Kathleen Kurowski

Acoustic and perceptual characteristics of voicing in fricatives and fricative clusters

Several types of measurements were made to determine the acoustic characteristics that distinguish between voiced and voiceless fricatives in various phonetic environments. The selection of measurements was based on a theoretical analysis that indicated the acoustic and aerodynamic attributes at the boundaries between fricatives and vowels. As expected, glottal vibration extended over a longer time in the obstruent interval for voiced fricatives than for voiceless fricatives, and there were more extensive transitions of the first formant adjacent to voiced fricatives than for the voiceless cognates. When two fricatives with different voicing were adjacent, there were substantial modifications of these acoustic attributes, particularly for the syllable-final fricative. In some cases, these modifications leads to complete assimilation of the voicing feature. Several perceptual studies with synthetic vowel-consonant-vowel stimuli and with edited natural stimuli examined the role of consonant duration, extent and location of glottal vibration, and extent of formant transitions on the identification of the voicing characteristics of fricatives. The perceptual results were in general consistent with the acoustic observations and with expectations based on the theoretical model. The results suggest that listeners base their voicing judgments of intervocalic fricatives on an assessment of the time interval in the fricative during which there is no glottal vibration. This time interval must exceed about 60 ms if the fricative is to be judged as voiceless, except that a small correction to this threshold is applied depending on the extent to which the first-formant transitions are truncated at the consonant boundaries.

Perceptual integration of the murmur and formant transitions for place of articulation in nasal consonants

This study reassessed the role of the nasal murmur and formant transitions as perceptual cues for place of articulation in nasal consonants across a number of vowel environments. Five types of computer-edited stimuli were generated from natural utterances consisting of [m n] followed by [i e a o u]: (1) full murmurs; (2) transitions plus vowel segments; (3) the last six pulses of the murmur; (4) the six pulses starting from the beginning of the formant transitions; and (5) the six pulses surrounding the nasal release (three pulses before and three pulses after). Results showed that the murmur provided as much information for the perception of place of articulation as did the transitions. Moreover, the highest performance scores for place of articulation were obtained in the six-pulse condition containing both murmur and transition information. The data support the view that it is the combination of nasal murmur plus formant transitions which forms an integrated property for the perception of place of articulation.

The foreign accent syndrome: A perspective

Abstract Although there are now a fair number of reported case studies of the foreign accent syndrome, there is little consensus about it. We provide a perspective on the foreign accent syndrome focusing on three areas for which there is as yet disagreement in the literature. These include whether the foreign accent syndrome is indeed a syndrome in its own right, whether the features of the disorder can be explicated in terms of a single underlying mechanism, and whether there is a common neural substrate that gives rise to this disorder. Based on a review of the literature and our own work, we propose that the foreign accent syndrome is properly considered a syndrome and that it is distinct in both its characteristics and underlying mechanism from an apraxia of speech, a dysarthria, and an aphasic speech output disorder. We hypothesize that a deficit in linguistic prosody underlies the foreign accent syndrome. And finally, we argue that the foreign accent syndrome emerges as a consequence of damage to the dominant language (usually left hemisphere) speech output motor system affecting the primary motor cortex and either its cortico-cortical connections or its cortico-subcortical projections.

Acoustic properties for place of articulation in nasal consonants.

The goal of this study was to determine whether acoustic properties could be derived for English labial and alveolar nasal consonants that remain stable across vowel contexts, speakers, and syllable positions. In experiment I, critical band analyses were conducted of five tokens each of [m] and [n] followed by the vowels [i e a o u] spoken by three speakers. Comparison of the nature of the changes in the spectral patterns from the murmur to the release showed that, for labials, there was a greater change in energy in the region of Bark 5–7 relative to that of Bark 11–14, whereas, for alveolars, there was a greater change in energy from the murmur to the release in the region of Bark 11–14 relative to that of Bark 5–7. Quantitative analyses of each token indicated that over 89% of the utterances could be appropriately classified for place of articulation by comparing the proportion of energy change in these spectral regions. In experiment II, the spectral patterns of labial and alveolar nasals produced in ...

On-Line Processing of Filler–Gap Constructions in Aphasia

Two experiments were conducted exploring on-line processing of filler-gap construction in aphasia. An auditory-auditory lexical decision paradigm was used to investigate whether Brocas and Wernickes aphasic patients show, as do normals, reactivation of the filler at the gap site. Experiment I investigated the processing of a number of filler-gap constructions including wh-questions, relative clauses as subject, relative clauses as object, and embedded wh-questions. Brocas aphasics showed reactivation of the filler at the gap site, whereas Wernickes aphasics did not. Experiment II examined object relative clauses and their processing by Brocas aphasics. In addition, we investigated whether the presence (or absence) of the relative pronoun played any role in on-line processing. Brocas aphasics performed as did normals. In addition, their performance was unaffected by the presence or absence of the relative pronoun. The results of these experiments suggest that Brocas aphasics do not have an impairment in processing or representing thematic relationships of NP arguments to predicates or relating traces to their antecedents.

The characteristics of voicing in syllable-initial fricatives in American English

This study investigated the acoustic characteristics of voicing in the production of fricative consonants. The fricatives [f v s z] were used in combination with the vowels [i e a o u] to create CV syllables, which were produced by four subjects both in a context condition (following voiced and voiceless velar stops) and in isolation. Analyses were conducted of the time course of glottal excitation during the fricative noise interval in the voiced and voiceless fricative stimuli. Results showed that the patterns of voicing in the fricative noise interval were influenced by the voicing characteristics of preceding stop consonants. Nonetheless, these carryover coarticulatory effects were short-lived, influencing only the first 10s of ms of the following segment. Despite the influence of phonetic context on the patterns of voicing, an acoustic measure relating to the presence or absence of glottal excitation at the acoustic boundaries of the fricative noise reliably classified a majority (93%) of the fricative consonants in terms of the phonetic category of voicing. Thus, while phonetic context affected the patterns of glottal excitation in the fricative noise interval, it did not affect the criterial attribute associated with the phonetic category of voicing.

PARADOXICAL FACILITATION: THE RESOLUTION OF FOREIGN ACCENT SYNDROME AFTER CEREBELLAR STROKE

Foreign accent syndrome (FAS) is a rare speech disorder characterized by a change in prosody and other speech variables yielding altered phonetic characteristics that are perceived as a foreign accent. Lesions associated with FAS typically involve left frontoparietal regions. However, 2 reported left-hemispheric stroke patients presenting with FAS also had hypoperfusion of the right cerebellum on 99mTc ECD SPECT imaging, presumably from diaschisis. In both cases, there was a close parallel between the normalization of the cerebellar perfusion and resolution of the clinical syndrome up to 3 years later despite continued hypoperfusion of left hemispheric structures.1,2 The authors argued that the temporal association between the clinical improvement and the right cerebellar perfusion suggested a functional role of the cerebellum in this speech disorder. We describe a unique case that provides convergent evidence for a causative role of the cerebellum in FAS. ### Case report. A right-handed English-speaking woman was 58 years of age at the time of her left frontoparietal infarct (figure, A), presenting with right upper limb paresis and aphemia. Within hours, the patient’s paresis resolved to a slight hand ataxia and her speech sounded like English spoken with an unlearned accent. Workup suggested an embolic event, and she was discharged on warfarin. The foreign accent persisted for approximately 3 years until she had a right inferior cerebellar hemorrhage (figure, B–D) from accidental excessive anticoagulation. Following this second stroke, the patient and her family noted that the foreign accent was no longer perceptible in her speech. …

The nature of speech production impairments in anterior aphasics: an acoustic analysis of voicing in fricative consonants.

This study investigated the acoustic characteristics of voicing in English fricative consonants produced by anterior aphasics and the effects of phonetic context on these characteristics. Three patients produced voiced and voiceless fricative-vowel syllables in isolation, following a voiced velar stop, and following a voiceless velar stop. Acoustic analyses were conducted of the amplitude and patterning of glottal excitation, as well as fricative noise duration. Results showed that, although the patients are able to coordinate the articulatory gestures for voicing in fricative consonants, they demonstrated abnormal patterns of glottal excitation in the amplitude measures, owing to weaker amplitudes of glottal excitation in voiced fricatives. Context effects failed to emerge because of dysfluent speech. These results suggest that the locus of the speech production deficit of anterior aphasics is not at the higher stages of phoneme selection or planning but rather in articulatory implementation, one related to laryngeal control.

ACOUSTIC PROPERTIES FOR THE PERCEPTION OF NASAL CONSONANTS

Publisher Summary This chapter presents a brief acoustic characterization of nasal consonants as a sound class, focusing on the acoustic complexity of the nasal manner of articulation. The focus of studies on the acoustics and perception of nasal consonants has changed in the last decade. Emphasis is currently placed on more generalized spectral patterns rather than on absolute frequencies, and on patterns of change over time rather than on spectral attributes at a particular point in time. These changes are the result of two concurrent developments in speech acoustics and speech perception research. One of these developments involved advances in analytic techniques that have led to a reformulation of the basic approach to the question of how and where the acoustic and perceptual attributes for the phonetic dimensions of speech may be instantiated. Characteristic of this new approach is an emphasis on dynamic or temporally driven analyses. These analyses have been widely applied in research on the sound classes of speech.

Consonant and vowel production of right hemisphere patients

Recent reports of subclinical phonetic deficits in posterior and most particularly in Wernickes aphasics have challenged the traditional dichotomy which characterized speech deficits in aphasia as anterior/phonetic and posterior/phonological. It is unclear whether the basis of the phonetic deficit in posterior aphasics reflects the fact that the speech production system extends to more posterior regions of the left hemisphere than previously thought or alternatively is the result of generalized brain damage effects. The present study explores the latter possibility by investigating the patterns of speech production in right hemisphere brain-damaged, non-aphasic patients with anterior and posterior lesions. Acoustic analyses conducted on a range of consonant and vowel parameters showed differences between the speech patterns of both anterior and posterior right hemisphere patients and that of Wernickes aphasics. These findings suggest that the subclinical deficit of Wernickes aphasics can not simply be ascribed to a generalized brain-damage effect and raise the possibility that the right hemisphere also plays some role, if only a minor one, in the phonetic implementation of speech.