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PubMed1985

An approach to normalization of coarticulation effects for vowels in connected speech.

A method is proposed to reduce the ambiguity of vowels in connected speech by normalizing the coarticulation effects. The method is applied to vowels in phonetic environments where great ambiguity would be likely to occur, taking as their features the first and second formant trajectories. The separability between vowel clusters is found to be greatly improved for the vowel samples. In addition, distribution of the vowels on a feature plane characterized by this method seems to reflect their perceptual nature when presented to listeners without isolation from their phonetic environments. The results suggest that the method proposed here is useful for automatic speech recognition and help infer some possible mechanisms underlying dynamic aspects of human speech recognition.

Female↗
PubMed1985

Contextual effects on vowel duration, closure duration, and the consonant/vowel ratio in speech production.

Acoustic measurements were conducted to determine the degree to which vowel duration, closure duration, and their ratio distinguish voicing of word-final stop consonants across variations in sentential and phonetic environments. Subjects read CVC test words containing three different vowels and ending in stops of three different places of articulation. The test words were produced either in nonphrase-final or phrase-final position and in several local phonetic environments within each of these sentence positions. Our measurements revealed that vowel duration most consistently distinguished voicing categories for the test words. Closure duration failed to consistently distinguish voicing categories across the contextual variables manipulated, as did the ratio of closure and vowel duration. Our results suggest that vowel duration is the most reliable correlate of voicing for word-final stops in connected speech.

Female↗
PubMed1986

A perceptual model of vowel recognition based on the auditory representation of American English vowels.

A quantitative perceptual model of human vowel recognition based upon psychoacoustic and speech perception data is described. At an intermediate auditory stage of processing, the specific bark difference level of the model represents the pattern of peripheral auditory excitation as the distance in critical bands (barks) between neighboring formants and between the fundamental frequency (F0) and first formant (F1). At a higher, phonetic stage of processing, represented by the critical bark difference level of the model, the transformed vowels may be dichotomously classified based on whether the difference between formants in each dimension falls within or exceeds the critical distance of 3 bark for the spectral center of gravity effect [Chistovich et al., Hear. Res. 1, 185-195 (1979)]. Vowel transformations and classifications correspond well to several major phonetic dimensions and features by which vowels are perceived and traditionally classified. The F1-F0 dimension represents vowel height, and high vowels have F1-F0 differences within 3 bark. The F3-F2 dimension corresponds to vowel place of articulation, and front vowels have F3-F2 differences of less than 3 bark. As an inherent, speaker-independent normalization procedure, the model provides excellent vowel clustering while it greatly reduces between-speaker variability. It offers robust normalization through feature classification because gross binary categorization allows for considerable acoustic variability. There was generally less formant and bark difference variability for closely spaced formants than for widely spaced formants. These findings agree with independently observed perceptual results and support Stevens' quantal theory of vowel production and perceptual constraints on production predicted from the critical bark difference level of the model.

Adult↗
PubMed1986

Differential use of temporal cues to the /s/-/z/ contrast by native and non-native speakers of English.

This study examined the effect of linguistic experience on perception of the English /s/-/z/ contrast in word-final position. The durations of the periodic ("vowel") and aperiodic ("fricative") portions of stimuli, ranging from peas to peace, were varied in a 5 X 5 factorial design. Forced-choice identification judgments were elicited from two groups of native speakers of American English differing in dialect, and from two groups each of native speakers of French, Swedish, and Finnish differing in English-language experience. The results suggested that the non-native subjects used cues established for the perception of phonetic contrasts in their native language to identify fricatives as /s/ or /z/. Lengthening vowel duration increased /z/ judgments in all eight subject groups, although the effect was smaller for native speakers of French than for native speakers of the other languages. Shortening fricative duration, on the other hand, significantly decreased /z/ judgments only by the English and French subjects. It did not influence voicing judgments by the Swedish and Finnish subjects, even those who had lived for a year or more in an English-speaking environment. These findings raise the question of whether adults who learn a foreign language can acquire the ability to integrate multiple acoustic cues to a phonetic contrast which does not exist in their native language.

Cues↗
PubMed1987

Review of text-to-speech conversion for English.

The automatic conversion of English text to synthetic speech is presently being performed, remarkably well, by a number of laboratory systems and commercial devices. Progress in this area has been made possible by advances in linguistic theory, acoustic-phonetic characterization of English sound patterns, perceptual psychology, mathematical modeling of speech production, structured programming, and computer hardware design. This review traces the early work on the development of speech synthesizers, discovery of minimal acoustic cues for phonetic contrasts, evolution of phonemic rule programs, incorporation of prosodic rules, and formulation of techniques for text analysis. Examples of rules are used liberally to illustrate the state of the art. Many of the examples are taken from Klattalk, a text-to-speech system developed by the author. A number of scientific problems are identified that prevent current systems from achieving the goal of completely human-sounding speech. While the emphasis is on rule programs that drive a format synthesizer, alternatives such as articulatory synthesis and waveform concatenation are also reviewed. An extensive bibliography has been assembled to show both the breadth of synthesis activity and the wealth of phenomena covered by rules in the best of these programs. A recording of selected examples of the historical development of synthetic speech, enclosed as a 33 1/3-rpm record, is described in the Appendix.

Communication Devices for People with Disabilities↗
PubMed1988

Use of syllable-scale timing to discriminate words.

Assuming that only primitive, imperfect phonetic labeling of speech could be achieved by an automatic speech segmenter, words from several small vocabularies were identified using discriminant analysis, where the locations of prominent acoustic boundaries were combined in the optimum linear fashion. A set of two-syllable words that shared the same spelling in a weak alphabet (using categories like stop closure, fricative, vowel, etc.), but that differed in such features as which syllable was stressed, the tensity of the vowel, the identity of particular segments, etc., was selected. Discriminant analysis on the vector of six segmental boundaries achieved recognition accuracy 6.3 times better than chance. The words were produced by six talkers at two speaking tempos and measured by hand from sound spectrograms. Testing was performed on productions different from those used in training. When more confusable words (sharing the same stress pattern) were employed, performance was still five times better than chance. In a third experiment, the first two word sets were combined, and a subset of the variables (four of them) shared in common was employed for identification. This time recognition using temporal information was still able to do a reasonable job of discriminating the words. The results suggest that considerable information is available in segmental timing for identifying words even when the phonetic labeling of speech is weak.

Female↗
PubMed1988

Trading relations in the perception of /r/-/l/ by Japanese learners of English.

The role of language-specific factors in phonetically based trading relations was examined by assessing the ability of 20 native Japanese speakers to identify and discriminate stimuli of two synthetic /r/-/l/ series that varied temporal and spectral parameters independently. Results of forced-choice identification and oddity discrimination tasks showed that the nine Japanese subjects who were able to identify /r/ and /l/ reliably demonstrated a trading relation similar to that of Americans. Discrimination results reflected the perceptual equivalence of temporal and spectral parameters. Discrimination by the 11 Japanese subjects who were unable to identify the /r/-/l/ series differed significantly from the skilled Japanese subjects and native English speakers. However, their performance could not be predicted on the basis of acoustic dissimilarity alone. These results provide evidence that the trading relation between temporal and spectral cues for the /r/-/l/ contrast is not solely attributable to general auditory or language-universal phonetic processing constraints, but rather is also a function of phonemic processes that can be modified in the course of learning a second language.

Adolescent↗
PubMed1990

Jaw and lip movements of deaf talkers producing utterances with known stress patterns.

This investigation determined whether prelingually deaf talkers could correctly produce stressed and unstressed syllables across known changes in stress patterning and phonetic composition. Three deaf and three hearing adults spoke sets of homogeneous syllable strings with stress patterns that they could tap successfully with a finger. Strain gauge transduction of lower lip and jaw movement indicated that both deaf and hearing subjects produced different displacements and durations for the stressed and unstressed syllables, regardless of the stress pattern. Jaw movement did not become more variable with changes in phonetic composition of the syllables. The results show no evidence that motoric abilities (as assessed in lip and jaw movements) limit deaf talkers in producing desired stress patterns.

Adult↗
PubMed1990

Effects of postlingual deafness on speech production: implications for the role of auditory feedback.

This study investigated some effects of postlingual deafness on speech by exploring selected properties of consonants, vowels, and suprasegmentals in the speech of seven totally, postlingually deafened individuals. The observed speech properties included parameters that function as phonological contrasts in English, as well as parameters that constitute primarily phonetic distinctions. The results demonstrated that postlingual deafness affects the production of all classes of speech sounds, suggesting that auditory feedback is implicated in regulating the phonetic precision of consonants, vowels, and suprasegmentals over the long term. In addition, the results are discussed in relation to factors that may influence the degree of speech impairment, such as age at onset of deafness.

Adolescent↗
PubMed1991

Age of learning affects the authenticity of voice-onset time (VOT) in stop consonants produced in a second language.

This study examined whether Spanish-English bilinguals are able to fully differentiate Spanish and English /t/ according to voice-onset time (VOT) if they learn English as a second language (L2) in early childhood. In experiment 1, VOT was measured in Spanish words spoken by Spanish monolinguals, in English words spoken by English monolinguals, and in Spanish and English words spoken by bilinguals who learned English either as young children or as adults. As expected, the Spanish monolinguals produced /t/ with considerably shorter VOT values than the English monolinguals. Also as expected, the late L2 learners produced English /t/ with "compromise" VOT values that were intermediate to the short-lag values observed for Spanish monolinguals and the long-lag values observed for English monolinguals. The early learners' VOT values for English /t/, on the other hand, did not differ from English monolinguals' VOT. The same pattern of results was obtained for stops in utterance-medial position and in absolute utterance-initial position. The results of experiment 1 were replicated in experiment 2, where bilingual subjects were required to produce Spanish and English utterances (sentences, phrases, words) in alteration. The results are interpreted to mean that individuals who learn an L2 in early childhood, but not those who learn an L2 later in life, are able to establish phonetic categories for sounds in the L2 that differ acoustically from corresponding sounds in the native language. It is hypothesized that the late L2 learners produced /t/ with slightly longer VOT values in English than Spanish by applying different realization rules to a single phonetic category.

Adult↗
PubMed1991

The use of prosody in syntactic disambiguation.

Prosodic structure and syntactic structure are not identical; neither are they unrelated. Knowing when and how the two correspond could yield better quality speech synthesis, could aid in the disambiguation of competing syntactic hypotheses in speech understanding, and could lead to a more comprehensive view of human speech processing. In a set of experiments involving 35 pairs of phonetically similar sentences representing seven types of structural contrasts, the perceptual evidence shows that some, but not all, of the pairs can be disambiguated on the basis of prosodic differences. The phonological evidence relates the disambiguation primarily to boundary phenomena, although prominences sometimes play a role. Finally, phonetic analyses describing the attributes of these phonological markers indicate the importance of both absolute and relative measures.

Humans↗
PubMed1993

Adequacy of auditory models to predict human internal representation of speech sounds.

A long-standing question that arises when studying a particular auditory model is how to evaluate its performance. More precisely, it is of interest to evaluate to what extent the model representation can describe the actual human internal representation. Here, this question is addressed in the context of speech perception. That is, given a speech representation based on the auditory system, to what extent can it preserve phonetic information that is perceptually relevant? To answer this question, a diagnostic system has been developed that simulates the psychophysical procedure used in the standard Diagnostic-Rhyme Test (DRT). In the psychophysical procedure, the subject has all the cognitive information needed for the discrimination task, a priori. Hence, errors in discrimination are due mainly to inaccuracies in the auditory representation of the stimulus. In the simulation, the human observer is replaced by an array of recognizers, one for each pair of words in the DRT database. The recognizer used [Ghitza and Sondhi, J. Acoust. Soc. Am. Suppl. 1 87, S107 (1990)] was designed to keep errors due to the recognition procedure to a minimum, so that the overall detected errors are due mainly to inaccuracies in the front-end representation. The system provides detailed diagnostics that show the error distributions among six phonetically distinctive features. Results are given for the behavior of two speech analysis methods, a representation based on the auditory system and one based on the Fourier power spectrum, in quiet and in a noisy environment. These results are compared with psychophysical results for the same database.

Acoustic Stimulation↗
PubMed1994

Low-pass filtering in amplitude modulation detection associated with vowel and consonant identification in subjects with cochlear implants.

Temporal auditory analysis of acoustic events in various frequency channels is influenced by the ability to detect amplitude modulations which for normal hearing involves low-pass filtering with a cutoff frequency around 100 Hz and a rejection slope of about 10 dB per decade. These characteristics were established in previous studies measuring modulation transfer functions. For cochlear implant subjects, the delivery of detailed amplitude modulation information has been recently shown to result in very significant improvements in speech understanding. Several previous studies on cochlear implant subjects have reported capacities for temporal resolution rather equivalent to those of normally hearing subjects but with some notable individual differences. Recently two studies on some cochlear implant subjects indicated modulation transfer functions often quite similar to those of normal hearing but exhibiting marked individual differences in shape and absolute sensitivity. The present study compared amplitude modulation detection and phonetic recognition in a group of cochlear implant subjects to determine the extent to which the two tasks are correlated. Nine individuals who had been implanted with an Ineraid device and who demonstrated open speech understanding ranging from excellent to poor were chosen and tested in the present study. For each subject modulation transfer functions were measured at the most apical electrode and phonetic recognition of isolated vowels and intervocalic consonants was assessed. Results showed a strong correlation between the depth of high-frequency rejection in modulation transfer functions and success in vowel and consonant intelligibility. These results emphasize the importance of temporal speech features and offer perspectives for customizing signal processing in cochlear implants.

Adult↗
PubMed1994

Stimulus variability and spoken word recognition. I. Effects of variability in speaking rate and overall amplitude.

The present experiments investigated how several different sources of stimulus variability within speech signals affect spoken-word recognition. The effects of varying talker characteristics, speaking rate, and overall amplitude on identification performance were assessed by comparing spoken-word recognition scores for contexts with and without variability along a specified stimulus dimension. Identification scores for word lists produced by single talkers were significantly better than for the identical items produced in multiple-talker contexts. Similarly, recognition scores for words produced at a single speaking rate were significantly better than for the corresponding mixed-rate condition. Simultaneous variations in both speaking rate and talker characteristics produced greater reductions in perceptual identification scores than variability along either dimension alone. In contrast, variability in the overall amplitude of test items over a 30-dB range did not significantly alter spoken-word recognition scores. The results provide evidence for one or more resource-demanding normalization processes which function to maintain perceptual constancy by compensating for acoustic-phonetic variability in speech signals that can affect phonetic identification.

Female↗
PubMed1995

Further tests of the "perceptual magnet effect" in the perception of [i]: identification and change/no-change discrimination.

The present study investigated the existence of a "perceptual magnet" effect [Kuhl, Percept. Psychophys. 50, 93-107 (1991)] in a speech perception experiment. Sixteen subjects experienced in phonetics, transcribed the [i] stimuli used by Kuhl (1991) or identified the stimuli as [i] or not-[i] in experiment 1. In experiments 2 and 3, 50 adults who were not trained in phonetics, participated in an identification task requiring them to decide whether the vowel sounds they heard were the "[i] in 'peep'" or "not the [i] in 'peep'. "They also completed a "change/no change" discrimination task with standards consisting of the "prototype" [i] and other nonprototype stimuli at 67, 75, and 120 mels away from the prototype. Results from the first study showed that listeners did not identify the 120-mel token previously used by Kuhl (1991) as the nonprototype standard stimulus in discrimination experiments as [i]. Sensitivity results from experiments 2 and 3, as measured with d-prime partially supported the "perceptual magnet" hypothesis as suggested by Kuhl (1991) whereas miss results did not. Findings indicated that d-prime, a nonbiased measure of subjects' discrimination ability, better represented the perceptual magnet effect than misses alone. Thus results suggested that subjects were better able to discriminate stimuli surrounding a less "prototypical" [i] vowel as demonstrated by greater sensitivity, faster reaction times for hits and fewer number of misses. However, current results may also be explained by increased auditory resolution rather than prototype-based, "magnet" effects. It was concluded that whereas the perceptual magnet effect may exist for particular vowel categories, more data are needed to better understand the role of prototypes in speech perception.

Humans↗
PubMed1996

The representation of Japanese moraic nasals.

Nasal consonants in syllabic coda position in Japanese assimilate to the place of articulation of a following consonant. The resulting forms may be perceived as different realizations of a single underlying unit, and indeed the kana orthographies represent them with a single character. In the present study, Japanese listeners' response time to detect nasal consonants was measured. Nasals in coda position, i.e., moraic nasals, were detected faster and more accurately than nonmoraic nasals, as reported in previous studies. The place of articulation with which moraic nasals were realized affected neither response time nor accuracy. Non-native subjects who knew no Japanese, given the same materials with the same instructions, simply failed to respond to moraic nasals which were realized bilabially. When the nasals were cross-spliced across place of articulation contexts the Japanese listeners still showed no significant place of articulation effects, although responses were faster and more accurate to unspliced than to cross-spliced nasals. When asked to detect the phoneme following the (cross-spliced) moraic nasal, Japanese listeners showed effects of mismatch between nasal and context, but non-native listeners did not. Together, these results suggest that Japanese listeners are capable of very rapid abstraction from phonetic realization to a unitary representation of moraic nasals; but they can also use the phonetic realization of a moraic nasal effectively to obtain anticipatory information about following phonemes.

Humans↗
PubMed1996

The effect of segment duration on the perceptual integration of nasals for adult and child speech.

It has been hypothesized that the acoustic properties within a temporal domain of 10 to 30 ms of boundaries between speech sounds contain significant information on the phonetic features of segments, and that these cues are perceptually integrated by the auditory system [Stevens, Phonetic Linguistics: Essays in Honor of Peter Ladefoged (Academic, London, 1985)]. The purpose of the current research was to examine the effects of stimulus duration adjacent to speech sound boundaries on the perceptual integration of place of articulation of nasals before and after disruption of the abrupt changes in spectra between the murmur and transition. In experiment I, three children, aged 3, 5, and 7 years, and an adult female and male produced consonant-vowel (CV) syllables consisting of [m] and [n] in four vowel contexts, [i ae u a]. Approximately 25-ms segments of the murmur and vowel transition adjacent to the speech sound boundary were digitally removed from these productions. Intervals of silence ranging from 0 to 2000 ms, which can potentially perturb integration processes, were inserted between these segments. The stimuli were then presented to adult listeners for the identification of the nasal. The main findings revealed a consistent decline in identification with gap durations up to 150 ms across speakers and vowel context. However, the adult labial feature was resistant to perceptual change as a function of gap duration. This result appeared to relate to formant transition duration, and not to response bias. In experiment II, stimuli with durations shorter than those in experiment I were further analyzed for adult speakers. The main finding was a quantification of the acoustic segment duration needed for perceptual integration of the murmur and vowel transition. Across both experiments, the results reveal a decline in the identification of both alveolar and labial nasals within a time interval mediated by short-term auditory memory, and that the duration of the acoustic segment needed for perceptual integration is longer for [n] than [m].

Adult↗
PubMed1997

Speech perception as pattern recognition.

This work provides theoretical and empirical arguments in favor of an approach to phonetics that is called double-weak. It is so called because it assumes relatively weak constraints both on the articulatory gestures and on the auditory patterns that map phonological elements. This approach views speech production and perception as distinct but cooperative systems. Like the motor theory of speech perception, double-weak theory accepts that phonological units are modified by context in ways that are important to perception. It further agrees that many aspects of such context dependency have their origin in natural articulatory processes. However, double-weak theory sides with proponents of auditory theories of phonetics by accepting that the real-time objects of perception are well-defined auditory patterns. Because speakers find ways to "orderly" output conditions" (Sussman et al., 1995), listeners are able to successfully decode speech using relatively simple pattern-recognition mechanisms. It is suggested that this situation has arisen through a stylization of gestural patterns to accommodate real-time limits of the perceptual system. Results from a new perceptual experiment, involving a four-dimensional stimulus continuum and a 10-category/hVC/response set, are shown to be largely compatible with this framework.

Attention↗