Stop Consonant-vowel Syllables Research Articles

Aerodynamic Threshold Measures for Reflecting Glottal Closure in Voice Disorders.

Previous work suggested that phonation threshold pressure (PTP), phonation threshold flow (PTF), and phonation threshold power (PTW) could be effective aerodynamic measures for quantifying glottal incompetence. This study examined how these measures could reflect varying extent of incomplete glottal closure in individuals with voice disorders. Thirty individuals formally diagnosed with glottal incompetence, including 10 with hypofunctional disorders (hypo group) and 20 with hyperfunctional disorders (hyper group), and 30 individuals with normal voice (control group) participated in the study. PTP was measured indirectly by intra-oral pressure during production of bilabial stop consonant-vowel syllables, PTF was measured during the sustained vowel /a/, and PTW was obtained as the product of PTP and PTF. The extent of incomplete glottal closure was quantified by normalized glottal gap (NGG) and normalized glottal gap area (NGGA) based on image analysis of videostroboscopic recordings of sustained /i/. Significant differences in all threshold measures (p < .05) were found among three participant groups with medium-to-large effect sizes (ηp2 = .128-.220), with significantly higher values for the hypo group than the control group and no significant differences between the hyper and control groups. Receiver operating characteristic (ROC) analysis showed the highest diagnostic or classification accuracy contrasting between the hypo and control groups (area under the ROC curve = .717-.757), with the highest classification accuracy for PTW. There were significant, moderate-to-strong positive correlations with NGG and NGGA for the disorders group (Pearson's r = .4244-.6226) and the hypo group (r = .5689-.8949). These measures could be effective for identifying glottal incompetence, especially for hypofunctional disorders. PTW could be more sensitive than PTP and PTF in reflecting the extent of incomplete glottal closure, consistent with theoretical predictions. Their relative sensitivities for quantifying distinct incomplete glottal closures specific to different voice disorders should be evaluated in future studies.

Perception of Incongruent Audiovisual Speech: Distribution of Modality-Specific Responses

Multimodal sensory integration in audiovisual (AV) speech perception is a naturally occurring phenomenon. Modality-specific responses such as auditory left, auditory right, and visual responses to dichotic incongruent AV speech stimuli help in understanding AV speech processing through each input modality. It is observed that distribution of activity in the frontal motor areas involved in speech production has been shown to correlate with how subjects perceive the same syllable differently or perceive different syllables. This study investigated the distribution of modality-specific responses to dichotic incongruent AV speech stimuli by simultaneously presenting consonant-vowel (CV) syllables with different places of articulation to the participant's left and right ears and visually. A dichotic experimental design was adopted. Six stop CV syllables /pa/, /ta/, /ka/, /ba/, /da/, and /ga/ were assembled to create dichotic incongruent AV speech material. Participants included 40 native speakers of Norwegian (20 women, M age = 22.6 years, SD = 2.43 years; 20 men, M age = 23.7 years, SD = 2.08 years). Findings of this study showed that, under dichotic listening conditions, velar CV syllables resulted in the highest scores in the respective ears, and this might be explained by stimulus dominance of velar consonants, as shown in previous studies. However, this study, with dichotic auditory stimuli accompanied by an incongruent video segment, demonstrated that the presentation of a visually distinct video segment possibly draws attention to the video segment in some participants, thereby reducing the overall recognition of the dominant syllable. Furthermore, the findings here suggest the possibility of lesser response times to incongruent AV stimuli in females compared with males. The identification of the left audio, right audio, and visual segments in dichotic incongruent AV stimuli depends on place of articulation, stimulus dominance, and voice onset time of the CV syllables.

Age-related differences in Voice-Onset-Time in Polish language users: An ERP study

Using the Mismatch Negativity (MMN) paradigm we investigated for the first time cortical responses to consonant - vowel (CV) syllables differing in Voice-Onset-Time (VOT) for Polish, a member of the Slavic group of languages. The study aimed at testing age-related effects on different ERP responses in young (20–30 years of age) and elderly (60–68 years) native Polish speakers. Participants were presented with a sequence of voiced and voiceless stop CV syllables /to/ and /do/ with different VOT values (−100 ms, −70 ms, −30 ms, −20 ms, +20 ms, +50 ms). We analyzed MMN and P1, N1, N1′, P2, N2 components. Our results showed an age-related decline in voicing perception in all tested ERP components. This decline could be explained in relation to a general slowing in neural processing with advancing age and may be associated with difficulties in temporal- and spectral-information processing in elderly people. Our findings revealed also that specific features of Slavic languages influence ERP morphology in a different way than reported in the literature for aspirating languages.

Temporal Encoding of Voice Onset Time in Young Children

Objective: Voice onset time (VOT) is an important parameter of speech that denotes the time interval between consonant onset and the onset of low frequency periodicity generated. In this study we examined the temporal encoding of voice onset time in the cortical auditory evoked response (CAEP) of young children. Methods: Scalp recoded CAEP were measured in 18 children aged from 5-8 participated (n=18). The N2 latency was evoked using differences in voice-onset-times (VOTs) using stop consonant-vowel syllables /ga/-/ka/. Results: A significant and systematic shift in the N2 latency was observed for differences in VOT. Conclusions: Our results demonstrate that temporal encoding of VOT exists in the developing cortical evoked response.

Reactive cognitive-control processes in free-report consonant–vowel dichotic listening

The relevance of cognitive-control processes has been frequently discussed and studied in the context of dichotic listening. Experimental and clinical studies indicate that directing attention to either of the two simultaneously presented phonological stimuli, but especially to the left-ear stimulus increases the requirements for cognitive-control processes. Here, we extend this view by reporting the results of a behavioural and a functional magnetic-resonance imaging (fMRI) experiment designed to analyse the involvement of cognitive-control processes also in a free-report dichotic-listening paradigm. It was hypothesised that dichotically presented pairs of stop–consonant–vowel syllables would provide different demands for cognitive-control processes as a function of the spectro-temporal overlap of the two stimuli. Accordingly, in Experiment 1 it was shown that dichotic syllables of high (e.g., /ba/ and /ga/) as opposed to low spectro-temporal overlap (e.g., /ba/ and /ka/) produce significantly faster and more correct answers, and are more often perceived as one syllable. In Experiment 2 it was further shown that pairs of low as compared to high spectro-temporal overlap trigger a more pronounced activation predominately in left-hemispheric, speech-associated brain regions, namely left posterior inferior sulcus/gyrus, bilaterally in pre-supplementary motor and mid-cingulate cortex as well as in the inferior parietal lobe. Taken together, behavioural and functional data indicate a stronger involvement of reactive cognitive control in the processing of low-overlap as opposed to high-overlap stimulus pairs. This supports the notion that higher-order, speech-related cognitive-control processes also are involved in a free-report dichotic-listening paradigm.

Intracranial Study of Speech-Elicited Activity on the Human Posterolateral Superior Temporal Gyrus

To clarify speech-elicited response patterns within auditory-responsive cortex of the posterolateral superior temporal (PLST) gyrus, time-frequency analyses of event-related band power in the high gamma frequency range (75-175 Hz) were performed on the electrocorticograms recorded from high-density subdural grid electrodes in 8 patients undergoing evaluation for medically intractable epilepsy. Stimuli were 6 stop consonant-vowel (CV) syllables that varied in their consonant place of articulation (POA) and voice onset time (VOT). Initial augmentation was maximal over several centimeters of PLST, lasted about 400 ms, and was often followed by suppression and a local outward expansion of activation. Maximal gamma power overlapped either the Nα or Pβ deflections of the average evoked potential (AEP). Correlations were observed between the relative magnitudes of gamma band responses elicited by unvoiced stop CV syllables (/pa/, /ka/, /ta/) and their corresponding voiced stop CV syllables (/ba/, /ga/, /da/), as well as by the VOT of the stimuli. VOT was also represented in the temporal patterns of the AEP. These findings, obtained in the passive awake state, indicate that PLST discriminates acoustic features associated with POA and VOT and serve as a benchmark upon which task-related speech activity can be compared.

A cross-linguistic examination of cortical auditory evoked potentials for a categorical voicing contrast

Behavioral perceptions and cortical auditory evoked potentials (CAEPs) from native English ( N = 10) and Spanish speakers ( N = 10) were recorded for speech stimuli that constitute phonetically relevant categories of voicing. The stimuli were synthesized bilabial stop consonant-vowel syllables in a continuum ranging from/ba/to/pa/that varied in voice onset time (VOT) from 0 to 60 ms. Different behavioral perceptions were evidenced by significantly different categorical phonetic boundaries between the two groups ( p < .0001). In contrast, there were no significant differences in CAEP component P1, N1, and P2 mean latencies or P1–N1 and N1–P2 amplitudes between groups ( p > .05). Peak P1, N1, and P2 response latencies and P1–N1 and N1–P2 amplitudes increased significantly with increasing VOTs ( p < .0001 and p < .001, respectively). There were no systematic changes in CAEP morphology that corresponded to listeners’ perceptual categorical boundaries. These findings are consistent with the notion that changes in morphology of the P1–N1–P2 response are related to acoustical changes in speech sounds and are independent of phonetic categorization of voicing cues across language groups.

Enhanced physiologic discriminability of stop consonants with prolonged formant transitions in awake monkeys based on the tonotopic organization of primary auditory cortex

Many children with specific language impairment (SLI) have difficulty in perceiving stop consonant-vowel syllables (e.g., /ba/, /ga/, /da/) with rapid formant transitions, but perform normally when formant transitions are extended in time. This influential observation has helped lead to the development of the auditory temporal processing hypothesis, which posits that SLI is causally related to the processing of rapidly changing sounds in aberrantly expanded windows of temporal integration. We tested a potential physiological basis for this observation by examining whether syllables varying in their consonant place of articulation (POA) with prolonged formant transitions would evoke better differentiated patterns of activation along the tonotopic axis of A1 in awake monkeys when compared to syllables with short formant transitions, especially for more prolonged windows of temporal integration. Amplitudes of multi-unit activity evoked by /ba/, /ga/, and /da/ were ranked according to predictions based on responses to tones centered at the spectral maxima of frication at syllable onset. Population responses representing consonant POA were predicted by the tone responses. Predictions were stronger for syllables with prolonged formant transitions, especially for longer windows of temporal integration. Relevance of findings to normal perception and that occurring in SLI are discussed.

Neural mechanisms of interstimulus interval-dependent responses in the primary auditory cortex of awake cats

BackgroundPrimary auditory cortex (AI) neurons show qualitatively distinct response features to successive acoustic signals depending on the inter-stimulus intervals (ISI). Such ISI-dependent AI responses are believed to underlie, at least partially, categorical perception of click trains (elemental vs. fused quality) and stop consonant-vowel syllables (eg.,/da/-/ta/continuum).MethodsSingle unit recordings were conducted on 116 AI neurons in awake cats. Rectangular clicks were presented either alone (single click paradigm) or in a train fashion with variable ISI (2–480 ms) (click-train paradigm). Response features of AI neurons were quantified as a function of ISI: one measure was related to the degree of stimulus locking (temporal modulation transfer function [tMTF]) and another measure was based on firing rate (rate modulation transfer function [rMTF]). An additional modeling study was performed to gain insight into neurophysiological bases of the observed responses.ResultsIn the click-train paradigm, the majority of the AI neurons ("synchronization type"; n = 72) showed stimulus-locking responses at long ISIs. The shorter cutoff ISI for stimulus-locking responses was on average ~30 ms and was level tolerant in accordance with the perceptual boundary of click trains and of consonant-vowel syllables. The shape of tMTF of those neurons was either band-pass or low-pass. The single click paradigm revealed, at maximum, four response periods in the following order: 1st excitation, 1st suppression, 2nd excitation then 2nd suppression. The 1st excitation and 1st suppression was found exclusively in the synchronization type, implying that the temporal interplay between excitation and suppression underlies stimulus-locking responses. Among these neurons, those showing the 2nd suppression had band-pass tMTF whereas those with low-pass tMTF never showed the 2nd suppression, implying that tMTF shape is mediated through the 2nd suppression. The recovery time course of excitability suggested the involvement of short-term plasticity. The observed phenomena were well captured by a single cell model which incorporated AMPA, GABAA, NMDA and GABAB receptors as well as short-term plasticity of thalamocortical synaptic connections.ConclusionOverall, it was suggested that ISI-dependent responses of the majority of AI neurons are configured through the temporal interplay of excitation and suppression (inhibition) along with short-term plasticity.

Brainstem encoding of voiced consonant–vowel stop syllables

Objective The purpose of this study is to expand our understanding of how the human auditory brainstem encodes temporal and spectral acoustic cues in voiced stop consonant–vowel syllables. Methods Auditory evoked potentials measuring activity from the brainstem of 22 normal learning children were recorded to the voiced stop consonant syllables [ga], [da], and [ba]. Spectrotemporal information distinguishing these voiced consonant–vowel syllables is contained within the first few milliseconds of the burst and the formant transition to the vowel. Responses were compared across stimuli with respect to their temporal and spectral content. Results Brainstem response latencies change in a predictable manner in response to systematic alterations in a speech syllable indicating that the distinguishing acoustic cues are represented by neural response timing (synchrony). Spectral analyses of the responses show frequency distribution differences across stimuli (some of which appear to represent acoustic characteristics created by difference tones of the stimulus formants) indicating that neural phase-locking is also important for encoding these acoustic elements. Conclusions Considered within the context of existing knowledge of brainstem encoding of speech–sound structure, these data are the beginning of a comprehensive delineation of how the human auditory brainstem encodes perceptually critical features of speech. Significance The results of this study could be used to determine how neural encoding is disrupted in the clinical populations for whom stop consonants pose particular perceptual challenges (e.g., hearing impaired individuals and poor readers).

On pure word deafness, temporal processing, and the left hemisphere

Pure word deafness (PWD) is a rare neurological syndrome characterized by severe difficulties in understanding and reproducing spoken language, with sparing of written language comprehension and speech production. The pathognomonic disturbance of auditory comprehension appears to be associated with a breakdown in processes involved in mapping auditory input to lexical representations of words, but the functional locus of this disturbance and the localization of the responsible lesion have long been disputed. We report here on a woman with PWD resulting from a circumscribed unilateral infarct involving the left superior temporal lobe who demonstrated significant problems processing transitional spectrotemporal cues in both speech and nonspeech sounds. On speech discrimination tasks, she exhibited poor differentiation of stop consonant-vowel syllables distinguished by voicing onset and brief formant frequency transitions. Isolated formant transitions could be reliably discriminated only at very long durations (> 200 ms). By contrast, click fusion threshold, which depends on millisecond-level resolution of brief auditory events, was normal. These results suggest that the problems with speech analysis in this case were not secondary to general constraints on auditory temporal resolution. Rather, they point to a disturbance of left hemisphere auditory mechanisms that preferentially analyze rapid spectrotemporal variations in frequency. The findings have important implications for our conceptualization of PWD and its subtypes.

Time and language – critical remarks on diagnosis and training methods of temporal-order judgment

A lively discussion concerning the causal relation between auditory temporal processing and phoneme identification has evolved over the last decades. Subjects with language impairments not only show deficits in the identification of stop-consonant vowel syllables, but also have problems detecting the temporal order of acoustic stimuli. Recently published studies claim that an improvement in phoneme discrimination can be achieved through the training of temporal-processing abilities. Critical assessment of these studies often reveals the following weaknesses: first, the diagnostic and training methods vary between studies, which makes comparisons difficult. Second, usually only mean differences between groups or before/after treatment are presented. The success in diagnosis and training of individuals or subgroups is not documented. Third, only few diagnostic measures employed have been tested for reliability. Furthermore, the tests have not been designed according to modern psychometric methods. Fourth, several training modules are used in parallel. The effects of temporal-processing training cannot be isolated. Possible approaches for detecting the possible causal relation between the time and the language domain are discussed.

Effects of general processing capacity and sustained selective attention on temporal processing performance of children with specific language impairment

This study investigated the potential influences of general processing capacity and sustained selective attention on the temporal processing of a group of children with specific language impairment (SLI) and a group of age-matched (CA) controls. Children completed a sustained selective auditory attention task and two speech processing tasks, the Speech Identification Task, representing a cognitively more complex task, and a standard speech discrimination task, representing a cognitively less complex task. The speech stimuli included two-formant, 40-ms transition [ba] and [da] consonant–vowel (CV) syllables and the nonstop CV syllable [sa]. We hypothesized, in accordance with Tallal's temporal processing deficit view, that if SLI children have a fundamental deficit in temporal processing, they should demonstrate poor performance on both speech processing tasks relative to CA children. By contrast, if the temporal processing problem of SLI children relates to a limitation in general processing capacity, the SLI children should show better performance on the discrimination task compared to the identification task. Alternatively, if poor sustained selective attention mediates SLI children's poor temporal processing, the SLI children should show poor performance on an independent measure of auditory attention, which in turn should account for a portion of the variance in any observed group differences in temporal processing. Results showed no group difference in sustained selective auditory attention. On the identification task, group, stimulus-type, and interaction effects emerged. SLI children performed more poorly than CA children, and stop CV syllables were identified less frequently than the nonstop CV syllable. On the discrimination task, there were no main effects or interactions for accuracy (Á score). For the reaction time analysis, only a stimulus-type effect was found, with children responding faster to the /sa/ syllable. Results were interpreted to suggest that these SLI children did not evidence a basic temporal processing deficit. Rather, the SLI children's poor identification task performance was interpreted to reflect an interaction between these children's more limited general processing capacity and the nature of the task.

Contralaterality of cortical auditory processing at the level of the M50/M100 complex and the mismatch field: a whole-head magnetoencephalography study.

Humans show a stronger cortical representation of auditory input at the opposite hemisphere each. To specify the temporal aspects of this contralaterality effect within the domain of speech stimuli, the present study recorded a series of evoked magnetic fields (M50, M100, mismatch field) subsequent to monaural application of stop consonant-vowel syllables using whole-head magnetoencephalography (MEG). The M50 components exhibited a skewed shape of cross-symmetrical distribution in terms of an initial maximum peak succeeded by a knot over the contralateral and a reversed pattern over the ipsilateral temporal lobe. Most presumably, this pattern of evoked fields reflects two distinct stages of central-auditory processing: (a) initial excitation of the larger contralateral and the smaller ipsilateral projection area of the stimulated ear; (b) subsequent transcallosal activation of the residual neurons, i.e. the targets of the non-stimulated ear, at either side. Previous studies using non-speech stimuli found contralaterality of central-auditory processing to extend to the M100 field. In contrast, a larger amplitude of ipsilateral M100 as compared to the respective opposite deflection emerged after stimulation of either ear. Finally, the computed magnetic analogues of mismatch negativity failed any significant laterality effects. These data provide first evidence for a distinct pattern of hemispheric differences at the level of the M50/M100 complex subsequent to monaural application of speech stimuli.

Neural correlates of duplex perception: a whole-head magnetencephalography study.

Simultaneous experience of the same acoustic stimulus in two distinct phenomenological modes, e.g. as a speech-like and as a non-speech event, is referred to as duplex perception (DP). The most widely investigated DP paradigm splits each of the stop consonant-vowel (CV) syllables /ga/ and /da/ into an isolated formant transient (chirp) and the remaining sound structure (base). The present study recorded mismatch fields in response to a series of dichotically applied base and chirp components using whole-head magnetencephalography (MEG). Preattentive mismatch fields showed larger amplitudes in response to contralateral deviants. During attention to the fused percept /da/, the left ear deviants chirps elicited an enhanced and posteriorly shifted dipole field over the ipsilateral hemisphere. These data provide first neurophysiological evidence that the integration of acoustic stimulus elements into a coherent syllable representation constitutes a distinct stage of left-hemisphere speech sound encoding.

A system for the assessment and training of temporal-order discrimination

Two programs were developed for psychophysical assessment and training of temporal-order thresholds in the visual and auditory modalities. Order threshold is defined as the minimum onset interval between two sensory events (stimulus onset asynchrony, SOA) that must exist before an observer is able to indicate the correct order of the events. Brain-injured patients with aphasia and children with language-learning impairments, i.e. those who have been diagnosed as performing poorly on temporal-order tasks and in discriminating stop-consonant vowel syllables, can effectively be trained by a feedback training procedure in which the SOA is manipulated. The performance in the temporal-order task and the ability to discriminate phonemes improves with this procedure. In the diagnostic program, the SOA is changed by an adaptive procedure that generates a sequence of SOAs converging to the threshold and is driven by the responses of the subject. The feedback-training program begins with the presentation of SOAs, which are slightly above the individual order threshold; they are subsequently varied according to the responses of the subject.

Temporal encoding of the voice onset time phonetic parameter by field potentials recorded directly from human auditory cortex.

Voice onset time (VOT) is an important parameter of speech that denotes the time interval between consonant onset and the onset of low-frequency periodicity generated by rhythmic vocal cord vibration. Voiced stop consonants (/b/, /g/, and /d/) in syllable initial position are characterized by short VOTs, whereas unvoiced stop consonants (/p/, /k/, and t/) contain prolonged VOTs. As the VOT is increased in incremental steps, perception rapidly changes from a voiced stop consonant to an unvoiced consonant at an interval of 20-40 ms. This abrupt change in consonant identification is an example of categorical speech perception and is a central feature of phonetic discrimination. This study tested the hypothesis that VOT is represented within auditory cortex by transient responses time-locked to consonant and voicing onset. Auditory evoked potentials (AEPs) elicited by stop consonant-vowel (CV) syllables were recorded directly from Heschl's gyrus, the planum temporale, and the superior temporal gyrus in three patients undergoing evaluation for surgical remediation of medically intractable epilepsy. Voiced CV syllables elicited a triphasic sequence of field potentials within Heschl's gyrus. AEPs evoked by unvoiced CV syllables contained additional response components time-locked to voicing onset. Syllables with a VOT of 40, 60, or 80 ms evoked components time-locked to consonant release and voicing onset. In contrast, the syllable with a VOT of 20 ms evoked a markedly diminished response to voicing onset and elicited an AEP very similar in morphology to that evoked by the syllable with a 0-ms VOT. Similar response features were observed in the AEPs evoked by click trains. In this case, there was a marked decrease in amplitude of the transient response to the second click in trains with interpulse intervals of 20-25 ms. Speech-evoked AEPs recorded from the posterior superior temporal gyrus lateral to Heschl's gyrus displayed comparable response features, whereas field potentials recorded from three locations in the planum temporale did not contain components time-locked to voicing onset. This study demonstrates that VOT at least partially is represented in primary and specific secondary auditory cortical fields by synchronized activity time-locked to consonant release and voicing onset. Furthermore, AEPs exhibit features that may facilitate categorical perception of stop consonants, and these response patterns appear to be based on temporal processing limitations within auditory cortex. Demonstrations of similar speech-evoked response patterns in animals support a role for these experimental models in clarifying selected features of speech encoding.

A vowel synthesizer based on formant sinusoids modulated by fundamental frequency

A vowel synthesis algorithm was developed resembling parallel formant synthesizers. However, the formants are computed as amplitude-and phase-modulated sinusoids instead of being represented by recursive filters or resonators. The fundamental frequency is imposed on the signal in the following way: Each pitch period exhibits an initial rise of a duration of π/2 of the first formant frequency; at the end of this ramp period all formants start as sinusoids at predefined phase angles and amplitudes, and successively undergo linear attenuation toward zero amplitude at the end of each pitch period. Adjacent pitch periods, thus, do not influence each other. In principle, the signals produced by this algorithm are similar to the output of parallel formant synthesizers [e.g., D. H. Klatt, J. Acoust. Soc. Am. 67, 971–995 (1980)]. However, by incremental sample-by-sample computation of the formants’ phase angles, formant frequencies are allowed to continuously change within single pitch periods. This new algorithm creates vowels as well as formant transitions signaling stop consonant–vowel syllables such as /ba/. The output signals exhibit a homogeneous, stereotypic voice quality. Because of its additive procedure, this method might allow us to implement a variety of further acoustic aspects of the human speaking voice in a well-controled manner.

Preattentive processing of consonant vowel syllables at the level of the supratemporal plane: a whole-head magnetencephalography study

A variety of clinical and experimental data indicate superiority of the left hemisphere with respect to the encoding of dynamic aspects of the acoustic speech signal such as formant transients, i.e., fast changes of spectral energy distribution across a few tens of milliseconds, which cue the perception of stop consonant vowel syllables. Using an oddball design, the present study recorded auditory evoked magnetic fields by means of a whole-head device in response to vowels as well as syllable-like structures. Both the N1m component (=the magnetic equivalent to the N1 response of the electroencephalogram (EEG)) and various difference waves between the magnetic fields to standard and respective rare events (MMNm=magnetic mismatch negativity) were calculated. (a) Vowel mismatch (/a/ against /e/) resulted in an enlarged N1m amplitude reflecting, most presumably, peripheral adaptation processes. (b) As concerns lateralized responses to syllable-like structures, only the shortest transient duration (=10 ms) elicited a significantly enhanced MMNm at the left side. Conceivably, the observed hemispheric difference contributes to prelexical parsing of the auditory signal rather than the encoding of linguistic categories.

A vowel synthesizer based on F0-modulated formant sinusoids

A vowel synthesis algorithm was developed resembling parallel formant synthesizers. However, formants are computed as amplitude- and phase-modulated sinusoids instead of being represented by recursive filters or resonators. The fundamental frequency is imposed on the signal in the following way: Each pitch period starts with a short initial rise of a duration of pi/2 of the first formant frequency; at the end of this ramp phase all formants start as sinusoids at pre-defined phase angles and amplitudes, and successively undergo linear attenuation toward zero amplitude at the end of each pitch period. Adjacent pitch periods, thus, do not influence each other. In principle, the signals produced by this algorithm resemble the output of parallel formant synthesizers [e.g., D. H. Klatt, J. Acoust. Soc. Am. 67, 971–995 (1980)]. However, by incremental sample-by-sample computation of the formants’ phase angles, formant frequencies are allowed to continuously change within single pitch periods. This algorithm produces vowels as well as formant transitions signaling stop consonant–vowel syllables such as /ba/, exhibiting a homogeneous, stereotypic voice quality. Because of its additive procedure, this method might allow for the implementation of a variety of further acoustic aspects of the human speaking voice in a well-controlled manner.