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4.10 Effect of visual and postural perturbation in VR-posturography
Chapter 4. Visual functions and Virtual Reality
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Posture-movement co-ordination when reaching in immersive visual virtual environment
O. Martin 1, L. Boissieux2, B. Julian2, J.D. Gascuel 2, C. Prablanc3. 1 Universitd Joseph Fourie~ UFRAPS-SPM, Grenoble,
2Artis-GRAVIR, 1NRIA Rh6nes-Alpes, Montbonnot, 31NSERM U534 Espace & Action, Bron, France Introduction: The virtual reality is more and more applied in neurobehavioural experiment such as goal-directed hand movement and postural equilibrium [1,2]. However, VE exposure often causes errors in the visual guidance of motor activities. Consequently, the development of the virtual environment must take into account the visuomotor transformation principles. The goal of this study was to identify how movement and balance motor commands are co-ordinated in order to integrate the unexpected modification of visual virtual scene. Methods and results: Subjects executed hand reaching toward stationary or moving virtual visual targets while standing. Targets were generated from Barcos video-projectors. Subjects wore stereo-glasses for 3D-vision. Kinematics of reaching and posture were recorded with an optotrak system synchronised with an AMTI forceplate. Hand kinematics and postural kinetics showed the maintenance of the online control of movement and balance in both reaching conditions. Discussion and conclusion: Results indicate that the visuomotor processes used by CNS to co-ordinate movement and posture in natural situation, still have a functional efficiency in immersive VE. This study has showed that variables describing the online corrective adjustments of movement and balance could be used to identify reliable visuomotor strategies, and serve as indicators of the comfort of the motor task and the ergonomics of VE.
References [l] Carrozzo M., Lacquaniti F. Virtual reality: a tutorial. Electroenceph. Clinic. Neurophysiol. 1998; 109:1 9. [2] Riva G. Virtual reality in neuroscience: a survey. In: Riva G, Wiederhold BK, Molinari E (Eds.), Virtual Environment in Clinical Psychology and Neuroscience, IOS Press, Amsterdam, 1998.
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Presence of a real hole does not affect the selection of alternate foot placement
R. Moraes, A.E. Patla. Department of Kinesiology, University of
Waterloo, Canada Introduction: Alternate foot placement has been studied by asking individuals to avoid a virtual planar obstacle that simulates a hole in the ground [1]. This study was designed to assess whether there is a difference between real and virtual paradigms. Methods: Participants (N 5) performed two blocks of walking trials in which they had to avoid either real (holes in the ground) or virtual (planar area of similar size and orientation as real holes) obstacles. They had two steps in which to plan and avoid stepping on the obstacle. Virtual holes were projected on a LCD monitor embedded under the walking surface. Kinematics and EMG data (from 14 muscles) were recorded. Alternate foot placement choices and EMG latencies were analyzed. Results: There was no difference in alternate foot placement between real and virtual conditions for each hole tested. There was also no difference between conditions for muscle latencies. As expected a significant interaction was found between choice and muscle latency, suggesting that for different choices, different muscle groups were recruited. Discussion and Conclusion: Similar foot placement choices and muscle activation patterns for real and virtual obstacle avoidance suggest that the virtual obstacle paradigm is an appropriate way to investigate selection strategies for alternate foot placement on a complex terrain.
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References [1] Patla AE, Prentice SD, Rietdyk S, Allard F, Martin C. What guides the selection of alternate foot placement during human locomotion. Exp Brain Res 1999; 128:441 450.
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Effect of visual and postural perturbation in VR-posturography
I. Pyykk62, E. Toppila 2, R Forsman 2, T. Tossavainen 3, J. Starck2.
1Department of Otolaryngology, University of Tampere, Finland," eFinnish Institute of Occupational Health Department of Physics, Finland," s University of Tampere, Department of computer science, Finland With virtual reality (VR) technique the balance can be tested in very unconventional way with visual and postural perturbations. The advantage of such system is that the testing situation becomes more realistic and thus more capable of revealing valuables information about the performance of postural system. In our postural plate it is possible to have a visual stimulus, postural stimulus or combined visual and postural stimulus. The combined stimulus consists of 30s period with visual and postural perturbations are in phase and 30s period when the perturbations are 180 degrees of phase. The transition from one phase to the second one occurred at a zero crossing of stimuli. 45 healthy controls and 106 patients with Meniere's disease were tested on the VR-platform. For both groups the sway velocity during the off-phase perturbation decreased in average by 10%. Among Meniere patients the relative change distribution (skewness 0.54) was different from the distribution of controls (skewness 0.94). This indicates that the Meniere patients have a different tendency of changing strategy than control when the perturbation changes. The visual dependence varies in among Meniere patients that may explain the periodic visual dominance that may lead to falls. However the result parameters could not be used as classifier between controls and patients. The VR-posturography can be further developed by using specific algorithms to analyze phase mismatch during phase reversal.
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Rapid visuomotor processes drive the leg regardless of balance constraints
R.E Reynolds, B.L. Day. MRC Human Movement Group, Sobell
dept. of Motor Neuroscience and Movement Disorders, Institute of Neurology, London, UK Introduction: When manually reaching for an object that unexpectedly moves, the hand is 'magnetically' drawn towards the object [1]. This occurs even before the subject perceives object motion [2], possibly through sub-cortical visuo-motor processes [3]. Whether a similar fast visuomotor process exists for the lower limb is open to question. Since foot trajectory and body motion are pre-planned and coupled at the start of a step [4,5], such automatic guidance of the foot toward a moving target could actually threaten balance. Methods: Subjects reached with their foot to a floor-mounted target which was made to jump 21 cm left or right at foot-offin ~1 of 96 trials. In a 'reach' condition, balance constraints were abolished by the use of hand-rails. In a separate 'step' condition, these constraints were reinstated. Foot kinematics and hip abductor EMG were recorded. Results: During the reach condition, foot trajectory was adjusted at around 120ms when the target jumped. EMG responses were seen at around lOOms. As expected, the balance constraints present during the step condition placed limitations on the ability to alter foot trajectory mid-swing, as compared with the reach (p <0.01). Surprisingly, the latencies of these rapid responses were unaffected by the extra limitations (p < 0.01). Discussion and Conclusion: We have demonstrated a rapid visuomotor pathway for the leg, as has previously been demonstrated for the arm. The short latency of the responses suggests that this pathway could be sub-cortical. Furthermore, when restrictions were placed upon the ability to alter foot-placement mid-swing, no latency
I•
Posture-movement co-ordination when reaching in immersive visual virtual environment
O. Martin 1, L. Boissieux2, B. Julian2, J.D. Gascuel 2, C. Prablanc3. 1 Universitd Joseph Fourie~ UFRAPS-SPM, Grenoble,
2Artis-GRAVIR, 1NRIA Rh6nes-Alpes, Montbonnot, 31NSERM U534 Espace & Action, Bron, France Introduction: The virtual reality is more and more applied in neurobehavioural experiment such as goal-directed hand movement and postural equilibrium [1,2]. However, VE exposure often causes errors in the visual guidance of motor activities. Consequently, the development of the virtual environment must take into account the visuomotor transformation principles. The goal of this study was to identify how movement and balance motor commands are co-ordinated in order to integrate the unexpected modification of visual virtual scene. Methods and results: Subjects executed hand reaching toward stationary or moving virtual visual targets while standing. Targets were generated from Barcos video-projectors. Subjects wore stereo-glasses for 3D-vision. Kinematics of reaching and posture were recorded with an optotrak system synchronised with an AMTI forceplate. Hand kinematics and postural kinetics showed the maintenance of the online control of movement and balance in both reaching conditions. Discussion and conclusion: Results indicate that the visuomotor processes used by CNS to co-ordinate movement and posture in natural situation, still have a functional efficiency in immersive VE. This study has showed that variables describing the online corrective adjustments of movement and balance could be used to identify reliable visuomotor strategies, and serve as indicators of the comfort of the motor task and the ergonomics of VE.
References [l] Carrozzo M., Lacquaniti F. Virtual reality: a tutorial. Electroenceph. Clinic. Neurophysiol. 1998; 109:1 9. [2] Riva G. Virtual reality in neuroscience: a survey. In: Riva G, Wiederhold BK, Molinari E (Eds.), Virtual Environment in Clinical Psychology and Neuroscience, IOS Press, Amsterdam, 1998.
I•
Presence of a real hole does not affect the selection of alternate foot placement
R. Moraes, A.E. Patla. Department of Kinesiology, University of
Waterloo, Canada Introduction: Alternate foot placement has been studied by asking individuals to avoid a virtual planar obstacle that simulates a hole in the ground [1]. This study was designed to assess whether there is a difference between real and virtual paradigms. Methods: Participants (N 5) performed two blocks of walking trials in which they had to avoid either real (holes in the ground) or virtual (planar area of similar size and orientation as real holes) obstacles. They had two steps in which to plan and avoid stepping on the obstacle. Virtual holes were projected on a LCD monitor embedded under the walking surface. Kinematics and EMG data (from 14 muscles) were recorded. Alternate foot placement choices and EMG latencies were analyzed. Results: There was no difference in alternate foot placement between real and virtual conditions for each hole tested. There was also no difference between conditions for muscle latencies. As expected a significant interaction was found between choice and muscle latency, suggesting that for different choices, different muscle groups were recruited. Discussion and Conclusion: Similar foot placement choices and muscle activation patterns for real and virtual obstacle avoidance suggest that the virtual obstacle paradigm is an appropriate way to investigate selection strategies for alternate foot placement on a complex terrain.
$19
References [1] Patla AE, Prentice SD, Rietdyk S, Allard F, Martin C. What guides the selection of alternate foot placement during human locomotion. Exp Brain Res 1999; 128:441 450.
I•
Effect of visual and postural perturbation in VR-posturography
I. Pyykk62, E. Toppila 2, R Forsman 2, T. Tossavainen 3, J. Starck2.
1Department of Otolaryngology, University of Tampere, Finland," eFinnish Institute of Occupational Health Department of Physics, Finland," s University of Tampere, Department of computer science, Finland With virtual reality (VR) technique the balance can be tested in very unconventional way with visual and postural perturbations. The advantage of such system is that the testing situation becomes more realistic and thus more capable of revealing valuables information about the performance of postural system. In our postural plate it is possible to have a visual stimulus, postural stimulus or combined visual and postural stimulus. The combined stimulus consists of 30s period with visual and postural perturbations are in phase and 30s period when the perturbations are 180 degrees of phase. The transition from one phase to the second one occurred at a zero crossing of stimuli. 45 healthy controls and 106 patients with Meniere's disease were tested on the VR-platform. For both groups the sway velocity during the off-phase perturbation decreased in average by 10%. Among Meniere patients the relative change distribution (skewness 0.54) was different from the distribution of controls (skewness 0.94). This indicates that the Meniere patients have a different tendency of changing strategy than control when the perturbation changes. The visual dependence varies in among Meniere patients that may explain the periodic visual dominance that may lead to falls. However the result parameters could not be used as classifier between controls and patients. The VR-posturography can be further developed by using specific algorithms to analyze phase mismatch during phase reversal.
I•
Rapid visuomotor processes drive the leg regardless of balance constraints
R.E Reynolds, B.L. Day. MRC Human Movement Group, Sobell
dept. of Motor Neuroscience and Movement Disorders, Institute of Neurology, London, UK Introduction: When manually reaching for an object that unexpectedly moves, the hand is 'magnetically' drawn towards the object [1]. This occurs even before the subject perceives object motion [2], possibly through sub-cortical visuo-motor processes [3]. Whether a similar fast visuomotor process exists for the lower limb is open to question. Since foot trajectory and body motion are pre-planned and coupled at the start of a step [4,5], such automatic guidance of the foot toward a moving target could actually threaten balance. Methods: Subjects reached with their foot to a floor-mounted target which was made to jump 21 cm left or right at foot-offin ~1 of 96 trials. In a 'reach' condition, balance constraints were abolished by the use of hand-rails. In a separate 'step' condition, these constraints were reinstated. Foot kinematics and hip abductor EMG were recorded. Results: During the reach condition, foot trajectory was adjusted at around 120ms when the target jumped. EMG responses were seen at around lOOms. As expected, the balance constraints present during the step condition placed limitations on the ability to alter foot trajectory mid-swing, as compared with the reach (p <0.01). Surprisingly, the latencies of these rapid responses were unaffected by the extra limitations (p < 0.01). Discussion and Conclusion: We have demonstrated a rapid visuomotor pathway for the leg, as has previously been demonstrated for the arm. The short latency of the responses suggests that this pathway could be sub-cortical. Furthermore, when restrictions were placed upon the ability to alter foot-placement mid-swing, no latency