Passive Arm Movements Research Articles

Development of a 4DoFs exoskeleton robot for passive arm movement assistance

Proper functioning of the upper limbs is important to manage essential activities of daily living. To provide assistance and rehabilitation to individuals with upper limb dysfunction due to conditions such as stroke or spinal cord injuries, we have developed a 4DoFs exoskeleton robot (ExoRob). The ExoRob was designed to be worn on the lateral side of the upper arm, to conform to a naturalistic range of movement for the shoulder and elbow joints. This paper focuses on the modelling, design, development, and control of the ExoRob. Experiments were carried out with healthy human subjects where trajectories tracking in the form of passive rehabilitation exercises were performed. Further experiments were carried out with the master exoskeleton arm (mExoArm, an upper-limb prototype exoskeleton arm) where subjects operate the mExoArm (like a joystick) to maneuver the ExoRob to provide passive rehabilitation. Experimental results show that the ExoRob can effectively perform passive rehabilitation exercises.

Mutual influences of upper and lower extremities during cyclic movements

The possibility of muscle activation of passive arm during its cyclic movements, imposed by active movements of contralateral arm or by experimenter was studied, as well as the influence of lower extremities cyclic movements onto arm muscles activity. In addition to that the activity of legs muscles was estimated in dependence on motor task condition for arms. Ten healthy supine subjects carried out opposite movements of arms with and without stepping-like movements of both legs. The experiment included three conditions for arm movements: 1) the active movements of both arms; 2) the active movements of one arm, when other entirely passive arm participated in the movement by force; 3) passive arm movement caused by experimenter. In the condition 2) additional load on active arm was applied (30 N and 60 N). In all three conditions the experiment was carried out with arms movements only or together with legs movements. The capability of passive moving arm muscles activation depended on increasing afferent inflow from muscles of contralateral arm was demonstrated. Emerging electrical activity was modulated in the arms movements cycle and depended on the degree of active arm loading. During combined active movements of arms and legs the reduction of activity in the flexor muscles of shoulder and forearm was observed. Concomitant arms movements increased the magnitude ofelectromiographic bursts during passive stepping-like movements in the most of recorded muscles, and the same increasing was only observed in biceps femoris and tibialis anterior muscles during active legs movement. The increasing of loading of one arm caused essential augmentation of EMG-activity in the majority of recording legs muscles. The data obtained are the additional proof of existence of functionally significant neuronal interaction both between arms and between upper and lower extremities, which is evidently depend on the intraspinal neuronal connections.

A novel robotic system for quantifying arm kinematics and kinetics: Description and evaluation in therapist-assisted passive arm movements post-stroke

We developed a system for quantitatively measuring arm movement. Our approach provides a method to simultaneously capture upper limb kinetic and kinematic data during assisted passive arm movements. Data are analysed with respect to Cartesian and upper limb coordinate systems to obtain upper limb joint angles and torques.We undertook an evaluation of the system in participants with stroke to show the feasibility of this approach. During rehabilitation after stroke, one aspect of treatment includes the physiotherapist applying assistive forces to move the impaired arm of the patient who remains passive. There is a dearth of published data on the relationship between upper limb kinematics and the underlying forces (kinetics) in this mode of physiotherapy treatment. Such quantitative data are crucial in facilitating research into therapy practice, for example by measuring variation in practice and determining dosage. An experienced therapist prescribed passive movements tailored to the needs of 16 participants with stroke (41–81 years) with a range of anthropometric sizes and motor impairments. Our novel measurement tool recorded kinematic and kinetic data at 100Hz for 6–11 movements per participant. The kinetic data show that the majority of movements fall within upper limits of 36.7N in shoulder elevation, 22.4N in shoulder protraction, 4.6Nm in shoulder abduction, 12.8Nm in shoulder flexion, 2.4Nm in shoulder rotation and 5.5Nm in elbow flexion. These data show the potential of this system to better understand arm movement, in particular to objectively evaluate physical therapy treatments and support development of robotic devices to facilitate upper limb rehabilitation.

DYNAMIC MODELING AND EVALUATION OF A ROBOTIC EXOSKELETON FOR UPPER-LIMB REHABILITATION

Proper functioning of the shoulder, elbow, and wrist movements play a vital role in the performance of essential daily activities. To assist physically disabled people with impaired upper-limb function, we have been developing an exoskeleton robot (ExoRob) to rehabilitate and to ease upper limb motion. The proposed ExoRob will be comprised of seven degrees of freedom (DOFs) to enable natural movements of the human upper-limb. This paper focuses on the kinematic and dynamic modeling of the proposed ExoRob that corresponds to human upper-limbs. For this purpose, a nonlinear computed torque control technique was employed. In simulations, trajectory tracking corresponding to typical rehabilitation exercises were carried out to evaluate the performances of the developed model and controller. For the experimental part, only 3DOFs (elbow, wrist flexion/extension, wrist abduction/adduction) were considered. Simulated and experimental results show that the controller was able to maneuver the proposed ExoRob efficiently in order to track the desired trajectories, which in this case consisted in passive arm movements. Such movements are widely used in therapy and were performed efficiently with the developed ExoRob and the controller.

Subthalamic span of oscillations predicts deep brain stimulation efficacy for patients with Parkinson's disease

The significance of oscillations that characterize the subthalamic nucleus in Parkinson's disease is still under debate. Here, we analysed the spectral and spatial characteristics of 314 microelectrode trajectories from 128 patients undergoing subthalamic nucleus deep brain stimulation surgery for Parkinson's disease. We correlated the subthalamic nucleus pathophysiology with the outcome of surgery, as evaluated by the third section of the Unified Parkinson's Disease Rating Scale (motor score), which was subdivided into tremor, rigidity, limb-bradykinesia and axial-bradykinesia subscores. beta-oscillatory activity (13-30 Hz) comprised a continuous stretch within the subthalamic nucleus, and was limited to a distinctly-bounded dorsolateral oscillatory region. Although less consistent and more sporadic, low-frequency (3-7 Hz) power was also increased in the dorsolateral oscillatory region. In contrast, the more ventral subthalamic nucleus was characterized by consistently reduced beta and increased gamma (30-100 Hz) activity. Neuronal responses to passive arm movement (analysed by their alignment to goniometer tracing of the joints' angular displacement) were significantly more common in the dorsolateral oscillatory region than the ventral subthalamic nucleus region (62 versus 25% of sites tested respectively, P<0.01). The length of the dorsolateral oscillatory region recorded in the macroelectrode-implanted trajectory predicted a favourable response to subthalamic nucleus deep brain stimulation (R=0.67, P<0.0001). This correlation was also evident for improvement in the specific symptom subscores of rigidity, limb-bradykinesia and axial-bradykinesia (P<0.05). Similarly, increased subthalamic nucleus beta power was associated with postoperative improvement. In contrast, the preoperative response to levodopa did not correlate with dorsolateral oscillatory region length (P=0.33), however, it did tend to be associated with increased beta (and decreased low frequency) subthalamic nucleus power. Finally, the active macroelectrode contact, independently selected by optimal clinical outcome, coincided with the dorsolateral oscillatory region centre. On average, the location of the active contact was not significantly different from the dorsolateral oscillatory region centre (P=0.10), but was significantly different from the subthalamic nucleus centre (P<0.0001). We conclude that the spatial extent of the dorsolateral oscillatory region, which overlaps the motor territories of the subthalamic nucleus, predicts the outcome of subthalamic nucleus deep brain stimulation. Thus the frequency and spatial characteristics of the subthalamic nucleus trajectory may be used for deep brain stimulation outcome optimization.

Does bracing influence brain activity during knee movement: an fMRI study

Studies have shown that proprioceptive inputs during active and passive arm movements are processed in the primary and secondary somatosensory cortex and supplementary motor area of the brain. At which level of the central nervous system proprioceptive signals coming from the knee are regulated remains to be elucidated. In order to investigate whether there is a detectable difference in brain activity when various proprioceptive inputs are exerted at the knee, functional magnetic resonance imaging (fMRI) was used. fMRI in 13 healthy, right leg-dominant female volunteers compared brain activation during flexion-extension movements of the right knee under three different conditions: with application of a tight knee brace, with application of a moderate tight knee sleeve, and without application of a brace or sleeve. Brain activation was detected in the primary sensorimotor cortex (left and right paracentral lobule) and in the left superior parietal lobule of the brain. There was a significantly higher level of brain activation with the application of the brace and sleeve, respectively, compared to the condition without a brace or sleeve. A significantly higher cortical activation was also seen when comparing the braced condition with the condition when a sleeve was applied. The results suggest that peripheral proprioceptive input to the knee joint by means of a brace or sleeve seems to influence brain activity during knee movement. The results of this study also show that the intensity of brain activation during knee movement can be influenced by the intensity of proprioceptive stimulation at the joint.

Perilously poor tendon-to-bone contact occurs with rotator cuff repairs occur during passive arm movement with single versus double-row repairs: A cadaver study

Introduction: During the early healing phase, abduction was postulated to result in lift-off with significant loss of tendon-to-bone (TTB) contact with single row repairs (SRR) as compared to transosseous-equivalent repairs (TOE). This would significantly compromise the ability of the tendon to heal. Materials and methods: Rotator cuff tears were created in the supraspinatus tendon of six fresh cadaveric human shoulders. A SRR was then performed using the OPUS AutoCuff System. ATekscan electronic pressure-sensor was placed between the supraspinatus tendon and bone and the sutures were tensioned with the shoulder in 0° abduction.

Early non-visual experience influences proprioceptive-spatial discrimination acuity in adulthood

The present study tested whether non-visual spatial experience affects later acuity of space perception. Congenitally blind adults who differed in the age acquired spatial knowledge via an orientation and mobility (O&M) training and matched sighted controls performed passive arm movements and judged the direction of the sensed movement. Proprioceptive-spatial discrimination acuity was assessed by an adaptive psychophysical procedure in two spatial coding conditions. In the egocentric coding condition, participants judged whether the hand trajectory felt left- or right-tilted in reference to a straight trajectory aligned to the transverse horizontal plane of the body midline axis. In the allocentric coding condition, they indicated whether the hand trajectory felt acute- or obtuse-angled in reference to a right angle. Proprioceptive-spatial acuity of congenitally blind participants significantly covaried with the age they attended an O&M training. The earlier the congenitally blind participants started the O&M training the more accurate was their space perception. Congenitally blind participants who underwent an O&M training after the age of 12 years showed poorer acuity than sighted controls. Congenitally blind participants with an earlier O&M training, however, approached the performance level of the sighted controls. The observed improvement in spatial acuity was more pronounced when judgements were given on the basis of an allocentric than an egocentric frame of reference. These findings suggest that proprioceptive-spatial acuity in adulthood depends on non-visual spatial experience during early development.

Characteristics of the Human Arm Based on a Musculoskeletal Model of Cooperative Motion between Two Humans

In this study, we considered a single rotational degree-of-freedom experimental system, in addition to a mass-spring-damper-friction biomechanical model of the human arm, and then investigated master-slave and master-semi-master cooperative motions. For the master-slave cooperative motion, we developed a mass-spring-friction biomechanical model for the slave's arm. Within the investigated range, we found the damping factor to be zero, and the stiffness and dynamic friction to be individually constant. We also determined the torque characteristics in the master-slave and master-semi-master cooperative motions. In the master-slave cooperative motion, although the master subject had to overcome the entire impedance resistance of the slave subject's arm, the master found it easier to slow down and stop the motion. In master-semi-master cooperative motion, when the semi-master subject switched from passive arm movement to active arm movement, the stiffness characteristics disappeared and constant torque characteristics were observed. At that moment, the master subject felt it took less effort to perform active arm movement. As a result, we assume that in human-robot cooperative tasks, during accelerating motion, we can apply the characteristics of the semi-master to a robot through torque control, and during deceleration (braking) motion, we can apply the slave characteristics to a robot by means of impedance control.

Long lasting aftereffect of a single prism adaptation: directionally biased shift in proprioception and late onset shift of internal egocentric reference frame

We aimed to dissociate components in prism adaptation and its aftereffect by using prism adaptation training in healthy humans. Arm proprioceptive aftereffects are usually measured by indicating the subjective straight ahead direction with eyes closed (S). This measure however could be affected by other components besides proprioception, such as an efferent motor component and internal egocentric reference frame. Here we report a very long lasting proprioceptive shift, detected by two measuring methods, that is a component of the adaptation aftereffects to left wedge prism glasses. In order to minimize possible active motor components, arm passive proprioceptive midsagittal judgment was measured (P). The subject's arm was passively brought from the right or left lateral position, and stopped by subjects' verbal order. The results from these different measurements of midsagittal judgment were compared for 7 days after prism adaptation. Surprisingly, we found two distinctly separate aftereffects of proprioceptive shift depending on the directions of the passive arm movement. The shift of the midsagittal plane appeared only when tested from the left (Pl). This indicates that our strong prism adaptation procedure affected proprioception in a directionally biased way and not a spatially ubiquitous way. Further, the early aftereffect seen in active straight ahead pointing (S) was mostly similar to this biased shift in proprioception (Pl). However the long lasting aftereffect in straight ahead pointing was independently maintained up to day 7, when the passive proprioception had returned to pretest level. These results indicate that active straight ahead pointing (S) involves other components in addition to the passively measurable proprioceptive component. We suggest a late onset shift in the internal egocentric reference frame is involved in S. Possible neural mechanisms for these phenomena are discussed.

Changes in cerebral blood flow induced by passive and active elbow and hand movements.

Transcranial Doppler ultrasonography (TCD) has been widely used to obtain information about changes in cerebral perfusion during motor activity after stroke. This type of application is greatly limited when severe motor deficits are present that impede the performance of an active motor task. In this study, we explored the effect of performing passive arm movements on cerebral perfusion. Twenty healthy subjects were investigated. A bilateral TCD monitoring of the middle cerebral artery (MCA) flow velocity was performed during the following experimental conditions: 1-min of active and passive flexion-extension elbow movement and 1-min of active and passive dorsal extension hand movement. Each task was performed with both left and right arms. The percentage increase in flow velocity from rest to task performance was calculated. Each task produced a significantly greater increase in mean flow velocity in the contralateral MCA with respect to the ipsilateral. When comparing the effect of passive and active tasks, no significant difference in mean flow velocity changes recorded in the ipsilateral and the contralateral MCA was detected regarding either elbow or hand movements. These findings demonstrate the possibility of obtaining information about changes in hemispheric cerebral perfusion during passive movements involving elbow and hand. This type of application deserves further attention in the study of cerebral functional changes following cerebral lesions.

Proprioceptive activity in primate primary somatosensory cortex during active arm reaching movements

1. We studied the activity of 254 cells in the primary somatosensory cortex (SI) responding to inputs from peripheral proprioceptors in a variety of tasks requiring active reaching movements of the contralateral arm. 2. The majority of cells with receptive fields on the proximal arm (shoulder and elbow) were broadly and unimodally tuned for movement direction, often with approximately sinusoidal tuning curves similar to those seen in motor and parietal cortex. 3. The predominant temporal response profiles were directionally tuned phasic bursts during movement and tonic activity that varied with different arm postures. 4. Most cells showed both phasic and tonic response components to differing degrees, and the population formed a continuum from purely phasic to purely tonic cells with no evidence of separate distinct phasic and tonic populations. This indicates that the initial cortical neuronal correlates of the introspectively distinguishable sensations of movement and position are represented in an overlapping or distributed manner in SI. 5. The directional tuning of the phasic and tonic response components of most cells was generally similar, although rarely identical. 6. We tested 62 cells during similar active and passive arm movements. Many cells showed large differences in their responses in the two conditions, presumably due to changes in peripheral receptor discharge during active muscle contractions. 7. We tested 86 cells in a convergent movement task in which monkeys made reaching movements to a single central target from eight peripheral starting positions. A majority of the cells (46 of 86, 53.5%) showed a movement direction-related hysteresis in which their tonic activity after movement to the central target varied with the direction by which the arm moved to the target. The directionality of this hysteresis was coupled with the movement-related directional tuning of the cells. 8. We recorded the discharge of 93 cells as the monkeys performed the task while compensating for loads in different directions. The large majority of cells showed a statistically significant modulation of activity as a function of load direction, which was qualitatively similar to that seen in motor cortex under similar task conditions. Quantitatively, however, the sensitivity of SI proprioceptive cells to loads was less than that seen in motor cortex but greater than in parietal cortex. 9. We interpret these results in terms of their implications for the central representation of the spatiotemporal form ("kinematics") of arm movements and postures. Most importantly, the results emphasize the important influence of muscle contractile activity on the central proprioceptive representation of active movements.

Ventilatory responses at the onset of passive movement and voluntary exercise with arms and legs

This study was undertaken to elucidate whether phase I appeared at the onset of voluntary and passive arm movements and to compare these results with those of similar leg movements. Instead of the conventional cranking exercise, seven male subjects performed alternately flexion-relaxation of both arms, extension-relaxation of both legs, and combined arm and leg exercise at the rate of about 60 min-1 for four breaths in a sitting position. Similar movements were accomplished passively by the experimenters. In all experiments, minute ventilation increased rapidly within the first breath after the onset of exercise. The difference of ventilation (delta value) between the mean of the first two breaths at the onset of voluntary exercise and that of five breaths during rest was significantly (P < 0.05) greater in arm (7.75 l min-1) than in leg (5.19 l min-1). Passive movement showed a similar tendency. Arm delta ventilation correlated highly (r = 0.74-0.91) with leg delta ventilation and the slope of the regression lines was about 1.2. Heart rate increased abruptly while cardiac output did not always increase rapidly at the onset of locomotion. Oxygen uptake in the voluntary leg exercise continued for 3 min was slightly but nonsignificantly higher than in the arm exercise, indicating the equality of the exercise intensity. In conclusion, ventilatory responses at the onset of the arm exercise are larger than those of the leg in both voluntary and passive conditions regardless of the muscle mass, suggesting the different neurogenic mechanism between arm and leg.

Tactile activity in primate primary somatosensory cortex during active arm movements: cytoarchitectonic distribution

1. Cells were recorded in areas 3b and 1 of the primary somatosensory cortex (SI) of three monkeys during active arm movements. Successful reconstructions were made of 46 microelectrode penetrations, and 298 cells with tactile receptive fields (RFs) were located as to cytoarchitectonic area, lamina, or both. 2. Area 3b contained a greater proportion of cells with slowly adapting responses to tactile stimuli and fewer cells with deep modality inputs than did area 1. Area 3b also showed a greater level of movement-related modulation in tactile activity than area 1. Other cell properties were equally distributed in the two areas. 3. The distribution of cells with low-threshold tactile RFs that also responded to lateral stretch of the skin or to passive arm movements was skewed toward deeper laminae than for tactile cells that did not respond to those manipulations. 4. The variation of activity of tactile neurons during arm movements in different directions was weaker in the superficial laminae than in deeper cortical laminae. 5. Cells with only increases in activity during arm movements were preferentially but not exclusively located in middle and superficial layers. Cells with reciprocal responses were found mainly in laminae III and V, whereas cells with only decreases in activity were concentrated in lamina V. 6. Overall, active arm movements evoke directionally tuned tactile and "deep" activity in areas 3b and 1, in particular in the deeper cortical laminae that are the source of the descending output pathways from SI.

Tactile activity in primate primary somatosensory cortex during active arm movements: correlation with receptive field properties.

1. Five hundred ninety-five single neurons with tactile receptive fields (RFs) on the contralateral arm were isolated in the primary somatosensory cortex (SI) of awake, behaving monkeys. 2. Fifty-eight percent of the tactile cells showed significantly different levels of activity during active movements of the arm in eight directions or during active maintenance of the arm over the target endpoints. 3. The discharge of many of the active tactile cells was unimodally tuned with movement direction and the pattern of the tactile population activity varied in a meaningful fashion with arm movement direction and posture. 4. The intensity of the arm-movement-induced activity was typically less than that evoked by direct tactile stimulation of the cell's RF. 5. The probability of task-related activity was correlated with certain RF properties, in particular the sensitivity of the cell to lateral stretch of the skin and to passive arm movements that avoided direct contact of the RF on any surface. 6. This suggests that task-related activity results mainly from the activation of tactile receptors by mechanical deformation of the skin as the arm changes geometry during movement. 7. These results demonstrate that tactile activity containing potential proprioceptive information is generated in SI during active arm movements that avoid direct contact of the skin with external surfaces. Whether or not this input contributes to the kinesthetic sensations evoked by the movements cannot be resolved by this study.

Pain expression in patients with shoulder pathology: validity, properties and relationship to sickness impact

This study dealt with the validity and correlates of facial expressions of pain. Twenty-four patients seeking treatment for gleno-humeral joint pain and 12 controls underwent a standardized physiotherapy assessment protocol involving active and passive arm movements, and experimental pain induced by pressure. Subjects rated pain intensity on each trial using categorical, sensory and affective scales. Independent of testing, they completed a questionnaire measure of sickness impact. Facial behavior was measured by an abbreviated version of the Facial Action Coding System. Facial actions that related to pain indices included eyebrow lowering, narrowing and closing of the eyes, lip pulling, nose wrinkling and mouth opening. Facial actions during clinical tests showed consistent relationships with sensory and affective pain scales. Greater physical disability was associated with more intense pain actions on active, but not passive, tests. The results support the validity and generality of facial measures of pain, show that they yield graded sensitive information and suggest that they encode information about the psychosocial context of pain problems. Theoretical implications of these findings are discussed.

Neural dynamics of planned arm movements: emergent invariants and speed-accuracy properties during trajectory formation.

A real-time neural network model, called the vector-integration-to-endpoint (VITE) model is developed and used to simulate quantitatively behavioral and neural data about planned and passive arm movements. Invariants o farm movements emerge through network interactions rather than through an explicitly precomputed trajectory. Motor planning occurs in the form of a target position command (TPC), which specifies where the arm intends to move, and an independently controlled GO command, which specifies the movement's overall speed. Automatic processes convert this information into an arm trajectory with invariant properties. These automatic processes include computation of a present position command (PPC) and a difference vector (DV). The DV is the difference between the PPC and the TPC at any time. The PPC is gradually updated by integrating the DV through time. The GO signal multiplies the DV before it is integrated by the PPC. The PPC generates an outflow movement command to its target muscle groups. Opponent interactions regulate the PPCs to agonist and antagonist muscle groups. This system generates synchronous movements across synergetic muscles by automatically compensating for the different total contractions that each muscle group must undergo. Quantitative simulations are provided of Woodworth's law, of the speed-accuracy trade-offknown as Fitts's law, of isotonic arm-movement properties before and after deafferentation, of synchronous and compensatory central-error-correction properties of isometric contractions, of velocity amplification during target switching, of velocity profile invariance and asymmetry, of the changes in velocity profile asymmetry at higher movement speeds, of the automarie compensation for staggered onset times of synergetic muscles, of vector cell properties in precentral motor cortex, of the inverse relation between movement duration and peak velocity, and of peak acceleration as a function of movement amplitude and duration. It is shown that TPC, PPC, and DV computations are needed to actively modulate, or gate, the learning of associative maps between TPCs of different modalities, such as between the eye-head system and the hand-arm system. By using such an associative map, looking at an object can activate a TPC of the hand-arm system, as Piaget noted. Then a VITE circuit can translate this TPC into an invariant movement trajectory. An auxiliary circuit, called the Passive Update of Position (PUP) model is described for using inflow signals to update the PPC during passive arm movements owing to external forces. Other uses of outflow and inflow signals are also noted, such as for adaptive linearization of a nonlinear muscle plant, and sequential readout of TPCs during a serial plan, as in reaching and grasping. Comparisons are made with other models of motor control, such as the mass-spring and minimumjerk models.

Prism Adaptation to Moving and Stationary Target Exposures

The magnitude of proprioceptive adaptation and visual adaptation to prism displacement was assessed for various target conditions during either observed, active or passive arm movements. Active arm movement was found superior to passive arm movement in the production of proprioceptive aftereffects and visual aftereffects. In addition, observation of a stationary target or a moving target during prism exposure produced significant proprioceptive adaptation for a passive arm viewing condition while enhancing such adaptation magnitude for an active arm movement situation. With no target present during prism exposure, significant proprioceptive adaptation was only found with active movement. The greatest visual aftereffect was produced when a moving target was observed during prism exposure. The results are interpreted in terms of an information-availability model of perceptual adaptation.

Arm-body adaptation with passive arm movements

Two experiments investigated the aftereffects of pointing with passive movements during exposure to 15-deg laterally displacing wedge pnsms. Experiment 1 compared exposure with passive and active supported movements when the aftereffects were measured with the arm still in the passive movement device. Following passive exposure and active supported exposure, 5.6 and 7.9 deg, respectively, of arm-body adaptation were measured. In Experiment 2, the passive and active supported exposure tasks were compared with a third task in which similar movements were made with the arm fully supported by the muscles. Aftereffects were measured with active test movements. The amount of arm-body adaptation measured following passive exposure was decreased to 2.8 deg, and following active supported exposure it was decreased to 2.8 deg, while following exposure with normal active movements, 5.3 deg of arm-body adaptation was found. The results suggest that when the arm remains outstretched during prism exposure, adaptation is specific to this extended posture.