摘要:

The ability of normal‐hearing children (aged 4 through 7 years) and adults to integrate information was measured in an auditory sample discrimination task. On each trial a pair of tonal sequences was played whose component frequencies were randomly drawn from two equal‐variance, Gaussian distributions with different means. The listeners task was to identify the sequence drawn from the distribution with the higher mean frequency. Performance was first evaluated as a function of the number of components in each sequence. Results showed that discrimination accuracy improved with increasing age until age 7, at which time performance was adult‐like. The 7‐year‐olds and the adults discriminated the sequences with increasing accuracy as the sequence length was increased, but the 4‐ to 6‐year‐old listeners, as a group, did not. Data were fitted with a model with two free parameters, one representing resolution of the components and presumed to reflect peripheral processing, and another representing central noise added to the decision process after the component information is combined [R. Lutfi, J. Acoust. Soc. Am.86, 934–944 (1989)]. On average, both parameters showed gradual changes as age increased, with adult‐like values by 7 years of age. Individual data however suggest that the changes in central noise with age may be less gradual than the changes in peripheral resolution. In a second condition, increases in component duration produced improved performance for the 7‐year‐olds and the adults, while that of the younger listeners remained the same. Fitted parameters suggested improvements in component resolution for the older children, with no changes in central noise levels. In a third condition, reducing the overlap in the distributions improved performance for only a few of several younger children. This improvement was attributable to lower levels of central noise. Overall, these results suggest that with increasing age children are better able to discriminate between sounds that are variable and have overlapping acoustic characteristics. This age‐related improvement may be attributed both to improvements in the ability to resolve the components and to reductions in central noise.

ISSN:0001-4966    

DOI:10.1121/1.416290

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The ability of cats to discriminate changes in the second formant of the vowel /ε/ was examined across a range of stimulus levels. Cats were trained to press and hold down a lever to produce a pulsed train of the standard vowel /ε/, and to release the lever only when a variant of /ε/ occurred. Six synthetic variants of /ε/ had the same first and third formants (F1andF3), but with the second formant (F2) located between 1700 and 2000 Hz. All stimuli were tested at levels of 10, 30, 50, and 70 dB SPL. Average difference thresholds for changes inF2(ΔF2) of the vowel /ε/ ranged from 87 to 36 Hz across levels of 10 to 70 dB SPL, and were only slightly above those of humans. Further, the ΔF2values were lower than pure‐tone ΔFvalues in the same frequency range, whereas humans exhibit higher ΔF2values than pure‐tone ΔFvalues in the same frequency range. Changes in the second formant in a negative direction (downwardF2shifts) were also found to be more difficult to detect than upwardF2shifts. These results suggest that, compared to pure tones, cats are better able to discriminate small changes in more complex, vowel‐like stimuli.

ISSN:0001-4966    

DOI:10.1121/1.416291

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Behavioral experiments measured the accuracy of the cat’s voluntary head orientation responses to bursts of broadband noise at 104 locations in the frontal sound field. Cats were presented sound stimuli at randomly selected locations and received a food reward for releasing a lever when a light‐emitting diode (LED) flashed at the same location. Head movements to the perceived location of the acoustic stimulus, and therefore expected location of the LED cue, were tracked by an electromagnetic sensor. Orientation responses to single sound bursts were directed to within 5° of the azimuth and elevation of sounds within 15° of the immediate frontal field and did not change for burst durations of 40, 100, and 200 ms. An increasing underestimation of target location was observed as the sound stimulus moved to more lateral azimuths and higher elevations. The ‘‘undershoot’’ phenomenon was reduced by allowing subjects to track paired stimulus bursts that repeated from the same location. These effects of sound location on the accuracy of orientation responses are predicted by the availability of mid‐frequency spectral cues for sound localization.

ISSN:0001-4966    

DOI:10.1121/1.416292

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The cat’s head‐related transfer function creates a directionally dependent mid‐frequency notch in the amplitude spectrum of a broadband sound as the stimulus propagates to the tympanic membrane [Riceetal., Hear. Res.58, 132–152 (1992)]. Our previous behavioral studies [May and Huang, J. Acoust. Soc. Am.100, 1059–1069 (1996)] have indicated that the cat’s sound‐evoked orientation responses are well directed to the azimuth and elevation of broadband noise bursts in the frontal sound field, where pinna‐based spectral notches are prominent and change systematically with sound direction. In the present study, the importance of mid‐frequency directional cues in the cat’s sound localization behavior was further evaluated by manipulating the frequency and bandwidth of orientation stimuli. The accurate pattern of orientation behavior seen previously with bursts of broadband noise was relatively unaffected when stimulus bandwidth was decreased to mid‐frequency bandpass noise of 5–18 kHz. In contrast, poorly directed head orientation responses were observed in tests with high‐pass noise (≳18 kHz) and mid‐frequency pure tones. When tested with narrow bands of mid‐frequency noise, cats oriented toward the spatial location where HRTF‐filtering properties most closely matched the stimulus spectrum. These results suggest that important sound localization cues are derived from mid‐frequency spectral features of the cat’s HRTF.

ISSN:0001-4966    

DOI:10.1121/1.416293

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The question of how well the temporal structure in pulsatile electrical stimulation is perceived, and the nature of the information that may be conveyed by this temporal structure, is of importance to the further development of speech processing strategies for cochlear implants. The two experiments described here investigated the perception of temporal fine structure in amplitude modulated 1‐kHz pulse trains, both when a single electrode position was used, and when the pulses alternated between two electrode positions. Five subjects with the Mini System 22 implant took part in these experiments. The amplitude modulations were constructed so that all dual‐electrode stimuli had the same temporal pattern on each individual electrode but differed in the aggregate temporal pattern. A hypothesis was investigated that subjects perceive the aggregate temporal pattern rather than the pattern at each individual electrode place, only when the electrodes are less than a critical distance apart. The first of these two experiments used a four‐interval forced‐choice task to measure the ability of subjects to detect changes in the aggregate temporal pattern. At electrode distances greater than 3 to 4 mm, subjects could no longer perceive the aggregate pattern, confirming the hypothesis. The second experiment used a single‐interval pitch estimation task to test the hypothesis that the perceptual differences in temporal patterns measured in the previous experiment were classified similarly to rate pitch differences by the subjects. The results confirmed this hypothesis, and showed that the pitch of the modulated stimuli could be predicted by the expected inter‐pulse intervals in the excited neural population.

ISSN:0001-4966    

DOI:10.1121/1.416294

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Acoustic and perceptual analyses of vowels, stops, and fricatives produced with and without an artificial palate were conducted. Recordings were made both immediately upon insertion of the palate and following a 15‐min adaptation period. Results of the acoustic analyses revealed significant alterations in the fricative spectra under conditions of perturbation with fewer, if any, changes in the vowels and stop consonants. Perceptual data confirmed these patterns and provided evidence of possible improvements in compensation over time. The data are compared to our previous studies of speech sound articulation under bite‐block conditions. Differences between adaptation to modifications of oral structure (artificial palate) and oral function (jaw fixation by a bite block) are considered.

ISSN:0001-4966    

DOI:10.1121/1.416286

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A new parameter, the area under the speech envelope, was used to evaluate the degree of speech dysfluency in stutterers. This parameter has been measured for 100‐s utterances of 30 fluent speakers and 30 stutterers speaking with simultaneous auditory feedback (SAF) and delayed auditory feedback (DAF). A correlation was found between the area under the speech envelope and the severity of stuttering. Thus for stutterers, this parameter can be used to evaluate the degree of the disturbance of fluency. The values of this parameter were significantly higher in fluent utterances than in nonfluent ones. The reduction of stuttering observed in stutterers under DAF was accompanied by an increase of the area under the speech envelope, making it comparable to the one measured for the utterances of fluent speakers.

ISSN:0001-4966    

DOI:10.1121/1.416295

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The perceptual magnet effect is one of the earliest known language‐specific phenomena arising in infant speech development. The effect is characterized by a warping of perceptual space near phonemic category centers. Previous explanations have been formulated within the theoretical framework of cognitive psychology. The model proposed in this paper builds on research from both psychology and neuroscience in working toward a more complete account of the effect. The model embodies two principal hypotheses supported by considerable experimental and theoretical research from the neuroscience literature: (1) sensory experience guides language‐specific development of an auditory neural map, and (2) a population vector can predict psychological phenomena based on map cell activities. These hypotheses are realized in a self‐organizing neural network model. The magnet effect arises in the model from language‐specific nonuniformities in the distribution of map cell firing preferences. Numerical simulations verify that the model captures the known general characteristics of the magnet effect and provides accurate fits to specific psychophysical data.

ISSN:0001-4966    

DOI:10.1121/1.416296

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Two experiments are reported in which a pitch‐level difference (PLD) model for prominence perception [Hermes and Rump, J. Acoust. Soc. Am.96, 83–92 (1994)] is subjected to further tests. The model holds that the contribution of pitch to the perceived degree of prominence is proportional to the difference in pitch level between the vocalic nuclei of the accented and the previous syllable. In experiment I, the influence of stretching and compressing the utterance in time was assessed. It was found that the predictions made by the model were not fully supported by the data. An alternative model was developed according to which pitch movements resynthesized in the same register lend equal prominence when pitch levels on the upper declination lines in the stimuli are equal. These two models gave different predictions when the lower declination lines are different. This was tested in experiment II. The results which are more or less between the predictions by the two models suggest that low pitch levels play a smaller role in prominence perception than high pitch levels do.

ISSN:0001-4966    

DOI:10.1121/1.416297

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The memory trace of the pitch sensation induced by a standard tone (S) can be strongly degraded by subsequently intervening sounds (I). Deutsch [Science168, 1604–1605 (1970)] suggested that the degradation is much weaker when theIsounds are words than when they are tones. In Deutsch’s study, however, the pitch relations betweenSand theIwords were not controlled. The first experiment reported here was similar to that of Deutsch except that the speech and nonspeech stimuli used asIsounds were matched in pitch. The speech stimuli were monosyllabic words derived from recordings of a real voice, whereas the nonspeech stimuli were harmonic complex tones with a flat spectral profile. These two kinds ofIsounds were presented at a variable pitch distance (Δ‐pitch) from theStone. In a same/different paradigm,Shad to be compared with a tone presented 6 s later; this comparison tone could be either identical toSor shifted in pitch by ±75 cents. The nature of theIsounds (spoken words versus tones) affected discrimination performance, but markedly less than did Δ‐pitch. Performance was better when Δ‐pitch was large than when it was small, for the speech as well as nonspeechIsounds. In a second experiment, theSsounds and comparison sounds were spoken words instead of tones. The differences to be detected were restricted to shifts in fundamental frequency (and thus pitch), the other acoustic attributes of the words being left unchanged. Again, discrimination performance was positively related to Δ‐pitch. This time, the nature of theIsounds (words versus tones) had no significant effect. Overall, the results suggest that, in auditory short‐term memory, the pitch of speech sounds is not stored differently from the pitch of nonspeech sounds.

ISSN:0001-4966    

DOI:10.1121/1.416298

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP