Search

It has been suggested that the first spectral peak and the first two spectral notches of head-related transfer functions (HRTFs) are cues for sound localization in the median plane. Therefore, to examine the mechanism for generating spectral peaks and notches, HRTFs were calculated from four head shapes using the finite-difference time-domain method. The comparison between HRTFs calculated from the whole head and the pinna-related transfer functions calculated from the segmented pinna indicated that the pinna determines the basic peak-notch pattern of the HRTFs. An analysis of the distribution patterns of pressure nodes and anti-nodes on the pinna computed in the steady state for sinusoidal excitations confirmed that the first three peaks correspond to the first three normal modes of the pinna. The analysis also revealed that at the first spectral notch frequencies, one or two anti-nodes appeared in the cymba and the triangular fossa, and a node developed in the concha. Furthermore, according to changes in the instantaneous pressure distribution patterns on the pinna, three types of mechanisms were hypothesized for inducing the node in the concha depending on the source elevation angle. [ABSTRACT FROM AUTHOR]

The present study investigated the extent to which native English listeners’ perception of Japanese length contrasts can be modified with perceptual training, and how their performance is affected by factors that influence segment duration, which is a primary correlate of Japanese length contrasts. Listeners were trained in a minimal-pair identification paradigm with feedback, using isolated words contrasting in vowel length, produced at a normal speaking rate. Experiment 1 tested listeners using stimuli varying in speaking rate, presentation context (in isolation versus embedded in carrier sentences), and type of length contrast. Experiment 2 examined whether performance varied by the position of the contrast within the word, and by whether the test talkers were professionally trained or not. Results did not show that trained listeners improved overall performance to a greater extent than untrained control participants. Training improved perception of trained contrast types, generalized to nonprofessional talkers’ productions, and improved performance in difficult within-word positions. However, training did not enable listeners to cope with speaking rate variation, and did not generalize to untrained contrast types. These results suggest that perceptual training improves non-native listeners’ perception of Japanese length contrasts only to a limited extent. [ABSTRACT FROM AUTHOR]

To provide a perceptual framework for the objective evaluation of durational rules in speech synthesis, two experiments were conducted to investigate the differences between vowel (V) onsets and V-offsets in their functions of marking the perceived temporal structure of speech. The first experiment measured the detectability of temporal modifications given in four-mora (CVCVCVCV) Japanese words. In the V-onset condition, the inter-onset intervals of vowels were uniformly changed (either expanded or reduced) while their inter-offset intervals were preserved. In the V-offset condition, this was reversed. These manipulations did not change the duration of the entire word. Each of the modified words was paired with its unmodified counterpart, and the pair was given to listeners, who were asked to rate the difference between the paired words. The results show that there were no significant differences in the listeners' abilities to detect the temporal modification between the V-onset and V-offset conditions. In the second experiment, the listeners were asked to estimate the differences they perceived in speaking rates for the same stimulus set as that of the first experiment. Interestingly, the results show a clear difference in the listeners' performance between the V-onset and V-offset conditions. Specifically, changing the V-onset intervals changed the perceived speaking rates, which showed a linear relation (r=-0.9) despite the fact that the duration of the entire word remained unchanged. In contrast, modifying the V-offset intervals produced no clear relation with the perceived speaking rates. The second experiment also showed that the listeners performed well in speaking rate discrimination (3.5%-5% in the change ratio). These results are discussed in relation to the differences in the listeners' temporal processing range (local or global) between the two experiments. [ABSTRACT FROM AUTHOR]

Human subjective acceptability of durational distortions in speech segments or portions is significantly affected by various segmental and sequential properties, e.g., the vowel color and temporal position in a word [Kato et al., J. Acoust. Soc. Am. 101, 2311-2322 (1997); 104, 540-549 (1998)]. The current study focused on the effects of phoneme class and original duration of speech portions in isolated words. In experiment 1, the effect of four classes of phoneme, i.e., vowel, nasal, voiceless fricative, and silent closure, on the acceptable modification range was tested. Six listeners evaluated the temporal acceptability of each of 49 words where one of the steady-state portions was subjected to durational modification from -75 ms (for shortening) to +75 ms (for lengthening) in 7.5-ms steps. The results showed that the listeners' acceptable modification ranges were narrowest for vowels, and widest for voiceless fricatives and silent closures, with nasals in between. The mean acceptable ranges for the least vulnerable phoneme class, i.e., voiceless fricative and silent closure, reached 143% or more of that for the most vulnerable class, i.e., vowel. The observed variation in the acceptable modification range due to the different phoneme class was highly correlated with the inherent loudness in each phoneme class. A larger inherent loudness yielded a narrower acceptable range. Experiment 2 tested the effect of the original, as produced, duration of steady-state speech portions using 30 words where the factors of phoneme class and original duration were designed in a factorial way. The results showed that the original durations affected the listeners' absolute acceptable ranges; the ranges were narrower for shorter original durations. There was a significant interaction between the factors of phoneme class and original duration. The effect of the original duration was larger for vowels than for fricatives. This interaction could be accounted for by the difference in the temporal structure spanning beyond the modified portion itself. © 2002 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Few perceptual studies of the temporal aspects of speech have investigated the influence of changes in segmental durations in terms of acceptability. Aiming to contribute to the assessment of rules for assigning segmental durations in speech synthesis, the current study measured the perceptual acceptability of changes in the segmental duration of vowels as a function of the segment attributes or context, such as base duration, temporal position in a word, vowel quality, and voicing of the following segment. Seven listeners estimated the acceptability of word stimuli in which one of the vowels was subjected to a temporal modification from -50 ms (for shortening) to +50 ms (for lengthening) in 5-ms steps. The temporal modification was applied to vowel segments in 70 word contexts; their durations ranged from 35-145 ms, the mora position in the word was first or third, the vowel quality was /[open_aye]/ or /i/, and the following segment was a voiced or an unvoiced consonant. The experimental results showed that the listeners' acceptable range of durational modification was narrower for vowels in the first moraic position in the word than for those in the third moraic position. The acceptable range was also narrower for the vowel /[open_aye]/ than for the vowel /i/, and similarly narrower for vowels followed by unvoiced consonants than for those followed by voiced consonants. The vowel that fell into the least vulnerable class (the third /i/, followed by a voiced consonant) required 140% of the modification of that which fell into the most vulnerable class (the first /[open_aye]/, followed by an unvoiced consonant) to yield the same acceptability decrement. In contrast, the effect of the original vowel duration on the acceptability of temporal modifications was not significant despite its wide variation (35-145 ms). © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Perceptual sensitivity to temporal modification in two consecutive speech segments was measured in word contexts to explore the following two questions: (1) whether there is an interaction between multiple segmental durations, and (2) what aspect of the stimulus context determines the perceptually salient temporal markers? Experiment 1 obtained acceptability ratings for words with temporal modifications. The results showed that the compensatory change in duration of a vowel (V) and its adjacent consonant (C) is not perceptually so salient as expected for the simultaneous modifications in the two segments. This finding suggests the presence of a time perception range wider than a single segment (V or C). The results of experiment 1 also showed that rating scores for compensatory modification between V and C do not depend on the temporal order of modified pairs (VC or CV), but rather on the loudness difference between V and C; the acceptability decreased when the loudness difference between V and C became high. This suggests that perceptually salient markers locate around major jumps in loudness. The second finding, the dependence on the loudness jump, was replicated in experiment 2, which utilized a detection task for temporal modifications on nonspeech stimuli modeling the time-loudness features of the speech stimuli. Experiment 3 further investigated the influence of the temporal order of V and C by utilizing the detection task for the speech stimuli instead of the acceptability ratings. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Japanese words can be distinguished by the length of phonemes, e.g., ‘‘chizu’’ (map) versus ‘‘chiizu’’ (cheese). Perceiving these length contrasts is therefore important for learning Japanese as a second language. The present study examined native English listeners’ perception of length contrasts at different speaking rates and in different contexts. Stimuli consisted of 20 Japanese word pairs that minimally contrasted in vowel length, and 10 synthesized nonwords. The nonwords were created by modifying the duration of the second vowel of the nonword ‘‘erete’’ along a continuum (from ‘‘erete’’ to ‘‘ereete’’). Stimuli were presented with or without a carrier sentence at three rates (fast, normal, slow). Rate was either fixed or randomized trial by trial. Sixteen native English and 16 native Japanese listeners participated in a single-stimulus, two-alternative forced-choice identification task. Results suggest that native Japanese listeners’ identification boundaries systematically shifted due to changes in speaking rate when the stimuli were in the context of a sentence with mixed rates of presentation. In contrast, native English listeners show a shift in the opposite direction, suggesting that they did not follow the variation in speaking rate. These results will be discussed from the viewpoint of training second-language phoneme perception. [Work supported by JSPS.] [ABSTRACT FROM AUTHOR]

To investigate the process of perceptual resynthesis of an ''auditory object,'' the apparent duration of a noise-replaced speech signal was measured. Subjects adjusted the duration of synthesized speech to subjectively match that of the target speech. When a portion of the target speech was replaced by a noise burst, the duration was perceived to be shorter than when no replacement was made. Besides this effect, the apparent duration of speech segments was found to be affected by their deviation from the internal template. The greater the physical duration of the target deviated from the ''naturally'' spoken token, the greater the degree of underestimation became. Interestingly, these two effects were independent of each other. This independence was replicated in the second experiment which tested wider range of durational deviations. Again, the apparent duration of noise-replaced speech was shorter than when no replacement was made. The apparent duration of gap-replaced speech was also measured in this experiment. The degree of underestimation was far greater for the latter case. These findings suggest that a shrinkage of duration occurs in the process of resynthesizing an ''auditory object'' where the process is assumed to be at a different stage than that utilizing speech-specific schema. [ABSTRACT FROM AUTHOR]

To investigate how the auditory mechanism restores the noise-replaced speech segments, the apparent durations for the perceptually restored speech were measured. The results were obtained that supports the hypothesis that the subjects restore the ''missed'' part of speech based on the internal template whose temporal structure corresponds to the ''original'' sample. The threshold of duration discrimination was measured using an up-and-down two-interval task. In one interval, a ''standard'' stimulus was presented that had the temporal structure of the natural sample. In the other interval, a ''comparison'' was presented in which the third mora was either lengthened or shortened. There were four conditions in a two-factorial design. The first factor was the noise replacement in the comparison, depending on whether the part of the modified segment in the comparison was replaced by a noise. The second factor was the noise replacement in the standard. In the lengthening direction, only the noise replacement in the comparison resulted in the increment of the discrimination threshold irrespective of the noise replacement in the standard. This suggests that only the noise replacement in the modified part is effective in the perceptual judgment of the durations. [ABSTRACT FROM AUTHOR]

Beyond the first peak of head-related transfer functions or pinna-related transfer functions (PRTFs) human pinnae are known to have two normal modes with "vertical" resonance patterns, involving two or three pressure anti-nodes in cavum, cymba, and fossa. However, little is known about individual variations in these modes, and there is no established model for estimating their center-frequencies from anthropometry. Here, with geometries of 38 pinnae measured, PRTFs were calculated and vertical modes visualized by numerical simulation. Most pinnae were found to have both Cavum-Fossa and Cavum-Cymba modes, with opposite-phase anti-nodes in cavum and either fossa or cymba, respectively. Nevertheless in both modes, fossa involvement varied substantially across pinnae, dependent on scaphoid fossa depth and cymba shallowness. Linear regression models were evaluated in mode frequency estimation, with 3322 measures derived from 31 pinna landmarks. The Cavum-Fossa normal mode frequency was best estimated [correlation coefficient r = 0.89, mean absolute error (MAE) = 257 Hz or 4.4%] by the distance from canal entrance to helix rim, and cymba horizontal depth. The Cavum-Cymba normal mode frequency was best estimated (r = 0.92, MAE = 247 Hz or 3.2%) by the sagittal-plane distance from concha floor to cymba anterior wall, and cavum horizontal depth.

The first (lowest) peak of head-related transfer functions (HRTFs) is known to be a concha depth resonance and a spectral cue in human sound localization. However, there is still no established model to estimate its center-frequency F1 and amplitude A1 from pinna anthropometry. Here, with geometries of 38 pinnae measured and their median-plane HRTFs calculated by numerical simulation, linear regression models were evaluated in estimating F1 and A1 from 25 concha depth and aperture measurements. F1 was best estimated (correlation coefficient r = 0.84, mean absolute error MAE = 118 Hz) by lateral distances from the base of the posterior cavum concha to the outer surface of the antitragus and antihelix (longest measures of concha depth). A1 was best estimated (r = 0.83, MAE = 0.84 dB) by the lateral distance from the ear-canal entrance to the side of the cheek near the anterior notch (shortest measure of concha depth) and by the equivalent diameter of the concha aperture. These results suggest that the first resonance's quarter-wavelength corresponds to the longest lateral extent of the concha and that its energy lost to the surrounding air depends on the concha aperture and the cavum concha's shortest lateral depth.