摘要:

The echolocation detection capabilities of a beluga (Delphinapterusleucas) and an Atlantic bottlenose dolphin (Tursiopstruncatus) were directly compared in a target detection experiment. Both animals were trained to detect targets in the presence of masking noise. Targets were stainless‐steel, water‐filled spheres 7.62 and 22.86 cm in diameter. Target ranges of 16.5 and 40 m were used with the 7.62‐cm sphere and 80 m with the 22.86‐cm sphere. Masking noise with a flat spectrum from 40–160 kHz was projected from a spherical transducer placed 4 or 5 m, depending on the target distance, from the animal hoop station in line with the target. Target detection performance was determined as a function of masking noise level at each target range. The echo‐to‐noise ratio (Ee/N0)maxfor the beluga at the 75% correct response threshold was approximatly 1.0 dB compared to about 10 dB for the dolphin. The differences of each animal’s detection performance across the threee ranges were consistent with target strength and transmission loss differences. It is speculated that the difference in performance between the two species may be due to differences in critical bandwidth, signal processing capability, or echolocation strategy.

ISSN:0001-4966    

DOI:10.1121/1.395192

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This article reports on investigations of the relative roles of simultaneous and nonsimultaneous masking on detection thresholds using natural speech utterances. Thresholds were obtained for 15−ms probe tones placed in the stop or flap closures of /ada/ and /idi/. Threshold elevations due to simultaneous and nonsimultaneous masking could be explained by the dynamics of neighboring speech spectra. Nonsimultaneous effects were related to spectra at least 30 ms around the probe tone. Although simultaneous masking is usually stronger than nonsimultaneous masking, the relative amplitude of adjacent speech segments in natural speech is sufficiently high near formant regions to cause noticeable effects of nonsimultaneous masking.

ISSN:0001-4966    

DOI:10.1121/1.395193

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The identification of front vowels was studied in normal‐hearing listeners using stimuli whose spectra had been altered to approximate the spectrum of vowels processed by auditory filters similar to those that might accompany sensorineural hearing loss. In the first experiment, front vowels were identified with greater than 95% accuracy when the first formant was specified in a normal manner and the higher frequency formants were represented by a broad, flat spectral plateau ranging from approximately 1600 to 3500 Hz. In the second experiment, the bandwidth of the first formant was systematically widened for stimuli with already flattened higher frequency formants. Normal vowel identification was preserved until the first formant was widened to six times its normal bandwidth. These results may account for the coexistence of abnormal vowel masking patterns (indicating flattened auditory spectra) and normal vowel recognition.

ISSN:0001-4966    

DOI:10.1121/1.395194

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This article reports on an experiment examining some perceptual consequences of correspondences between accent patterns, the distribution of plus and minus focus, and the distribution of new and given information in Dutch spoken sentences. ‘‘Accent patterns’’ refer here to the distribution of intonational accents over spoken sentences. Each accent marks a sentence constituent asplusfocus, i.e., as highlighted by the speaker. Constituents not so marked are calledminusfocus. The main questions examined here are to what extent are plus focus constituents generally perceived as conveyingnewinformation, and minus focus constituents as conveying earlier introduced orgiveninformation. The linguistic material for the experiment was formed by brief radio news items, each two sentences long. Leading sentences determined the distribution of new and given information in target sentences. The accent patterns and, hence, the possible focus distributions in the target utterances were varied systematically by manipulating their synthetic pitch contours according to the rules for Dutch intonation. Subjects were asked to rate on a scale from 1–10 the acceptability of each possible combination of a leading with a target utterance. Results showed that the most preferred or acceptable distributions of new and given information closely match the distributions of plus and minus focus. It was also found that new information can hardly ever acceptably be associated with minus focus, but given information can rather often, although not always, acceptably be associated with plus focus. This appears to be limited to certain conditions, defined by a combination of syntactic and focus structure of the sentence. In these conditions, plus focus cannot be perceived only as signaling new information, but also as highlighting thematic relations with the context. These results are related to work on text‐to‐speech systems.

ISSN:0001-4966    

DOI:10.1121/1.395195

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Acoustic information about the place of articulation of a prevocalic nasal consonant is distributed over two distinct signal portions, the nasal murmur and the onset of the following vowel. The spectral properties of these signal portions are perceptually important, as is their relationship (the pattern of spectral change). A series of experiments was conducted to investigate to what extent relational place of articulation information derives from a peripheral auditory interaction, viz., short‐term adaptation caused by the murmur. Experimental manipulations intended to disrupt the effects of such adaptation included separation of the murmur and the vowel by intervals of silence, presentation to different ears, and reversal of order. Other tests of the possible role of adaptation included manipulation of murmur duration, murmur–vowel cross splicing, and high‐pass filtering of the excised vowel onset. While the results of several experiments were compatible with the peripheral adaptation hypothesis, others did not support it. An alternative hypothesis, that the manner cues provided by the murmur are crucial for accurate place judgments, was also discredited. It was concluded that, at least under good listening conditions, the perception of spectral relationships does not depend on peripheral auditory enhancement and probably rests on a central comparison process.

ISSN:0001-4966    

DOI:10.1121/1.395196

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Humans and monkeys were compared in their differential sensitivity to various acoustic cues underlying voicing contrasts specified by voice‐onset time (VOT) in utterance‐initial stop consonants. A low‐uncertainty repeating standardAXprocedure and positive‐reinforcement operant conditioning techniques were used to measure difference limens (DLs) along a VOT continuum from −70 ms (prevoiced /ba/) to 0 ms (/ba/) to +70 ms (/pa/). For all contrasts tested, human sensitivity was more acute than that of monkeys. For voicing lag, which spans a phonemic contrast in English, human DLs for a /ba/(standard)‐to‐/pa/(target) continuum averaged 8.3 ms compared to 17 ms for monkeys. Human DLs for a /pa/‐to‐/ba/ continuum averaged 11 ms compared to 25 ms for monkeys. Larger species differences occurred for voicing lead, which is phonemically nondistinctive in English. Human DLs for a /ba/‐to‐prevoiced/ba/ continuum averaged 8.2 ms and were four times lower than monkeys (35 ms). Monkeys did not reliably discriminate prevoiced /ba/‐to‐/ba/, whereas humans DLs averaged 18 ms. The effects of eliminating cues in the English VOT contrasts were also examined. Removal of the aspiration noise in /pa/ greatly increased the DLs and reaction times for both humans and monkeys, but straightening out theF1 transition in /ba/ had only minor effects. Results suggest that quantitative differences in sensitivity should be considered when using monkeys to model the psychoacoustic level of human speech perception.

ISSN:0001-4966    

DOI:10.1121/1.395144

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The goal of this study was to determine the extent to which the difficulty experienced by impaired listeners in understanding noisy speech can be explained on the basis of elevated tone‐detection thresholds. Twenty‐one impaired ears of 15 subjects, spanning a variety of audiometric configurations with average hearing losses to 75 dB, were tested for reception of consonants in a speech‐spectrum noise. Speech level, noise level, and frequency‐gain characteristic were varied to generate a range of listening conditions. Results for impaired listeners were compared to those of normal‐hearing listeners tested under the same conditions with extra noise added to approximate the impaired listeners’ detection thresholds. Results for impaired and normal listeners were also compared on the basis of articulation indices. Consonant recognition by this sample of impaired listeners was generally comparable to that of normal‐hearing listeners with similar threshold shifts listening under the same conditions. When listening conditions were equated for articulation index, there was no clear dependence of consonant recognition on average hearing loss. Assuming that the primary consequence of the threshold simulation in normals is loss of audibility (as opposed to suprathreshold discrimination or resolution deficits), it is concluded that the primary source of difficulty in listening in noise for listeners with moderate or milder hearing impairments, aside from the noise itself, is the loss of audibility.

ISSN:0001-4966    

DOI:10.1121/1.395145

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This article presents two sets of experiments concerning the ability to discriminate changes in the phase spectra of wideband periodic sounds. In the first set, a series of local phase changes is used to modify the envelopes of the waves appearing at the outputs of a range of auditory filters. The size of the local phase change required for discrimination is shown to be strongly dependent on the repetition rate, intensity, and spectral location of the signal. In the second set of experiments, a global phase change is used to produce a progressive phase shift between the outputs of successive auditory filters, without changing the envelopes of the filtered waves. Contrary to what is often assumed, listeners can discriminate between‐channel phase shifts once the total time delay across the channels containing the signal reaches 4–5 ms. In this case, however, the discrimination is largely independent of signal parameters other than bandwidth. A highly simplified model of the cochlea, consisting of an auditory filter bank and units that record the times of the larger peaks in the filter outputs, is developed to explain the two contrasting sets of results.

ISSN:0001-4966    

DOI:10.1121/1.395146

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In most of the previous studies (see Green, 1987) concerning the detection of a change in spectral shape, or ‘‘profile analysis,’’ the listener’s task was to detect an increment to a single component of an otherwise equal‐amplitude, multicomponent background. An important theoretical issue is whether listeners’ sensitivity to more complex spectral changes can be predicted from these results. In the present investigation, the sensitivity of a single group of listeners to a wide variety of simple and complex spectral changes was determined. After collecting the data, it was noted that almost all the thresholds could be predicted by a simple calculation scheme that assumed detection of a change in spectral shape occurs when the addition of the signal to the flat, multicomponent background produces a sufficient difference in level betweenonlytworegions of the spectrum. Unfortunately, this scheme, while successful for our limited set of data, fails to account for other ‘‘profile’’ data, namely, those obtained when the number of components is altered.

ISSN:0001-4966    

DOI:10.1121/1.395147

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Previous research has indicated that frequency discrimination performance is poorer for tones presented near the sharp spectral edge of a low‐pass noise than for tones presented near the edge of a high‐pass noise, or for tones in the same low‐pass noise with high‐pass noise added [Emmerichetal., J. Acoust. Soc. Am.80, 1668–1672 (1986)]. The present study extends these findings in order to investigate how the steepness of the spectral edges of low‐ and high‐pass maskers influences the discriminability of tones presented near these edges. Frequency discrimination was measured in each of three high‐ and low‐pass noise backgrounds (which differed in the steepness of their filter skirts). The following results were obtained: (1) In the low‐pass noise background, frequency discrimination performance improved as the filter skirt became more gradual; (2) in the high‐pass noise background, performance first improved and then became poorer as the filter skirt became shallower; and (3) performance in low‐pass noise was poorer than that in high‐pass noise for the two steepest slopes employed (96 and 72 dB/oct) but not for the shallower slope (36 dB/oct). Results are discussed in the context of lateral suppression and edge pitch effects, and of a trade‐off between possible edge effects and masking.

ISSN:0001-4966    

DOI:10.1121/1.395148

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP