Speech segment durations and quantity in Icelandic.

Icelandic has a phonologic contrast of quantity, distinguishing long and short vowels and consonants. Perceptual studies have shown that a major cue for quantity in perception is relational, involving the vowel-to-rhyme ratio. This cue is approximately invariant under transformations of rate, thus yielding a higher-order invariant for the perception of quantity in Icelandic. Recently it has, however, been shown that vowel spectra can also influence the perception of quantity. This holds for vowels which have different spectra in their long and short varieties. This finding raises the question of whether the durational contrast is less well articulated in those cases where vowel spectra provide another cue for quantity. To test this possibility, production measurements were carried out on vowels and consonants in words which were spoken by a number of speakers at different utterance rates in two experiments. A simple neural network was then trained on the production measurements. Using the network to classify the training stimuli shows that the durational distinctions between long and short phonemes are as clearly articulated whether or not there is a secondary, spectral, cue to quantity.     

Using links between speech perception and speech production to evaluate different acoustic metrics: a preliminary report

This paper examines whether correlations between speech perception and speech production exist, and, if so, whether they might provide a way of evaluating different acoustic metrics. The cues listeners use for many phonemic distinctions are not known, often because many different acoustic cues are highly correlated with one another, making it difficult to distinguish among them. Perception-production correlations may provide a new means of doing so. In the present paper, correlations were examined between acoustic measures taken on listeners' perceptual prototypes for a given speech category and on their average production of members of that category. Significant correlations were found for VOT among stop consonants, and for spectral peaks (but not centroids or skewness) for voiceless fricatives. These results suggest that correlations between speech perception and production may provide a methodology for evaluating different proposed acoustic metrics.     

Illusory continuity of interrupted speech: speech rate determines durational limits

Deleted segments of speech can be restored perceptually if they are replaced by a louder noise. An earlier study of this "phonemic restoration effect" found that, when recorded discourse was interrupted periodically by noise, the durational limit for illusory continuity corresponded to the average word duration. The present study employed a different passage of discourse recorded by a different speaker. Durational limits for apparent continuity of discourse interrupted by noise were measured at the normal (original) playback speed, as well as at rates that were 15% greater and 15% less. At the normal playback rate, once again the limit of continuity approximated the average word duration--but of especial interest was the finding that changes in playback rate produced proportional changes in continuity limits. These results, together with other evidence, suggest that phonemic restorations represent a special linguistic application of a general auditory mechanism (auditory induction) producing appropriate syntheses of obliterated sounds, and that for discourse the limits of illusory continuity correspond to a fixed amount of verbal information, and not a fixed temporal value.     

On the role of the amplitude envelope for the perception of [b] and [w]

This study investigated the role of the amplitude envelope in the vicinity of consonantal release in the perception of the stop-glide contrast. Three sets of acoustic [b-w] continua, each in the vowel environments [a] and [i], were synthesized using parameters derived from natural speech. In the first set, amplitude, formant frequency, and duration characteristics were interpolated between exemplar stop and glide endpoints. In the second set, formant frequency and duration characteristics were interpolated, but all stimuli were given a stop amplitude envelope. The third set was like the second, except that all stimuli were given a glide amplitude envelope. Subjects were given both forced-choice and free-identification tasks. The results of the forced-choice task indicated that amplitude cues were able to override transition slope, duration, and formant frequency cues in the perception of the stop-glide contrast. However, results from the free-identification task showed that, although presence of a stop amplitude envelope turned all stimuli otherwise labeled as glides to stops, the presence of a glide amplitude envelope changed stimuli labeled otherwise as stops to fricatives rather than to glides. These results support the view that the amplitude envelope in the vicinity of the consonantal release is a critical acoustic property for the continuant / noncontinuant contrast. The results are discussed in relation to a theory of acoustic invariance.     

Syllable structure and integration of voicing and manner of articulation information in labial consonant identification

Speech perception requires the integration of information from multiple phonetic and phonological dimensions. A sizable literature exists on the relationships between multiple phonetic dimensions and single phonological dimensions (e.g., spectral and temporal cues to stop consonant voicing). A much smaller body of work addresses relationships between phonological dimensions, and much of this has focused on sequences of phones. However, strong assumptions about the relevant set of acoustic cues and/or the (in)dependence between dimensions limit previous findings in important ways. Recent methodological developments in the general recognition theory framework enable tests of a number of these assumptions and provide a more complete model of distinct perceptual and decisional processes in speech sound identification. A hierarchical Bayesian Gaussian general recognition theory model was fit to data from two experiments investigating identification of English labial stop and fricative consonants in onset (syllable initial) and coda (syllable final) position. The results underscore the importance of distinguishing between conceptually distinct processing levels and indicate that, for individual subjects and at the group level, integration of phonological information is partially independent with respect to perception and that patterns of independence and interaction vary with syllable position.     

The discrimination of vowel duration by infants

Three groups of nine 5-11-month-old infants provided evidence of discrimination of speechlike stimuli differing only in vowel duration. Ease of discrimination was directly related to the magnitude of the ratio of the longer to shorter vowel. Group one infants discriminated three vowel duration contrasts (with ratios of 0.33, 0.67, and 1.0) embedded in a synthetic [mad] syllable; group two discriminated these same duration contrasts within the bisyllable [ samad ], and group three in the trisyllable [ masamad ]. In all cases, the contrasting durations were carried by the last vowel of the synthetic word. These same three infant groups failed to provide evidence of discrimination of a final position released stop consonant contrast ([mat] versus [mad]) cued by voice excitation during closure of the [d] and not the [t]. These results suggest that vowel duration may be a primary cue for infants' perception of the voicing of final position stop consonants.     

冲击阻尼板的尺寸辨识与声线索提取

针对冲击板的物理属性辨识问题,研究了尺寸辨识的恒定声线索提取及其在听觉感知中所起的作用。设计并完成了三组主观评价实验,实验1分析了录音和合成声作为声刺激对尺寸辨识的影响。实验2和实验3分别针对铝板和木板的冲击声,通过不相似主观评价实验获得尺寸辨识的感知空间和对应力学空间维度,计算了不同声特征的信息精确度。最后,对比实验2和实验3的结果给出了尺寸辨识的恒定声线索,根据声线索与感知结果的相关性分析了听者的尺寸感知策略。结果表明,听者利用录音和合成声均获得了较好的尺寸辨识结果,且听者趋向于利用与尺寸有关的恒定声线索来完成感知任务,而忽略那些容易受其他声源属性影响的声信息。      

Assimilation and contrast in the phonetic perception of vowels.

The perceptual mechanisms of assimilation and contrast in the phonetic perception of vowels were investigated. In experiment 1, 14 stimulus continua were generated using an /i/-/e/-/a/ vowel continuum. They ranged from a continuum with both ends belonging to the same phonemic category in Japanese, to a continuum with both ends belonging to different phonemic categories. The AXB method was employed and the temporal position of X was changed under three conditions. In each condition ten subjects were required to judge whether X was similar to A or to B. The results demonstrated that assimilation to the temporally closer sound occurs if the phonemic categories of A and B are the same and that contrast to the temporally closer sound occurs if A and B belong to different phonemic categories. It was observed that the transition from assimilation to contrast is continuous except in the /i'/-X-/e/ condition. In experiment 2, the total duration of t 1 (between A and X) and t 2 (between X and B) was changed under five conditions. One stimulus continuum consisted of the same phonemic category in Japanese and the other consisted of different phonemic categories. Six subjects were required to make similarity judgements of X. The results demonstrated that the occurrence of assimilation and contrast to the temporally closer sound seemed to be constant under each of the five conditions. The present findings suggest that assimilation and contrast are determined by three factors: the temporal position of the three stimuli, the acoustic distance between the three stimuli on the stimulus continuum, and the phonemic categories of the three stimuli.     

A probabilistic framework for landmark detection based on phonetic features for automatic speech recognition

A probabilistic framework for a landmark-based approach to speech recognition is presented for obtaining multiple landmark sequences in continuous speech. The landmark detection module uses as input acoustic parameters (APs) that capture the acoustic correlates of some of the manner-based phonetic features. The landmarks include stop bursts, vowel onsets, syllabic peaks and dips, fricative onsets and offsets, and sonorant consonant onsets and offsets. Binary classifiers of the manner phonetic features-syllabic, sonorant and continuant-are used for probabilistic detection of these landmarks. The probabilistic framework exploits two properties of the acoustic cues of phonetic features-(1) sufficiency of acoustic cues of a phonetic feature for a probabilistic decision on that feature and (2) invariance of the acoustic cues of a phonetic feature with respect to other phonetic features. Probabilistic landmark sequences are constrained using manner class pronunciation models for isolated word recognition with known vocabulary. The performance of the system is compared with (1) the same probabilistic system but with mel-frequency cepstral coefficients (MFCCs), (2) a hidden Markov model (HMM) based system using APs and (3) a HMM based system using MFCCs.     

The use of acoustic cues for phonetic identification: effects of spectral degradation and electric hearing

Although some cochlear implant (CI) listeners can show good word recognition accuracy, it is not clear how they perceive and use the various acoustic cues that contribute to phonetic perceptions. In this study, the use of acoustic cues was assessed for normal-hearing (NH) listeners in optimal and spectrally degraded conditions, and also for CI listeners. Two experiments tested the tense/lax vowel contrast (varying in formant structure, vowel-inherent spectral change, and vowel duration) and the word-final fricative voicing contrast (varying in F1 transition, vowel duration, consonant duration, and consonant voicing). Identification results were modeled using mixed-effects logistic regression. These experiments suggested that under spectrally-degraded conditions, NH listeners decrease their use of formant cues and increase their use of durational cues. Compared to NH listeners, CI listeners showed decreased use of spectral cues like formant structure and formant change and consonant voicing, and showed greater use of durational cues (especially for the fricative contrast). The results suggest that although NH and CI listeners may show similar accuracy on basic tests of word, phoneme or feature recognition, they may be using different perceptual strategies in the process.     

Measuring Causal Invariance Formally

Invariance is one of several dimensions of causal relationships within the interventionist account. The more invariant a relationship between two variables, the more the relationship should be considered paradigmatically causal. In this paper, I propose two formal measures to estimate invariance, illustrated by a simple example. I then discuss the notion of invariance for causal relationships between non-nominal (i.e., ordinal and quantitative) variables, for which Information theory, and hence the formalism proposed here, is not well suited. Finally, I propose how invariance could be qualified for such variables.     

Characteristics of listener sensitivity to talker-specific phonetic detail

Previous research shows that listeners are sensitive to talker differences in phonetic properties of speech, including voice-onset-time (VOT) in word-initial voiceless stop consonants, and that learning how a talker produces one voiceless stop transfers to another word with the same voiceless stop [Allen, J. S., and Miller, J. L. (2004). J. Acoust. Soc. Am. 115, 3171-3183]. The present experiments examined whether transfer extends to words that begin with different voiceless stops. During training, listeners heard two talkers produce a given voiceless-initial word (e.g., pain). VOTs were manipulated such that one talker produced the voiceless stop with relatively short VOTs and the other with relatively long VOTs. At test, listeners heard a short- and long-VOT variant of the same word (e.g., pain) or a word beginning with a different voiceless stop (e.g., cane or coal), and were asked to select which of the two VOT variants was most representative of a given talker. In all conditions, which variant was selected at test was in line with listeners' exposure during training, and the effect was equally strong for the novel word and the training word. These findings suggest that accommodating talker-specific phonetic detail does not require exposure to each individual phonetic segment.     

Effects of repeated production on vowel distinctiveness within nonwords

In the present study acoustic distinctiveness of vowels within nonwords with repeated production was investigated. Participants were 9 males and 15 females divided into two groups. Participants repeated 6 nonwords varying in phonemic composition. The mean Euclidean distance (MED) of the vowels from each production of a nonword from the center of the F1/F2 space was calculated. The changes in MED with repeated production were analyzed using linear mixed effects regression. Results revealed an increase in MED, indicating greater vowel dispersion, for the three-syllable nonwords and a significant decrease, i.e., greater reduction, in vowel dispersion for the six-syllable nonwords. Findings support the dynamic influence of sublexical processes on phonetic realization in speech production.     

Influence of following context on perception of the voiced-voiceless distinction in syllable-final stop consonants

This paper reports acoustic measurements and results from a series of perceptual experiments on the voiced-voiceless distinction for syllable-final stop consonants in absolute final position and in the context of a following syllable beginning with a different stop consonant. The focus is on temporal cues to the distinction, with vowel duration and silent closure duration as the primary and secondary dimensions, respectively. The main results are that adding a second syllable to a monosyllable increases the number of voiced stop consonant responses, as does shortening of the closure duration in disyllables. Both of these effects are consistent with temporal regularities in speech production: Vowel durations are shorter in the first syllable of disyllables than in monosyllables, and closure durations are shorter for voiced than for voiceless stops in disyllabic utterances of this type. While the perceptual effects thus may derive from two separate sources of tacit phonetic knowledge available to listeners, the data are also consistent with an interpretation in terms of a single effect; one of temporal proximity of following context.     

Lexical frequency and acoustic reduction in spoken Dutch

This study investigates the effects of lexical frequency on the durational reduction of morphologically complex words in spoken Dutch. The hypothesis that high-frequency words are more reduced than low-frequency words was tested by comparing the durations of affixes occurring in different carrier words. Four Dutch affixes were investigated, each occurring in a large number of words with different frequencies. The materials came from a large database of face-to-face conversations. For each word containing a target affix, one token was randomly selected for acoustic analysis. Measurements were made of the duration of the affix as a whole and the durations of the individual segments in the affix. For three of the four affixes, a higher frequency of the carrier word led to shorter realizations of the affix as a whole, individual segments in the affix, or both. Other relevant factors were the sex and age of the speaker, segmental context, and speech rate. To accommodate for these findings, models of speech production should allow word frequency to affect the acoustic realizations of lower-level units, such as individual speech sounds occurring in affixes.     

An auditory basis for the stimulus-length effect in the perception of stops and glides

To investigate possible auditory factors in the perception of stops and glides (e.g., /b/ vs /w/), a two-category labeling performance was compared on several series of /ba/-/wa/ stimuli and on corresponding nonspeech stimulus series that modeled the first-formant trajectories and amplitude rise times of the speech items. In most respects, performance on the speech and nonspeech stimuli was closely parallel. Transition duration proved to be an effective cue for both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets, and the category boundaries along the transition-duration dimension did not differ significantly in the two cases. When the stop/glide distinction was signaled by variation in transition duration, there was a reliable stimulus-length effect: A longer vowel shifted the category boundary toward greater transition durations. A similar effect was observed for the corresponding nonspeech stimuli. Variation in rise time had only a small effect in signaling both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets. There was, however, one discrepancy between the speech and nonspeech performance. When the stop/glide distinction was cued by rise-time variation, there was a stimulus-length effect, but no such effect occurred for the corresponding nonspeech stimuli. On balance, the results suggest that there are significant auditory commonalities between the perception of stops and glides and the perception of acoustically analogous nonspeech stimuli.     

The role of medial consonant transitions in word perception.

In VCV nonsense forms (such as /epsilondepsilon/, while both the CV transition and the VC transition are perceptible in isolation, the CV transition dominates identification of the stop consonant. Thus, the question arises, what role, if any, do VC transitions play in word perception? Stimuli were two-syllable English words in which the medial consonant was either a stop or a fricative (e.g., "feeding" and "gravy"). Each word was constructed in three ways: (1) the VC transition was incompatible with the CV in either place, manner of articulation, or both; (2) the VC transition was eliminated and the steady-state portion of first vowel was substituted in its place; and (3) the original word. All versions of a particular word were identical with respect to duration, pitch contour, and amplitude envelope. While an intelligibility test revealed no differences among the three conditions, data from a paired comparison preference task and an unspeeded lexical decision task indicated that incompatible VC transitions hindered word perception, but lack of VC transitions did not. However, there were clear differences among the three conditions in the speeded lexical decision task for word stimuli, but not for nonword stimuli that were constructed in an analogous fashion. We discuss the use of lexical tasks for speech quality assessment and possible processes by which listeners recognize spoken words.     

Dynamic specification of coarticulated vowels

An adequate theory of vowel perception must account for perceptual constancy over variations in the acoustic structure of coarticulated vowels contributed by speakers, speaking rate, and consonantal context. We modified recorded consonant-vowel-consonant syllables electronically to investigate the perceptual efficacy of three types of acoustic information for vowel identification: (1) static spectral "targets," (2) duration of syllabic nuclei, and (3) formant transitions into and out of the vowel nucleus. Vowels in /b/-vowel-/b/ syllables spoken by one adult male (experiment 1) and by two females and two males (experiment 2) served as the corpus, and seven modified syllable conditions were generated in which different parts of the digitized waveforms of the syllables were deleted and the temporal relationships of the remaining parts were manipulated. Results of identification tests by untrained listeners indicated that dynamic spectral information, contained in initial and final transitions taken together, was sufficient for accurate identification of vowels even when vowel nuclei were attenuated to silence. Furthermore, the dynamic spectral information appeared to be efficacious even when durational parameters specifying intrinsic vowel length were eliminated.     

Coarticulation in sequences of two nonhomorganic stop consonants: perceptual and acoustic evidence

This study investigated whether any perceptually useful coarticulatory information is carried by the release burst of the first of two successive, nonhomorganic stop consonants. The CV portions of natural VCCV utterances were replaced with matched synthetic stimuli from a continuum spanning the three places of stop articulation. There was a sizable effect of coarticulatory cues in the natural-speech portion on the perception of the second stop consonant. Moreover, when the natural VC portions including the final release burst were presented in isolation, listeners were significantly better than chance at guessing the identity of the following, "missing" syllable-initial stop. The hypothesis that the release burst of a syllable-final stop contains significant coarticulatory information about the place of articulation of a following, nonhomorganic stop was further confirmed in acoustic analyses which revealed significant effects of CV context on the spectral properties of the release bursts. The relationship between acoustic stimulus properties and listeners' perceptual responses was not straightforward, however.