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Biomedical subjects

A Löfqvist

Publications and source records attributed to A Löfqvist.

At least 19 recordsLinked to original sources
PubMed1998

Dynamics of intergestural timing: a perturbation study of lip-larynx coordination.

In this study, downward-directed mechanical perturbations were applied to the lower lip during both repetitive (/...paepaepae.../) and discrete (/pe'saepaepl/) utterances in order to examine the perturbation-induced changes of intergestural timing between syllables (i.e., between the bilabial and laryngeal gestures for successive /p/'s) and within phonemes (i.e., between the bilabial and laryngeal gestures within single /p/'s). Our findings led us to several conclusions. First, steady-state (phase-resetting) analyses of the repetitive utterances indicated both that "permanent" phase shifts existed for both the lips and the larynx after the system returned to its pre-perturbation rhythm and that smaller steady-state shifts occurred in the relative phasing of these gestures. These results support the hypothesis that central intergestural dynamics can be reset by peripheral articulatory events. Such resetting was strongest when the perturbation was delivered within a "sensitive phase" of the cycle, during which the downwardly directed lower-lip perturbation opposed the just-initiated, actively controlled bilabial closing gesture for /p/. Although changes in syllable duration were found for other perturbed phases, these changes were simply transient effects and did not indicate a resetting of the central "clock." Second, analyses of the transient portions of the perturbed cycles of the repetitive utterances indicated that the perturbation-induced steady-state phase shifts are almost totally attributable to changes occurring during the first two perturbed cycles. Finally, the transient changes in speech timing induced by perturbations in the discrete sequences appeared to share a common dynamical basis with the changes to the repetitive sequences. We conclude by speculating on the type of dynamical system that could generate these temporal patterns.

Adult↗
PubMed1997

Lip and jaw kinematics in bilabial stop consonant production.

This paper reports two experiments, each designed to clarify different aspects of bilabial stop consonant production. The first one examined events during the labial closure using kinematic recordings in combination with records of oral air pressure and force of labial contact. The results of this experiment suggested that the lips were moving at a high velocity when the oral closure occurred. They also indicated mechanical interactions between the lips during the closure, including tissue compression and the lower lip moving the upper lip upward. The second experiment studied patterns of upper and lower lip interactions, movement variability within and across speakers, and the effects on lip and jaw kinematics of stop consonant voicing and vowel context. Again, the results showed that the lips were moving at a high velocity at the onset of the oral closure. No consistent influences of stop consonant voicing were observed on lip and jaw kinematics in five subjects, nor on a derived measure of lip aperture. The overall results are compatible with the hypothesis that one target for the lips in bilabial stop production is a region of negative lip aperture. A negative lip aperture implies that to reach their virtual target, the lips would have to move beyond each other. Such a control strategy would ensure that the lips will form an air light seal irrespective of any contextual variability in the onset positions of their closing movements.

Female↗
PubMed1994

Speech motor control.

The development of new measurement techniques and improved models of the larynx and the vocal tract have significantly advanced our understanding of speech motor control. Recently, several groups have been using electromagnetic transduction techniques to record tongue movements. The laryngeal vibrations have been modeled and studied using techniques from non-linear dynamics. Computational models of supraglottal movements have been proposed and tested. A connectionist model that synthesizes the results obtained from observing the effects of variations in rate, stress, and phonetic context on speech kinematics has recently been proposed.

Humans↗
PubMed1994

Lip-larynx coordination in speech: effects of mechanical perturbations to the lower lip.

This experiment investigates the coordination between the larynx and the lips and jaw in voiceless consonant production using an experimental paradigm where a mechanical perturbation is applied to an articulator. Three subjects received unexpected perturbations to the lower lip during the transition between the first vowel and the first stop in /i'pip/. Movements of the upper articulators (lips and jaw) were recorded using an optoelectronic technique. Laryngeal responses were monitored using transillumination; intraoral pressure and the acoustic signal were also recorded. Results showed that laryngeal abduction was delayed following lip perturbation and that the duration of the laryngeal adduction gesture was lengthened. The oral movements toward closure of two of the subjects were modified and all subjects showed modification of the oral release movements in the perturbed conditions. All subjects showed an increased movement velocity and displacement of the upper lip, lower lip, and jaw in the oral opening phase. First trial compensation, however, was not observed in two of the three subjects. The results are discussed with respect to the speech perturbation literature and the notion of coordinative structures.

Biomechanical Phenomena↗
PubMed1994

Tongue body kinematics in velar stop production: influences of consonant voicing and vowel context.

This study examines vertical and horizontal tongue body movements in VCV sequences, where the consonant is a voiced or voiceless velar stop. The movement data were recorded using a magnetic transduction technique in two subjects. Consistent with studies of lip and jaw kinematics, the duration of the tongue body raising movement towards closure for the consonant was longer for the voiced stop. In contrast to lip and jaw movements, peak velocity and amplitude of the raising movements were consistently higher for the voiced stop. The larger displacement of the closing movement for the voiced stop was due to a lower starting position of the movement during the preceding vowel. Examination of the tongue body lowering movement for the vowel preceding the velar stop showed it to be longer when the following stop was voiced. Also this lowering movement had a higher peak velocity and amplitude in the voiced environment. These results thus suggest that both the lowering and raising movements in the VC sequence are affected by the voicing status of the consonant. In addition, the second vowel in the VCV sequence showed reliable influences on tongue body movements for the first vowel and the consonant.

Humans↗
PubMed1994

Speech motor coordination and control: evidence from lip, jaw, and laryngeal movements.

The movements of the lower lip, jaw, and larynx during speech were examined for two different speech actions involving oral closing for /p/ and oral constriction for /f/. The initial analysis focused on the manner in which the different speech articulators were coordinated to achieve sound production. It was found that the lip, jaw, and laryngeal movements were highly constrained in their relative timing apparently to facilitate their coordination. Differences were noted in the degree to which speech articulator timing covaried dependent on the functional characteristics of the action. Movements associated with coordinating multiple articulators for a single sound were more highly constrained in their relative timing than were movements associated with sequencing of individual sounds. The kinematic patterns for the different articulators were found to vary in a number of systematic ways depending on the identity of the sound being produced, the phonetic context surrounding the target sound, and whether one versus two consonants were produced in sequence. The results are consistent with an underlying organization reflecting the construct of the phoneme. It is suggested that vocal tract actions for the sounds of the language are stored in memory as motor programs and sequenced together into larger meaningful units during speaking. Speech articulator motion for the different vowel sounds was found to be influenced by the identity of the following consonant, suggesting that speech movements are modified in chunks larger than the individual phonetic segments. It appears that speech production is a hierarchical process with multiple levels of organization transforming cognitive intent into coherent and perceptually identifiable sound sequences.

Adult↗
PubMed1989

A voice accumulation--validation and application.

Studies of vocal behavior under natural conditions require suitable techniques for obtaining records of voice use. We describe the operation of a newly designed voice accumulator that allows registration of fundamental frequency and phonation time during a 12-hour period. The device is based on microprocessors and allows accumulation of the voice fundamental frequency within 60-600 Hz. The voice signal is picked up by a contact microphone attached to the front part of the neck. Analysis of fundamental frequency distribution and phonation time is made on a personal computer. Validation of the device shows it to provide accurate measurements of fundamental frequency, although it tends to underestimate phonation time. In a field test, the accumulator was used to analyze vocal behavior during two work-days in a group of nurses and a group of speech pathologists. Overall, the speech pathologists had a lower fundamental frequency level and higher values of phonation time than the nurses. These field results confirm the validation of the voice accumulator.

Adult↗
PubMed1989

The cricothyroid muscle in voicing control.

Initiation and maintenance of vibrations of the vocal folds require suitable conditions of adduction, longitudinal tension, and transglottal airflow. Thus manipulation of adduction/abduction, stiffening/slackening, or degree of transglottal flow may, in principle, be used to determine the voicing status of a speech segment. This study explores the control of voicing and voicelessness in speech with particular reference to the role of changes in the longitudinal tension of the vocal folds, as indicated by cricothyroid (CT) muscle activity. Electromyographic recordings were made from the CT muscle in two speakers of American English and one speaker of Dutch. The linguistic material consisted of reiterant speech made up of CV syllables where the consonants were voiced and voiceless stops, fricatives, and affricates. Comparison of CT activity associated with the voiced and voiceless consonants indicated a higher level for the voiceless consonants than for their voiced cognates. Measurements of the fundamental frequency (F0) at the beginning of a vowel following the consonant show the common pattern of higher F0 after voiceless consonants. For one subject, there was no difference in cricothyroid activity for voiced and voiceless affricates; in this case, the consonant-induced variations in the F0 of the following vowel were also less robust. Consideration of timing relationships between the EMG curves for voiced and voiceless consonants suggests that the differences most likely reflect control of vocal-fold tension for maintenance or suppression of phonatory vibrations. The same mechanism also seems to contribute to the well-known difference in F0 at the beginning of vowels following voiced and voiceless consonants.

Adult↗
PubMed1988

Laryngeal kinematics in voiceless obstruents produced by hearing-impaired speakers.

During normal production of voiceless consonants several events occur simultaneously in the vocal tract. These events must be temporally coordinated. Earlier work has indicated that a breakdown in interarticulator timing can contribute to the characteristic voiced-voiceless errors produced by hearing-impaired speakers. The present study examines kinematic details of the laryngeal articulatory gesture in 2 deaf speakers and a control subject using transillumination of the larynx. Results indicate that hearing-impaired speakers often do not produce differences between stops and fricatives in the kinematic details of the gesture. That is to say, although hearing speakers commonly use a larger laryngeal gesture for fricatives than for stops and also show durational differences of the abduction and the adduction phases between phonetic categories, the hearing-impaired subjects did not make them. Also, the deaf speakers participating in this study were more variable in the kinematic measures.

Biomechanical Phenomena↗
PubMed1984

Laryngeal muscles and articulatory control.

The present study continues earlier work on laryngeal control in speech with particular reference to adjustments in Swedish voiceless consonants and consonant cluster. Electromyographic recordings were obtained from four intrinsic laryngeal muscles together with simultaneous transillumination and acoustic signals. Results indicate that the vocalis and lateral cricoarytenoid muscles participate in the control of both articulation and phonation (F0). The interarytenoid muscle appeared to be involved only in articulatory adjustments. Activity in the cricothyroid was mostly related F0 change; however, this muscle also showed an increase in activity for voiceless sounds. In addition, the vocalis muscle appeared to participate in glottal adduction without complete closure in voiceless clusters with the lateral cricoarytenoid and the interarytenoid playing no particular roles. The results suggest the need of studying laryngeal behavior in speech within a general systems famework for movement control.

Electromyography↗
PubMed1983

Laryngeal vibrations: a comparison between high-speed filming and glottographic techniques.

This study was designed to compare information on laryngeal vibrations obtained by high-speed filming, photoglottography (PGG), and electroglottography (ECG). Simultaneous glottographic signals and high-speed films were obtained from two subjects producing steady phonation. Measurements of glottal width were made at three points along the glottis in the anterior--posterior dimension and aligned with the other records. Results indicate that PGG and film measurements give essentially the same information for peak glottal opening and glottal closure. The EGG signal appears to reliably indicate vocal-fold contact. Together, PGG and EGG may provide much of the information obtained from high-speed filming as well as potentially detect horizontal phase differences during opening and closing.

Electrodiagnosis↗