Syllable-initial Consonants Research Articles

Influences of formant bandwidth and auditory frequency selectivity on identification of place of articulation in stop consonants

Can supra-normal spectral contrast in an acoustical speech signal compensate for the degraded frequency selectivity accompanying hearing losses of cochlear origin? To answer this question, two sets of stimuli were synthesized: whispered exemplars of “bet”, “debt”, “get” (the initial set) and “bib”, “bid”, “big” (the final set). Spectral contrast was increased by narrowing the bandwidths of the first five formants; contrast was reduced by broadening their bandwidths. Subjects were adults either with audiometrically-normal hearing or with moderate hearing impairments of cochlear origin. For both groups of listeners, accuracy of identification decreased as formant bandwidth increased. In the mean data of both groups for syllable-final identification, there was a tendency for accuracy to increase when format bandwidths were set to half their nominally normal values. Psychoacoustical measures of frequency selectivity correlated robustly with accuracy of identification, but again only for final consonants. These results suggest that factors in addition to reduced frequency resolution and reduced absolute sensitivity set limits on the accuracy of speech identification in cases of cochlear hearing loss, particularly for syllable-initial consonants. Possible candidates, not explored here, are reduced temporal resolution and an increased susceptibility to backward masking. The very limited benefits for speech identification which resulted from reducing formant-bandwidths may reflect the inability of that transformation to compensate for impairments to temporal auditory processing, as well as for extreme impairments to frequency resolution.

Intelligibility of consonants in VCV fragments excised from connected speech

Confusions between pairs of intervocalic consonants excised from connected speech were investigated under several conditions of speech degradation: digital voice processing, noise, bandpass limiting. The stimuli were created by digitally extracting only the VCV portion from read sentences such as the following: “…wants to study teals and their breeding patterns.” /“…wants to study seals and their breathing patterns.” When these were presented to listeners, the distribution of the types of errors that were made, e.g., voicing, nasality, place of articulation, differed from those made on citation form syllable-initial consonants. Intervocalic consonants that were taken from word initial position scored higher initially than those taken from word medial or word final position, but the medial and final segments dropped less under mild degradations than did the initial ones. [Work supported by ONR.]

Converging sources of evidence on spoken and perceived rhythms of speech: Cyclic production of vowels in monosyllabic stress feet.

The article reviews the literature from psychology, phonetics, and phonology bearing on production and perception of syllable timing in speech. A review of the psychological and phonetics literature suggests that production of vowels and consonants are interleaved in syllable sequences in such a way that vowel production is continuous or nearly so. Based on that literature, a hypothesis is developed concerning the perception of syllable timing assuming that vowel production is continuous. The hypothesis is that perceived syllable timing corresponds to the times sequencing of the vowels as produced and not to the timing either of vowel onsets as conventionally measured or of syllable-initial consonants. Three experiments support the hypothesis. One shows that information present during the portion of an acoustic signal in which a syllable-initial consonant predominates is used by listeners to identify the vowel. Compatibly, this information for the vowel contributes to the vowel's perceived duration. Finally, a measure of the perceived timing of a syllable correlates significantly with the time required to identify syllable-medial vowels but not with time to identify the syllable-initial consonants. Further support for the proposed mode of vowel-consonant production and perception is derived from the literature on phonology. Language-specific phonological conventions can be identified that may reflect exaggerations and conventionalizations of the articulatory tendency for vowels to be produced continuously in speech.

Phonetic perception: evidence for context-dependent and context-independent processing.

In a series of experiments a selective adaptation technique was used to examine the dependencies that arise in processing phonetically relevant acoustic information in syllable-initial consonants. The pattern of results, identical across two vowel contexts, indicated that voice-onset-time specifying a voicing contrast and the spectral form of the initial transitions specifying a place of articulation contrast are processed in a mutually dependent fashion. A different pattern was revealed, however, for the processing of the spectral form of the transitions specifying a place contrast and the duration of the transitions specifying a manner contrast. Specifically, the data indicated that transition duration is processed independently of the spectral characteristics of the transitions, even though the processing of the spectral characteristics of the transitions is dependent on their duration. On the basis of these findings, the following conclusions were drawn: First, there are distinct patterns of interaction during speech processing; second, the system does not operate entirely in a context-conditioned fashion; and third, at early stages of processing the speech signal is not treated holistically, but rather undergoes analysis in terms of those acoustic dimensions that provide information about phonetic distinctions.

Organization in the perception of segmental and suprasegmental information by infants

In this study, we investigated whether infants are capable of discriminating not only differences in pitch and syllable-initial consonants but also the manner in which these components are combined. Using a modification of the high-amplitude sucking procedure, we found that three- and four-month-old infants were able to recognize rearrangements of these components, which, together with earlier findings, indicates that the infant's speech processing system is sensitive to the organization in the basic elements of human language.

Articulatory rate and perceptual constancy in phonetic perception.

The perception of syllable-initial stop consonants as voiced (/b/, /d/, /g/) or voiceless (/p/, /t/, /k/) was shown to depend on the prevailing rate of articulation. Reducing the articulatory rate of a precursor phrase causes a greater proportion of test consonants to be identified as voiced. Subsequent experiments demonstrated that this effect depends almost entirely on variation in the duration of the syllable immediately preceding the test syllable; this, the duration of the intervening silent stop closure, and the duration of the test syllable itself all influenced the identification of the stop as voiced or voiceless. Variation in the tempo of a nonspeech melody produced no effect on the perception of embedded test syllables. Those manipulations which produce the major part of the influence of rate do so not by changing the context in which the stop is perceived, but rather by changing temporal concomitants of the constriction, occlusion, and release phases of the articulation of the stop itself. For this reason, an explanation for such effects based on extrinsic timing in perception is found to be wanting. Timing should, in the main, be regarded as intrinsic to the acoustical specifications of phonetic events, a view that is compatible with recent reformulations of the problem of timing control in speech production.

Discrimination of information for manner of articulation

Infants, between the ages of 2 and 4 months, were able to discriminate small differences in the acoustic information that is sufficient to signal the adult phonetic contrast based on manner of articulation, namely, the nasal-stop distinction in syllable-initial consonants. In addition, the discriminability function for this information was found to be discontinuous, being peaked at the region of the adult phonetic boundary.

The features of the larynx: N-ary or binary?

Multivalued features have generally not been permitted on the classificatory level of representation by generative phonologists. It is found necessary, however, to posit a multivalued scalar feature "glottal width" on the classificatory level of representation in order to provide a satisfactory explanation of the diachronic tone splits conditioned by the phonation type of the syllable-initial consonants among the languages and dialects of the Tai language family in Southeast Asia. The feature "glottal width" consists of a lineraly ordered set of terms along a single physical continuum that extends from the widest open position of the glottis to the fully closed position (i.e. glottal stop). Other proposed sets of laryngeal features are tested against this evidence and found to be inadequate. A binary feature "vibrating" is also proposed within this theoretical framework.