Stop Identification Research Articles

Identification of stops in consonant sequences extracted from continuous speech

At the 114th meeting of the Acoustical Society of America, experiments on the listener's ability to identify singleton stop consonants in syllable‐initial and noninitial position, and stops in noninitial homorganic nasal‐stop clusters, were reported. The stimuli, consisting of portions of speech extracted from continuous sentences, were drawn from a corpus of about 3600 sentences spoken by over 450 talkers. This paper further investigates the effect of intervening consonants on the listener's decision. Ten listeners identified stops in clusters with semivowels. With the exception of /dr/ and /tr/ (which were confused primarily with the /ǰ,č/), the listener's performance (96.1% correct) was comparable to that of singleton stops (97.1%). Another group of listeners identified stops preceded by /s/ or /z/. The listener's performance (overall 88.3%) was dependent upon the identity of the fricative and whether or not the stop was in a cluster with the preceding /s/. Results will be compared with singleton stop identification tasks. [Work supported by DARPA under Contract No. N00014‐82‐K‐0727, monitored through the Office of Naval Research.]

Identification of stop consonants from continuous speech in limited context

This paper describes a series of perceptual experiments aimed at evaluating listeners' ability to identify singleton stop consonants. The stimuli consisted of portions of speech extracted from a corpus of about 3600 sentences spoken by over 4.50 talkers. A variety of factors, such as the stress pattern, syllable position, and phonemic environment, were systematically varied to determine the extent to which these factors influence the listeners' decision. At least 20 listeners heard syllable‐initial stops in one task and nonsyllable‐initial stops in another. In each task, only the immediate surrounding context was available. Overall identification rates were better than 97% for syllable‐initial stops and 85% for the noninitial stops. In the syllable‐initial case, 75% of the errors were in voicing, predominantly voiced stops being heard as their voiceless counterparts. For the noninitial stops, 88% of the errors were also in voicing. However, in this task, most of the errors were voiceless stops heard as voiced. Almost 70% of the errors for the noninitial stops involved alveolars, whereas no particular place of articulation accounted for most of the errors for the initial stops. Factors other than syllable position will also be discussed, and comparisons will be made to other stop identification studies. [Work supported by DARPA under contract N00014‐82‐K‐0727, monitored through the Office of Naval Research.]

Perception of intervocalic stop consonants: the contributions of closure duration and formant transitions.

Acoustic analyses of vowel-consonant-vowel (VCV) utterances indicate that they generally include formant transitions from the first vowel into a period of closure (VC transitions), and transitions out of the closure into the second vowel (CV transitions). Three experiments investigated the perceptual importance of the VC transitions, the CV transitions, and the closure period in identification of medial stop consonants varying in place of articulation. Experiment 1 compared identification of members of synthetic VC and CV continua with those from VCV series made by concatenating corresponding VC and CV stimuli using various closure durations. Experiment 2 examined identification of VCV stimuli constructed with only VC, only CV, or both VC and CV transitions; again closure duration was systematically varied. Experiment 3 correlated CV and VC identification with identification of VCV stimuli. Neither closure duration nor formant transition structure (i.e., only VC, only CV, or both) had an independent effect on identification. Instead, the formant structure and closure duration together strongly affected stop identification. When both VC and CV transitions were present, the CV transitions contributed somewhat more to identification of medial stops with short closures, than the VC transitions did. With longer closure durations, neither set of transitions appeared to determine perceived place of articulation in any simple way. Overall, the data indicate that the perception of a medial consonant is more than simply a (weighted) sum of its parts.

Towards an expert system for automatic stop consonant identification

The adequacies of three sets of acoustic measurements for stop consonant recognition were assessed by examining the performance of a trained human spectrogram reader in a stop identification task. The data sets consisted principally of(1) gray‐level pictures (wideband spectrograms); (2) two‐dimensional line drawings (LPC spectra and short‐time energy contours); and (3) tables of numerical measurements (e.g., frequencies, amplitudes, and bandwidths of spectral peaks). The reader's task was to identify the initial consonant in /CVb/ syllables selected from a corpus containing all combinations of the six stop consonants /b,d,g,p,t,k/ with the six vowels /i,e,ae,a,o,u/ as spoken by three male and three female talkers. The objective of the experiment was to identify an appropriate set of measurements for use in a knowledge‐based expert system for automatic stop consonant identification. Results of the experiment will be presented and discussed in the context of this objective.

Multiple features analysis of intervocalic English plosives.

A controlled study involving a multi-feature acoustic analysis of intervocalic English plosives has been conducted for the purpose of evaluating acoustic stop features for automatic stop recognition. Both time-domain and frequency-domain features were measured via computer interaction. The resulting discrete density functions allowed for a comparative evaluation of individual (and in some instance conditional or combined) feature contributions to stop identification. This evaluation consisted of the maximum a posteriori probability of a correct identification of either the voicing mode (voiced or voiceless) or the place of articulation (labial, alveolar, or palato-velar) of a stop independent of the talker or of a limited phonetic context. These features included variations on ten acoustic features for voicing mode identification and seven for place-of-articulation identification. The data base for this study consisted of five male and five female talkers producing all permutations of the stops C epsilon /p,t,k,b,d,g/ and vowels V epsilon /i,e,a,u/ in the sentence frame "please say /h 'CVt/ again." While the results indicate that the acoustic features of burst/formant-onset frequency and voice onset time (VOT) are the two single most salient features for stop identification, several additional features are also shown to provide important redundancy for identification. The often overlooked time-domain features of "double-burst release" and "voicing during stop closure" were found to be particularly useful in providing such redundancy.

Stop identification from vocalic transition plus vowel segments of CV and VC syllables: a follow-up study.

In a recent article in the Journal [L. C. W. Pols and M. E. H. Schouten, J. Acoust. Soc. Am. 64, 1333-1337 (1978)], it was concluded that perception experiments which present CV syllables with the consonant bursts deleted invoke a "click sensation" and that this sensation has a deleterious affect on the perception of the consonants. In order to directly assess the "click sensation" hypothesis, a computer-based speech editing system was used which smooths onsets and offsets of stimuli and therefore eliminates the possibility of an acoustic click. Subjects identified voiced and voiceless stops from vocalic transition + vowel stimuli edited from CV and VC syllables. The findings were as follows: (1) Consonant identification from vocalic transition + vowel segments in VC syllables was significantly greater than that from vocalic transition + vowel segments in CV syllables; and (2) The superiority of the scores for VC vocalic transition + vowel segment was found for both voiced and voiceless stops, but it was not as great for voiced stops. Although there are differences in magnitude of findings between this study and those which employed other deletion techniques, the reliability and direction of the results were similar. The results do not support the "click sensation"hypothesis and suggest that other mechanisms must account for differences between CV and VC syllables in the perception of sound segments.

Mobility Aids for the Blind

In order for blind or partially sighted persons to get about in the typical urban environment we first must recognize what problems face the individual in the typical areas of street identification, bus stop identification and route information determination, obstacle avoidance, and safe path maintenance in such situations as the railroad crossing. Although proper initial planning and design would remove many of the problems in the first place, most cities already have created mobility obstacles that must somehow be corrected—but on a cost-effective basis. This paper outlines some of the corrective measures that could be implemented with minimum cost.

Order effect of acoustic segments of VC and CV syllables on stop and vowel identification.

The purpose of this study was to determine the importance of the vocalic transition relative to other acoustic cues in the perception of both CV and VC syllables. Subjects identified stops, /p, t, k, b, d, g/ and vowels, /i, u, 3/ from the aperiodic, aperiodic + vocalic transition, vocalic transition, and vocalic transition + vowel segments edited from VC and CV syllables. The major findings were as follows: (1) no significant difference was found in consonant identification scores between aperiodic, aperiodic + vocalic transition, and vocalic transition segments in CV syllables compared to those in VC syllables; (2) consonant identifications from vocalic transition + vowel segments in VC syllables were significantly greater than those from vocalic transition + vowel segments in CV syllables; (3) no significant difference was found in vowel identification scores between aperiodic + vocalic transition, vocalic transition + vowel, and vocalic transition segments in CV syllables compared to those in VC syllables; and (4) vowel identifications from aperiodic segments were significantly greater in CV syllables than in VC syllables. The results revealed a significant right-to-left perceptual advantage for both vowels and consonants. The findings for consonant identification emphasize the importance of the temporal order relationship between the vocalic transition and steady-state vowels in the perceptual process.

Vocalic transitions in the perception of voiceless initial stops.

Two experiments were conducted in order to test the transition dependency and integration hypotheses of speech perception. These two models emphasize the importance of vocalic transitions in stop−vowel syllables for different reasons. The transition−dependency model regards the vocalic transition as a primary cue for stop identification, and the integration model holds that the transition prevents backward masking. Nine stop−vowel monosyllables were treated, resulting in a set of (1) syllables in which the vocalic transition was deleted (Experiment 1), and (2) various nonsyllabic segments—the aperiodic portion, the aperiodic portion plus the vocalic transition, the vocalic transition, and the vocalic transition plus the vowel (Experiment 2). Recognition scores obtained for these stimuli indicate that the vocalic transition is neither a sufficient nor necessary cue for voiceless stop recognition and that the aperiodic portion of the consonant carries the heaviest perceptual load. Subject Classification: 70.30.