Place Of Articulation In Stop Consonants Research Articles

Perceptual Weighting of Stop Consonant Cues by Normal and Impaired Listeners in Reverberation Versus Noise

To determine if listeners with normal hearing and listeners with sensorineural hearing loss give different perceptual weightings to cues for stop consonant place of articulation in noise versus reverberation listening conditions. Nine listeners with normal hearing (23-28 years of age) and 10 listeners with sensorineural hearing loss (31-79 years of age, median 66 years) participated. The listeners were asked to label the consonantal portion of synthetic CV stimuli as either /p/ or /t/. Two cues were varied: (a) the amplitude of the spectral peak in the F4/F5 frequency region of the burst was varied across a 30-dB range relative to the adjacent vowel peak amplitude in the same frequency region, (b) F2/F3 formant transition onset frequencies were either appropriate for /p/, /t/ or neutral for the labial/alveolar contrast. Weightings of relative amplitude and transition cues for voiceless stop consonants depended on the listening condition (quiet, noise, or reverberation), hearing loss, and age of listener. The effects of age with hearing loss reduced the perceptual integration of cues, particularly in reverberation. The effects of hearing loss reduced the effectiveness of both cues, notably relative amplitude in reverberation. Reverberation and noise conditions have different perceptual effects. Hearing loss and age may have different, separable effects.

F2 Locus Equations: Phonetic Descriptors of Coarticulation in 17- to 22-Month-Old Children

The general purpose of this research was to describe coarticulation across voiced stop consonant place of articulation in 10 children younger than 2 years of age. A total of 1,182 voiced stop CV productions was analyzed using the locus equation metric, which yielded 3 regression lines that described the relation of F2 onset and F2 vowel for /bV/, /dV/, and /gV/ productions. The results revealed significant differential effects for slope and y-intercept as a function of stop consonant place of articulation. The ordering of the mean slope values for stop consonant place of articulation was /g/>/b/ and /d/, indicating that /g/ was produced with significantly greater coarticulation than /b/ or /d/. However, the unique vowel allophonic pattern of [g] coarticulation reported in the literature for English-speaking adults was generally not learned by these young children. Group and individual coarticulation trends are described in relation to developmental theories of sound acquisition. Results suggest that early coarticulation patterns are phoneme specific.

Effects of hearing impairment on the perception and neural representation of time-varying spectral cues

Differences in phonetic boundaries versus normal controls suggest that listeners with hearing impairment (HI) have difficulty categorizing stop consonant place of articulation based solely on the dynamic spectral information present in the second formant transition (F2), even when the stimuli are amplified. This may be due to a degraded ability of the central auditory nervous system to process time-varying spectral cues despite ensuring overall audibility. However, increasing the overall level of the stimuli may not result in improved audibility of F2. To determine if spectral shaping of F2 improves performance of listeners with HI, psychometric functions and N1-P2 cortical responses were compared in 10 older listeners with normal hearing versus 10 older listeners with HI. Stimuli were synthetic consonant-vowels along a /ba/-/da/-/ga/ place-of-articulation continuum in an unshaped and shaped condition. Generally, behavioral and N1-P2 results indicate that, with shaping, categorization of /d/ and /g/ improves. These findings suggest that enhanced audibility of F2 through spectral shaping does improve perception of stop consonant stimuli. However, categorical boundaries for the individuals with HI are shifted lower in frequency with shaping for all phonemes versus normal controls, indicating that enhancing audibility improves but does not completely normalize categorization performance.

Classification of stop consonant place of articulation

In this study we develop an experimental procedure for examining the relative importance of knowledge-based cues for identifying place of articulation for stop consonants. A set of acoustic attributes is selected for place classification of stops: amplitude and energy of burst, formant movement of adjacent vowels, spectrum of noise after the release, and some temporal cues. The ability of each attribute to separate the three places is evaluated by the classification error based on the distributions of its values for the three places, and another quantifier based on F ratio. These two quantifiers generally agree and show how well each individual attribute separates the three places. Linear discriminant function analysis is used to address the relative importance of these attributes when combinations are used. Their discriminating abilities and the ranking of their relative importance to the classification in different vowel and voicing contexts are reported. The overall findings are that attributes relating to the burst spectrum in relation to the vowel contribute most effectively, while formant transition is somewhat less effective. The approach used in this study can be applied to different classes of sound, as well as stops in different noise environments. [Work supported by NIH Grant Number DC 02978.]

Perceptual weighting of relative amplitude and formant transition cues in aided CV syllables.

The current study explored the changes in weighting of relative amplitude and formant transition cues that may be caused by a K-amp circuit. Twelve listeners with normal hearing and 3 listeners with sensorineural hearing loss labeled the stop consonant place of articulation of synthetic consonant-vowel stimuli. Within the stimuli, two acoustic cues were varied: the frequency of the onset of the second and third formant (F2/F3) transitions and the relative amplitude between the consonant burst and the following vowel in the fourth and fifth formant (F4/ F5) frequency region. The variation in the two cues ranged from values appropriate for a voiceless labial stop consonant to a voiceless alveolar stop consonant. The listeners labeled both the unaided stimuli and the stimuli recorded through a hearing aid with a K-amp circuit. An analysis of variance (ANOVA) model was used to calculate the perceptual weight given each cue. Data from listeners with normal hearing show a change in relative weighting of cues between aided and unaided stimuli. Pilot data from the listeners with hearing loss show a more varied pattern, with more weight placed on relative amplitude. These results suggest that calculation of perceptual weights using an ANOVA model may be worthwhile in Future studies examining the relationship between acoustic information presented by a hearing aid and the subsequent perception by the listener with hearing loss.

Effect of a Single-Channel Wide Dynamic Range Compression Circuit on Perception of Stop Consonant Place of Articulation

Previous studies have shown that altering the amplitude of a consonant in a specific frequency region relative to an adjacent vowel's amplitude in the same frequency region will affect listeners' perception of the consonant place of articulation. Hearing aids with single-channel, fast-acting wide dynamic range compression (WDRC) alter the overall consonant-vowel (CV) intensity ratio by increasing consonant energy. Perhaps one reason WDRC has had limited success in improving speech recognition performance is that the natural amplitude balances between consonant and vowel are altered in crucial frequency regions, thus disturbing the aforementioned amplitude cue for determining place of articulation. The current study investigated the effect of a WDRC circuit on listeners' perception of place of articulation when the relative amplitude of consonant and vowel was manipulated. The stimuli were a continuum of synthetic CV syllables stripped of all place cues except relative consonant amplitudes. Acoustic analysis of the CVs before and after hearing aid processing showed a predictable increase in high-frequency energy, particularly for the burst of the consonant. Alveolar bursts had more high-frequency energy than labial bursts. Twenty-five listeners with normal hearing and 5 listeners with sensorineural hearing loss labeled the consonant sound of the CV syllables in unaided form and after the syllables were recorded through a hearing aid with single-channel WDRC. There were significantly more listeners who were unable to produce a category boundary when labeling the aided stimuli. Of those listeners who did yield a category boundary for both aided and unaided stimuli, there were significantly more alveolar responses for the aided condition. These results can be explained by the acoustic analyses of the aided stimuli.

Improving consonant intelligibility for Ineraid patients fit with continuous interleaved sampling (CIS) processors by enhancing contrast among channel outputs.

In Experiment 1 the objective was to determine whether patients who have been implanted with the Ineraid electrode array perform better on tests of consonant identification when signals are processed through a continuous interleaved sampling (CIS) processor than when signals are processed through an analogue (Ineraid) processor. In Experiment 2 the objective was to determine, for patients using the CIS strategy, whether identification accuracy for stop consonant place of articulation could be improved by enhancing differences in the patterns of the signal processor channel outputs. In Experiment 1, 16 consonants were presented in VCV format for identification. In Experiment 1 the CIS patients evidence difficulty in identifying /p t k/. Therefore, in Experiment 2 the voiceless stop consonants were presented in two stimulus conditions. In one, the stimuli were unfiltered. In the other, the stimuli were individually filtered so as to enhance the differences in channel outputs for /p/, /t/, and /k/. In Experiment 1 the patients performed better with CIS processors than with analogue processors. In Experiment 2 the "enhanced" stimuli were identified with better accuracy than were the unfiltered stimuli. We confirm that Ineraid patients achieve higher scores on tests of consonant identification when using a CIS processor than when using an analogue processor. Errors in identification of stop consonant place of articulation, when using a CIS processor, are due to the similarity in the patterns of the processor's channel outputs. By showing that consonant intelligibility can be improved by filtering, we show that we have not reached the limit of speech understanding that can be supported by the population of neural elements remaining in our patients' auditory systems.

Tonotopic organization of responses reflecting stop consonant place of articulation in primary auditory cortex (A1) of the monkey

Current source density and multiunit activity elicited by stop consonant-vowel syllables were examined in primary auditory cortex of an awake monkey. Relative amplitudes of the speech-evoked responses were determined by the onset spectra of the consonants and the tonotopic organization. This finding supports the psychoacoustic hypothesis that the onset spectra of stop consonants are important determinants for the discrimination of place of articulation.

Stimulus factors influencing the identification of voiced stop consonants by normal-hearing and hearing-impaired adults.

The effects of mild-to-moderate hearing impairment on the perceptual importance of three acoustic correlates of stop consonant place of articulation were examined. Normal-hearing and hearing-impaired adults identified a stimulus set comprising all possible combinations of the levels of three factors: formant transition type (three levels), spectral tilt type (three levels), and abruptness of frequency change (two levels). The levels of these factors correspond to those appropriate for /b/, /d/, and /g/ in the /ae/ environment. Normal-hearing subjects responded primarily in accord with the place of articulation specified by the formant transitions. Hearing-impaired subjects showed less-than-normal reliance on formant transitions and greater-than-normal reliance on spectral tilt and abruptness of frequency change. These results suggest that hearing impairment affects the perceptual importance of cues to stop consonant identity, increasing the importance of information provided by both temporal characteristics and gross spectral shape and decreasing the importance of information provided by the formant transitions.

Extending formant transitions may not improve aphasics' perception of stop consonant place of articulation

Synthetic speech stimuli were used to investigate whether aphasics' ability to perceive stop consonant place of articulation was enhanced by the extension of initial formant transitions in CV syllables. Phoneme identification and discrimination tests were administered to 12 aphasic patients, 5 fluent and 7 nonfluent. There were no significant differences in performance due to the extended transitions, and no systematic pattern of performance due to aphasia type. In both groups, discrimination was generally high and significantly better than identification, demonstrating that auditory capacity was retained, while phonetic perception was impaired; this result is consistent with repeated demonstrations that auditory and phonetic processes may be dissociated in normal listeners. Moreover, significant rank order correlations between performances on the Token Test and on both perceptual tasks suggest that impairment on these tests may reflect a general cognitive rather than a language-specific deficit.

Effect of burst amplitude on the perception of stop consonant place of articulation.

We have examined the effects of the relative amplitude of the release burst on perception of the place of articulation of utterance-initial voiceless and voiced stop consonants. The amplitude of the burst, which occurs within the first 10-15 ms following consonant release, was systematically varied in 5-dB steps from -10 to +10 dB relative to a "normal" burst amplitude for two labial-to-alveolar synthetic speech continua--one comprising voiceless stops and the other, voiced stops. The distribution of spectral energy in the bursts for the labial and alveolar stops at the ends of the continuum was consistent with the spectrum shapes observed in natural utterances, and intermediate shapes were used for intermediate stimuli on the continuum. The results of identification tests with these stimuli showed that the relative amplitude of the burst significantly affected the perception of the place of articulation of both voiceless and voiced stops, but the effect was greater for the former than the latter. The results are consistent with a view that two basic properties contribute to the labial-alveolar distinction in English. One of these is determined by the time course of the change in amplitude in the high-frequency range (above 2500 Hz) in the few tens of ms following consonantal release, and the other is determined by the frequencies of spectral peaks associated with the second and third formants in relation to the first formant.

Susceptibility to spread of masking in normal and sensorineural hearing‐impaired listeners

To determine whether upward spread of masking is responsible for failure to identify stop consonant place of articulation, sensorineural hearing‐impaired subjects grouped according to etiological basis of hearing disorder were tested on a speech and a nonspeech task. Two‐formant consonant ‐ vowel syllables varying along a /b d g/ continuum were presented for identification at moderate and high intensity when formant amplitudes were equal and when F1 amplitude was attenuated by 6, 12, and 18 dB. In the second experiment, noise‐on‐tone masking functions were generated using seven narrow bands of noise at moderate and high intensity. Upward spread of masking could be demonstrated in speech and nonspeech tasks, irrespective of the subjects' age, audiometric configuration, or etiology of hearing impairment. Attenuation of F1 produced varying results on phoneme labelling performance among groups. The outcome of these experiments showed that while listeners with noise‐induced hearing loss showed substantial impr...

Distribution of acoustic cues for stop consonant place of articulation in VCV syllables.

Most theoretical accounts of the identification of stop consonant place of articulation have focused on how bursts and formant transitions conspire to signal place in CV syllables. In the present series of experiments we have examined the identification of place in VCV syllables and have found that not only do the burst and opening transitions affect the judgement of place, but so also do the closing transitions and the duration of the closure interval. This outcome is consistent with the outcomes of many other experiments in showing that there are multiple acoustic events which bear on the identification of a given phone and that those acoustic events are distributed over time. Theoretical accounts of place identification based on data of this kind may prove viable than theories based on data from the identification of place in the absolute, syllable-initial position.

Identification of synthetic /bdg/ by hearing‐impaired listeners under monotic and dichotic formant presentation

Individuals with sensorineural hearing losses of both flat and sloping configuration evidence difficulty in identifying stop consonant place of articulation. To assess whether upward spread of masking is responsible for this difficulty, we presented hearing-impaired listeners with stimuli from a /ba da ga/ continuum in both monotic and dichotic (F1 to one ear; F2/F3 to the other ear) listening conditions. In the monotic conditions, listeners with similar audiograms evidence great variability in identification performance. In the dichotic conditions performance did not generally improve. For a few listeners, however, the improvement was striking. At moderate levels of signal presentation, upward spread of masking does not appear to be responsible for the poor identification of place by the majority of listeners with moderate hearing losses.

Some effects of acoustic attributes of speech on the processing of phonetic feature information.

How do acoustic attributes of the speech signal contribute to feature-processing interactions that occur in phonetic classification? In a series of five experiments addressed to this question, listeners performed speeded classification tasks that explicitly required a phonetic decision for each response. Stimuli were natural consonant-vowel syllables differing by multiple phonetic features, although classification responses were based on a single target feature. In control tasks, no variations in nontarget features occurred, whereas in orthogonal tasks nonrelevant feature variations occurred but had to be ignored. Comparison of classification times demonstrated that feature information may either be processed separately as independent cues for each feature or as a single integral segment that jointly specifies several features. The observed form on processing depended on the acoustic manifestations of feature variation in the signal. Stop-consonant place of articulation and voicing cues, conveyed independently by the pattern and excitation source of the initial formant transitions, may be processed separately. However, information for consonant place of articulation and vowel quality, features that interactively affect the shape of initial formant transitions, are processed as an integral segment. Articulatory correlates of each type of processing are discussed in terms of the distinction between source features that vary discretely in speech production and resonance features that can change smoothly and continuously. Implications for perceptual models that include initial segmentation of an input utterance into a phonetic feature representation are also considered.

Identification of synthetic /bdg/ by hearing impaired listeners in monotic and dichotic listening conditions

Individuals with sensorineural hearing losses of both flat and sloping configuration evidence difficulty in speech understanding. To assess whether upward spread of masking of F1 is responsible for the poor identification of stop consonant place of articulation, we presented to hearing impaired listeners stimuli from along a [ba da ga] continuum in both monotic and dichotic (F1 to one ear; F2/F3 to the other ear) listening conditions. In the monotic conditions, hearing impaired listeners with similar audiograms evidenced great variability in labeling performance. In the dichotic conditions. performance did not generally improve although for a few listeners the improvement was striking. We suspect that upward spread of masking is not generally responsible for the poor identification of place in listeners with moderate, flat, and sloping sensorineural hearing losses.