摘要:

This paper examines how the difference limen for level, ΔL, is affected by stimulus bandwidth and variability. The ΔL’s were measured in three normal listeners using an adaptive two‐interval, forced‐choice procedure. The 30‐ms stimuli were a 3‐kHz tone and nine noise bands with half‐power bandwidths ranging from 50 Hz–12 kHz. Except for the 12‐kHz bandwidth, which was a low‐pass noise, the noise bands were centered at 3 kHz. The ΔL’s were measured for both frozen and random noises presented at 30, 60, or 90 dB SPL overall. For frozen noises, the same sample of noise was presented throughout a block of 50 trials; for the random noises, different samples of noise were used in each interval of the trials. Results show that the ΔL’s are higher for random than for frozen noises at narrow bandwidths, but not at wide bandwidths. The ΔL’s for frozen narrow‐band noises decrease with increasing level and are similar to those for the pure tone, whereas the ΔL’s for wideband noises are only slightly smaller at 90 than at 30 dB SPL. An unexpected finding is that the ΔL’s are larger at 60 than at 30 dB SPL for both frozen and random noises with bandwidths greater than one critical band. The effect of bandwidth varies with level: The ΔL’s decrease with increasing bandwidth at low levels, but are nearly independent of bandwidth at 90 dB SPL. The interaction of bandwidth and level is consistent with the multiband excitation‐pattern model [M. Florentine and S. Buus, J. Acoust. Soc. Am.70, 1646–1654 (1981)], but the nonmonotonic behavior of ΔLas a function of level suggests modifications to the model.

ISSN:0001-4966    

DOI:10.1121/1.399057

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Detection thresholds were measured for sinusoidal vibrations applied to the thenar eminence and volar forearm. Stimuli were applied via a 0.72‐cm2circular contactor, with and without a rigid surround. At low frequencies, below about 40 Hz, the thresholds were higher without the surround than with the surround. However, in contrast to earlier reports, the shape of the threshold function was the same with and without the surround, suggesting that the temporal and spatial tuning characteristics of the non‐Pacinian I (NP I) channel are independent.

ISSN:0001-4966    

DOI:10.1121/1.399550

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In adaptive psychophysical procedures, the stimulus should be presented at a relatively high level rather than near the middle of the psychometric function, which is often defined as the ‘‘threshold’’ value. For some psychometric functions, the optimal stimulus placement level produces 84% to 94% correct responses in a two‐alternative forced‐choice task. This result is disquieting because the popular two‐down one‐up rule tracks a relatively low percentage of correct responses, 70.7%. Computer simulations and a variety of psychometric functions were used to confirm the validity of this analysis. These simulations also demonstrate that the precise form of the psychometric function is not critical in achieving the high efficiencies. Finally, data from human listeners indicate that the standard deviation of threshold estimates is indeed larger when the stimulus presented on each trial is at a stimulus level corresponding to 70.7% rather than 94% correct responses.

ISSN:0001-4966    

DOI:10.1121/1.399058

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This investigation determined whether prelingually deaf talkers could correctly produce stressed and unstressed syllables across known changes in stress patterning and phonetic composition. Three deaf and three hearing adults spoke sets of homogeneous syllable strings with stress patterns that they could tap successfully with a finger. Strain gauge transduction of lower lip and jaw movement indicated that both deaf and hearing subjects produced different displacements and durations for the stressed and unstressed syllables, regardless of the stress pattern. Jaw movement did not become more variable with changes in phonetic composition of the syllables. The results show no evidence that motoric abilities (as assessed in lip and jaw movements) limit deaf talkers in producing desired stress patterns.

ISSN:0001-4966    

DOI:10.1121/1.399059

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Research indicates that, when the first and second formants of a vowel are separated by less than about 3.5 Bark, perception of its height and some other aspects of its quality is determined by some weighted average of the low‐frequency spectrum, rather than by particular harmonic or hypothetical formant frequencies (as is the case with more widely spaced formants). This spectral averaging has been called the center of gravity (COG) effect. Although the existence of the effect is generally accepted, the factors that govern it are poorly understood. One possibility is that the influence of the spectral envelope on perceived vowel quality increases as low‐frequency spectral prominences become less well defined. A series of three experiments examined this possibility in: (1) nasal vowels, where the lowest spectral prominence is broader and flatter than that of oral vowels; (2) one‐ versus two‐formant vowels with bandwidths appropriate for oral vowels; and (3) two‐formant vowels with very narrow or very wide bandwidths. The results of these experiments show that, when two or more spectral peaks lie within 3.5 Bark of one another,F1 and the centroid (an amplitude‐weighted average frequency that estimates the COG in the low‐frequency spectrum) roughly determine the boundaries within which the perceptual COG lies; the frequencies of spectral peaks dominate responses when formant bandwidths are narrow, whereas overall spectral shape exerts more influence when spectral prominences are wide. Assuming that all vowels undergo the same processing, it is suggested that vowel quality, particularly height, is determined both by the frequency of the most prominent harmonics in the low‐frequency region and by the slopes of the skirts in the vicinity of these harmonics. These two effects are most clearly separable in vowels with poorly defined spectral prominences whose shape cannot be adequately described by specifying the frequencies and degree of prominence of just one or two harmonics, or hypothetical formant peaks.

ISSN:0001-4966    

DOI:10.1121/1.399060

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Perception is influenced both by characteristics of the stimulus, and by the context in which it is presented. The relative contributions of each of these factors depend, to some extent, on perceiver characteristics. The contributions of word and sentence context to the perception of phonemes within words and words within sentences, respectively, have been well studied for normal, young adults. However, far less is known about these context effects for much younger and older listeners. In the present study, measures of these context effects were obtained from young children (ages 4 years 6 months to 6 years 6 months) and from older adults (over 62 years), and compared with those of the young adults in an earlier study [A. Boothroyd and S. Nittrouer, J. Acoust. Soc. Am.84, 101–114 (1988)]. Both children and older adults demonstrated poorer overall recognition scores than did young adults. However, responses of children and older adults demonstrated similar context effects, with two exceptions: Children used the semantic constraints of sentences to a lesser extent than did young or older adults, and older adults used lexical constraints to a greater extent than either of the other two groups.

ISSN:0001-4966    

DOI:10.1121/1.399061

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

There is limited documentation available on how sensorineurally hearing‐impaired listeners use the various sources of phonemic information that are known to be distributed across time in the speech waveform. In this investigation, a group of normally hearing listeners and a group of sensorineurally hearing‐impaired listeners (with and without the benefit of amplification) identified various consonant and vowel productions that had been systematically varied in duration. The consonants (presented in a /haCa/ environment) and the vowels (presented in a /bVd/ environment) were truncated in steps to eliminate various segments from the end of the stimulus. The results indicated that normally hearing listeners could extract more phonemic information, especially cues to consonant place, from the earlier occurring portions of the stimulus waveforms than could the hearing‐impaired listeners. The use of amplification partially decreased the performance differences between the normally hearing listeners and the unaided hearing‐impaired listeners. The results are relevant to current models of normal speech perception that emphasize the need for the listener to make phonemic identifications as quickly as possible.

ISSN:0001-4966    

DOI:10.1121/1.399062

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Using only three measures of the waveform, the zero‐crossing rate, the logarithm of the root‐mean‐square (rms) energy, and the derivative of the log rms energy with respect to time [termed rate of rise (ROR)], voiceless plosives (including affricates) can be distinguished from voiceless fricatives in word‐initial, medial, and final positions. Peaks in the ROR contour are considered for significance to the plosive/fricative distinction by examining the log rms energy and zero‐crossing rate. Then, the magnitude of the first significant peak in the ROR contour is used as the primary classifier. The algorithm was tested on 1364 tokens (720 word‐initial tokens produced by four female and four male speakers; 360 word‐medial tokens produced by two males and two females; 320 word‐final tokens produced by two males and two females). Data from two male and two female speakers (360 word‐initial tokens) were used as a training set, and the remaining data were used as a test set. The overall rate of correct classification was 96.8%. Implications of this result are discussed.

ISSN:0001-4966    

DOI:10.1121/1.399063

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The motivation of this study is the poor performance of speech recognizers on the stop consonants. To overcome this weakness, word initial and word final stop consonants are modeled at a subphonemic (microsegmental) level. Each stop consonant is segmented into a few relatively stationary microsegments: silence, voice bar, burst, and aspiration. Microsegments of certain phonemically different stops are trained together due to their similar spectral properties. Microsegmental models of burst and aspiration are conditioned on the adjacent vowel category: front versus nonfront vowels. The resulting context‐dependent microsegmental hidden Markov models (HMMs) for six stops possess the desired properties for a compromise between modeling accuracy and modeling robustness. They allow the recognizer to focus discrimination onto those regions of a stop that serve to distinguish it from other stops. Use of these models in recognition experiments for word lists consisting of CVC words reduces the error rate by 35% compared with the result obtained by using one HMM for each stop phoneme.

ISSN:0001-4966    

DOI:10.1121/1.399064

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

When a focused Gaussian ultrasonic beam in soft tissue normally impinges on the boundary of a contiguous bone, reflection and transmission occur. Taking account of the reflection, the steady‐state temperature elevation along the beam axis for this case was calculated. The effect of perfusion is also included.

ISSN:0001-4966    

DOI:10.1121/1.399065

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP