Identification Of Stop Consonants Research Articles

Identification of stop consonants produced by an acoustically-driven model of a child-like vocal tract

A model of a child-like vocal tract has been developed such that the deformation patterns superimposed on a vowel substrate to generate coarticulated consonants are specified by a time-varying set of directional shifts in the first three resonance frequencies. These deflection patterns are denoted as a combination of three numbers each of which can vary between -1 and 1; a negative value implies a downward shift in a resonance frequency whereas an upward shift results for positive value. For example, a “bilabial” consonant specified as [-1,-1,-1] would be transformed via calculations of acoustic sensitivity functions to a time-varying vocal tract shape that presents the expected constriction at the lips, but also modifies other parts of the vocal tract that may be necessary for producing the appropriate formant transitions into and out of the consonant. Using this model, three sets of 30 VCV utterances were generated in which the values of deflection patterns were set to produce vocal tract shapes that hy...

Perception of voicing and place of articulation in labial and alveolar English stop consonants

AbstractDistinctive features define a multidimensional structure that must be implemented in speech production and perception. A multilevel Gaussian General Recognition Theory model is presented as a model of multidimensional feature perception. The model is fit to data from three experiments probing identification of noise-masked, naturally-produced labial and alveolar English stop consonants [p], [b], [t], and [d] in onset (syllable-initial) and coda (syllable-final) position. The results indicate systematic perceptual deviations from simple place and voicing structure in individual subjects and at the group level. Comparing onset and coda positions shows that syllable position modulates the deviation patterns, and comparing speech-shaped noise and multi-talker babble indicates that deviations from simple feature structure are reasonably robust to variation in noise characteristics. Possible causes of the observed perceptual confusion patterns are discussed, and extensions of this work to studies of feature structure in speech production and investigation of non-native speech perception are briefly outlined.

Contextual influences on speech perception in developmental populations

A major goal of speech perception research has been to describe how listeners recognize individual consonants and vowels from the speech stream given rampant acoustic-phonetic variability in their instantiation. Findings in healthy adults indicate that listeners achieve perceptual stability, at least in part, by dynamically adjusting phonetic boundaries to accommodate contextual influences in speech production. The current work examines the developmental trajectory of such functional plasticity in typically developing children. Across two experiments, we examined the influence of speaking rate and place of articulation on stop consonant identification. Stimuli consisted of three voice-onset-time continua: “goal” to “coal” at a fast speaking rate, “goal” to “coal” at a slow speaking rate, and “bowl” to “pole” at a slow speaking rate. The results showed that 8-10-year-old children are sensitive to how these contextual influences pattern in speech production. Specifically, the identification responses indicated that the voicing boundary was located at longer VOTs for the slow compared to the fast speaking rate continuum and for the velar compared to the labial continuum. These findings suggest that perceptual sensitivity to contextual influences in speech production emerges early in development, illustrating a critical role for functional plasticity toward the healthy end-state system.

Effects of variation on processing of word-medial consonants

The present study investigates processing of variation in word-medial stops and the role of this variation in phoneme recognition. Variation in word-medial stops has been shown to influence lexical access, but it is unclear whether this variation also affects recognition at the phoneme level [Tucker, J. Phonet., 39, (2011), 312–318]. A phoneme monitoring task is used to investigate the role of production variation in the identification of word-medial stop consonants. Following Warner and Tucker [J. Acoust. Soc. Am. 130, (2012), 1606–1617], the stimuli comprise English nonwords with target consonants [b], [p], [d], [t], [g], [k] in an intervocalic post-stress position produced with a range of production variation. This variation was grouped into three sets including groups at each extremes and a group in the middle of the range. The acoustic characteristics of the stops, which reflect this variation (e.g., consonant duration and intensity difference) were extracted and used to model the reaction times collected during the phoneme monitoring experiment. The reaction times were statistically modeled using a linear mixed-effects regression. Models of spoken word recognition and models of lexical storage are used to interpret the results and the contribution of the results to our understanding of these models is discussed.

Masker location uncertainty reveals evidence for suppression of maskers in two-talker contexts

In many natural settings, spatial release from masking aids speech intelligibility, especially when there are competing talkers. This paper describes a series of three experiments that investigate the role of prior knowledge of masker location on phoneme identification and spatial release from masking. In contrast to previous work, these experiments use initial stop-consonant identification as a test of target intelligibility to ensure that listeners had little time to switch the focus of spatial attention during the task. The first experiment shows that target phoneme identification was worse when a masker played from an unexpected location (increasing the consonant identification threshold by 2.6 dB) compared to when an energetically very similar and symmetrically located masker came from an expected location. In the second and third experiments, target phoneme identification was worse (increasing target threshold levels by 2.0 and 2.6 dB, respectively) when the target was played unexpectedly on the side from which the masker was expected compared to when the target came from an unexpected, symmetrical location in the hemifield opposite the expected location of the masker. These results support the idea that listeners modulate spatial attention by both focusing resources on the expected target location and withdrawing attentional resources from expected locations of interfering sources.

Relation of vocal tract shape, formant transitions, and stop consonant identification.

The present study was designed to investigate the relation of formant transitions to place-of-articulation for stop consonants. A speech production model was used to generate simulated utterances containing voiced stop consonants, and a perceptual experiment was performed to test their identification by listeners. Based on a model of the vocal tract shape, a theoretical basis for reducing highly variable formant transitions to more invariant formant deflection patterns as a function of constriction location was proposed. A speech production model was used to simulate vowel-consonant-vowel (VCV) utterances for 3 underlying vowel-vowel contexts and for which the constriction location was incrementally moved from the lips toward the velar part of the vocal tract. These simulated VCVs were presented to listeners who were asked to identify the consonant. Listener responses indicated that phonetic boundaries were well aligned with points along the vocal tract length where there was a shift in the deflection polarity of either the 2nd or 3rd formant. This study demonstrated that regions of the vocal tract exist that, when constricted, shift the formant frequencies in a predictable direction. Based on a perceptual experiment, the boundaries of these acoustically defined regions were shown to coincide with phonetic categories for stop consonants.

Improvement of consonant identification in noise by spectro-temporal enhancement.

Our previous studies have shown that perception of vowels and consonants in long-term speech-shaped noise (LTSSN) by listeners with normal and impaired hearing is improved significantly by spectro-temporal enhancement resulting from modifications in the spectral modulation domain. The present study manipulated several parameters of enhancement processing including length of the analysis window and size of fast Fourier transform (FFT) analysis to determine which parameters produce the greatest improvement in stop consonant identification in the presence of LTSSN and cafeteria noise for normal-hearing listeners. The speech signals were presented at 70-dB sound pressure level and the signal-to-noise ratio was varied in fixed steps. Results indicated that identification of stop consonants increased by about 10 percentage points in LTSS noise and by about 25 percentage points in cafeteria noise when the length of analysis window was 200 ms and the FFT size was 512 points. Subsequent acoustic analyses showed that such perceptual improvement may be due to enhancement of formant transitions relative to background competition.

Pattern Playback revisited: Unvoiced stop consonant perception

Among the most influential publications in speech perception is Liberman, Delattre, and Cooper's [Am. J. Phys. 65, 497-516 (1952)] report on the identification of synthetic, voiceless stops generated by the Pattern Playback. Their map of stop consonant identification shows a highly complex relationship between acoustics and perception. This complex mapping poses a challenge to many classes of relatively simple pattern recognition models which are unable to capture the original finding of Liberman et al. that identification of /k/ was bimodal for bursts preceding front vowels but otherwise unimodal. A replication of this experiment was conducted in an attempt to reproduce these identification patterns using a simulation of the Pattern Playback device. Examination of spectrographic data from stimuli generated by the Pattern Playback revealed additional spectral peaks that are consistent with harmonic distortion characteristic of tube amplifiers of that era. Only when harmonic distortion was introduced did bimodal /k/ responses in front-vowel context emerge. The acoustic consequence of this distortion is to add, e.g., a high-frequency peak to midfrequency bursts or a midfrequency peak to a low-frequency burst. This likely resulted in additional /k/ responses when the second peak approximated the second formant of front vowels. Although these results do not challenge the main observations made by Liberman et al. that perception of stop bursts is context dependent, they do show that the mapping from acoustics to perception is much less complex without these additional distortion products.

Effects of Stimulus Presentation Level on Stop Consonant Identification in Normal-Hearing and Hearing-Impaired Listeners

The purpose of the present study was to determine whether varying the presentation level of stop consonant stimuli resulted in similar phonetic boundary shifts for listeners with normal and impaired hearing. Sixteen normal-hearing and 16 hearing-impaired listeners categorized synthetic speech stimuli as /b/, /d/, or /g/. The onset frequency of F2 varied from 900 to 2300 Hz (100-Hz steps), and the presentation level varied from 92 to 62 dB SPL (10-dB steps) for each stimulus presentation. Hearing-impaired listeners had significantly more missing boundary values than normal-hearing listeners; however, the correlation between the number of missing boundary values and hearing sensitivity was not significant. Comparison of boundary shift with level demonstrated that hearing-impaired listeners had a smaller boundary shift with increasing level than normal-hearing listeners. The amount of boundary shift was not correlated with audibility. The results of the current study suggest that increasing the presentation level of a signal does not result in performance similar to that of listeners with normal hearing.

Age differences for stop-consonant and vowel perception in adults.

The purpose of this study was to determine the role of static, dynamic, and integrated cues for perception in three adult age groups, and to determine whether age has an effect on both consonant and vowel perception, as predicted by the "age-related deficit hypothesis." Eight adult subjects in each of the age ranges of young (ages 20-26), middle aged (ages 52-59), and old (ages 70-76) listened to synthesized syllables composed of combinations of [b d g] and [i u a]. The synthesis parameters included manipulations of the following stimulus variables: formant transition (moving or straight), noise burst (present or absent), and voicing duration (10, 30, or 46 ms). Vowel perception was high across all conditions and there were no significant differences among age groups. Consonant identification showed a definite effect of age. Young and middle-aged adults were significantly better than older adults at identifying consonants from secondary cues only. Older adults relied on the integration of static and dynamic cues to a greater extent than younger and middle-aged listeners for identification of place of articulation of stop consonants. Duration facilitated correct stop-consonant identification in the young and middle-aged groups for the no-burst conditions, but not in the old group. These findings for the duration of stop-consonant transitions indicate reductions in processing speed with age. In general, the results did not support the age-related deficit hypothesis for adult identification of vowels and consonants from dynamic spectral cues.

Contrast effects do not underlie effects of preceding liquids on stop-consonant identification by humans.

Contrast effects do not underlie effects of preceding liquids on stop-consonant identification by humans.

Enhancing the speech envelope of continuous interleaved sampling processors for cochlear implants.

A new method to code the speech envelope in continuous interleaved sampling (CIS) processors for cochlear implants is proposed. In this enhanced envelope, the rapid adaptation seen in the response of auditory nerves to sound stimuli is incorporated. Two strategies, one using the standard envelope (CIS) and one using the enhanced envelope (EECIS), were tested perceptually with six postlingually deafened users of the LAURA cochlear implant. The tests included identification of stop consonants in three different vowel contexts and monosyllabic consonant-vowel-consonant (CVC) words. Significant improvements in correct identification scores were observed for stop consonants in intervocalic /a/ context (p = 0.026): average results varied from 46% correct for CIS to 55% for EECIS. This improvement was mainly due to the better transmission of place of articulation. The differences in identification scores for stop consonants in /i/ and /u/ context were not significant. The identification scores for the medial vowels of the CVC words were significantly higher when the EECIS strategy was used: average results increased from 39% correct to 46% correct (p = 0.018). No significant differences were observed between the results for initial and final consonants of the CVC words. The present results demonstrate that the inclusion of the rapid adaptation in the speech processing for cochlear implants can improve speech intelligibility.

General contrast effects in speech perception: effect of preceding liquid on stop consonant identification.

When members of a series of synthesized stop consonants varying acoustically in F3 characteristics and varying perceptually from /da/ to /ga/ are preceded by /al/, subjects report hearing more /ga/ syllables relative to when each member is preceded by /ar/ (Mann, 1980). It has been suggested that this result demonstrates the existence of a mechanism that compensates for coarticulation via tacit knowledge of articulatory dynamics and constraints, or through perceptual recovery of vocal-tract dynamics. The present study was designed to assess the degree to which these perceptual effects are specific to qualities of human articulatory sources. In three experiments, series of consonant-vowel (CV) stimuli varying in F3-onset frequency (/da/-/ga/) were preceded by speech versions or nonspeech analogues of /al/ and /ar/. The effect of liquid identity on stop consonant labeling remained when the preceding VC was produced by a female speaker and the CV syllable was modeled after a male speaker's productions. Labeling boundaries also shifted when the CV was preceded by a sine wave glide modeled after F3 characteristics of /al/ and /ar/. Identifications shifted even when the preceding sine wave was of constant frequency equal to the offset frequency of F3 from a natural production. These results suggest an explanation in terms of general auditory processes as opposed to recovery of or knowledge of specific articulatory dynamics.

Relational perception of formants and stop consonants: Evidence from missing first formant stimuli

If the first formant (F1) is missing, does the listener treat the second formant (F2) as the effective ‘‘F1’’ or does he/she substitute a default value for F1? Is stop consonant identification dictated by relational or absolute formant frequencies (e.g., locus theory)? To answer these questions, an experiment was carried out in which subjects identified synthetic consonant–vowel (CV) stimuli whereF 1 had a transition that rose into the vowel, had no transition (i.e., a flat transition), or was absent. Listeners identified stimuli with a rising F1 transition as either /ba/ or /da/ depending on the F2 transition, and stimuli with no F1 transition as /a/. For stimuli where F1 was absent and F2 had a rising transition, listeners perceived either /ba/ or /da/ depending on the F3 transition; and for stimuli with F1 absent and no F2 transition, listeners perceived /a/. Thus preliminary findings suggest that when F1 is missing, subjects do indeed treat F2 as ‘‘F1,’’ and respectively, F3 as ‘‘F2,’’ leading to the conclusion that stop consonant identification is not dictated by absolute formant frequencies, but uses relative measures. The results have implications for models of stop consonant perception. [Work supported by NIH grant DC00194-02.]

Stop consonant perception in 3‐ and 4‐year‐old children.

The purpose of this study was to examine the importance of different acoustic properties for the perception of place of articulation in young children and adults. Ten adults and ten children in both of the age groups, 3 and 4 years, listened to synthesized consonant–vowel syllables comprised of all combinations of [b d g] and [i]. The synthesis parameters included manipulations of the following stimulus variables: formant transition (moving or straight), noise burst (present or absent), and voicing duration (10 or 46 ms). In a recent study [R. N. Ohde et al., J. Acoust. Soc. Am. 97, 3800–3812 (1995)] of children between 5 and 11 years of age, there was no difference between children and adults in terms of the perceptual weight placed on the dynamic formant transition cue. However, in the current study, preliminary findings indicate that young children’s identification of stop consonants was higher for moving transitions than straight transitions. In addition, the children’s identification of stops was frequently poor in the [i] context. Overall, these results suggest that children pay particular attention to dynamic cues in the early period of sound acquisition, and that they have reduced auditory sensitivity for acoustic correlates of place of articulation in the [i] context. [Work supported by NIDCD.]

Age‐related changes in the categorical perception of stop consonants.

The study focused on changes in the categorical perception of intial stop consonants as a function of age and hearing status. The identification of intial stop consonants differing in voicing and place of articulation relies on an integration of multiple acoustic cues (VOT, character of the noise burst, onset frequency and direction of the second and third formant transitions). Four hundred subjects, divided into four age groups (20–85 years) and into three hearing groups, participated in experiments that required the identification of syllables [ba] or [pa] and [ba], [da], or [ga] along synthesized continua. Stimuli were presented to subjects via headphones at 75 dB SPL. Results demonstrated that the phonemic boundary of the [ba–pa] continuum was shifted towards a longer VOT as a function of age and hearing status. Moreover, the phonemic boundaries between [ba] and [da], and between [da] and [ga], demonstrated by older and hearing impaired subjects were shifted toward [d] and [g] categories as compared to young subjects with normal hearing. The observed changes may be due to the age‐related deterioration of ability to analyze brief signals and ability to integrate multiple acoustical cues. [Work supported by Health and Welfare of Canada.]

A developmental study of the perception of onset spectra for stop consonants in different vowel environments

The purpose of this study was to assess the perceptual role of integration and dynamic time-varying spectral cues for stop consonants in children and adults. Stop-consonant syllables were synthesized in the context of two vowels, /i, ɑ /. These syllables were synthesized with and without bursts, and contained formant motions and/or formant onset frequencies appropriate for each stop-consonant place of articulation. In addition, syllable duration varied between 10 to 46 ms. Children at five age levels, 4, 5, 7, 9, and 11, and a control group of adults were trained to identify the consonant as either /b/, /d/, or /g/. Preliminary findings indicate that dynamic time-varying spectral changes are not essential for accurate identification of stop consonants across all contexts. The results also show that the integration of noise bursts and formant onset frequencies, and syllable duration improve identification of alveolar and velar stops, particularly for children. The findings will be discussed relative to: (1) the differences between children and adults in processing integration and dynamic time-varying spectral cues, and (2) the developmental role of stimulus duration in the perception of stop consonants. [Work supported by NIH, DC00464.]

A knowledge-based system for stop consonant identification based on speech spectrogram reading

In order to formalize the information used in spectrogram reading, a knowledge-based system for identifying spoken stop consonants was developed. Speech spectrogram reading involves interpreting the acoustic patterns in the image to determine the spoken utterance. One must selectively attend to many different acoustic cues, interpret their significance in light of other evidence, and make inferences based on information from multiple sources. The evidence, obtained from both spectrogram reading experiments and from teaching spectrogram reading, indicates that the process can be modeled with rules. Formalizing spectrogram reading entails refining the language used to describe acoustic events in the spectrogram, selecting a set of relevant acoustic events that distinguish among phonemes, and developing rules which map these acoustic attributes into phonemes. One way to assess how well the knowledge used by experts has been captured is by embedding the rules in a computer program. A knowledge-based system was selected because the expression and use of knowledge are explicit. The emphasis was in capturing the acoustic descriptions and modeling the reasoning used by human spectrogram readers. In this paper, the knowledge acquisition and knowledge representation, in terms of descriptions and rules, are described. A performance evaluation and error analysis are also provided, and the performance of an HMM-based phone recognizer on the same test data is given for comparison.

Age-related differences in processing dynamic acoustic cues to initial stops.

The present study examines possible age-related differences in the ability to process rapidly changing acoustic information in the identification and discrimination of initial stop consonants. As described in Fox etal. [J. Acoust. Soc. Am. 89, 1935(A) (1991)], older adults show lower accuracy rates in identifying both consonants and vowels in so-called ‘‘silent-center’’ tokens. Such results are compatible with the suggestion that older listeners have greater difficulty than younger listeners in processing dynamic acoustic cues, such as those represented by consonant transitions. Two sets of stimuli were created: one set represented a 7-step [beh]–[deh] continuum with a 40-ms transition followed by a 150-ms steady-state vowel; the second set was composed of a 7-step [beh]–[deh] continuum with the same transition followed by a 10-ms vowel. There were two sets of normal hearing listeners including 15 listeners aged 20–24 and 15 listeners aged 60–75. There was an identification task and two AX discrimination tasks (with either a 500- or 2000-ms ISI). Older listeners showed shallower slopes in their identification functions than did the younger listeners, particularly in the stimuli composed primarily of formant transitions. In the discrimination task, older listeners were significantly less sensitive to formant transition differences than were the younger listeners, but there were no significant differences related to interstimulus interval. [Work supported, in part, by an NIA grant to R. Fox.]

Influences of Formant Bandwidth on Identification of Stop Consonants

Influences of Formant Bandwidth on Identification of Stop Consonants