Consonant-vowel Transitions Research Articles

A neural model predicting context effects in the identification of stops and glides

One class of phonetic context effects involves durational contrasts: A signal can be perceived as a stop consonant or a glide, depending on the length of the adjacent segment. For example, the syllable [wa] is perceived as [ba] if the steady-state frequencies corresponding to the vowel are lengthened. Thus the vocalic information affects reported phonetic judgments of the prior consonantal segment. The neural model presented processes consonant–vowel transitions and steady-state vowel signals by transient and sustained channels. This model predicts the experimental effects of vowel duration, CV transition rate, and frequency extent in identifying [ba] and [wa]. The product of a leaky integrator’s output with the quotient of two linear expressions in the stimulus parameters generates the model’s output. With a single small set of parameters, the model predicts over 99% of the variance in two data sets [J. L. Miller and A. M. Liberman, Percept. Psychophys. 25(6), 457–465 (1979); Schwab et al., Percept. Psychophys. 29(2), 121–128 (1981)]. It outperforms a number of simple alternative models. Implications for other phonetic distinctions and physiological analogs to the model in monkey cortex are described. [Work supported by AFOSR and ONR.]

Vocal tract aerodynamics in /aCa/ utterances: Measurements

This paper examines air flow patterns at vowel-consonant and consonant-vowel transitions. Oral air flow was recorded in six speakers of American English producing reiterant speech. The air flow signal was inverse filtered to obtain an estimate of the glottal pulse. Measurements were made of peak and minimum flow, open quotient, pulse area and fundamental frequency. The results show that at the transitions between vowels and voiceless consonants the pulse properties show large variations. In particular, the source is characterized by a breathy mode of phonation. Breathiness was indexed by large values of peak and minimum flow, and an open quotient close to 1. The observed variations can be accounted for by the laryngeal adjustments that are made for voiceless consonants, in particular the glottal opening movement and its phasing with the oral articulatory events. Individual differences suggest that speakers vary in their use of the longitudinal tension of the vocal folds in controlling voicelessness.

Perceptual evaluation of infant CV transitions

The transition portion of the speech signal has been identified as critical to the perception of both consonants and vowels. Furui [J. Acoust. Soc. Am. 72, 43–50 (1986)] demonstrated that, for adult speakers, a 10‐ms segment of the transition centered on the area of maximum spectral movement contained the most critical information for joint consonant and vowel perception and that a period roughly 50 ms long (including the aforementioned 10‐ms critical interval) was sufficient for CV syllable perception. An investigation of the perceptual cues contained within consonant‐vowel (CV) transitions of infants ages 6–15 months was begun. CV‐like syllables were selected from the vocalizations of two infants, a male and a female, and presented to listeners for identification. Truncated versions in which portions of the transition were systematically deleted were also presented for identification and critical intervals for the perception of consonant, vowel, and syllable were calculated and compared with those obtained for adult speakers. Comparisons across age levels were also made.

An unrestricted vocabulary Arabic speech synthesis system

A method for synthesizing Arabic speech has been developed which uses a reasonably sized set of subphonetic elements as the synthesis units to allow synthesis of unlimited-vocabulary speech of good quality. The synthesis units have been defined after a careful study of the phonetic properties of modern standard Arabic, and they consist of central steady-state portions of vowels, central steady-state portions of consonants, vowel-consonant and consonant-vowel transitions, and some allophones. A text-to-speech system which uses this method has also been developed. The input of the system is ordinary Arabic spelling with diacritics and/or simple numeric expressions. Synthesis is controlled by several text-to-speech rules which are formulated and developed as algorithms more suited for computer handling of the synthesis process. The rules are required for converting the input text into phonemes, converting the phonemes into phonetic units, generating the synthesis units from the phonetic units, and concatenating the synthesis units to form spoken messages. The suitability of the method for synthesizing Arabic has been shown by realizing all its functions on a personal computer and by conducting understandability test on synthesized speech.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Integral processing of phonemes: evidence for a phonetic mode of perception.

To investigate the extent and locus of integral processing in speech perception, a speeded classification task was utilized with a set of noise-tone analogs of the fricative-vowel syllables (fae), (integral of ae), (fu), and (integral of u). Unlike the stimuli used in previous studies of selective perception of syllables, these stimuli did not contain consonant-vowel transitions. Subjects were asked to classify on the basis of one of the two syllable components. Some subjects were told that the stimuli were computer generated noise-tone sequences. These subjects processed the noise and tone separably. Irrelevant variation of the noise did not affect reaction times (RTs) for the classification of the tone, and vice versa. Other subjects were instructed to treat the stimuli as speech. For these subjects, irrelevant variation of the fricative increased RTs for the classification of the vowel, and vice versa. A second experiment employed naturally spoken fricative-vowel syllables with the same task. Classification RTs showed a pattern of integrality in that irrelevant variation of either component increased RTs to the other. These results indicate that knowledge of coarticulation (or its acoustic consequences) is a basic element of speech perception. Furthermore, the use of this knowledge in phonetic coding is mandatory, even in situations where the stimuli do not contain coarticulatory information.

Phonetic information is integrated across intervening nonlinguistic sounds.

When the fricative noise of a fricative-vowel syllable is replaced by a noise from a different vocalic context, listeners experience delays in identifying both the fricative and the vowel (Whalen, 1984): mismatching the information in the fricative noise for vowel and consonant identity with the information in the vocalic segment appears to hamper processing. This effect was argued to be due to integration of the information relevant to phonetic categorization. The present study was intended to eliminate an alternative explanation based on acoustic discontinuities. Noises and vowels were again cross-spliced, but, in addition, the first 60 msec of the vocalic segment (which comprised the consonant-vowel transitions) either had a nonlinguistic noise added to it or was replaced by that noise. The fricative noise and the majority of the vocalic segment were left intact, and both were quite identifiable. Mismatched consonant information caused delays both for original stimuli and for ones with the noise added to the transitions. Mismatched vowel information caused delays for all stimuli, both originals and ones with the noise. Additionally, syllables with a portion replaced by noise took longer to identify than those that had the noise added to them. When asked explicitly to tell the added versions from the replaced, subjects were unable to do so. The results indicate that listeners integrate all relevant information, even across a nonlinguistic noise. Completely replacing the signal delayed identifications more than did adding the noise to the original signal. This was true despite the fact that the subjects were not aware of any difference.

A spectrographic investigation of consonant-vowel transitions in the speech of deaf adults

A spectrographic investigation was carried out on the speech of normal-hearing and deaf speakers; the research attempted to answer questions concerning formant transitions, coarticulation and neutralization of vowels in the speech of the deaf adults. Recordings were made of each subject reading a constant carrier phrase into which a changing medial monosyllable was embedded. The deaf subjects chosen for this investigation were judged to be above average in intelligibility (for deaf talkers that is); they exhibited a profound bilateral hearing loss of early onset. Wide band spectrograms were made of selected recorded stimulus items. The results indicated that the transitions of deaf speakers had a restricted range and slower rate of movement than did those of the normal talkers. Further, the speech of the deaf showed relatively few coarticulation effects, their vowel formants tended to be neutralized and they tended to begin any given articulatory sequence in a manner similar to any other regardless of context.

Influence of encoding and acoustic similarity on the ear advantage and lag effect in dichotic listening.

Experiments with simultaneous and time lag dichotic listening conditions were used to test two hypotheses concerning the right ear advantage and lag effect in dichotic listening. One hypothesis is based on the similarity of acoustic spectra, and the other is based on a categorization of speech sounds as being either encoded or not encoded. Natural vowels and consonant-vowel syllables were used to obtain seven different types of speech stimuli: stop vowel syllables, fricative vowel syllables, stop burst noise, fricative noise, stop vowel transitions, fricative vowel transitions and steady state vowels. The presentation conditions were monaural, simultaneous dichotic, and dichotic with interaural time delays of 15, 30, 60, and 90 msec. With monaural presentations, all stimuli were identifiable above chance levels. For the simultaneous dichotic condition, significant right ear advantages occurred for stop vowel syllables, fricative vowel syllables, stop burst noise, and steady state vowels. For the time lag conditions, stop vowel syllables, stop bursts, and fricative noise produced consistent lag effects, but steady state vowels produced consistent lead effects. In general, the results gave stronger support to the hypothesis of acoustic similarity than to the encoding hypothesis in that stop burst noise produced both a right ear advantage and a lag effect whereas consonant-vowel transitions produced neither a right ear advantage nor a lag effect.

The role of consonant-vowel transitions in the perception of the stop and nasal consonants.

The role of consonant-vowel transitions in the perception of the stop and nasal consonants.