摘要:

In scanning tomographic acoustic microscopy (STAM), projection error correction is necessary for high-resolution tomographic reconstruction. In this paper, both phase and alignment errors are examined. These errors arise from several sources, including the quadrature receiver channels, the unknown initial phase term, and any misalignment in the rotational scan. The data acquisition process and the image formation algorithm for the STAM are reviewed, and a description of error estimation and correction is also presented. Experimental results from the STAM are included to demonstrate the capability and effectiveness of the error-removal techniques.

ISSN:0001-4966    

DOI:10.1121/1.422770

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Responses to various steady-state vowels were recorded in single units in the primary auditory cortex (AI) of the barbiturate-anaesthetized ferret. Six vowels were presented (/a/, /ɛ/, 2 different /i/’s, and 2 different /u/’s) in a natural voiced and a synthetic unvoiced mode. In addition, the responses to broadband stimuli with a sinusoidally shaped spectral envelope (called ripple stimuli) were recorded in each cell, and the response field (RF), which consists of both excitatory and inhibitory regions, was derived from the ripple transfer function. We examined whether the vowel responses could be predicted using a linear ripple analysis method [Shamma et al., Auditory Neurosci.1, 233–254 (1995)], i.e., by cross correlating the RF of the single unit, and the smoothed spectral envelope of the vowel. We found that for most AI cells (71%) the relative responses to natural vowels could be predicted on the basis of this method. Responses and prediction results for unvoiced and voiced vowels were very similar, suggesting that the spectral fine structure may not play a significant role in the neuron’s response to the vowels. Predictions on the basis of the entire RF were significantly better than based solely on best frequency (BF) (or “place”). These findings confirm the ripple analysis method as a valid method to characterize AI responses to broadband sounds as we proposed in a previous paper using synthesized spectra [Shamma and Versnel, Auditory Neurosci.1, 255–270 (1995)].

ISSN:0001-4966    

DOI:10.1121/1.422771

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Temporal gap detection thresholds were measured between perceptually dissimilar electrical markers in cochlear implant listeners. Both markers were presented to the same electrode pair. The amplitude and pulse rate of the first marker were fixed, and gap thresholds were measured as a function of either the pulse rate or the amplitude of the second marker. In either case, U-shaped functions were obtained, with lowest gap thresholds occurring when the two markers were similar in both amplitude and pulse rate. Because the two markers were presented to the same electrode pair, the data cannot be accounted for on the basis of across-channel interactions. It is hypothesized that when different markers are used, the perceptual discontinuity from the first marker to the second is similar to the sensation of a brief gap, and dominates the gap detection process. Thus, gap threshold functions with electrically dissimilar markers serve more as indicators of perceptual distance between the markers and less as measures of temporal resolution.

ISSN:0001-4966    

DOI:10.1121/1.422772

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Traditionally, psychophysical data have been predicted either by constructing models of the peripheral auditory system or by applying signal detection theory (SDT). Frequently, the theoretical detection performance predicted by SDT is greater than that observed experimentally and a nonphysiologically based “internal noise” source is often added to the system to compensate for the discrepancy. A more appropriate explanation may be that traditional SDT approaches either incorporate little or no physiology or make simplifying assumptions regarding the density functions describing the physiological data. In the work presented here, an integrated approach, which combines SDT and a physiologically based model of the human auditory system, is proposed as an alternate method of quantifying detection performance. To validate this approach, the predicted detection performance for a simultaneous masking task is compared to predictions obtained from traditional methods and to experimental data. Additionally, the sensitivity of the integrated method is thoroughly investigated. The results suggest that by combining SDT with a physiologically based auditory model, thereby capitalizing on the strengths of each individual method, the previously observed discrepancies can be partially explained as the result of physical processes inherent in the auditory system rather than unspecified “internal noise” and more accurate predictions of psychophysical behavior can be obtained.

ISSN:0001-4966    

DOI:10.1121/1.422773

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Intensity discrimination for a 6-kHz sinusoidal pedestal was measured in quiet and in the presence of a noise background. In the first experiment, the level of a 30-ms pedestal was fixed at 45 dB SPL and presented in the temporal and spectral center of a 110-ms notched noise. For a noise spectrum level of between 0 and 15 dB the noise produced a substantial reduction in the Weber fraction, i.e., an improvement in detectability, compared to the condition without the noise. The second experiment showed that, unlike the situation with notched noise, narrow-band noise produced no performance improvement, suggesting that the effect is dependent on noise frequency components outside the critical band of the pedestal. The third experiment showed that the improvement also occurred for a 6-ms pedestal presented in a 10-ms gap between two bursts of notched noise. The experiment rules out an explanation for the effect of the noise in terms of suppression on the basilar membrane. Finally, the effect was shown to decrease as the gap between the noise bursts was increased, in a manner at least broadly consistent with the decay of the temporal excitation pattern. It is suggested that the improvement in intensity discrimination in notched noise is due to an across-frequency comparison mechanism similar to “profile analysis,” perhaps operating on a temporally smoothed central representation of the stimulus.

ISSN:0001-4966    

DOI:10.1121/1.422774

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Auditory filters broaden with increasing level. Using a recently developed method of fitting filter shapes to notched-noise masking data that explicitly models the nonlinear changes in filter shape across level, results at 2 kHz from 9 listeners over a wide range of levels and notch widths are reported. Families of roex(p,w,t)filter shapes lead to models which account well for the observed data. The primary effect of level is a broadening in the tails of the filter as level increases. In all cases, models with filter parameters depending on probe level fit the data much better than masker-dependent models. Thus auditory filter shapes appear to be controlled by their output, not by their input. Notched-noise tests, if performed at a single level, should use a fixed probe level. Filter shapes derived in this way, and normalized to have equal tail gain, are highly reminiscent of measurements made directly on the basilar membrane, including the degree of compression evidenced in the input–output function.

ISSN:0001-4966    

DOI:10.1121/1.422775

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Interaural-delay sensitivity to high-frequency(⩾3 kHz)sinusoidal-frequency-modulated (SFM) tones is examined for rates from 25 to 800 Hz and depths of−12to 18 dB. Comparison is made to thresholds obtained for sinusoidal-amplitude-modulated (SAM) tones for the same observers and modulation rates. Both SAM and SFM threshold-by-rate functions are U-shaped with optimum sensitivity to SFM tones occurring at higher rates(fm=200–400 Hz)compared to those for SAM tones(fm=100–200 Hz).Effects of modulation depth were examined for rates from 50 to 300 Hz. In all cases thresholds improved considerably with increasing modulation depth. It is also shown that a hybrid dichotic signal composed of an SFM tone presented to one ear and an SAM tone to the other, can perceptually fuse and be lateralized, with the contingency that both stimuli have equal modulation rates but not necessarily equal carrier frequencies. Using bandpass noise to restrict off-frequency listening, it was shown that for this stimulus, observers can use information from filters either below or above the carrier frequency. Consistent with FM-to-AM conversion from cochlear bandpass filtering, several important differences between the SAM- and SFM-tone data can be predicted from a nonstationary stochastic model of binaural interaction whose parameters are uniquely determined from the SAM-tone data.

ISSN:0001-4966    

DOI:10.1121/1.422776

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Across-channel interactions in multi-electrode cochlear implant patients may be critical to their performance in the natural auditory environment. One measure of channel interaction can be obtained using forward masking. The patterns of threshold shift were obtained as a function of the separation between masker and probe electrode pairs in four Nucleus-implanted patients with varying levels of speech recognition. In the three subjects with better speech recognition (N4, N7, and N13), the masking patterns showed the least parameter dependence. In the subject with the lowest speech scores (N3), the masking patterns showed the greatest dependence on masker level and on probe delay. Masking as a function of masker level also reflected these differences: N3’s functions showed the greatest changes for different probe delays. Similar rates of recovery were observed in the three good performers (time constant approximately 70 ms). In contrast, subject N3’s recovery function shows a more rapid recovery. These data indicate that channel interaction is individually variable and parameter dependent, both of which may play a role in the perception of dynamic stimuli in the natural auditory environment.

ISSN:0001-4966    

DOI:10.1121/1.422777

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

In experiment 1 NoSo and NoSπ thresholds for a 500-Hz pure tone were obtained in a low-fluctuation masking noise and a high-fluctuation masking noise for six normal-hearing listeners. The noise bandwidth was 10 Hz. In agreement with previous investigations, the NoSo thresholds were lower in low-fluctuation noise than in high-fluctuation noise. For three listeners, NoSπ thresholds were similar for the two types of noise, while for the other three listeners, NoSπ thresholds werehigherfor low-fluctuation noise than for high-fluctuation noise. In experiment 2, the masker was created by amplitude modulating a 500-Hz pure tone by a 0–10-Hz low-pass noise. The degree of masker fluctuation was controlled by adjusting the average modulation depth (100%, 63%, 40%, and 25%). The signal was a 10-Hz-wide noise centered on 500 Hz. Results were similar to those of experiment 1: for the NoSo conditions, signal detection improved with decreasing degree of fluctuation, and for NoSπ conditions, the results were subject dependent. For three listeners, NoSπ thresholds were again similar in the two types of noise, while for the other three listeners, NoSπ thresholds were again higher in low-fluctuation noise than in high-fluctuation noise. The results showed that a high degree of masker fluctuation sometimes facilitates NoSπ detection. It is possible that the binaural detection mechanism utilizes the relatively good signal-to-noise ratios that occur in the low power or “dip” regions of fluctuating masker waveforms.

ISSN:0001-4966    

DOI:10.1121/1.422778

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A masking level difference (MLD) paradigm was used to investigate the influence of stimulus envelope and stimulus fine-structure characteristics on monaural andbinaural hearing. The degree of masker envelope fluctuation was manipulated byselecting narrow-band noises (50 Hz) on a continuum of values of the normalized fourth moment of the envelope. The noises were specified as low-noise noise (LNN), medium-noisenoise (MNN), and high-noise noise (HNN). Fine-structure cues were studied by measuring thresholds at 500 and 4000 Hz, regions in which the availability of such cues to theauditory system differ substantially. In addition, thresholds were measured for Gaussian noise maskers(GN) and for maskers having a flat magnitude spectrum, termed equal-magnitude noise (EMN) maskers. The results indicated lower NoSo thresholds for LNN than for the other fourmasker types. Furthermore, there were no differences in threshold for maskers having moderate and high degrees of envelope fluctuation (MNN and HNN). The NoSπ thresholds werenot significantly different across masker type and were characterized by large individual differences among the seven listeners. The results are considered in relation to models ofmonaural and binaural processing. Consistent with previous reports, the results indicate that binauraldetection depends on interaural differences in the stimulus envelope and fine structure at low frequenciesand changes in the envelope at high frequencies.

ISSN:0001-4966    

DOI:10.1121/1.423112

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP