Biomedical subjects

David J Ostry

Publications and source records attributed to David J Ostry.

14 recordsLinked to original sources

PubMed2006

Somatosensory precision in speech production.

Speech production is dependent on both auditory and somatosensory feedback. Although audition may appear to be the dominant sensory modality in speech production, somatosensory information plays a role that extends from brainstem responses to cortical control. Accordingly, the motor commands that underlie speech movements may have somatosensory as well as auditory goals. Here we provide evidence that, independent of the acoustics, somatosensory information is central to achieving the precision requirements of speech movements. We were able to dissociate auditory and somatosensory feedback by using a robotic device that altered the jaw's motion path, and hence proprioception, without affecting speech acoustics. The loads were designed to target either the consonant- or vowel-related portion of an utterance because these are the major sound categories in speech. We found that, even in the absence of any effect on the acoustics, with learning subjects corrected to an equal extent for both kinds of loads. This finding suggests that there are comparable somatosensory precision requirements for both kinds of speech sounds. We provide experimental evidence that the neural control of stiffness or impedance--the resistance to displacement--provides for somatosensory precision in speech production.

Acoustic Stimulation↗

PubMed2006

Neural averaging in motor learning.

The capacity for skill development over multiple training episodes is fundamental to human motor function. We have studied the process by which skills evolve with training by progressively modifying a series of motor learning tasks that subjects performed over a 1-mo period. In a series of empirical and modeling studies, we show that performance undergoes repeated modification with new learning. Each in a series of prior training episodes contributes such that present performance reflects a weighted average of previous learning. Moreover, we have observed that the relative weighting of skills learned wholly in the past changes with time. This suggests that the neural substrate of skill undergoes modification after consolidation.

Arm↗

PubMed2005

Transfer and durability of acquired patterns of human arm stiffness.

Previous studies have shown that the nervous system can produce anticipatory adjustments that alter the mechanical behavior of the arm in order to resist environmental disturbances. In the present paper, we focus on the ability of subjects to transfer acquired stiffness patterns to other parts of the workspace and on the durability of stiffness adaptations. To explore the transfer of stiffness control, subjects were trained at the left of the workspace to resist the effects of a single-axis disturbance that was applied by a robotic device. Following training, they were tested for transfer at the right. One group of subjects experienced similar torques at the left and right of the workspace, whereas the other group of subjects experienced similar forces at the hand. Following the initial training at the left, the observed orientation of the hand-stiffness ellipse rotated in the direction of the disturbance. In tests at the right, transfer was observed only when the direction of disturbance resulted in torques that were similar to those experienced during training. The results thus suggest that under the conditions of this experiment stiffness control is acquired and transfers in a joint- or muscle-based system of coordinates. A second experiment assessed the durability of an acquired stiffness pattern. Subjects were trained on 2 consecutive days to resist a single-axis disturbance. On a third day, the direction of the disturbance was switched by 90 degrees . Substantial interference with the new adaptation was observed. This suggests that stiffness training results in durable changes to the neural signals that underlie stiffness control.

Adaptation, Physiological↗

PubMed2005

Voluntary control of human jaw stiffness.

Recent studies of human arm movement have suggested that the control of stiffness may be important both for maintaining stability and for achieving differences in movement accuracy. In the present study, we have examined the voluntary control of postural stiffness in 3D in the human jaw. The goal is to address the possible role of stiffness control in both stabilizing the jaw and in achieving the differential precision requirements of speech sounds. We previously showed that patterns of kinematic variability in speech are systematically related to the stiffness of the jaw. If the nervous system uses stiffness control as a means to regulate kinematic variation in speech, it should also be possible to show that subjects can voluntarily modify jaw stiffness. Using a robotic device, a series of force pulses was applied to the jaw to elicit changes in stiffness to resist displacement. Three orthogonal directions and three magnitudes of forces were tested. In all conditions, subjects increased the magnitude of jaw stiffness to resist the effects of the applied forces. Apart from the horizontal direction, greater increases in stiffness were observed when larger forces were applied. Moreover, subjects differentially increased jaw stiffness along a vertical axis to counteract disturbances in this direction. The observed changes in the magnitude of stiffness in different directions suggest an ability to control the pattern of stiffness of the jaw. The results are interpreted as evidence that jaw stiffness can be adjusted voluntarily, and thus may play a role in stabilizing the jaw and in controlling movement variation in the orofacial system.

Adult↗

PubMed2005

Generalization of motor learning based on multiple field exposures and local adaptation.

Previous studies have used transfer of learning over workspace locations as a means to determine whether subjects code information about dynamics in extrinsic or intrinsic coordinates. Transfer has been observed when the torque associated with joint displacement is similar between workspace locations-rather than when the mapping between hand displacement and force is preserved-which is consistent with muscle- or joint-based encoding. In the present study, we address the generality of an intrinsic coding of dynamics and examine how generalization occurs when the pattern of torques varies over the workspace. In two initial experiments, we examined transfer of learning when the direction of a force field was fixed relative to an external frame of reference. While there were no beneficial effects of transfer after training at a single location (experiments 1 and 2), excellent performance was observed at the center of the workspace after training at two lateral locations (experiment 2). Experiment 3 and associated simulations assessed the characteristics of this generalization. In these studies, we examined the patterns of transfer observed after adaptation to force fields that were composed of two subfields that acted in opposite directions. The experimental and simulated data are consistent with the idea that information about dynamics is encoded in intrinsic coordinates. The nervous system generalizes dynamics learning by interpolating between sets of control signals, each locally adapted to different patterns of torques.

Adaptation, Physiological↗

PubMed2005

The Haskins optically corrected ultrasound system (HOCUS).

The tongue is critical in the production of speech, yet its nature has made it difficult to measure. Not only does its ability to attain complex shapes make it difficult to track, it is also largely hidden from view during speech. The present article describes a new combination of optical tracking and ultrasound imaging that allows for a noninvasive, real-time view of most of the tongue surface during running speech. The optical system (Optotrak) tracks the location of external structures in 3-dimensional space using infrared emitting diodes (IREDs). By tracking 3 or more IREDs on the head and a similar number on an ultrasound transceiver, the transduced image of the tongue can be corrected for the motion of both the head and the transceiver and thus be represented relative to the hard structures of the vocal tract. If structural magnetic resonance images of the speaker are available, they may allow the estimation of the location of the rear pharyngeal wall as well. This new technique is contrasted with other currently available options for imaging the tongue. It promises to provide high-quality, relatively low-cost imaging of most of the tongue surface during fairly unconstrained speech.

Humans↗

PubMed2004

Stimulation of the posterior parietal cortex interferes with arm trajectory adjustments during the learning of new dynamics.

Substantial neurophysiological evidence points to the posterior parietal cortex (PPC) as playing a key role in the coordinate transformation necessary for visually guided reaching. Our goal was to examine the role of PPC in the context of learning new dynamics of arm movements. We assessed this possibility by stimulating PPC with transcranial magnetic stimulation (TMS) while subjects learned to make reaching movements with their right hand in a velocity-dependent force field. We reasoned that, if PPC is necessary to adjust the trajectory of the arm as it interacts with a novel mechanical system, interfering with the functioning of PPC would impair adaptation. Single pulses of TMS were applied over the left PPC 40 msec after the onset of movement during adaptation. As a control, another group of subjects was stimulated over the visual cortex. During early stages of learning, the magnitude of the error (measured as the deviation of the hand paths) was similar across groups. By the end of the learning period, however, error magnitudes decreased to baseline levels for controls but remained significantly larger for the group stimulated over PPC. Our findings are consistent with a role of PPC in the adjustment of motor commands necessary for adapting to a novel mechanical environment.

Adaptation, Physiological↗

PubMed2004

Is interlimb transfer of force-field adaptation a cognitive response to the sudden introduction of load?

Recently, Criscimagna-Hemminger et al. (2003) reported a pattern of generalization of force-field adaptation between arms that differs from the pattern that occurs across different configurations of the same arm. Although the intralimb pattern of generalization points to an intrinsic encoding of dynamics, the interlimb transfer described by these authors indicates that information about force is represented in a frame of reference external to the body. In the present study, subjects adapted to a viscous curl-field in two experimental conditions. In one condition, the field was introduced suddenly and produced clear deviations in hand paths; in the second condition, the field was introduced gradually so that at no point during the adaptation process could subjects observe or did they have to correct for a substantial kinematic error. In the first case, a pattern of interlimb transfer consistent with Criscimagna-Hemminger et al. (2003) was observed, whereas no transfer of learning between limbs occurred in the second condition. The findings suggest that there is limited transfer of fine compensatory-force adjustment between limbs. Transfer, when it does occur, may be primarily the result of a cognitive strategy that arises as a result of the sudden introduction of load and associated kinematic error.

Adaptation, Physiological↗

PubMed2004

Learning to control arm stiffness under static conditions.

We used a robotic device to test the idea that impedance control involves a process of learning or adaptation that is acquired over time and permits the voluntary control of the pattern of stiffness at the hand. The tests were conducted in statics. Subjects were trained over the course of 3 successive days to resist the effects of one of three different kinds of mechanical loads: single axis loads acting in the lateral direction, single axis loads acting in the forward/backward direction, and isotropic loads that perturbed the limb in eight directions about a circle. We found that subjects in contact with single axis loads voluntarily modified their hand stiffness orientation such that changes to the direction of maximum stiffness mirrored the direction of applied load. In the case of isotropic loads, a uniform increase in endpoint stiffness was observed. Using a physiologically realistic model of two-joint arm movement, the experimentally determined pattern of impedance change could be replicated by assuming that coactivation of elbow and double joint muscles was independent of coactivation of muscles at the shoulder. Moreover, using this pattern of coactivation control we were able to replicate an asymmetric pattern of rotation of the stiffness ellipse that was observed empirically. These findings are consistent with the idea that arm stiffness is controlled through the use of at least two independent co-contraction commands.

Adult↗

PubMed2004

Baby hands that move to the rhythm of language: hearing babies acquiring sign languages babble silently on the hands.

The "ba, ba, ba" sound universal to babies' babbling around 7 months captures scientific attention because it provides insights into the mechanisms underlying language acquisition and vestiges of its evolutionary origins. Yet the prevailing mystery is what is the biological basis of babbling, with one hypothesis being that it is a non-linguistic motoric activity driven largely by the baby's emerging control over the mouth and jaw, and another being that it is a linguistic activity reflecting the babies' early sensitivity to specific phonetic-syllabic patterns. Two groups of hearing babies were studied over time (ages 6, 10, and 12 months), equal in all developmental respects except for the modality of language input (mouth versus hand): three hearing babies acquiring spoken language (group 1: "speech-exposed") and a rare group of three hearing babies acquiring sign language only, not speech (group 2: "sign-exposed"). Despite this latter group's exposure to sign, the motoric hypothesis would predict similar hand activity to that seen in speech-exposed hearing babies because language acquisition in sign-exposed babies does not involve the mouth. Using innovative quantitative Optotrak 3-D motion-tracking technology, applied here for the first time to study infant language acquisition, we obtained physical measurements similar to a speech spectrogram, but for the hands. Here we discovered that the specific rhythmic frequencies of the hands of the sign-exposed hearing babies differed depending on whether they were producing linguistic activity, which they produced at a low frequency of approximately 1 Hz, versus non-linguistic activity, which they produced at a higher frequency of approximately 2.5 Hz - the identical class of hand activity that the speech-exposed hearing babies produced nearly exclusively. Surprisingly, without benefit of the mouth, hearing sign-exposed babies alone babbled systematically on their hands. We conclude that babbling is fundamentally a linguistic activity and explain why the differentiation between linguistic and non-linguistic hand activity in a single manual modality (one distinct from the human mouth) could only have resulted if all babies are born with a sensitivity to specific rhythmic patterns at the heart of human language and the capacity to use them.

Hand↗

PubMed2003

A critical evaluation of the force control hypothesis in motor control.

The ability to formulate explicit mathematical models of motor systems has played a central role in recent progress in motor control research. As a result of these modeling efforts and in particular the incorporation of concepts drawn from control systems theory, ideas about motor control have changed substantially. There is growing emphasis on motor learning and particularly on predictive or anticipatory aspects of control that are related to the neural representation of dynamics. Two ideas have become increasingly prominent in mathematical modeling of motor function--forward internal models and inverse dynamics. The notion of forward internal models which has drawn from work in adaptive control arises from the recognition that the nervous system takes account of dynamics in motion planning. Inverse dynamics, a complementary way of adjusting control signals to deal with dynamics, has proved a simple means to establish the joint torques necessary to produce desired movements. In this paper, we review the force control formulation in which inverse dynamics and forward internal models play a central role. We present evidence in its favor and describe its limitations. We note that inverse dynamics and forward models are potential solutions to general problems in motor control--how the nervous system establishes a mapping between desired movements and associated control signals, and how control signals are adjusted in the context of motor learning, dynamics and loads. However, we find little empirical evidence that specifically supports the inverse dynamics or forward internal model proposals per se. We further conclude that the central idea of the force control hypothesis--that control levels operate through the central specification of forces--is flawed. This is specifically evident in the context of attempts to incorporate physiologically realistic muscle and reflex mechanisms into the force control model. In particular, the formulation offers no means to shift between postures without triggering resistance due to postural stabilizing mechanisms.

Animals↗

PubMed2003

Somatosensory basis of speech production.

The hypothesis that speech goals are defined acoustically and maintained by auditory feedback is a central idea in speech production research. An alternative proposal is that speech production is organized in terms of control signals that subserve movements and associated vocal-tract configurations. Indeed, the capacity for intelligible speech by deaf speakers suggests that somatosensory inputs related to movement play a role in speech production-but studies that might have documented a somatosensory component have been equivocal. For example, mechanical perturbations that have altered somatosensory feedback have simultaneously altered acoustics. Hence, any adaptation observed under these conditions may have been a consequence of acoustic change. Here we show that somatosensory information on its own is fundamental to the achievement of speech movements. This demonstration involves a dissociation of somatosensory and auditory feedback during speech production. Over time, subjects correct for the effects of a complex mechanical load that alters jaw movements (and hence somatosensory feedback), but which has no measurable or perceptible effect on acoustic output. The findings indicate that the positions of speech articulators and associated somatosensory inputs constitute a goal of speech movements that is wholly separate from the sounds produced.

Acoustic Stimulation↗

PubMed2002

Transfer of motor learning across arm configurations.

It has been suggested that the learning of new dynamics occurs in intrinsic coordinates. However, it has also been suggested that elements that encode hand velocity, and hence act in an extrinsic frame of reference, play a role in the acquisition of dynamics. To reconcile claims regarding the coordinate system involved in the representation of dynamics, we have used a procedure involving the transfer of force-field learning between two workspace locations. Subjects made point-to-point movements while holding a two-link manipulandum. Subjects were first trained to make movements in a single direction at the left of the workspace. They were then tested for transfer of learning at the right of the workspace. Two groups of subjects were defined. For the subjects in group j, movements at the left and right workspace locations were matched in terms of joint displacements. For the subjects in group h, movements in the two locations had the same hand displacements. Workspace locations were chosen such that for group j, the paths (for training and testing) that were identical in joint space were orthogonal in hand space. The subjects in group j showed good transfer between workspace locations, whereas the subjects in group h showed poor transfer. These results are in agreement with the idea that new dynamics are encoded in intrinsic coordinates and that this learning has a limited range of generalization across joint velocities.

Adult↗

PubMed2002

Relationship between jaw stiffness and kinematic variability in speech.

Humans produce speech by controlling a complex biomechanical apparatus to achieve desired speech sounds. We show here that kinematic variability in speech may be influenced by patterns of jaw stiffness. A robotic device was used to deliver mechanical perturbations to the jaw to quantify its stiffness in the mid-sagittal plane. Measured jaw stiffness was anisotropic. Stiffness was greatest along a protrusion-retraction axis and least in the direction of jaw raising and lowering. Consistent with the idea that speech movements reflect directional asymmetries in jaw stiffness, kinematic variability during speech production was found to be high in directions in which stiffness is low and vice versa. In addition, for higher jaw elevations, stiffness was greater and kinematic variability was less. The observed patterns of kinematic variability were not specific to speech-similar patterns appeared in speech and nonspeech movements. The empirical patterns of stiffness were replicated by using a physiologically based model of the jaw. The simulation studies support the idea that the pattern of jaw stiffness is affected by musculo-skeletal geometry and muscle-force-generating abilities with jaw geometry being the primary determinant of the orientation of the stiffness ellipse.

Adult↗