Stop Closure Duration Research Articles

Psychoacoustic model of categorical perception for speech and nonspeech continua

The model assumes: (1) that categorization of a stimulus continuum xl,xi+1…,xn is made according to whether the stimuli fall above or below a decision “boundary,” xB, i < B < n; that discrimination between any two stimulus values, xp, xr, of the continuum is based on the physical parameter φ, where φ = |xp − xr|/|xr − xB|; xp, is the member of the stimulus pair that is proximal to the boundary, and xr the one that is remote from it. That is, discrimination is based on the distance between the pair of stimuli, proportional to the distance between the boundary and the remote stimulus of the pair. For both speech and nonspeech continua it is found that, given a distance |xp − xr|, the parameter φ reaches a sharp maximum for stimuli near the boundary, xB, and decreases monotonically as the distance between the remote stimulus of the pair and the boundary increases. The model was used to predict discrimination data for VOT [Wood, J. Acoust. Soc. Am. 60, 1381–1389 (1976); Elman, J. Acoust. Soc. Am. 65, 190–207 (1979)], onset of F2 transition and duration of stop closure [Elman, ibid.), and noise‐buzz sequences [Miller et al., J. Acoust. Soc. Am. 60, 410–417 (1976)]. For most of these data, discriminability appeared to be an increasing function of φ. A corollary of the model is that enhanced discriminability around the boundary is a consequence of the listener adopting such boundary, rather than vice versa. [Supported by NRC Postdoctoral Fellowship to the author.]

Oral sensory and temporal articulatory changes as a result of lateral auditory interruptions during speech

Lingual vibrotactile thresholds were obtained for 10 normal subjects under four different conditions: (1) bilateral auditory masking during reading, (2) right ear auditory masking during reading, (3) left ear auditory masking during reading, (4) no auditory masking during reading. Baseline thresholds were obtained prior to any exposure to masking. To investigate changes in the articulatory patterns of the subjects under masking conditions, four acoustic measurements were obtained from a test word embedded in a stimulus sentence: (1) stop closure duration, (2) voice onset time, (3) vowel duration, (4) duration of final stop closure. The different types of auditory disruptions during speech production resulted in a decrease in lingual sensitivity as well as temporal reorganization of articulatory speech patterns. Although fluctuations were observed in speech segment measurements during masking conditions, laterality of masking appears to have no effect on temporal articulatory speech patterns.

The influence of tempo on stop closure duration as a cue for voicing and place

The closure interval of post-stress medial stops varies in duration due to phonological voicing and place of articulation, as well as speaking tempo. In this experiment the closure duration of the medial stop in rabid was varied over a range of 10 to 120 ms with no glottal pulsing during the closure. Embedded after fast and slow carrier sentences, the variants were identified as ratted, rabid, or rapid. The locus of the perceptual boundary between /b/ and flap at about 30 ms was not significantly influenced by the tempo of the carrier, while the locus of the /b/–/p/ boundary at 75 ms moved nearly 10 ms toward shorter values in the fast carrier sentence. These results, interpreted in terms of constraints on speech production, were taken to imply that closure duration as a voicing cue must be defined relative to speaking tempo. The flap effect suggests that closure duration can sometimes be a decisive cue to place of articulation capable of overriding even naturally produced spectral information.

The reliability of closure features as cues to medial stop voicing in English

The evidence that closure duration is a cue to the voicing of medial stops in English trochees is as convincing as any we have for other acoustic features considered to be factors governing the linguistic interpretation of speech signals. Measurements of natural speech show /b/ closures to be regularly shorter than /p/ closures in words such as rabid rapid, and there are experimental data to indicate that this difference has perceptual/phonetic significance. Another closure feature, glottal pulsing, also plays a role in the /b/-/p/ distinction in medial position. New data gathered to test the reliability of these two features as cues to the intelligibility of naturally produced tokens of rabid rapid indicate (1) stop closure duration does not suffice to separate /b/ from /p/ across speakers, (2) the phonetic effect of manipulating silent “closure” differs greatly for different tokens of the source word produced by a single speaker, and (3) the effect of replacing buzz with silence in natural tokens of rabid is similarly unpredictable. Thus it appears that neither the duration nor the acoustic nature of the closure is sufficient to predict listeners' phonetic interpretations of the acoustic segment corresponding to the interval of articulatory occlusion. [Supported by NICHHD to Haskins Laboratories.]

Relative duration of stop closure and fricative noise across speaking rate

Words distinguished by a fricative-affricate contrast (dish-ditch and lash-latch) were produced in sentence contexts by native English speakers at five successively increasing speaking rates, from their slowest natural rate to their fastest rate possible without misarticulation. Durations of stop closures and fricative noises in the affricate cases, or fricative noises alone in the fricative cases, were measured from oscillograms. Least mean-squares lines relating durations of these acoustic segments to sentence duration were fitted to these data. Slopes of these functions were generally smaller for stop closures than for fricative noises, indicating that stop closures are more stable in duration across speaking rate than are fricative noises. The results are related to recent perceptual studies of the fricative-affricate distinction [e.g., A. M. Liberman, B. H. Repp, T. Eccardt, and D. Pesetsky, J. Acoust. Soc. Am. 62, S78(A)(1977)]. [Work supported by NINCDS and NICHD.]

Larynx height and intraoral air pressure during voiced stop production

Transglottal airflow is necessary for voicing. During complete oral closure, however, the capacity of the vocal tract to absorb this airflow is insufficient for the voiced stop closure durations commonly observed in speech. Some additional mechanism(s) to absorb glottal airflow must be present, and several have been suggested. This paper focuses on the hypothesis that larynx lowering is one such mechanism. To test this hypothesis, simultaneous larynx height and intraoral air pressure data were recorded for intervocalic /p, b/. Differences in the findings for the voiced and voiceless stop consonants will be evaluated.

Laryngeal timing constraints in plosive‐vowel and fricative‐vowel syllables, or: Is VOT really the best measure of glottal‐supraglottal timing?

Voice‐onset time (VOT) is generally defined as the time interval between release of an occlusive consonant and the onset of vocal‐cord vibration. This description, however, does not allow a simple comparison of glottal‐supraglottal timing between syllables initiated with stop and fricative manners of articulation, since the time of release associated with fricative is less well defined than that associated with stops. We compare glottal‐supraglottal timing across consonant manner of articulation by normalizing the duration of selected target utterances spoken in a sentence frame by 15 subjects, and deriving a measure which expresses the timing of glottal‐supraglottal events relative to the duration of a potential unit of articulatory encoding, viz., the syllable. Additional motivation for developing an alternative measure to VOT comes from preliminary data reported by Umeda and Coker [J. Phonetics 2, 1–5 (1974)], which suggests that stop closure duration and VOT are not independent in connected speech. We...

How accurately must a speaker time his articulations?

Native speakers of a language can detect quite small departures from correct timing in the production of a sentence, which implies that they understand the rules used by the speaker to determine the timing of his articulations. In order to find out what the temporal constraints are on the speaker, an experiment was designed to measure the just noticeable difference (JND) for phoneme duration in natural speech. The stimuli were produced by an electronic equivalent of tape cutting and splicing. The incremental and decremental JND's were measured for the duration of the closure interval of a/p/, in initial position and in intervocalic position, in a stressed and an unstressed syllable, and for the duration of, if necessary, a stressed and an unstressed vowel. JND's were also measured for stimuli in which the duration of a stop and an adjacent vowel were altered simultaneously in opposite directions. 1) The results are not compatible with Weber's law. 2) Subjects were generally more sensitive to changes in vowel duration than to changes in stop-closure duration. 3) Subjects were no more sensitive to changes in the duration of a phoneme when the change was compensated in the following phoneme than when it was not compensated.