally well suited in describing subjective loudness perception, but some discrepancies in criteria spectral quality ratings and subjective perception existed. Finally, perception of annoyance changed based on the frequency and prominence of tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Modifications to the existing criteria are recommended.

Theoretical detection ranges for acoustic based manatee avoidance technology

The West Indian manatee (Trichechus manatus latirostris) has become endangered partly because of watercraft collisions in Florida's coastal waterways. To reduce the number of collisions, warning systems based upon detecting manatee vocalizations have been proposed. One aspect of the feasibility of an acoustically based warning system relies upon the distance at which a manatee vocalization is detectable. Assuming a mixed spreading model, this paper presents a theoretical analysis of the system detection capabilities operating within various background and watercraft noise conditions. This study combines measured source levels of manatee vocalizations with the modeled acoustic properties of manatee habitats to develop a method for determining the detection range and hydrophone spacing requirements for acoustic based manatee avoidance technologies. In quiet environments (background noise approximately 70 dB) it was estimated that manatee vocalizations are detectable at approximately 250 m, with a 6 dB detection threshold, In louder environments (background noise approximately 100dB) the detection range drops to 2.5 m. In a habitat with 90 dB of background noise, a passing boat with a maximum noise floor of 120 dB would be the limiting factor when it is within approximately 100 m of a hydrophone. The detection range was also found to be strongly dependent on the manatee vocalization source level.

Effect of optical property estimation accuracy on tomographic bioluminescence imaging: simulation of a combined optical–PET (OPET) system

Inevitable discrepancies between the mouse tissue optical properties assumed by an experimenter and the actual physiological values may affect the tomographic localization of bioluminescent sources. In a previous work, the simplifying assumption of optically homogeneous tissues led to inaccurate localization of deep sources. Improved results may be obtained if a mouse anatomical map is provided by a high-resolution imaging modality and optical properties are assigned to segmented tissues. In this work, the feasibility of this approach was explored by simulating the effect of different magnitude optical property errors on the image formation process of a combined optical–PET system. Some comparisons were made with corresponding simulations using higher spatial resolution data that are typically attainable by CCD cameras. In addition, simulation results provided insights on some of the experimental conditions that could lead to poor localization of bioluminescent sources. They also provided a rough guide on how accurately tissue optical properties need to be known in order to achieve correct localization of point sources with increasing tissue depth under low background noise conditions.

Visual search deficits in Parkinson's disease are attenuated by bottom-up target salience and top-down information

Patients with Parkinson's disease (PD), a degenerative disorder primarily affecting the nigrostriatal dopamine system, exhibit deficits in selecting task-relevant stimuli in the presence of irrelevant stimuli, such as in visual search tasks. However, results from previous studies suggest that these deficits may vary as a function of whether selection must rely primarily on the “bottom-up” salience of the target relative to background stimuli, or whether “top-down” information about the identity of the target is available to bias selection. In the present study, moderate-to-severe medicated PD patients and age-matched controls were tested on six visual search tasks that systematically varied the relationship between bottom-up target salience (feature search, noisy feature search, conjunction search) and top-down target knowledge (Target Known versus Target Unknown). Comparison of slope and intercepts of the RT × set size function provided information about the efficiency of search and non-search (e.g., decision, response) components, respectively. Patients exhibited higher intercepts than controls as bottom-up target salience decreased, however these deficits were disproportionately larger under Target Unknown compared to Target Known conditions. Slope differences between PD and controls were limited to the Target Unknown Conjunction condition, where patients exhibited a shallower slope in the target absent condition, indicating that they terminated search earlier. These results suggest that under conditions of high background noise, medicated PD patients were primarily impaired in decision and/or response processes downstream from the target search itself, and that the deficit was attenuated when top-down information was available to guide selection of the target signal.

Verification of the directivity index and other measures of directivity in predicting directional benefit

The relationship between various directivity measures and subject performance with directional microphone hearing aids was determined. Test devices included first‐ and second‐order directional microphones. Recordings of sentences and noise (Hearing in Noise Test, HINT) were made through each test device in simple, complex, and anisotropic background noise conditions. Twenty‐six subjects, with normal hearing, were administered the HINT test recordings, and directional benefit was computed. These measures were correlated to theoretical, free‐field, and KEMAR DI values, as well as front‐to‐back ratios, in situ SNRs, and a newly proposed Db‐SNR, wherein a predictive value of the SNR improvement is calculated as a function of the noise source incidence. The different predictive scores showed high correlation to the measured directional benefit scores in the complex (diffuse‐like) background noise condition (r=0.89−0.97, p<0.05) but not across all background noise conditions (r=0.45−0.97, p<0.05). The Db‐SNR approach and the in situ SNR measures provided excellent prediction of subject performance in all background noise conditions (0.85−0.97, p<0.05) None of the predictive measures could account for the effects of reverberation on the speech signal (r=0.35−0.40, p<0.05).