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At least 55 records · Page 3Linked to original sources
PubMed1994

Simulation of free-field sound sources and its application to studies of cortical mechanisms of sound localization in the cat.

We synthesized a set of signals (clicks) for earphone delivery whose waveforms and amplitude spectra, measured at the eardrum, mimic those of sounds arriving from a free-field source. The complete stimulus set represents 1816 sound-source directions, which together surround the head to form a 'virtual acoustic space' for the cat. Virtual-space stimuli were delivered via calibrated earphones sealed into the external meatus in cats under barbiturate anesthesia. Neurons recorded in AI cortex exhibited sensitivity to the direction of sound in virtual acoustic space. The aggregation of effective sound directions formed a virtual space receptive field (VSRF). At 20 dB above minimal threshold, VSRFs fell into one of several categories based on spatial dimension and location. Most VSRFs were confined to either the contralateral (59%) or ipsilateral (10%) sound hemifield. Seven percent spanned the frontal quadrants and 16% were omnidirectional. Eight percent fit into no clear category and were termed 'complex'. The size, shape, and location of VSRFs remained stable over many hours of recording. The results are in essential agreement with free-field studies. VSRFs were found to be shaped by excitatory and inhibitory interactions of activity arriving from the two ears. Some cortical neurons were found to preserve the spectral information in the free-field sound which was generated by the acoustical properties of the head and pinna, filtered by the cochlea and transmitted by auditory nerve fibers.

Acoustic Stimulation↗
PubMed2004

Spatial discrimination of sound sources in the horizontal plane following an adapter sound.

The effect of a preceding (adapter) sound on the spatial discrimination of two subsequent, successively presented (target) sounds was tested in the horizontal plane. The adapter and the first target were located in front of the subject or 30 degrees to the right of the midline; both sounds were presented either at the same location or at different locations. The second target was located to the right or the left of the first. Sound spectra of the 3-s adapter and the 100-ms targets were either high (4.5-18 kHz) or low (1-4 kHz) in frequency. Fifteen subjects judged the position of the second target relative to the first in a two-alternative forced-choice paradigm. In comparison with a no-adapter control condition, in which no sound preceded, discrimination performance was increased when adapter and first target were presented at the same location and when both sounds consisted of the same frequency spectrum. No improvement occurred when adapter and targets differed in location or frequency. The results are consistent with previous results on post-adaptation discrimination of interaural time differences. Possibly, spatial adaptation of the underlying mechanisms of auditory localization may explain the discrimination aftereffect.

Acoustic Stimulation↗
PubMed1996

Sound orientation behavior in cats. II. Mid-frequency spectral cues for sound localization.

The cat's head-related transfer function creates a directionally dependent mid-frequency notch in the amplitude spectrum of a broadband sound as the stimulus propagates to the tympanic membrane [Rice et al., Hear. Res. 58, 132-152 (1992)]. Our previous behavioral studies [May and Huang, J. Acoust. Soc. Am. 100, 1059-1069 (1996)] have indicated that the cat's sound-evoked orientation responses are well directed to the azimuth and elevation of broadband noise bursts in the frontal sound field, where pinna-based spectral notches are prominent and change systematically with sound direction. In the present study, the importance of mid-frequency directional cues in the cat's sound localization behavior was further evaluated by manipulating the frequency and bandwidth of orientation stimuli. The accurate pattern of orientation behavior seen previously with bursts of broadband noise was relatively unaffected when stimulus bandwidth was decreased to mid-frequency bandpass noise of 5-18 kHz. In contrast, poorly directed head orientation responses were observed in tests with high-pass noise (> 18 kHz) and mid-frequency pure tones. When tested with narrow bands of mid-frequency noise, cats oriented toward the spatial location where HRTF-filtering properties most closely matched the stimulus spectrum. These results suggest that important sound localization cues are derived from mid-frequency spectral features of the cat's HRTF.

Animals↗
PubMedDate not supplied

Sound pressure level of running speech: percentile level statistics and equivalent continuous sound level.

Sound pressure level estimates of running speech must accurately reflect everyday communication in an appropriate unit of measure. Several factors may influence the overall sound pressure level of speech under everyday circumstances, such as age of the listener and speaker, speaking distance, surrounding noise and room acoustics. It is very difficult to estimate how all these factors will combine to affect speech intensity in a given situation. Without that knowledge it is best to deal with measures that reflect running speech in a representative sample of talkers. As to measuring units, there is considerable variation in the way speech intensity is measured and quantified. Due to their fluctuating nature, sound pressure levels of running speech require some type of averaging over time. Equivalent continuous sound levels (Leq) and percentile levels (L(N)) by definition reflect temporal distribution of sound energy. The aim of this study was to collect time-weighted sound pressure level estimates of speech in order to obtain normative descriptive statistics. 400 volunteers between 7 and 95 years of age participated in the study, providing a sample representative of official local demographic data. Descriptive statistics of overall Leq and eleven L(N )measures are presented. Overall Leq is extrapolated to other speaker-listener distances and absorption coefficients. 3 x 2 ANOVA analyses are used to screen the data for significant differences among gender and age groups. Restrictions and advantages of time-weighting units for speech intensity level are discussed, as well as their relevance for audiometry and voice pathology.

Adolescent↗
PubMed1997

Adaptive reduction of heart sounds from lung sounds using a wavelet-based filter.

A new adaptive method for heart sounds reduction from lung sounds, based on wavelet transform, is presented in this paper. The use of a wavelet transform domain filtering technique as an adaptive de-noising tool, implemented in lung sounds analysis, is introduced. The multiresolution representations of the signal, produced by wavelet transform, are used for signal structure extraction. Experimental results have shown that implementation of this wavelet-based filter in lung sound analysis results in an efficient reduction of heart sounds from lung sounds, producing an almost noise-free output signal.

Adult↗
PubMed1991

[Analysis of transmission of continuous adventitious lung sounds in asthmatic patients--a comparison with continuous sounds due to bronchial stenosis].

We studied the acoustic features of continuous adventitious lung sounds in asthmatic patients, and analyzed the characteristics of transmission by comparing the continuous sounds in asthmatic patients with those due to bronchial stenosis. The results were as follows. 1) Continuous adventitious lung sounds in patients with bronchial stenosis confirmed by bronchoscopy were well transmitted to the neck over the trachea. Therefore, it was demonstrated that continuous adventitious lung sounds generated in the lung are able to be transmitted to the tracheal region. 2) Continuous adventitious lung sounds in asthmatic patients were divided into monophonic tones and polyphonic tones, according to sound spectrographic findings. From the results of the coherence analysis, the monophonic tones were considered to be generated in the right or left lung, and were well transmitted to the neck over the trachea. The origin of the polyphonic tones was unknown, but they were also relatively well transmitted to the neck over the trachea. It was confirmed that the tracheal region is a very important location for auscultating and monitoring asthmatic patients.

Adult↗
PubMed1990

[Study on occlusal sounds in children. (1). Influences of the velocity of tooth tapping on the occlusal sound].

The purpose of this study was to evaluate the influence of the maximum velocity of the mouth closing phase on the occlusal sound. Six subjects examined were divided into two groups (children and young adults). Occlusal sounds generated by the tooth tapping were obtained with in microelectronic condenser microphone placed on infra-orbital and external auditory canal. Three parameters were used for the measuring points such as 1) maximum velocity of the closing phase, 2) maximum amplitude of the occlusal sound, 3) duration of the occlusal sound. The results obtained in the present study were as follows: 1) The waveform of occlusal sounds obtained from infra-orbital showed more clearly than that obtained from the external auditory canal. 2) With increasing velocity, both the values of maximum amplitude and duration showed a tendency to increase in both groups. 3) The prolonging of the duration was apparent in the children. The results obtained in the study suggest that the analysis of the occlusal sounds generated by tooth tapping can apply to aid in the functional diagnosis of occlusion in children.

Adult↗
PubMed1976

[Variations in the loudness of a brief sound compared to another brief sound as a function of the duration of both sounds].

Loudness equalizations between two short 2500 Hz tones (15 to 120 ms, about 50 dB SPL) were made. One tone, either the first or the second one, was twice as long as the other. The intensity level differences between tones of the same loudness were calculated. Results show that the relations between duration and loudness of the tones differ for different subjects. Nevertheless the calculated differences diminished with subject experience. Subject evaluations in accordance with the intensity levels of tones, i.e. independently of the duration, were quite often obtained even for the pairs 15 ms-30 ms.

Acoustic Stimulation↗
PubMed1979

Suggested threshold sound pressure levels for frequency-modulated (warble) tones in the sound field.

The problems inherent in using frequency-specific stimuli in the sound field to determine threshold sensitivity are reviewed, including a discussion of some of the specific problems encountered when introducing pure tones, narrow bands of noise, and frequency-modulated (FM) tones. The results of two experiments are reported. In Experiment I, the relationship between pure tones and frequency-modulated tones is developed under earphones in an anechoic chamber, and in two sound-isolated auditory test rooms (not anechoic). Experiment I resulted in the development of a reference threshold sound pressure level for frequency-modulated signals in the sound field. In Experiment II the reference level was applied to a clinical test facility and evaluated with a group of hearing-impaired individuals. The results suggest that the sound-field reference levels accurately reflect monaural threshold under earphones, when the earphone is calibrated to the ANSI, 1969 standard, and the sound field is calibrated to the suggested standard.

Acoustic Stimulation↗
PubMed1993

The relationship between sound transfer functions from free sound field to the eardrum and temporary threshold shift.

Three groups of 12 subjects were utilized for an experiment in which the temporary threshold shift due to a free-field exposure was measured and compared to the sound transfer functions from free-sound field to the subjects' eardrums. Subject selection was based upon their sound transfer functions and the requirement of normal hearing. The subjects were assigned to one of three groups depending on their dominantly sound transfer function frequency: Low, middle, or high. A probe tube with a miniature microphone was used for the measurement of the sound transfer functions in 1/3-oct bands. The measurements were performed in frequency bands from 0.2 to 20 kHz with one direction of sound incidence: 0 degree azimuth and 0 degree elevation. The subjects were exposed twice to a 2-kHz and twice to a 4-kHz narrow-band noise monotonically on four different occasions. Pre- and postexposure sweep Békésy audiograms were recorded and the temporary threshold shift calculated as the difference between the two. The averaged temporary threshold shifts differed significantly among groups.

Acoustic Stimulation↗
PubMed1976

A test of the practical value of estimating breath sound intensity. Breath sounds related to measured ventilatory function.

Each of four examiners performed standardized physical examinations on a group of patients who had just undergone tests of ventilatory function. The intensity of breath sounds heard with deep inspiration was graded on a rating scale of 0 to 4; the grades in six areas of the chest were added to give a total score, with possible values ranging from 0 to 24. Correlation of breath-sound scores with percentage of predicted forced expiratory volume in one second (FEV1) was significant at the 1 percent level for all of the examiners. Differences between the examiners in their assessment of breath sounds were not statistically significant. Grading the loudness of breath sounds was a poor screening test for mild ventilatory abnormality, but normal breath sounds nearly excluded the possibility of severe reduction in the FEV1. Definitely reduced breath-sound intensity was strong evidence for the presence of obstructive pulmonary disease.

Adult↗