Engineering Papers⌕ Search

Engineering topics

Lackner, J. R.

Publications and source records attributed to Lackner, J. R..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

The role of reafference in recalibration of limb movement control and locomotion

The reafference model has frequently been used to explain spatial constancy during eye and head movements. We have found that its basic concepts also form part of the information processing necessary for the control and recalibration of reaching movements. Reaching was studied in a novel force environment--a rotating room that creates centripetal forces of the type that could someday substitute for gravity in space flight, and Coriolis forces which are side effects of rotation. We found that inertial, noncontacting Coriolis forces deviate the path and endpoint of reaching movements, a finding that shows the inadequacy of equilibrium position models of movement control. Repeated movements in the rotating room quickly lead to normal movement patterns and to a failure to perceive the perturbing forces. The first movements made after rotation stops, without Coriolis forces present, show mirror-image deviations and evoke perception of a perturbing force even though none is present. These patterns of sensorimotor control and adaptation can largely be explained on the basis of comparisons of efference copy, reafferent muscle spindle, and cutaneous mechanoreceptor signals. We also describe experiments on human locomotion using an apparatus similar to that which Mittelstaedt used to study the optomotor response of the Eristalis fly. These results show that the reafference principle relates as well to the perception of the forces acting on and exerted by the body during voluntary locomotion.

NASA Discipline Neuroscience↗
NASA NTRS1997

The effect of optokinetic stimulation on daytime sleepiness

This study examined the effect of optokinetic stimulation on objective sleepiness, as measured by the Multiple Sleep Latency Test (MSLT). The Nightcap, a portable sleep monitor, was used in a novel way to perform MSLTs, as well as record sleep in the home. Subjects wore the Nightcap for seven consecutive nights. On days 3 and 5 of the protocol, subjects came into the lab for an MSLT. On the experimental day, subjects underwent 10 minutes optokinetic stimulation (OKS), resulting in moderate motion sickness prior to each MSLT trial. Although subjects in the OKS condition reported significantly more drowsiness than controls, this did not result in significantly reduced sleep latencies.

NASA Discipline Neuroscience↗
NASA NTRS1997

Coupling of fingertip somatosensory information to head and body sway

Light touch contact of a fingertip with a stationary surface can provide orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip provide sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, we asked to which extent somatosensory cues are part of the postural control system, that is, which sensory signal supports this coupling? We investigated postural control not only when the contact surface was stationary, but also when it was moving rhythmically (from 0.1 to 0.5 Hz). In doing so, we brought somatosensory cues from the hand into conflict with other parts of the postural control system. Our focus was the temporal relationship between body sway and the contact surface. Postural sway was highly coherent with contact surface motion. Head and body sway assumed the frequency of the moving contact surface at all test frequencies. To account for these results, a simple model was formulated by approximating the postural control system as a second-order linear dynamical system. The influence of the touch stimulus was captured as the difference between the velocity of the contact surface and the velocity of body sway, multiplied by a coupling constant. Comparison of empirical results (relative phase, coherence, and gain) with model predictions supports the hypothesis of coupling between body sway and touch cues through the velocity of the somatosensory stimulus at the fingertip. One subject, who perceived movement of the touch surface, demonstrated weaker coupling than other subjects, suggesting that cognitive mechanisms introduce flexibility into the postural control scheme.

NASA Discipline Neuroscience↗
NASA NTRS1996

Motor function in microgravity: movement in weightlessness

Microgravity provides unique, though experimentally challenging, opportunities to study motor control. A traditional research focus has been the effects of linear acceleration on vestibular responses to angular acceleration. Evidence is accumulating that the high-frequency vestibulo-ocular reflex (VOR) is not affected by transitions from a 1 g linear force field to microgravity (<1 g); however, it appears that the three-dimensional organization of the VOR is dependent on gravitoinertial force levels. Some of the observed effects of microgravity on head and arm movement control appear to depend on the previously undetected inputs of cervical and brachial proprioception, which change almost immediately in response to alterations in background force levels. Recent studies of post-flight disturbances of posture and locomotion are revealing sensorimotor mechanisms that adjust over periods ranging from hours to weeks.

NASA Program Flight↗
NASA NTRS1996

Haptic cues for orientation and postural control in sighted and blind individuals

Haptic cues from fingertip contact with a stable surface attenuate body sway in subjects even when the contact forces are too small to provide physical support of the body. We investigated how haptic cues derived from contact of a cane with a stationary surface at low force levels aids postural control in sighted and congenitally blind individuals. Five sighted (eyes closed) and five congenitally blind subjects maintained a tandem Romberg stance in five conditions: (1) no cane; (2,3) touch contact (< 2 N of applied force) while holding the cane in a vertical or slanted orientation; and (4,5) force contact (as much force as desired) in the vertical and slanted orientations. Touch contact of a cane at force levels below those necessary to provide significant physical stabilization was as effective as force contact in reducing postural sway in all subjects, compared to the no-cane condition. A slanted cane was far more effective in reducing postural sway than was a perpendicular cane. Cane use also decreased head displacement of sighted subjects far more than that of blind subjects. These results suggest that head movement control is linked to postural control through gaze stabilization reflexes in sighted subjects; such reflexes are absent in congenitally blind individuals and may account for their higher levels of head displacement.

NASA Discipline Neuroscience↗
NASA NTRS1995

Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm

1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur despite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

Non-NASA Center↗
NASA NTRS1995

The role of haptic cues from rough and slippery surfaces in human postural control

Haptic information is critically important in complex sensory-motor tasks such as manipulating objects. Its comparable importance in spatial orientation is only beginning to be recognized. We have shown that postural sway in humans is significantly reduced by lightly touching a stable surface with a fingertip at contact force levels far below those physically necessary to stabilize the body. To investigate further the functional relationship between contact forces at the hand and postural equilibrium, we had subjects stand in the tandem Romberg stance while being allowed physically supportive (force contact) and non-physically supportive (touch contact) amounts of index fingertip force on surfaces with different frictional characteristics. Mean sway amplitude (MSA) was reduced by over 50% with both touch and force contact of the fingertip, compared to standing without fingertip contact. No differences in MSA were observed when touching rough or slippery surfaces. The amplitude of EMG activity in the peroneal muscles and the timing relationships between fingertip forces, body sway and EMG activity suggested that with touch contact of the finger or with force contact on a slippery surface long-loop "reflexes" involving postural muscles were stabilizing sway. With force contact of the fingertip on a rough surface, MSA reduction was achieved primarily through physical support of the body. This pattern of results indicates that light touch contact cues from the fingertip in conjunction with proprioceptive signals about arm configuration are providing information about body sway that can be used to reduce MSA through postural muscle activation.

NASA Discipline Neuroscience↗
NASA NTRS1994

Rapid adaptation to Coriolis force perturbations of arm trajectory

1. Forward reaching movements made during body rotation generate tangential Coriolis forces that are proportional to the cross product of the angular velocity of rotation and the linear velocity of the arm. Coriolis forces are inertial forces that do not involve mechanical contact. Virtually no constant centrifugal forces will be present in the background when motion of the arm generates transient Coriolis forces if the radius of body rotation is small. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished as movement began. The reaching movements were made prerotation, during rotation at 10 rpm in a fully enclosed rotating room, and postrotation. During testing the subject was seated at the center of the room and pointed radially. Neither visual nor tactile feedback about movement accuracy was present. 3. In experiment 1, subjects reached at a fast or slow rate and their hands made contact with a horizontal surface at the end of the reach. Their initial perrotary movements were highly significantly deviated relative to prerotation in both trajectories and end-points in the direction of the transient Coriolis forces that had been generated during the reaches. Despite the absence of visual and tactile feedback about reaching accuracy, all subjects rapidly regained straight movement trajectories and accurate endpoints. Postrotation, transient errors of opposite sign were present for both trajectories and endpoints. 4. In a second experiment the conditions were identical except that subjects pointed just above the location of the extinguished target so that no surface contact was involved. All subjects showed significant initial perrotation deviations of trajectories and endpoints in the direction of the transient Coriolis forces. With repeated reaches the trajectories, as viewed from above, again became straight, but there was only partial restoration of endpoint accuracy, so that subjects reached in a straight line to the wrong place. Aftereffects of opposite sign were transiently present in the postrotary movements. 5. These observations fail to support current equilibrium point models, both alpha and lambda, of movement control. Such theories would not predict endpoint errors under our experimental conditions, in which the Coriolis force is absent at the beginning and end of a movement. Our results indicate that detailed aspects of movement trajectory are being continuously monitored on the basis of proprioceptive feedback in relation to motor commands. Adaptive compensations can be initiated after one perturbation despite the absence of either visual or tactile feedback about movement trajectory and endpoint error. Moreover, movement trajectory and end-point can be remapped independently.(ABSTRACT TRUNCATED AT 400 WORDS).

Non-NASA Center↗
NASA NTRS1994

Stabilization of posture by precision contact of the index finger

Postural sway during quiet stance increases if sight of the surroundings is denied. We studied how sensory-motor information about body displacement provided by contact of the index finger with a stationary bar can be used to stabilize balance in the absence of vision. Stabilization equivalent to the contribution conferred by vision was achieved at contact force levels less than 1 N. This value is much below that necessary to provide significant physical stabilization of the body. We interpret our findings in relation to tactile thresholds for motion detection, "precision grip," and proprioceptive and sensory-motor information about the configuration of the arm to the torso. In conditions allowing higher force levels at the fingertip (5-8 N), subjects assumed a passively stable state to stabilize their stance.

Non-NASA Center↗
NASA NTRS1994

Use of promethazine to hasten adaptation to provocative motion

In an earlier study, the authors found that severely motion sick individuals could be greatly relieved of their symptoms by intramuscular injections of promethazine (50 mg) or scopolamine (.5 mg). Comparable 50-mg injections of promethazine also have been found effective in alleviating symptoms of space motion sickness. The concern has risen, however, that such drugs may delay or retard the acquisition of adaptation to stressful environments. In the current study, we controlled arousal using a mental arithmetic task and precisely equated the exposure history (number of head movements during rotation) of a placebo, control group and an experimental group who had received promethazine. No differences in total adaptation or in rates of adaptation were present between the two groups. Another experimental group also received promethazine and was allowed to make as many head movements as they could, before reaching nausea, up to 800. This group showed a greater level of adaptation than the placebo group. These results suggest a strategy for dealing with space motion sickness that is described.

Non-NASA Center↗
NASA NTRS1994

Fingertip contact influences human postural control

Touch and pressure stimulation of the body surface can strongly influence apparent body orientation, as well as the maintenance of upright posture during quiet stance. In the present study, we investigated the relationship between postural sway and contact forces at the fingertip while subjects touched a rigid metal bar. Subjects were tested in the tandem Romberg stance with eyes open or closed under three conditions of fingertip contact: no contact, touch contact (< 0.98 N of force), and force contact (as much force as desired). Touch contact was as effective as force contact or sight of the surroundings in reducing postural sway when compared to the no contact, eyes closed condition. Body sway and fingertip forces were essentially in phase with force contact, suggesting that fingertip contact forces are physically counteracting body sway. Time delays between body sway and fingertip forces were much larger with light touch contact, suggesting that the fingertip is providing information that allows anticipatory innervation of musculature to reduce body sway. The results are related to observations on precision grip as well as the somatosensory, proprioceptive, and motor mechanisms involved in the reduction of body sway.

NASA Discipline Neuroscience↗
NASA NTRS1993

Orientation and movement in unusual force environments

A manned space mission to Mars might take as long as 1 year each way. Consequently, artificial gravity is being considered as a way of preventing the debilitating effects of long-duration exposure to microgravity on the human body. The present article discusses some of the problems associated with adapting to the rotation levels that might be used to generate artificial gravity. It also describes how exposure to background-force levels greater or less than the 1-G force of Earth gravity affects orientation and movement control. The primary emphasis of the article is that human movement and orientation control are dynamically adapted to the 1-G force background of Earth and that accommodation to altered force levels or to rotating environments requires a wide range of adaptive changes.

Parabolic Flight↗
NASA NTRS1993

Gravitoinertial force level influences arm movement control

1. The ability to move the forearm between remembered elbow joint angles immediately after rapid increases or decreases of the background gravitoinertial force (G) level was measured. The movements had been well-practiced in a normal 1G environment before the measurements in high-(1.8G) and low-force (0G) environments. The forearm and upper arm were always unsupported to maximize the influence of altered G-loading and to minimize extraneous cues about arm position. 2. Horizontal and vertical movement planes were studied to measure the effects of varying the G load in the movement plane within a given G background. Rapid and slow movements were studied to assess the role of proprioceptive feedback. 3. G level did not affect the amplitude of rapid movements, indicating that subjects were able to plan and to generate appropriate motor commands for the new G loading of the arm. The amplitude of slow movements was affected by G level, indicating that proprioceptive feedback is influenced by G level. 4. The effects of G level were similar for horizontal and vertical movements, indicating that proprioceptive information from supporting structures, such as the shoulder joint and muscles, had a role in allowing generation of the appropriate motor commands. 5. The incidence and size of dynamic overshoots were greater in 0G and for rapid movements. This G-related change in damping suggests a decrease in muscle spindle activity in 0G. A decrease in muscle spindle activity in 0G and an increase in 1.8G are consistent with the results of our prior studies on the tonic vibration reflex, locomotion, and perception of head movement trajectory in varying force backgrounds.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1991

Space adaptation syndrome: multiple etiological factors and individual differences

Space motion sickness is a significant operational concern in the American and Soviet space programs. Nearly 70% of all astronauts and cosmonauts are affected to some degree during their first several days of flight. It is now beginning to appear that space motion sickness like terrestrial motion sickness is the consequence of multiple etiological factors. As we come to understand basic mechanisms of spatial orientation and sensory-motor adaptation we can begin to predict etiological factors in different motion environments. Individuals vary greatly in the extent to which they are susceptible to these different factors. However, individuals seem to be relatively self-consistent in terms of their rates of adaptation to provocative stimulation and their retention of adaptation. Attempts to relate susceptibility to motion sickness during the microgravity phases of parabolic flight maneuvers to vestibular function under 1G and 0G test conditions are described.

short duration↗
NASA NTRS1989

Altered sensory-motor control of the head as an etiological factor in space-motion sickness

Mechanical unloading during head movements in weightlessness may be an etiological factor in space-motion sickness. We simulated altered head loading on Earth without affecting vestibular stimulation by having subjects wear a weighted helmet. Eight subjects were exposed to constant velocity rotation about a vertical axis with direction reversals every 60 sec. for eight reversals with the head loaded and eight with the head unloaded. The severity of motion sickness elicited was significantly higher when the head was loaded. This suggests that altered sensory-motor control of the head is also an etiological factor in space-motion sickness.

NASA Discipline Neuroscience↗
NASA NTRS1986

Head movements in non-terrestrial force environments elicit motion sickness - Implications for the etiology of space motion sickness

Space motion sickness has become an operational concern in manned space flight. Considerable evidence exists that head movements in free fall, especially pitch movements, are provocative until adaptation occurs. The question arises whether space motion sickness is an unique nosological entity or is due to body movements in a nonterrestrial force environment, a force environment for which the body's dynamic sensory-motor adaptions to 1 G are no longer appropriate. To evaluate this issue, subjects were asked to make controlled head movements during exposure to high gravitoinertial force levels, 1.8-2.0 G, in parabolic flight maneuvers. Head movements in pitch with eyes open were most evocative of motion sickness, yaw movements with eyes covered were least provocative. This pattern is identical to that which occurs when the same types of head movements are made in the free fall phase of parabolic maneuvers. It appears that space motion sickness is the consequence of prolonged exposure to a nonterrestrial force background rather than of exposure to free fall per se.

Lackner, J. R.↗
NASA NTRS1986

Sudden emesis following parabolic flight maneuvers Implications for space motion sickness

Episodes of emesis unaccompanied by the usual prodomal signs of motion sickness have been reported by astronauts in the Space Shuttle program. Such reports have raised the issue whether space motion sickness has different characteristics from terrestrial motion sickness. Evidence is presented here from parabolic flight experiments that sudden vomiting can occur in response to a provocative vestibular stimulus even when no premonitory symptoms are being experienced. Accordingly, in chronic exposure conditions, the absence of prominent signs or symptoms of motion sickness does not necessarily mean an absence of sensitization.

Lackner, J. R.↗