摘要:

An evoked otoacoustic emission (OAE) measurement technique is proposed to better control for probe distortion. Each double-evoking (2E) stimulus sequence includes three, equal-duration subsequences defined as follows:s1(t)is a single chirp or click,s2(t)=εs1(t−τ)is a copy ofs1with relative amplitude ε and delay τ, ands12(t)=s1(t)+s2(t)is the superposition of the first two stimuli. The pressure response to each subsequence isp1,p2,andp12,respectively. The double chirp-evoked distortion product (2ChDP) and double click-evoked otoacoustic emission (2CEOAE) are defined bypD=p12−(p1+p2).The 2ChDP response may be time compressed to analyze as an equivalent 2CEOAE response. The 2E response family provides a complementary representation between DP measurements and double click-evoked OAE measurements. A technique based on nonlinear coherence quantifies random noise in terms of a nonlinear signal-to-noise ratio.

ISSN:0001-4966    

DOI:10.1121/1.423057

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Measurements of double-click-evoked otoacoustics emissions (2CEOAEs) and double-chirp distortion products (2ChDPs) are reported for normal-hearing adults based upon theory presented in an earlier report [Keefe, J. Acoust. Soc. Am.103, 3489–3498 (1998)]. The nonlinear acoustic response of a probe assembly used in ear-canal measurements is tested in a calibration cavity to compare the double-evoked (2E) technique with existing OAE techniques. The 2E technique reduces the peak distortion by approximately 30 dB relative to existing click-evoked techniques. The 2E subtraction of click responses is partially analogous to current techniques in that the linear response is eliminated, but differs in that high-frequency measurements are improved by eliminating time gating of the cochlear response, and low-frequency measurements are improved by reducing probe distortion, especially when two acoustic sources are used. Because time gating is eliminated, it is straightforward to measure the onset of a click-evoked OAE. The nonlinear coherence function is used to measure the nonlinear distortion signal-to-noise ratio (DNR) for the 2ChDPs and 2CEOAEs. The DNR is typically 20–30 dB. An intermittent noise rejection technique is implemented in real time that compares a currently acquired ear-canal response with a stored response. Dissimilar responses indicate the presence of intermittent noise, and the noise-contaminated responses are thereby discarded before ensemble averaging.

ISSN:0001-4966    

DOI:10.1121/1.423058

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The two most salient dichotic pitches, the Huggins pitch (HP) and the binaural edge pitch (BEP), are produced by applying interaural phase transitions of 360 and 180 degrees, respectively, to a broadband noise. This paper examines accounts of these pitches, concentrating on a “central activity pattern” (CAP) model and a “modified equalization-cancellation” (mE-C) model. The CAP model proposes that a dichotic pitch is heard at frequencyfwhen an individual across-frequency scan in an interaural cross-correlation matrix contains a sharp peak atf.The mE-C model proposes that a dichotic pitch is heard when a plot of interaural decorrelation against frequency contains a peak atf.The predictions of the models diverge for the BEP at very narrow transition bandwidths: the mE-C model predicts that salience is sustained, while the CAP model predicts that salience declines and that the dominant percept is of the in-phase segment of the noise. Experiment 1 showed that the salience of the BEP was sustained at the narrowest bandwidths that could be generated (0.5% of the transition frequency). Experiment 2 confirmed that the pitch of a BEP produced by a 0.5% transition bandwidth was close to the frequency of the transition band. Experiment 3 showed that pairs of simultaneous narrow 180-degree transitions, whose frequencies corresponded to vowel formants, were perceived as the intended vowels. Moreover, the same vowels were perceived whether the in-phase portion of the noise lay between the two transition frequencies or on either side of them. In contrast, different patterns of identification responses were made todioticband-pass and band-stop noises whose cutoff frequencies corresponded to the same formants. Thus, the vowel-identification responses made to the dichotic stimuli were not based on hearing the in-phase portions of the noise as formants. These results are not predicted by the CAP model but are consistent with the mE-C model. It is argued that the mE-C model provides a more coherent and parsimonious account of many aspects of the HP and the BEP than do alternative models.

ISSN:0001-4966    

DOI:10.1121/1.423059

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The predictions of three models are compared with respect to existing experimental data on the perception of the Fourcin pitch (FP) and the dichotic repetition pitch (DRP). Each model generates a central spectrum (CS), which is examined for peaks at frequencies consistent with the perceived pitches. A modified equalization-cancellation (mE-C) model of binaural unmasking [Culling and Summerfield, J. Acoust. Soc. Am.98, 785–797 (1995)] generates a CS which reflects the degree of interaural decorrelation present in each frequency channel. This model accounts for the perceived frequencies of FPs, but produces no output for DRP stimuli. A restricted equalization-cancellation (rE-C) model [Bilsen and Goldstein, J. Acoust. Soc. Am.55, 292–296 (1974)] sums the time-varying excitation in corresponding frequency channels, without equalization, to form a CS. A central activity pattern (CAP) model [Raatgever and Bilsen, J. Acoust. Soc. Am.80, 429–441 (1986)] generates a CS by scanning an interaural cross-correlation matrix across frequency. The rE-C and CAP models yield inaccurate predictions of the perceived frequencies of FPs, but predict the occurrence of the DRP and its correct pitch. The complementary predictions of the mE-C model compared to the rE-C and CAP models, together with the evidence that the FP is clearly audible for the majority of listeners, while the DRP is faintly heard by a minority of listeners, suggest that the mE-C model provides the best available account of the FP, and that the DRP is produced by a separate mechanism.

ISSN:0001-4966    

DOI:10.1121/1.423060

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Two experiments investigated the shape of the binaural temporal window using a detection task. In experiment 1, a 10-ms tone burst was presented binaurally out-of-phase during a burst of white noise, which changed from being interaurally uncorrelated, to correlated, and back to uncorrelated. The tone occurred during the correlated portion of the noise in one interval of each 2I-FC trial. Detection thresholds were recorded using a 2-down/1-up adaptive procedure. Thresholds were measured for different durations of correlated noise (0–960 ms), frequencies of tone burst (125, 250, 500, and 1000 Hz) and levels of noise [20, 30, 40, and 50 dB(SPL)/Hz]. Window shapes based on nine candidate functions were fitted to the data using the assumption that the binaural masking release was related to the overall interaural correlation of noise admitted by the window. Fitted windows included both a forward and a backward lobe. Gaussian functions tended to give closer fits than exponential and rounded-exponential functions, and simple functions gave more parsimonious fits that those which included dynamic-range-limiting terms. Using simple Gaussian fits, the shape of the window was largely independent of frequency and level, and the windows for individual listeners had equivalent rectangular durations ranging from 55 to 188 ms. The asymmetry was variable, although forward lobes were generally shorter than backward lobes. Experiment 2 ruled out the possibility that the forward lobe might be an artefact caused by distraction of the listener, when the interaural phase change in the noise closely followed the signal. In this experiment, the out-of-phase tone was presented during a burst of partially correlated noise which changed, after a variable interval, to a fully correlated noise. Thresholds for detecting the tone rose (i.e., performance worsened) as the interval was increased. Distraction would have produced the opposite effect.

ISSN:0001-4966    

DOI:10.1121/1.423061

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Monaurally measured temporal gap detection (TGD) thresholds characteristically increase as the frequency difference is increased over a range of about half an octave to an octave between two sinusoids that mark the onset and offset of the silent gap. For greater sinusoidal frequency separations, the TGD thresholds often become asymptotic. This pattern probably reflects two different processes. The first process likely reflectswithin-channelprocessing within a single auditory filter or channel. The second process is less certain, but may reflectbetween-channelprocessing of the silent gap stimulus across two or more independent frequency channels. To evaluate the hypothesis that asymptotic monaural gap detection can be explained by a simplebetween-channelprocess, TGD thresholds were measured as a function of frequency separation between a pregap sinusoid presented to the left ear (channel 1) and a postgap sinusoid, of higher frequency, presented to the right ear (channel 2). The rationale for dichotic presentation of the sinusoidal markers and gap signal followed from the fact that the gap detection task must be performed between two independent channels by combining the outputs from each channel (ear) and recovering the gap information centrally. The resulting TGD thresholds for pregap sinusoids from 250 to 4000 Hz were relatively invariant and increased only slightly with increasing marker frequency separation. The average TGD thresholds for four listeners were in the range of 30 to 40 ms, which corresponded closely with their asymptotic TGD thresholds for the same set of stimulus conditions measured monaurally. This correspondence of the two data sets supports an across-frequency,between-channelprocess for asymptotic monaural gap detection at marker frequency separations greater than about half an octave.

ISSN:0001-4966    

DOI:10.1121/1.423084

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Comodulation masking release (CMR) is the detection advantage conferred by coherence of amplitude modulation across masker frequency. This phenomenon has typically been described in terms of across-frequency comparisons or in terms of cueing, where analysis of the output of an auditory filter in the region of the signal is aided by the outputs of independent auditory filters. An alternative approach is to assume a broad initial predetection filter, one which encompasses frequencies generally thought to fall into disparate auditory filters. These two basic approaches are compared. Stimuli consisted of comodulated maskers, spaced in frequency at one of three fixed intervals, with fine structure that either produced strong envelope beats in the summed waveform or did not. The signal was a pure tone of random starting phase. For the smallest masker frequency spacing detection of a high-frequency signal seemed to be improved in the presence of envelope beats, while detection of a low-frequency signal seemed to be degraded by envelope beats. These results are discussed in terms of the number of maskers assumed to sum in an auditory filter and the relative availability of within- and between-channel cues. This explanation is consistent with an initial stage of auditory filtering and is fundamentally inconsistent with a broad initial filter. Results for larger masker frequency spacings showed this trend less reliably, a finding that was further explored via data from a modulation discrimination task.

ISSN:0001-4966    

DOI:10.1121/1.423062

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Behavioral detection thresholds, auditory filter widths, and temporal modulation transfer functions were obtained from four starlings before, during, and after 11 days of subcutaneous injections of kanamycin, an aminoglycoside antibiotic. Birds were operantly conditioned to respond to pure tones and amplitude modulated noises ranging in frequency from 0.25 to 7 kHz using adaptive staircase procedures and were tested daily for 92 days after the first injection of aminoglycoside. All birds had threshold shifts of at least−60 dBat frequencies above 4 kHz. Lower frequencies were affected in some birds, although none of the birds had hearing loss below 3 kHz. All four birds had wider auditory filters at 5 kHz immediately after the aminoglycoside series. Any changes in frequency resolution at frequencies below 5 kHz were slight, transitory, and rarely observed. Two of the four birds had permanently wider auditory filters at 5 kHz. Temporal modulation transfer functions were briefly affected in two birds during the time of greatest threshold shift. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 60 days. Recovery in frequency resolution lagged behind auditory threshold by about 10 days. Normal temporal resolution was observed in the context of impaired intensity and frequency resolution. Changes in auditory threshold and frequency resolution were closely associated for all birds at 5 kHz, but were correlated with statistical significance in only two birds. Scanning electron microscopy was performed on all four birds after 90 days of recovery and confirmed that the extent of initial damage was consistent with the pattern of observed hearing loss.

ISSN:0001-4966    

DOI:10.1121/1.423085

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Like humans, animals that use acoustic stimuli to perceive their world ought to be able to parse the auditory scene into functionally significant sounds. The ability to do so ought to have significant adaptive value when, for example, an animal can identify the sounds of a predator among other natural noises. In earlier work it was shown that a species of songbird, the European starling, can identify excerpts of both its own song and songs from other avian species when the songs are mixed concurrently with other natural signals. In this experiment it is demonstrated that starlings can segregate two synthetic pure-tone sequences when the sequences differ in frequency. Taken together, the experiments show that at least one nonhuman species is capable of auditory scene analysis both for natural and for non-natural acoustic stimuli. This suggests in turn that auditory scene analysis may be a general perceptual process that occurs in many species that make use of acoustic information.

ISSN:0001-4966    

DOI:10.1121/1.423063

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A single even harmonic added to an odd-harmonic complex is often judged to be more salient than its odd neighbors in a clarity rating task [Roberts and Bregman, J. Acoust. Soc. Am.90, 3050–3060 (1991)]. This study used similar complexes in a two-interval forced-choice procedure. Each interval consisted of a complex tone followed by a pure tone, whose frequency matched that of a harmonic in one interval but was changed by ±0.5×fundamental frequency in the other. Subjects were asked to identify the matching interval. Since the pure tone followed the complex tone, it could not cue listening to a particular frequency region. The possibility of cross-interval cuing was reduced by changing the fundamental frequency between intervals (100–150 Hz range). The procedure was designed to maximize the effects on performance of differences in immediate perceptual salience between the partials. The added even harmonic was typically judged with greater accuracy than its odd neighbors (experiment 1), though this effect was greatly reduced for harmonics above 8 (experiment 2). The even–odd difference persisted when the original stimuli were made inharmonic by applying a frequency shift of 15%, but was abolished for stimuli consisting of successive partials (experiment 3).

ISSN:0001-4966    

DOI:10.1121/1.423086

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP