摘要:

Conflicting conclusions have been drawn regarding cochlear distortion products from cochlear microphonic (CM) studies [e.g., Dallos,The Auditory Periphery(Academic, New York, 1973)], and from neural studies [Kim and Molnar, inThe Nervous System, edited by Tower, (Raven, New York, 1975), and Kimet al., Scand. Audiol. (in press)]. The former studies conclude that there are no mechanically propagated distortion products in CM responses for sound pressure levels (SPLs) below 70 dB (re20 μN/m2). The latter studies however, conclude that the distortion products (f2‐f1and (2f1‐f2) are (1) generated in the cochlear region where the primary‐frequency responses are both large, and (2) propagate mechanically like single‐tone responses over the region apical to the generation region even at low SPLs (e.g., 34 dB). To help resolve this conflict, we measured CM responses in the chinchilla. We sought and found predominant distortion products (f2‐f1) and (2f1‐f2) by systematic variation of stimulus frequencies and SPLs with distortion frequency near the characteristic frequency (CF) of the recording site (turn two or three). We subsequently varied the distortion frequency around the CF, e.g., by fixingf1well above the CF and varyingf2. We have observed that the distortion amplitude in CM obtained with SPLs as low as 25 dB shows tuning characteristics similar to the single‐tone response. We conclude, in agreement with the neural studies, that our CM data reflect mechanically propagating distortion products. Possible explanations for the previous contrary conclusions are discussed. [Supported by NIH Grants NS07498, NS07057, NS00162, RR00396.]

ISSN:0001-4966    

DOI:10.1121/1.2017472

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Recent research has demonstrated that a great deal of frequency specific information is available in evoked responses from the eighth nerve and the brain stem. In electrocochleography and brain‐stem evoked response audiometry very short tone bursts or pips (i.e., 2 ms duration with 1 ms rise/fall) are used to avoid artifacts. We questioned the extent to which frequency selectivity might be degraded by the use of such short and transient stimuli since physically they have substantially broader spectra than pure tones and subjectively they lack tonality. An automatic tracking procedure was used to obtain tuning functions from human subjects via a tone‐on‐tone masking paradigm. The results suggest that there is little loss in the apparent frequency selectivity with decreasing duration of the probe stimuli as long as the intensity of the tone pip is kept relatively low. Due to the threshold power integration phenomenon this means that sharp tuning may be seen only at sensation levels less than 10 dB for a pip of, say, 2 ms. The tips of the tuning functions seem to disappear at a set sound pressure level of the probe, regardless of duration. The implications for evoked response audiometry will be discussed. At this juncture it appears that, at least under certain conditions, responses elicited by even very brief tone bursts reflect an impressive degree of frequency specificity.

ISSN:0001-4966    

DOI:10.1121/1.2017479

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

BSER (wave V) latency shifts to filtered click stimuli were measured. A square wave pulse was filtered to obtain clicks centered at 250, 500, 1000, 2000, 4000, and 6300 Hz. The filtered clicks were transduced monaurally to seven subjects at a rate of 10/s at 50, 40, 30, and 20 dB HL. Wave V latencies were measured from the first compression of the stimulus waveform. BSERs were extractable at all frequency and intensity combinations. A decrease in frequency and intensity caused a systematic increase in wave V latency, as well as a depression in waveform amplitude. Wave V latency shifts due to frequency and intensity changes generally agreed with the results of other investigators [A. J. Klein and D. C. Teas, J. Acoust. Soc. Am.63, 1887–1895 (1978)]

ISSN:0001-4966    

DOI:10.1121/1.2017485

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Major portions of the right hemisphere of conscious rabbit were stereotaxically mapped for auditory and nonauditory responsive regions. Extracellular activity was recorded from 101 auditory units. Acoustic stimuli were tone and white‐noise bursts, 130 ms in duration, with 5 ms rise/fall times, presented 1/s. A silastic earmold fitted to the rabbit's external auditory meatus positioned the earphone, sound measuring microphone, and calibrated probe tube assembly so as to direct the sound source as close as possible to the eardrum. Cells with well‐defined characteristic frequencies (CFs), ranging from 0.4 to 23 kHz. comprised approximately 60% of the population. Tuning curves were heterogeneous in shape. Latency of response onset ranged from 7 to 100 ms. Spontaneous rates less than 1 spike/s and up to 32 spikes/s were measured, and appeared to increase with cortical depth. A variety of temporal response patterns (PST histograms) were measured. Several units exhibited variable responses, such as occasional or inconsistent firing to stimulus presentations. Surgical procedures, sound delivery and recording techniques for unit recording in the conscious rabbit will be described. Characteristics of stimulus‐evoked and background activity will be compared with neuronal activity in auditory cortex previously reported in other species. [Work supported by NIH Grant No. 2R01 NS12317.]

ISSN:0001-4966    

DOI:10.1121/1.2017488

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Measures of acoutic volume‐backscattering spectra using explosive sources were made in the eastern North Atlantic and southern Norwegian Sea (southwest and northeast of the Faeroe Islands) during August 1978. The experimental data were analyzed from 300 to 20 000 Hz with a resolution of 40 Hz. Spectra from both areas are noticeably different, particularly below 10 kHz where most volume scattering is caused by fishes possessing gas‐filled swimbladders. Daytime spectra in the Norwegian Sea were dominated by a strong low‐frequency peak between 1500–2000 Hz; concomitant high‐resolution depth recordings indicated large concentrations of discrete targets layered between 100–350 m. The blue whiting,Micromesistius poutassou, is known to inhabit the entire area in commercial quantities during this time of year at these depths and is of the proper length (i.e., bladder size) to cause this strong peak. Daytime spectra of the southerly area exhibit features comparable with those commonly observed at midlatitudes which is attributed to swim‐bladder resonance of smaller, mesopelagic fishes commonly associated with deep scattering layers.

ISSN:0001-4966    

DOI:10.1121/1.2017494

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Source level spectra for 14 large merchant ships have been measured with hydrophones at about 400 m from the ships' tracks. The measured broadband levels tend to be fairly constant from 20 or 30 Hz down to 4 or 5 Hz, instead of decreasing. A possible cause of these high measured low‐frequency levels is flow‐induced noise radiated from the turbulent boundary layer on the ship's hull [E. A. Vecchio and C. A. Wiley, J. Acoust. Soc. Am.53, 596–601(1975)]. This paper presents results of calculating the radiated flow‐induced noise, as received at the experimental ranges. The smooth‐plate expressions for boundary layer thickness and source spectral density have been modified to conform to typical hull roughness. The computed levels, above 5 Hz, are generally less than 10 dB from the measured received levels, suggesting that flow‐induced noise is an important component of merchant ship radiated noise from about 5 to 20 Hz.

ISSN:0001-4966    

DOI:10.1121/1.2017502

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

At Ocean Acre, the volume backscatter strengthS(z;f), 12–15.5 kHz, associated with the daytime deep scattering layer in the main thermocline region is due to backscattering from swimbladder fish. In the NDI model forS(z;f) developed previously for light‐sensitive layers, it is assumed that the number densityn(z) of “effective scatterers” is determined by a Gaussian distribution of “preferred” light intensity valuesItracked by the scatterers. thatIdecays with depth according to Lambert's law, and that the average backscatter cross section δ(z;f) is a constant, δ(f). This model is found to describe the daytime deep scatterer profileSonly ifIis replaced by an analogous “preferred” variableI′with an exponential decay rate approximately one‐tenth the extinction coefficient for light. Thus, some other environmental factor than light intensity primarily determines the shape of theS‐profile for this layer. Here a physical interpretation of the NDI′ model is developed by showing that (1) measured abundance profilesnb(z) of swimbladder fish in the daytime deep scattering layer are described by the NDI′ model and (2), the exponentially decayingI′required by the model is obtained ifI′is identified with a simple logarithmic function of the temperature field.

ISSN:0001-4966    

DOI:10.1121/1.2017512

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Evaluation of general population hearing level data yields significant differences by Race and Sex. These differences are most obvious in industrial populations investigated to date. In order to define these differences and gain a better understanding of possible causes, white and black NINEP samples have been obtained. A comparison is made between hearing levels representing the black and white NINEPs. Significant differences between male and female and black and white populations are observed. These differences are frequency dependent and are most pronounced in the male populations. [Work supported by The Rockefeller Foundation.]

ISSN:0001-4966    

DOI:10.1121/1.2017515

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The state of knowledge in several areas of music perception will be reviewed. Topics to be covered include principles of organization and grouping, tonal shape analyzing mechanisms, rhythm, and tempo, the role of memory, and the perception of instrumental timbre. The field as a whole is currently undergoing rapid expansion. This is due in large part to recent technological advances which have facilitated the generation of complex auditory stimuli with precisely controlled parameters. Given the developing interest among scientists, music theorists, who have traditionally been rationalistic in their approach, are also turning their attention to empirical issues. Thus, we see emerging a new and strong interaction between musical acoustics on the one hand and music theory on the other. It is expected that considerable advances will be made in the understanding of music perception over the next decade.

ISSN:0001-4966    

DOI:10.1121/1.2017516

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

During the lifetime of the Acoustical Society of America, certain developments have led to an improved understanding of the physical and tonal properties of woodwind instruments. These developments include theoretical analysis, instrumentation for measuring acoustical properties, and high speed digital computing. This paper will review past work, summarize the present state of our knowledge. and offer some conjectures on the future. The content is restricted to a consideration of mechanical‐reed woodwinds, although comparable things could be said about “air‐reed” woodwinds. The following aspects will be discussed: (1) acceptable bore shapes; (2) theory of tone holes; (3) experimental measurement of input impedance: (4) numerical calculation of input impedance; (5) implications of input impedance: (6) reed and air‐column interaction: (7) small‐amplitude, steady‐state vibrations: (8) medium‐amplitude, nonbeating, steady‐state vibrations; (9) functional modeling of arbitrary amplitude transient and steady‐state vibrations: (10) tonal analysis‐synthesis and spectral properties; and (11) tonal perception.

ISSN:0001-4966    

DOI:10.1121/1.2017519

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP