摘要:

Masked detection thresholds were measured at a center frequency of 2500 Hz for a range of noise signal bandwidths (W=62 to 6000 Hz) and durations (T=10 to 480 ms) approximating that found acoustically in speech. The signals were presented in an uncorrelated 480‐ms, 6000‐Hz‐wide masker. The masker was presented: (1) at a constant spectrum level (53 dB SPL/Hz) or (2) with the overall level varied randomly over a 50‐dB range from interval to interval of a trial. Performance was disrupted in the random‐level masker only for the condition where the signal and uncorrelated masker were gated on and off simultaneously and were matched spectrally. Time constants (τ) estimated from temporal integration functions fit to the masked detection threshold data were related inversely toWforWbroader than the critical bandwidth. Sensitivity to the noise signals was evaluated in the context of an optimum‐detection model (Green, 1960). The results did not follow the prediction of a constant bandwidth‐duration (WT) product, but may be understood in terms of cues available to the listener from the relative combination of signal and masker parameters. At least three cues for detection were identified in these experiments: (1) a relative timing cue, (2) a spectral shape cue, and (3) a traditional energy cue compared across observation intervals. The relative timing cue and spectral shape cue together contributed as much as a 10‐ to 12‐dB advantage relative to detection based on the traditional energy cue alone. A new multi‐cue detection model for predicting the masked detection thresholds was derived. Predictions from the new model were highly correlated (r=0.95) with the empirically measured masked detection thresholds.

ISSN:0001-4966    

DOI:10.1121/1.410470

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Thresholds were measured for the detection of differences in the depth of 5‐Hz frequency modulation (FM). In the first experiment, listeners detected differences between sequentially presented sinusoidal carriers. The Weber fractions for FM depth decreased from about 0.5 to about 0.3 as the baseline depth was increased from 2.5% to 20%, and were slightly higher for a carrier frequency of 0.5 kHz compared to carrier frequencies of 1, 2, and 4 kHz. In the second experiment, complex carriers were used consisting of consecutive harmonics of 125‐ and 250‐Hz fundamentals (f0’s), bandpass filtered between 1375 and 1875 Hz. Performance was worse with these stimuli than with the sinusoidal carriers: The Weber fractions for the 250‐Hzf0ranged from about 0.4 to about 2.0 across listeners, and were roughly invariant with baseline depth. The Weber fractions for the 125‐Hzf0showed a steady decrease from about 3.2 to about 0.6 as the baseline depth was increased from 2.5% to 20%, so that threshold corresponded, approximately, to a constant increase in FM depth, independent of baseline depth. The absolute detectability of the FM may have been a limiting factor for the lower two baseline depths at thisf0. In the final experiment, psychometric functions were measured for the detection of simultaneous across‐frequency differences in FM depth. Three conditions were tested; in the first of these the two carriers to be compared were 666‐ and 1500‐Hz pure tones. In the second condition the two carriers were complex tones, both withf0’s of 250 Hz, filtered between 125 and 625 Hz and between 1375 and 1875 Hz, respectively. The third condition was similar, except that the two (complex) carriers had differentf0’s of 111 and 250 Hz. In the first and third conditions performance was extremely poor, even when the FM depths of the two carriers to be discriminated were 10% and 50%. Listeners did perform substantially better, however, on the second condition. The implications of these results for the idea that listeners use differences in FM depth to perceptually segregate concurrent sounds are discussed.

ISSN:0001-4966    

DOI:10.1121/1.410472

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Binaural loudness matching and intermodal magnitude matching experiments were performed to test systematically the origins of the phenomenon observed earlier that the variability of binaural loudness matches was larger when sound intensity was varied in the normal ear than when it was varied in the contralateral ear with raised threshold and loudness recruitment. In the experiments, the raised threshold and loudness recruitment were produced by masking a 1‐kHz tone with narrow‐band random noise. In intermodal experiments, magnitude matches were performed between the masked tone and the length of lines projected on a translucent window pan. The results are consistent with the earlier observations. They show in addition that the variability depends on the slope of the matching functions in a complicated, not previously anticipated way, irrespective of whether the functions are intra‐ or intermodal. More specifically, for moderate slopes, the variability in the ear with loudness recruitment decreased as the slope increased. The reverse was true for the unmasked ear or the line length—when the slope was large, the variability increased with the slope. Since the variability decreased in one ear and increased in the other, the ratio of the variabilities increased as the slope increased. When the slope was equal to one, both variabilities tended to be the same.

ISSN:0001-4966    

DOI:10.1121/1.411436

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Growth‐of‐masking functions were obtained for sinusoidal signals at three frequencies (fs), 0.25, 1.0, and 4.0 kHz, using maskers that were always higher in frequency than the signal. Five different maskers were used, chosen so as to evaluate the influence of temporal fluctuations in the maskers and of combination products produced by the interaction of components within the maskers: A sinusoid (S); a narrow‐band noise with a bandwidth of 16 Hz (N); a noise with a slightly wider bandwidth equal to 0.75 times the equivalent rectangular bandwidth (ERB) of the auditory filter at eachfs(W); a noise with a very wide bandwidth equal to 0.4fsand with lower cut‐off frequency and spectrum level matched to those of masker W (V); and a sinusoidal carrier frequency modulated by a noise, and matched in bandwidth and center frequency to masker N (F). The center frequencies of maskers S, N, W, and F were either 1.1fsor 1.2fs. Masker S generally produced the smallest amount of masking and gave growth‐of‐masking functions with the shallowest slopes (much less than unity). Results were similar for maskers N and F; both produced slightly more masking than masker S and growth‐of‐masking functions with slightly greater slopes than masker S. Maskers W and V produced more masking than the other maskers, and gave growth‐of‐masking functions with steeper slopes. For all maskers, the slopes of the growth‐of‐masking functions were lower at the greater signal‐masker frequency separation. It is suggested that the results for the two maskers with the greatest bandwidth (W and V) were influenced by combination bands produced by the interaction of components within the masker. The results for the maskers with very small bandwidths (S, N, and F), suggest that the upper side of the auditory filter increases in slope with increasing level.

ISSN:0001-4966    

DOI:10.1121/1.410473

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

This paper reports a study of an absolute pitch possessor who, upon administration of the psychoactive drug Tegratol (carbamazepine), experienced a significant change in her pitch perception. The subject’s performance both in producing, as well as in identifying, random‐frequency tones was measured, covering the period of administration of the drug, as well as control periods before and after. The main effect of the drug was a downward shift of the perceived pitch as compared to the two control periods. The magnitude of the shift was observed to increase with increasing fundamental frequency of the stimulus; the average shift was about one semitone. Detailed results on the frequency dependence and time dependence of the pitch shifts are presented. This may be the first documented report of a significant, reversible change of pitch perception caused by a medication.

ISSN:0001-4966    

DOI:10.1121/1.411437

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Temporal modulation transfer functions (TMTFs) were measured in listeners aged 4 years to adult in order to characterize the development of temporal resolution in children. Four age groups were tested, 4–5 years of age, 6–7 years of age, 9–10 years of age, and adult. Sensitivity to sinusoidal modulation of a noise carrier (a bandpass noise from 200–1200 Hz) was determined for modulation frequencies of 5, 20, 100, 150, and 200 Hz. The data from all listeners indicated decreasing sensitivity to modulation as a function of increasing frequency of modulation. Time constants were derived from the 3‐dB down points of functions that were fitted to the data. No age effects were observed for the derived time constants. However, sensitivity to modulation was found to be reduced in the children 4–5 and 6–7 years of age, as compared to adults, and in the children 4–5 years of age as compared to children 9–10 years of age. The agreement of time constant across all age groups was interpreted as indicating that the peripheral encoding of the temporal envelope is probably adultlike in children aged 4 years and above; however, young children appear to be relatively inefficient in processing the information underlying modulation detection.

ISSN:0001-4966    

DOI:10.1121/1.410474

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

It has already been established that simultaneous activation of two intracochlear electrodes can evoke a pitch percept which is intermediate to that of either electrode when activated by itself. In the present study, this result has been extended to nonsimultaneous activation of nearby electrodes. Pitch perception was investigated for electric stimuli presented on one or two intracochlear electrode pairs. All stimuli were pulse trains of period 4 ms. In the dual‐electrode stimuli, each period contained two biphasic pulses, separated by 0.4 ms, with one pulse for each electrode pair. These stimuli were compared with loudness‐balanced single‐electrode stimuli, having one pulse per period, generated on the same electrode pairs. Their pitches were ranked in a two‐alternative forced‐choice procedure by five experienced users of the 22‐electrode implant manufactured by Cochlear Pty Limited. The studies showed that the pitch of a dual‐electrode stimulus was intermediate to, and moved monotonically between, those of the component electrode pairs as the relative currents were altered in an orderly fashion. Intermediate pitches were achieved in all subjects at a range of cochlear positions, for electrode separations generally up to 3 mm. In half the cases a significantly different intermediate pitch could be created between adjacent electrodes. Further studies are necessary to establish whether intermediate pitches can be obtained at larger separations, as for simultaneous stimulation, and how they are affected by other factors such as the time between pulses or the spatial extent of the stimulation.

ISSN:0001-4966    

DOI:10.1121/1.410475

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The normalized cross‐correlation function between the amplitude and frequency fluctuations of 11 spontaneous otoacoustic emissions was measured. A significant correlation was found in seven subjects. The correlation coefficient ranged from −0.37 to +0.65 across subjects. In four subjects, the amplitude fluctuation lagged the frequency fluctuation. The time lag was between 1.6 and 5.5 ms. The results were interpreted using a noise‐perturbed limit‐cycle oscillator with nonlinear (Duffing) stiffness as a model for a spontaneous emission. The data show that the relative increase of the nonlinear stiffness in this model was between −0.010 and +0.015. This indicates that an even‐order nonlinear stiffness plays a minor role in the emission generator.

ISSN:0001-4966    

DOI:10.1121/1.411438

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Spatial pressure distributions have been measured in the ear canals of ten cats and analyzed to obtain the energy reflection properties of the middle ear over a 10‐ to 25‐kHz range of frequencies. Considerable intersubject variability is observed, much of which can be correlated with the condition of the tympanic membrane. For ears judged to be in good condition, reflection coefficients typically take values of about 0.2 between 15 and 25 kHz, indicating good matching of the dynamical properties of the auditory system to the ear canal sound field. At lower frequencies, the reflection coefficients tend to be somewhat higher and at higher frequencies the reflection coefficients increase quite rapidly with frequency. For ears judged to be in poorer condition, energy reflection coefficients of 0.5 and 0.9 were determined for the 15‐ to 25‐kHz range. The variations of sound pressure along the canal (about 10 dB, even in well‐coupled systems) confirm that single point pressure measurements may be inappropriate for defining the acoustical input at higher frequencies and new measures for specifying the input should be investigated. The net flow of acoustic energy into the auditory system, the sound power, is one possibility. Some initial measurements of sound power, obtained from analysis of the spatial pressure distributions, are presented.

ISSN:0001-4966    

DOI:10.1121/1.410461

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

There are two major approaches to the problem of signal deconvolution: Direct methods attempt to explicitly form an inverse operator, while iterative methods rely on successive approximations. In general, direct methods are computationally efficient. Iterative methods enjoy advantages in terms of ill‐conditioning and flexibility; in particular, they are easily modified to incorporate constraints that force the solution to exhibit features knownapriori. It has previously been shown that the classical direct least squares and regularized least‐squares inverse operator methods are equivalent in the limit to corresponding iterative solution methods. In some cases, multiple blurring operators can be used to convert instances of ill‐posed problems into ones that are well‐posed. A new iterative restoration that corresponds to the direct inversion solution associated with multiple operators is formulated here. This method has the advantages of the constrained iterative routines as well as the advantages associated with multiple operator direct inverse deconvolution. Examples are presented to illustrate that combining a constrained iterative technique with multiple operators can yield a restoration superior to that of a single operator constrained iterative estimate alone or that of a multiple operator direct inverse estimate alone.

ISSN:0001-4966    

DOI:10.1121/1.410462

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP