VC Syllables Research Articles

Identification of vowels in CV and VC syllables

Previous research [W. Strange, R. Verbrugge, and D. Shankweiler, “Consonant environment specifies vowel identity,” Status Rep. Speech Res. Haskins Lab. SR 37/38, 209–216, (1974}] showed that isolated steady‐state vowels were misidentified far more often than were vowels produced by the same talkers in a fixed consonant frame, /p‐p/. Phenological and acoustic hypotheses suggest opposite differential contributions of the initial and final consonants in aiding vowel identification. In the present study, we compared the identification of nine American English vowels spoken by six adult talkers in four conditions: /p/‐vowel, vowel‐/p/, /p/‐vowel‐/p/, and isolated vowels. Isolated vowels and vowels in /p/‐vowel syllables yielded approximately twice as many errors as vowels in the /p/‐vowel‐/p/ condition; vowels in vowel‐/p/ context were identified almost as well as in the /p/‐vowel‐/p/ syllables. Errors for individual vowels in each of the conditions were analyzed to determine whether phonological constraints could accounts for the results. [Work supported by NIMH, NICHD.]

Phoneme errors on a nonsense syllable test

In an effort to construct a test which permits detailed analysis of the phonemic errors made by naive hearing-impaired individuals under conditions of hearing aid use, we have developed a closed response nonsense syllable test consisting of CV, VC, and CVC syllables organized into modules. The modules differ with respect to the class of consonants represented, the consonant position within the syllable, and the vowel context (/i/, /a/, or /u/). Responses to syllables within a given module are limited to syllables within the same module. The response foils (which correspond to all the syllables within a module) include the most frequent perceptual confusions reported for normal-hearing and hearing-impaired individuals. The resulte of tests administered to hearing-impaired individuals under difficult listening conditions indicate a pattern of errors consistent with those reported by previous investigators, including (1) greater errors on final than on initial consonants; (2) greater errors on unvoiced than on voiced consonants; and (3) a dependence of consonant identification on vowel context. [Research supported by NINCDS.]

Perception of vowel and syllable duration in VC and CVC syllables

Results of previous experiments [Raphael et al., “Vowel information conveyed by consonant transitions,” J. Acoust. Soc. Am. 57, Suppl. No. 1, S49(A) (1975)] indicate that perceptual cues for initial consonants are, in part, incorporated by listeners into their estimates of vowel/syllable duration when they make voicing judgments of word‐final consonants. In the present experiment the inventory of initial consonants tested was expanded to include those containing voiced transitions of varying durations, both contiguous and noncontiguous with those of the following vowel; aperiodic transitions; and transitionless noise. Results indicate that listeners incorporate more of the duration of initial consonant cues when they are conveyed by formants than when they are not; when the formants are periodic rather than aperiodic; and when the formants are contiguous with those of the following vowel than when they are not. The degree of incorporation was also found to vary directly with the duration of the formant transitions.

Vowel information conveyed by consonant transitions

It is well established that information specifying place and manner of articulation for stop consonants is conveyed by the transitions of the vocalic segment. The purpose of this study was to determine whether these transitions also convey information about vocalic duration. Accordingly, four series of synthetic stimuli were generated: three of the series consisted of CVC syllables in which the initial C transitions were set at durations of 30, 60, and 90 msec; a fourth series consisted of VC syllables. In all four series the duration of the steady-state portion of the vowel was varied from 10 to 190 msec in 10-msec steps. The final consonant was synthesized with transitions appropriate for an unreleased /d/. Listeners were asked to identify the final consonant as voiced or voiceless (/t/ or /d/). For vowel steady states of equal duration, the addition of initial consonant transitions caused a shift in the perceptual boundary between the voiced and voiceless categories. This outcome suggests how a portion of the initial “consonant” transition is used by the listener in computation of “vowel” duration, at least for the purpose of cueing the voicing distinction in final position.

Effect of speech-sound cue on ear asymmetry in dichotic listening.

Under conditions of dichotic presentation, subjects were asked to identify (1) the vowels /i, e, o/ produced in isolation and in CV syllables, (2) the voiceless stops /p, t, k/ produced in CV syllables and from consonant-noise cues spliced from CV syllables, and (3) the voiced stops /b, d, g/ from consonant-noise cues and initial formant transition cues spliced from CV syllables and from final formant transition cues spliced from VC syllables. The same stimuli were also presented monaurally with continuous contralateral noise and monaurally with pulsed contralateral noise. Under the dichotic condition, right-ear advantages were found for stops identified from voiced consonant-noise cues (52.2 % v. 46.0%), from voiceless consonant-noise cues (71.2% v. 61.0% and from CV syllables (76.6% ν. 58.7%). The differences between ears were negligible for the vowel and formant transition stimuli. There was evidence of ear dominance under the pulsed contralateral noise condition which was similar to that found for the dichotic condition. Results did not support the encoded hypothesis that right-ear dominance is dependent on formant transition cues but did support the hypothesis that right-ear dominance increases as the similarity of the competing stimuli increases.

The Effect of Delayed Channel on the Perception of Dichotically Presented VC Syllables

Subjects were asked to identify pairs of dichotically asynchronous (by 0–180 msec) vowel-stop consonant syllables (VCs). Results were compared to those obtained in a previous study in which the essentially temporally reversed versions of these syllables (i.e., CVs) were used [R. J. Porter, Jr., J. Acoust. Soc. Am. 54, 286(A) (1973)]. As has been found in the case of CVs, the lagging member of the VC pair was more accurately identified than was the leading (“lag effect”). An interesting aspect of the VC data was, however, that the maximal lag effect was seen at a 90-msec syllable onset asynchony rather than the 60-msec observed for CVs. These results extend the generality of the lag effect and suggest that the processing of VCs may have a different temporal course than that for CVs. [Work supported in part by NIH Grant Funds.]

Different memory functions for consonants and vowels

Different memory functions were obtained for consonants (C) and vowels (V) in a serial recall task. In general, the most recently heard vowels in a sequence were easier to recall than the most recently heard consonants. This effect was observed for auditorily presented sequences of CV or VC syllables, but was not observed for visually presented stimuli. The results were explained in terms of a limited capacity acoustic storage in which vowels are preserved longer than consonants. Retrieval of the last vowels from this storage was presumed to cause the vowel recency effect.

Coarticulation Effects in the Identification of Final Plosives

In a comparison of the relative contributions of releases and formant transitions to the correct identification of final plosive consonants, Wang [JSHR 2, 66–73 (1959)] found little difference between identification scores of released final /p t k/ and final /p t k/ whose releases had been eliminated by tape-cutting. The former ranged between 90 and 98%, the latter between 73 and 85%. The present investigation compares the perception of released final /p t k/ (following the vowels /i æ a u/) with the perception of final /p t k/ derived from VCV utterances (in which C = /p t k/ and V = /i æ a u/) from which both the second vowel and the consonant release were deleted by tape-cutting. In such VC syllables, the transition to the consonant is modified by the anticipation of the following vowel. For all consonants combined, listeners achieved correct scores of 80.67% for released and 39.00% for unreleased final plosives. The greatest number of misidentifications were associated with /a/. It appears that the anticipation of a following /a/ produces changes in transitions that prevent correct identification of the consonant without the presence of a release. By comparison, initial plosives and plosives derived from VCV utterances by the deletion of the initial vowel were equally easily identifiable: listeners achieved 89.22% correct identification under both conditions.

Relation of intraoral air pressure to oral cavity size.

The purpose of this study was to investigate whether the size of the oral cavity of a speaker was related to pressures occurring in the mouth during speech. Of the three previous studies that considered size and pressure, two report a positive relationship and one found no relationship. Six young adult males were selected as subjects on the basis of cavity dimensions obtained from measurements of lateral headplates and molar widths. Each repeated CV and VC syllables composed of /t/, /d/ and /n/, and /i/ and /a/. These syllables were produced at two relative intensity levels and at two rates of utterance. Pressure measures obtained during repetition of the speech sample showed no systematic trends associated with cavity size, different vowels, rates of utterance, or syllabic position. Mean pressure differences were found between consonants and relative intensity levels.

Relation of Intraoral Air Pressure to Oral Cavity Size

The purpose of this study was to investigate whether the size of the oral cavity of a speaker was related to pressures occurring in the mouth during speech. Of the three previous studies that considered size and pressure, two report a positive relationship and one found no relationship. Six young adult males were selected as subjects on the basis of cavity dimensions obtained from measurements of lateral headplates and molar widths. Each repeated CV and VC syllables composed of /t/, /d/ and /n/, and /i/ and /a/. These syllables were produced at two relative intensity levels and at two rates of utterance. Pressure measures obtained during repetition of the speech sample showed no systematic trends associated with cavity size, different vowels, rates of utterance, or syllabic position. Mean pressure differences were found between consonants and relative intensity levels.

Perception of segments of VCCV utterances.

Perceptual confusions among Swedish consonants in VC and CV syllables are investigated. The stimuli were produced by splitting natural VCCV utterances in two halves at various points in time. The initial and final stimuli so obtained were used for two separate listening tests. The perceptual errors associated with the various VC and CV stimuli of any given VCCV utterance are analyzed with respect to the manner, place, and voicing features of the intervocalic consonant. Explanations of these errors in terms of acoustic and linguistic properties of the stimuli are attempted.

AIR FLOW DURING THE PRODUCTION OF SELECTED CONSONANTS.

The rate of air flow during the production of selected consonant sounds in both CV and VC syllables was studied. It was found that in the case of both CV and VC utterances the absence of voicing for a given consonant was associated with a greater rate of air flow than during the production of its voiced cognate and that the flow rates for stops, fricatives, and vowel-like sound groupings decrease in that order. It was also learned that the production of terminal consonants was more variable with regard to flow rate than were initial consonants.

Word Intelligibility of Time Compressed Speech

By sampling, compressing, abutting, storing, and speed reduction, Fairbanks and associates have shown that comprehension is good for: (1) connected speech compressed 50% (0.5) in time, and (2) a single PB list compressed up to 0.15. In 1929, Fletcher and associates using turntable speedup with its attendant frequency distortion found that CV, VC, and CVC syllables dropped rapidly in intelligibility at speedup corresponding to time reductions of 0.8 (down about 30% at 0.7). In one case a complex technique using simple language showed great advantage. In the other case a simple technique showed limited advantage using difficult speech material. In our work on message (simple language) storage schemes, the desirability of obtaining time compressed speech with simple modifications of existing equipment has become evident. Preliminary experimental data show that by using speedup of tape-recorded speech, numbers, and flight phrases can tolerate time compressions of 0.6 without serious loss in intelligibility, and PB words lose only 5% in intelligibility with a time compression of 0.7.