摘要:

Studies were undertaken to investigate the ability of a user of the Nucleus multi-electrode cochlear implant to judge pitch in the context of musical intervals. The subject had qualified as a musical instrument tuner before he received his implant, and was able to judge the intervals between electrical sensations with neither training nor the guidance of familiar melodies. The procedures used were interval estimation, and interval production by the method of adjustment. The pitch of the electrical stimulation was controlled by varying the pulse repetition rate, the active electrode position, or two combinations of these parameters. Further studies employed sinusoidally amplitude modulated pulse trains with varying modulation frequency. The results showed that rate or modulation frequency could convey musical pitch information over a limited range (approximately two octaves). The data were directly comparable with the relationship between musical intervals and frequency for normal hearing. The pitch related to electrode place varied in accordance with the tonotopic organization of the cochlea, and also appeared to be able to support musical intervals. When both place and rate varied together, the place-related pitch was generally dominant. In all cases, the judgement of intervals tended to diverge from their acoustic counterparts as the intervals became larger.

ISSN:0001-4966    

DOI:10.1121/1.418177

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Furukawa and Moore [S. Furukawa and B. C. J. Moore, J. Acoust. Soc. Am.100, 2299–2312 (1996)] found that the detection of frequency modulation (FM) imposed on two inharmonically related carriers was better when the FM was coherent across carriers than when it was incoherent. Here, “coherence” refers to whether the pattern of frequency change over time was identical or different across carriers. The present paper was designed to explore three possible mechanisms underlying this effect. Thresholds were measured for the detection of a single cycle of sinusoidal FM imposed on two sinusoidal carriers. The FM of each carrier was equally detectable, as determined in preliminary experiments. A continuous pink-noise background was used to mask the outputs of auditory filters tuned between the two carrier frequencies. The modulation rate was either 2.5, 5, or 10 Hz. Three combinations of carrier frequencies were used, varying in the extent to which the carriers were harmonically related (1050 and 2069 Hz; 1100 and 2000 Hz; and 1100 and 1925 Hz). The carrier frequencies were either fixed at these values, or were randomly varied (roved) from one trial to another (±10%) keeping the frequency ratio constant. Performance for coherent FM was generally better than for incoherent FM. The effect of FM coherence was greater at the lowest modulation rate and was slightly greater when the carrier frequencies were fixed throughout a block of trials than when they were roved. For the two lowest modulation rates, the effect of FM coherence was greater for carriers that were (nearly) harmonically related. It is proposed that sensitivity to FM coherence depends partly on comparing patterns of phase locking to the carriers; this is done most effectively at low modulation rates. However, two other factors may play a small role. These are: sensitivity to the coherence of amplitude modulation induced in the auditory system by the FM (which is somewhat disrupted by roving the carrier frequencies); and sensitivity to fluctuations in the residue pitch evoked by the two carriers (the residue pitch being less salient for inharmonically related carriers).

ISSN:0001-4966    

DOI:10.1121/1.418147

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Two versions of a cascade of delay, gain following delay, and add circuits were used to generate iterated rippled noise (IRN) stimuli. IRN stimuli produce a repetition pitch whose pitch strength relative to the noise percept can be varied by changing the type of circuit, the attenuation, or the number of iterations in the circuit. The repetition pitch of IRN is different when the delayed noise is subtracted (gain0) to the undelayed noise. In the case of subtraction, IRN pitch is often ambiguous having two or more pitches. Listeners were asked to use pitch strength to discriminate between various pairs of IRN stimuli generated with different gains, different network circuits, and different number of iterations. For most conditions the gain was less than one. The data were described by a description based on an exponential function of the largest peak of the autocorrelation function of IRN stimuli [W. A. Yost, J. Acoust. Soc. Am.100, 511–518 (1996)] processed such that the spectral dominance region is emphasized. These results suggest that the strength of the pitch of IRN stimuli can be described by temporal processing mechanisms as might be revealed by autocorrelation.

ISSN:0001-4966    

DOI:10.1121/1.418148

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Saberi and Perrott [Acustica81, 272–275 (1995)] found that the in-head lateralization of a relatively long-duration pulse train could be controlled by the interaural delay of the single pulse pair that occurs at onset. The present study examined this further, using an acoustic pointer measure of lateralization, with stimulus manipulations designed to determine conditions under which lateralization was consistent with the interaural onset delay. The present stimuli were wideband pulse trains, noise-burst trains, and inharmonic complexes, 250 ms in duration, chosen for the ease with which interaural delays and correlations of select temporal segments of the stimulus could be manipulated. The stimulus factors studied were the periodicity of the ongoing part of the signal as well as the multiplicity and ambiguity of interaural delays. The results, in general, showed that the interaural onset delay controlled lateralization when the steady state binaural cues were relatively weak, either because the spectral components were only sparsely distributed across frequency or because the interaural time delays were ambiguous. Onset dominance can be disrupted by sudden stimulus changes within the train, and several examples of such changes are described. Individual subjects showed strong left–right asymmetries in onset effectiveness. The results have implications for understanding how onset and ongoing interaural delay cues contribute to the location estimates formed by the binaural auditory system.

ISSN:0001-4966    

DOI:10.1121/1.418149

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Speech reception thresholds (SRTs) were obtained for different azimuths of up to three interfering sound sources in a simulated (“virtual”) spatial arrangement. For the SRT measurements a fast subjective threshold assessment method was used. The reduction in SRT relative to the reference threshold caused by spatial separation of target and interference signal is called the intelligibility level difference (ILD). For normal listeners, the maximum ILD was achieved at 105° or 255° azimuth of a single noise source when the target emanated from the front (0° azimuth). The ILD decreased rapidly if the number of interfering signals was increased and if they were located on opposite sides of the head. When using continuous speech as interference, this decrease of ILD was less pronounced. These findings indicate that the binaural system can suppress interference from only one azimuthal region at a time and can utilize temporal pauses in the interference to suppress a second interference from a different direction. For eight sensorineural impaired listeners, the maximum attainable ILD for one interfering noise source was reduced in a way not predictable from the audiogram. The ability to exploit pauses in the signal of an interfering talker was also reduced. Hence, hearing-impaired listeners are handicapped in realistic spatial interference situations both by an increased monaural SRT and a reduced binaural noise reduction ability.

ISSN:0001-4966    

DOI:10.1121/1.418150

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A new experimental technique for studying binaural processing at high frequencies is introduced. Binaural masking level differences (BMLDs) for the conditionsN0SπandNπS0were measured for a tonal signal in narrow-band noise at 125, 250, and 4000 Hz. In addition, “transposed” stimuli were generated, which were centered at 4000 Hz, but were designed to preserve within the envelope the temporal “fine-structure” information available at the two lower frequencies. The BMLDs measured with the 125-Hz transposed stimuli were essentially the same as BMLDs from the regular 125-Hz condition. The transposed 250-Hz stimuli generally produced smaller BMLDs than the stimuli centered at 250 Hz, but the pattern of results as a function of masker bandwidth was the same. The patterns of results from the transposed stimuli are different from those of the 4000-Hz condition and, consistent with the low-frequency masker data, generally show higher BMLDs. The results indicate that the mechanisms underlying binaural processing at low and high frequencies are similar, and that frequency-dependent differences in BMLDs probably reflect the inability of the auditory system to encode the temporal fine structure of high-frequency stimuli.

ISSN:0001-4966    

DOI:10.1121/1.418151

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Current medical-legal practices as well as an international standard (ISO 1999) assume the permanent threshold shifts produced by exposure to noise add (in dB) to the threshold shifts caused by increased chronological age (presbyacusis). This assumption, known as the additivity rule, was tested in an animal model. Mongolian gerbils, born and raised in a quiet vivarium, were exposed at age 18 months to a 3.5-kHz pure tone for 1 h at 113 dB SPL. At 6-weeks post-exposure, permanent threshold shifts in the exposed ear were approximately 20 dB in the 4- to 8-kHz region. Thresholds in the nonexposed, control ear were unaffected by the exposure. Animals were then allowed to age in the quiet vivarium until age 36 months and then were retested. Thus in a given animal, aging-only effects were assessed in one ear (internal control) and noise-plus-aging effects were assessed in the other (test) ear. A second control was mean age-related threshold shift measured in 48 gerbils who were born and raised in the quiet vivarium. This group is referred to as a non-noise-exposed population (population control). Using the additivity rule, predictions with either the internal or population control significantly overestimated noise-plus-aging effects. Use of the ISO 1999 compression factor reduced the overestimations by 0–5 dB. The intensity rule produced the most accurate predictions. These results suggest that the interaction of noise-induced permanent threshold shift and age-related threshold shift is not straightforward and that current medical-legal methods using the additivity rule overestimate the contribution of “noise effects.”

ISSN:0001-4966    

DOI:10.1121/1.418152

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Numerical estimates of loudness and pitch for electric pulse rates were obtained from 14 patients using the 22 electrode cochlear implant manufactured by Cochlear Limited. Six patients were postlinguistically deafened adults, and eight patients were adults and children who became deaf very early in life. Comparisons were made between two types of pulse rate patterns. The SPP pulse pattern presented a single pulse every period, the inverse of the pulse rate. The MPP pulse pattern presented multiple pulses in the first half of the period, using a rate of 1000 pulses/s, with no stimulation in the second half of the period. The pulse rates used for the SPP and MPP pulse patterns were 71.4–500 pulses/s, which corresponded to periods of 14–2 ms. For the SPP pulse pattern, the total number of pulses over the duration of the stimulus increased with increases in pulse rate, while for the MPP pulse pattern, the total number of pulses remained constant. Pitch and loudness estimates were obtained from the postlinguistically deafened patients for the SPP and MPP pulse patterns, and from the early-deafened patients for the MPP pulse pattern. Loudness estimates for the SPP pulse pattern increased with increases in pulse rate for all postlinguistically deafened patients. Loudness estimates for the MPP pulse pattern decreased with increases in pulse rate for three of the six postlinguistically deafened patients and for six of the eight early-deafened patients. For the other patients (three postlinguistically deafened and two early-deafened), loudness estimates marginally increased with increases in pulse rate. Pitch estimates for the SPP and MPP pulse patterns increased with increases in pulse rate for the six postlinguistically deafened patients. For the early-deafened patients, pitch estimates for the MPP pulse patterns increased with increases in pulse rate for only five of the eight patients. For the other three early-deafened patients, pitch estimates were similar to the loudness estimates and decreased with increases in pulse rate.

ISSN:0001-4966    

DOI:10.1121/1.418178

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In English and a large number of African and Southeast Asian languages, voice quality along a tense–lax dimension covaries with advancement of the tongue root in vowels: a laxer voice quality co-occurs with a more advanced tongue root. As laxing the voice increases energy in the first harmonic relative to higher ones and advancing the tongue root lowersF1, the acoustic consequences of these two articulations may integrate perceptually into a higher-level perceptual property, here called spectral “flatness.” Two Garner-paradigm experiments evaluated this interaction across nearly the entire range of tense–lax voice qualities and a narrow range ofF1values. The acoustic consequences of laxness and advanced tongue root integrated into spectral flatness for tenser and laxer but not for intermediate voice qualities. Detection-theoretic models developed in earlier work proved highly successful in representing the perceptual interaction between these dimensions.

ISSN:0001-4966    

DOI:10.1121/1.418179

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Measured vertical profiles of temperature and wind are used to model infrasound propagation over a representative high savanna habitat typically occupied by the African elephant,Loxodonta africana, to predict calling distance and area as a function of the meteorological variables. The profiles were measured up to 300 m above the surface by tethered balloon-borne instruments in Etosha National Park, Namibia, during the late dry season. Continuous local surface layer measurements of wind and temperature at 5 and 10 m provide the context for interpreting the boundary layer profiles. The fast field program (FFP) was used to predict the directionally dependent attenuation of a 15-Hz signal under these measured atmospheric conditions. The attenuation curves are used to estimate elephant infrasonic calling range and calling area. Directionality and calling range are shown to be controlled by the diurnal cycle in wind (shear) and temperature. Low-level nocturnal radiative temperature inversions and low surface wind speeds make the early evening the optimum time for the transmission of low-frequency sound at Etosha, with range at a maximum and directionality at a minimum. As the night progresses, a nocturnal low-level wind maximum (jet) forms, reducing upwind range and calling area. The estimated calling area drops rapidly after sunrise with the destruction of the inversion. Daytime calling areas are usually less than 50 km2, while early evening calling areas frequently exceed 200 km2and are much less directional. This marked diurnal cycle will be present in any dry savanna climate, with variations due to local topography and climate. Calling range and low-frequency sound propagation cannot be effectively understood without knowledge of meteorological controls.

ISSN:0001-4966    

DOI:10.1121/1.418180

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP