Little is known on how the CNS would select its movement options when a person faces a novel or r... more Little is known on how the CNS would select its movement options when a person faces a novel or recurring perturbation of two opposing types (slip or trip) while walking. The purposes of this study were (1) to determine whether young adults' adaptation to repeated slips would interfere with their recovery from a novel trip, and (2) to investigate the generalized strategies after they were exposed to a mixed training with both types of perturbation. Thirty-two young adults were assigned to either the training group, which first underwent repeated-slip training before encountering a novel, unannounced trip while walking, or to the control group, which only experienced the same novel, unannounced trip. The former group would then experience a mix of repeated trips and slips. The results indicated that prior adaptation to slips had only limited interference during the initial phase of trip recovery. In fact, the prior repeated-slip exposure had primed their reaction, which mitigated any error resulting from early interference. As a result, they did not have to take a longer compensatory step for trip recovery than did the controls. After the mixed training, subjects were able to converge effectively the motion state of their center of mass (in its position and velocity space) to a stable and generalized "middle ground" steady-state. Such movement strategies not only further strengthened their robust reactive control of stability, but also reduced the CNS' overall reliance on accurate context prediction and on feedback correction of perturbation-induced movement error.
Similar adaptations improve both proactive and reactive control of center-of-mass (COM) stability... more Similar adaptations improve both proactive and reactive control of center-of-mass (COM) stability and limb support against gravity during different daily tasks (e.g., sit-to-stand and walking) as a consequence of perturbation training for resisting falls. Yet it is unclear whether – or to what extent – such similarities actually promote inter-task generalization. The purpose of this study was therefore to determine whether young adults could indeed transfer their adaptive control, acquired from sit-to-stand-slip, to improve their likelihood of a recovery from an unannounced novel slip in walking. Subjects underwent either repeated slips during sit-to-stand before experiencing an unannounced, novel slip during walking (training group, N=20), or they received no prior training before the same gait-slip (control group, N=23). The subjects demonstrated training-induced generalization of their improved proactive control of stability in post-training (unperturbed) gait pattern that was more stable against backward balance loss than was that of their own pre-training pattern as well the gait pattern of the subjects in the control group. Upon the unannounced novel gait-slip, the training group showed significantly lower incidence of both falls and balance loss than that shown by the control, resulting from the improvements in the reactive control of limb support and slip velocity, which directly influenced the control of their COM stability. Such transfer could occur when the subjects’ central nervous system recalibrates the non-task-specific, generalized representation of stability limits during the initial training to guide both their feed-forward adjustments and their feedback responses. The findings of the inter-task generalization suggests that behavioral changes induced via the perturbation training paradigm have the potential to prevent falls across the spectrum of cyclic and non-cyclic activities.
Background and Objective. Following stroke, subjects retain the ability to adapt interlimb symmet... more Background and Objective. Following stroke, subjects retain the ability to adapt interlimb symmetry on the split-belt treadmill. Critical to advancing our understanding of locomotor adaptation and its usefulness in rehabilitation is discerning whether adaptive effects observed on a treadmill transfer to walking over ground. We examined whether aftereffects following split-belt treadmill adaptation transfer to overground walking in healthy persons and those poststroke. Methods. Eleven poststroke and 11 age-matched and gendermatched healthy subjects walked over ground before and after walking on a split-belt treadmill. Adaptation and aftereffects in step length and double support time were calculated. Results. Both groups demonstrated partial transfer of the aftereffects observed on the treadmill (P < .001) to overground walking (P < .05), but the transfer was more robust in the subjects poststroke (P < .05). The subjects with baseline asymmetry after stroke improved in asymmetry of step length and double limb support (P = .06). Conclusions. The partial transfer of aftereffects to overground walking suggests that some shared neural circuits that control locomotion for different environmental contexts are adapted during split-belt treadmill walking. The larger adaptation transfer from the treadmill to overground walking in the stroke survivors may be due to difficulty adjusting their walking pattern to changing environmental demands. Such difficulties with context switching have been considered detrimental to function poststroke. However, we propose that the persistence of improved symmetry when changing context to overground walking could be used to advantage in poststroke rehabilitation.
A person's awareness of potential slippery walking conditions induces a cautious gait pattern... more A person's awareness of potential slippery walking conditions induces a cautious gait pattern. The purposes of this study were to determine whether neuromechanical changes associated with such cognitive conditioning are sufficient to alter the outcome of a slip and whether the effects of such conditioning are comparable to those of motor training. Prior to their own first slip exposure, 18 young subjects watched videos and slides demonstrating where and how the slip would occur and how people adapted to repeated-slip exposure (observe). The outcomes of the first slip exposure experienced by another 16 subjects who did not receive any such information were used as controls (naïve). The latter subjects subsequently experienced an additional 23 slips and thus served in a dual-role as the motor training group (motor). Gait stability as measured against backward loss of balance (BLOB) was obtained for pre- and postslip instances. A protective step landing posterior to the slipping-li...
Evidence of long-term modification of behavior—in particular, gait alterations in response to rep... more Evidence of long-term modification of behavior—in particular, gait alterations in response to repeated exposure to slips—within the locomotor-balance control system is limited. The purpose of this study was to examine whether improvements in fall-resisting behavior as reflected by improvements in gait stability could be retained on a long-term basis. Eight healthy young subjects were exposed to a block of repeated slip trials during a single acquisition session consisting of five repeated slip exposures; the same subjects were then re-tested using the same protocol at a minimum of 12 mo later. Pre- and postslip gait stability for all slip trials was measured at touchdown (slipping limb) and liftoff (contralateral limb) based on the center of mass state (i.e., its instantaneous position and velocity) relative to the base of support (BOS) and the predicted thresholds for backward loss of balance. In the acquisition session, subjects were able to increase pre- and postslip stability, w...
The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and t... more The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and then caused them to slip unexpectedly on the untrained left side. Authors retested participants with a right slip and a left slip at 1 week, 2 weeks, 1 month, and 4 months. The authors found that preslip stability on the first untrained left slip improved and was significantly greater than that on the first right slip, which probably contributed to the reduction in incidence of falls from ∼30% to ∼10%. Postslip stability and base of support (BOS) slip velocity were similar to those on the first right slip and much lower than those on the last right slip. Increases in pre-and postslip stabilities and BOS slip velocity during the left slip led to reductions in backward balance loss (BLOB) from ∼95% on initial left slip to ∼60% and to ∼25% on the 1st and 3rd retest sessions, respectively. In contrast, BLOB remained at a constant ∼40% level on the right slip of the same retest sessions. The results indicate a partial immediate transfer and a possible latent transfer.
A vital functional plasticity of humans is their ability to adapt to threats to posture stability... more A vital functional plasticity of humans is their ability to adapt to threats to posture stability. The purpose of this study was to investigate adaptations to repeated trips in walking. Sixteen young adults were recruited and exposed to the sudden (electronic-mechanical) release of an obstacle, 11cm in height, in the path of over ground walking during the mid-to-late left swing phase. Although none of the subjects fell on the first of eight unannounced, consecutive trips, all of them had to rely on compensatory step with a step length significantly longer than their regular to reduce their instability. In the subsequent trials, they were able to rapidly make adaptive adjustments in the control of their center-of-mass (COM) stability both proactively and reactively (i.e., before and after hitting or crossing the obstacle), such that the need for taking compensatory step was substantially diminished. The proactive adaptations included a reduced forward COM velocity that lessened forward instability and an elevated toe clearance that reduced the likelihood of obstacle contact. The reactive adjustments were characterized by improved trunk control (by reducing its forward rotation) and limb support (by increasing hip height) and reduced forward instability (by both the posterior COM shift and the reduction in its forward velocity). These findings suggest that young adults can adapt appropriately to repeated trip perturbations and to reduce trip-induced excessive instability in both proactive and reactive manners.
Introduction: In this study we investigated whether vestibular loss (VL) subjects can integrate p... more Introduction: In this study we investigated whether vestibular loss (VL) subjects can integrate prosthetic auditory feedback of trunk sway into balance commands to provide improved control of trunk sway. Methods: We examined trunk sway of 6 compensated bilateral peripheral VL subjects when provided either angular position or velocity based auditory feedback during stance and gait tasks. Roll and pitch angular trunk disl~lacements were recorded with angular velocity transducers (SwayStar TM system) mounted just above the waist. The two types of feedback or no feedback were provided to the subject in random order. Feedback was delivered via 4 loudspeakers placed left, right, front and back of the test environment. Sway greater than preset thresholds caused a tone to be emitted from the speaker towards which the subject moved. The tone volume increased with increasing angle or angular velocity amplitude. Results: Stance tasks showed reduced sway with feedback. Specifically for the task of standing on 1 leg eyes open with position auditory feedback, sway amplitudes were indistinguishable from those of normal controls, whereas without feedback, sway was significantly larger. For gait tasks there was a decrease in trunk sway with velocity feedback. Conclusions: These results indicate that subjects with VL can incorporate the auditory prosthetic sensory information into balance commands. Position information appears more useful in reducing trunk sway during stance tasks and angular velocity during gait tasks. Future work will need to determine the effect of a training time on the improvement in balance control using such a prosthetic device.
The properties of adaptation within the locomotor and balance control systems directed towards im... more The properties of adaptation within the locomotor and balance control systems directed towards improving one's recovery strategy for fall prevention are not well understood. The purpose of this study was to examine adaptive control of gait stability to repeated slip exposure leading to a reduction in backward loss of balance (and hence in protective stepping). Fourteen young subjects experienced a block of slips during walking. Pre-and post-slip onset stability for all slip trials was obtained as the shortest distance at touchdown (slipping limb) and lift-off (contralateral limb), respectively, between the measured center of mass (COM) state, that is, position and velocity relative to base of support (BOS) and the mathematically predicted threshold for backward loss of balance. An improvement in pre-and post-slip onset stability correlated with a decrease in the incidence of balance loss from 100% (first slip) to 0% (fifth slip). While improvements in preslip stability were affected by a proactive anterior shift in COM position, the significantly greater post-slip onset improvements resulted from reductions in BOS perturbation intensity. Such reactive changes in BOS perturbation intensity resulted from a reduction in the demand on post-slip onset braking impulse, which was nonetheless influenced by the proactive adjustments in posture and gait pattern (e.g., the COM position, step length, flat foot landing and increased knee flexion) prior to slip onset. These findings were indicative of the maturing process of the adaptive control. This was characterized by a shift from a reliance on feedback control for postural correction to being influenced by feedforward control, which improved pre-slip stability and altered perturbation intensity, leading to skateover or walkover (>0.05 m or <0.05 m displacement, respectively) adaptive strategies. Finally, the stability at contralateral limb lift-off was highly predictive of balance loss occurrence and its subsequent rapid reduction, supporting the notion of the internal representations of stability limits that could be modified and updated, as a key component in the adaptive control.
The authors examined the impact of (a) awareness of impending slip and (b) priming (to accelerate... more The authors examined the impact of (a) awareness of impending slip and (b) priming (to accelerate learning) on interlimb transfer of acquired stability control. Among the participants, 12 of 24 young individuals were not informed of 2 impending slips on the nontrained left-side (UNWARN), whereas the other 12 knew the exact timing and location of the 1st left slip (WARN) following 24 right-side slips, given to all participants while walking. Both groups reduced the backward loss of balance (BLOB) incidence from 100% on the first slip to 0% on 24th slip. The authors found significantly better transfer of the improved stability control in WARN than in UNWARN, resulting in a greater reduction in BLOB on the 1st left slip (55% vs. 92%, respectively). The priming was evident with no BLOB on the 2nd left slip versus 50% on the 2nd right slip. Thus, the interlimb generalization can be improved by cognition and evidenced in priming.
A person's ability to transfer the acquired improvements in the control of center of mass (COM) s... more A person's ability to transfer the acquired improvements in the control of center of mass (COM) state stability to slips induced in everyday conditions can have profound theoretical and practical implications for fall prevention. This study investigated the extent to which such generalization could take place. A training group (n ϭ 8) initially experienced 24 right-side slips in blocked-and-random order (from the 1st unannounced, novel slip, S-1 to the last, S-24) resulting from release of a low-friction moveable platform in walking. They then experienced a single unannounced slip while walking on an oillubricated vinyl floor surface (V-T). A control group (n ϭ 8) received only one unannounced slip on the same slippery floor (V-C). Results demonstrated that the incidence of balance loss and fall on V-T was comparable to that on S-24. In both trials, fall and balance-loss incidence was significantly reduced in comparison with that on S-1 or on V-C, resulting from significant improvements in the COM state stability. The observed generalization indicates that the control of COM stability can be optimally acquired to accommodate alterations in environmental constraints, and it may be broadly coded and easily modifiable within the CNS. Because of such mechanisms, it is possible that the locomotor-balance skills acquired with the aid of low-friction moveable platforms can translate into resisting falls encountered in daily living.
Stability improvements made in a single acquisition session with merely five slips in walking are... more Stability improvements made in a single acquisition session with merely five slips in walking are sufficient to prevent backward balance loss (BLOB) at the end of session, but not after 12 mo. The purpose of this study was to determine whether the effect of an enhanced single acquisition session would be retainable if tested sooner, at intervals of Յ4 mo. Twentyfour young subjects were exposed to blocks of slip, nonslip, and both types of trials during walking at their preferred speed in the acquisition session. In each of the four follow-up sessions around 1 wk, 2 wk, 1 mo, and 4 mo later, these same subjects experienced only a single slip after eight to 13 unperturbed walking trials in an otherwise identical setup. Gait stability was obtained as the shortest distance between the measured center of mass (COM) state (position and velocity) and the mathematically predicted threshold for BLOB at preand postslip, corresponding to the instants of touchdown of the slipping limb and liftoff of the contralateral limb, respectively. During the acquisition session, pre-and postslip stability improved significantly, resulting in a reduction of BLOB from 100% in the first slip (S1) to 0% in the last slip (S24), with improvements converging to a steady state, that enabled all of the subjects to avoid BLOB, regardless of whether a slip occurred. During retest sessions, subjects' preslip stability was not different from that in S24, but was greater than that in S1. Their postslip stability was also greater than that in S1 but less than that in S24, resulting in BLOB at a 40% level. No difference was found in any of these aspects between each follow-up session. These adaptive changes were associated with a range of individual differences, varying from no detectable deterioration in all aspects (n ϭ 8) to a consistent BLOB in all follow-ups (n ϭ 3). Our findings demonstrated the extent of plasticity of the CNS, characterized by rapid acquisition of a stable COM state under unpredictable slip conditions and retention of such improvements for months, resulting in a reduced occurrence of unintended backward falling.
Page 1. WE2A-5 Performance Analysis of the Detector for the Structured Irregular LDPC Coded MIMO-... more Page 1. WE2A-5 Performance Analysis of the Detector for the Structured Irregular LDPC Coded MIMO-OFDM System Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving, TX 75039 Email: {Kyeong. ...
Abstract. The paper presents a dynamic data-driven mixed reality en-vironment to complement a ful... more Abstract. The paper presents a dynamic data-driven mixed reality en-vironment to complement a full-scale bio-terror preparedness exercise. The environment consists of a simulation of the virtual geographic loca-tions involved in the exercise scenario, along with an artificially ...
The Purdue Homeland Security Institute assisted in a live bioterrorism response exercise organize... more The Purdue Homeland Security Institute assisted in a live bioterrorism response exercise organized by the Indiana Department of Homeland Security and Jennings County at the Muscatatuck Urban Training Center. A simulation environment is developed to comple-ment the live ...
Page 1. Efficient Linear Equalization for High Data Rate Downlink CDhlA Signaling Jianzhong Zhang... more Page 1. Efficient Linear Equalization for High Data Rate Downlink CDhlA Signaling Jianzhong Zhang. Tejas Bhatt and Giridhar klandyam cliarliezhang, tejasbhatt, giridliar.rnandyamQnokia.com Nokia Research Center, Irving, TX 75039 ...
Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving,... more Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving, TX 75039 Email: [email protected] ... Ronald A. Iltis Department of Electrical and Computer Engineering University of California Santa Barbara, California 93106 ...
Little is known on how the CNS would select its movement options when a person faces a novel or r... more Little is known on how the CNS would select its movement options when a person faces a novel or recurring perturbation of two opposing types (slip or trip) while walking. The purposes of this study were (1) to determine whether young adults&amp;amp;#39; adaptation to repeated slips would interfere with their recovery from a novel trip, and (2) to investigate the generalized strategies after they were exposed to a mixed training with both types of perturbation. Thirty-two young adults were assigned to either the training group, which first underwent repeated-slip training before encountering a novel, unannounced trip while walking, or to the control group, which only experienced the same novel, unannounced trip. The former group would then experience a mix of repeated trips and slips. The results indicated that prior adaptation to slips had only limited interference during the initial phase of trip recovery. In fact, the prior repeated-slip exposure had primed their reaction, which mitigated any error resulting from early interference. As a result, they did not have to take a longer compensatory step for trip recovery than did the controls. After the mixed training, subjects were able to converge effectively the motion state of their center of mass (in its position and velocity space) to a stable and generalized &amp;amp;quot;middle ground&amp;amp;quot; steady-state. Such movement strategies not only further strengthened their robust reactive control of stability, but also reduced the CNS&amp;amp;#39; overall reliance on accurate context prediction and on feedback correction of perturbation-induced movement error.
Similar adaptations improve both proactive and reactive control of center-of-mass (COM) stability... more Similar adaptations improve both proactive and reactive control of center-of-mass (COM) stability and limb support against gravity during different daily tasks (e.g., sit-to-stand and walking) as a consequence of perturbation training for resisting falls. Yet it is unclear whether – or to what extent – such similarities actually promote inter-task generalization. The purpose of this study was therefore to determine whether young adults could indeed transfer their adaptive control, acquired from sit-to-stand-slip, to improve their likelihood of a recovery from an unannounced novel slip in walking. Subjects underwent either repeated slips during sit-to-stand before experiencing an unannounced, novel slip during walking (training group, N=20), or they received no prior training before the same gait-slip (control group, N=23). The subjects demonstrated training-induced generalization of their improved proactive control of stability in post-training (unperturbed) gait pattern that was more stable against backward balance loss than was that of their own pre-training pattern as well the gait pattern of the subjects in the control group. Upon the unannounced novel gait-slip, the training group showed significantly lower incidence of both falls and balance loss than that shown by the control, resulting from the improvements in the reactive control of limb support and slip velocity, which directly influenced the control of their COM stability. Such transfer could occur when the subjects’ central nervous system recalibrates the non-task-specific, generalized representation of stability limits during the initial training to guide both their feed-forward adjustments and their feedback responses. The findings of the inter-task generalization suggests that behavioral changes induced via the perturbation training paradigm have the potential to prevent falls across the spectrum of cyclic and non-cyclic activities.
Background and Objective. Following stroke, subjects retain the ability to adapt interlimb symmet... more Background and Objective. Following stroke, subjects retain the ability to adapt interlimb symmetry on the split-belt treadmill. Critical to advancing our understanding of locomotor adaptation and its usefulness in rehabilitation is discerning whether adaptive effects observed on a treadmill transfer to walking over ground. We examined whether aftereffects following split-belt treadmill adaptation transfer to overground walking in healthy persons and those poststroke. Methods. Eleven poststroke and 11 age-matched and gendermatched healthy subjects walked over ground before and after walking on a split-belt treadmill. Adaptation and aftereffects in step length and double support time were calculated. Results. Both groups demonstrated partial transfer of the aftereffects observed on the treadmill (P < .001) to overground walking (P < .05), but the transfer was more robust in the subjects poststroke (P < .05). The subjects with baseline asymmetry after stroke improved in asymmetry of step length and double limb support (P = .06). Conclusions. The partial transfer of aftereffects to overground walking suggests that some shared neural circuits that control locomotion for different environmental contexts are adapted during split-belt treadmill walking. The larger adaptation transfer from the treadmill to overground walking in the stroke survivors may be due to difficulty adjusting their walking pattern to changing environmental demands. Such difficulties with context switching have been considered detrimental to function poststroke. However, we propose that the persistence of improved symmetry when changing context to overground walking could be used to advantage in poststroke rehabilitation.
A person's awareness of potential slippery walking conditions induces a cautious gait pattern... more A person's awareness of potential slippery walking conditions induces a cautious gait pattern. The purposes of this study were to determine whether neuromechanical changes associated with such cognitive conditioning are sufficient to alter the outcome of a slip and whether the effects of such conditioning are comparable to those of motor training. Prior to their own first slip exposure, 18 young subjects watched videos and slides demonstrating where and how the slip would occur and how people adapted to repeated-slip exposure (observe). The outcomes of the first slip exposure experienced by another 16 subjects who did not receive any such information were used as controls (naïve). The latter subjects subsequently experienced an additional 23 slips and thus served in a dual-role as the motor training group (motor). Gait stability as measured against backward loss of balance (BLOB) was obtained for pre- and postslip instances. A protective step landing posterior to the slipping-li...
Evidence of long-term modification of behavior—in particular, gait alterations in response to rep... more Evidence of long-term modification of behavior—in particular, gait alterations in response to repeated exposure to slips—within the locomotor-balance control system is limited. The purpose of this study was to examine whether improvements in fall-resisting behavior as reflected by improvements in gait stability could be retained on a long-term basis. Eight healthy young subjects were exposed to a block of repeated slip trials during a single acquisition session consisting of five repeated slip exposures; the same subjects were then re-tested using the same protocol at a minimum of 12 mo later. Pre- and postslip gait stability for all slip trials was measured at touchdown (slipping limb) and liftoff (contralateral limb) based on the center of mass state (i.e., its instantaneous position and velocity) relative to the base of support (BOS) and the predicted thresholds for backward loss of balance. In the acquisition session, subjects were able to increase pre- and postslip stability, w...
The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and t... more The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and then caused them to slip unexpectedly on the untrained left side. Authors retested participants with a right slip and a left slip at 1 week, 2 weeks, 1 month, and 4 months. The authors found that preslip stability on the first untrained left slip improved and was significantly greater than that on the first right slip, which probably contributed to the reduction in incidence of falls from ∼30% to ∼10%. Postslip stability and base of support (BOS) slip velocity were similar to those on the first right slip and much lower than those on the last right slip. Increases in pre-and postslip stabilities and BOS slip velocity during the left slip led to reductions in backward balance loss (BLOB) from ∼95% on initial left slip to ∼60% and to ∼25% on the 1st and 3rd retest sessions, respectively. In contrast, BLOB remained at a constant ∼40% level on the right slip of the same retest sessions. The results indicate a partial immediate transfer and a possible latent transfer.
A vital functional plasticity of humans is their ability to adapt to threats to posture stability... more A vital functional plasticity of humans is their ability to adapt to threats to posture stability. The purpose of this study was to investigate adaptations to repeated trips in walking. Sixteen young adults were recruited and exposed to the sudden (electronic-mechanical) release of an obstacle, 11cm in height, in the path of over ground walking during the mid-to-late left swing phase. Although none of the subjects fell on the first of eight unannounced, consecutive trips, all of them had to rely on compensatory step with a step length significantly longer than their regular to reduce their instability. In the subsequent trials, they were able to rapidly make adaptive adjustments in the control of their center-of-mass (COM) stability both proactively and reactively (i.e., before and after hitting or crossing the obstacle), such that the need for taking compensatory step was substantially diminished. The proactive adaptations included a reduced forward COM velocity that lessened forward instability and an elevated toe clearance that reduced the likelihood of obstacle contact. The reactive adjustments were characterized by improved trunk control (by reducing its forward rotation) and limb support (by increasing hip height) and reduced forward instability (by both the posterior COM shift and the reduction in its forward velocity). These findings suggest that young adults can adapt appropriately to repeated trip perturbations and to reduce trip-induced excessive instability in both proactive and reactive manners.
Introduction: In this study we investigated whether vestibular loss (VL) subjects can integrate p... more Introduction: In this study we investigated whether vestibular loss (VL) subjects can integrate prosthetic auditory feedback of trunk sway into balance commands to provide improved control of trunk sway. Methods: We examined trunk sway of 6 compensated bilateral peripheral VL subjects when provided either angular position or velocity based auditory feedback during stance and gait tasks. Roll and pitch angular trunk disl~lacements were recorded with angular velocity transducers (SwayStar TM system) mounted just above the waist. The two types of feedback or no feedback were provided to the subject in random order. Feedback was delivered via 4 loudspeakers placed left, right, front and back of the test environment. Sway greater than preset thresholds caused a tone to be emitted from the speaker towards which the subject moved. The tone volume increased with increasing angle or angular velocity amplitude. Results: Stance tasks showed reduced sway with feedback. Specifically for the task of standing on 1 leg eyes open with position auditory feedback, sway amplitudes were indistinguishable from those of normal controls, whereas without feedback, sway was significantly larger. For gait tasks there was a decrease in trunk sway with velocity feedback. Conclusions: These results indicate that subjects with VL can incorporate the auditory prosthetic sensory information into balance commands. Position information appears more useful in reducing trunk sway during stance tasks and angular velocity during gait tasks. Future work will need to determine the effect of a training time on the improvement in balance control using such a prosthetic device.
The properties of adaptation within the locomotor and balance control systems directed towards im... more The properties of adaptation within the locomotor and balance control systems directed towards improving one's recovery strategy for fall prevention are not well understood. The purpose of this study was to examine adaptive control of gait stability to repeated slip exposure leading to a reduction in backward loss of balance (and hence in protective stepping). Fourteen young subjects experienced a block of slips during walking. Pre-and post-slip onset stability for all slip trials was obtained as the shortest distance at touchdown (slipping limb) and lift-off (contralateral limb), respectively, between the measured center of mass (COM) state, that is, position and velocity relative to base of support (BOS) and the mathematically predicted threshold for backward loss of balance. An improvement in pre-and post-slip onset stability correlated with a decrease in the incidence of balance loss from 100% (first slip) to 0% (fifth slip). While improvements in preslip stability were affected by a proactive anterior shift in COM position, the significantly greater post-slip onset improvements resulted from reductions in BOS perturbation intensity. Such reactive changes in BOS perturbation intensity resulted from a reduction in the demand on post-slip onset braking impulse, which was nonetheless influenced by the proactive adjustments in posture and gait pattern (e.g., the COM position, step length, flat foot landing and increased knee flexion) prior to slip onset. These findings were indicative of the maturing process of the adaptive control. This was characterized by a shift from a reliance on feedback control for postural correction to being influenced by feedforward control, which improved pre-slip stability and altered perturbation intensity, leading to skateover or walkover (>0.05 m or <0.05 m displacement, respectively) adaptive strategies. Finally, the stability at contralateral limb lift-off was highly predictive of balance loss occurrence and its subsequent rapid reduction, supporting the notion of the internal representations of stability limits that could be modified and updated, as a key component in the adaptive control.
The authors examined the impact of (a) awareness of impending slip and (b) priming (to accelerate... more The authors examined the impact of (a) awareness of impending slip and (b) priming (to accelerate learning) on interlimb transfer of acquired stability control. Among the participants, 12 of 24 young individuals were not informed of 2 impending slips on the nontrained left-side (UNWARN), whereas the other 12 knew the exact timing and location of the 1st left slip (WARN) following 24 right-side slips, given to all participants while walking. Both groups reduced the backward loss of balance (BLOB) incidence from 100% on the first slip to 0% on 24th slip. The authors found significantly better transfer of the improved stability control in WARN than in UNWARN, resulting in a greater reduction in BLOB on the 1st left slip (55% vs. 92%, respectively). The priming was evident with no BLOB on the 2nd left slip versus 50% on the 2nd right slip. Thus, the interlimb generalization can be improved by cognition and evidenced in priming.
A person's ability to transfer the acquired improvements in the control of center of mass (COM) s... more A person's ability to transfer the acquired improvements in the control of center of mass (COM) state stability to slips induced in everyday conditions can have profound theoretical and practical implications for fall prevention. This study investigated the extent to which such generalization could take place. A training group (n ϭ 8) initially experienced 24 right-side slips in blocked-and-random order (from the 1st unannounced, novel slip, S-1 to the last, S-24) resulting from release of a low-friction moveable platform in walking. They then experienced a single unannounced slip while walking on an oillubricated vinyl floor surface (V-T). A control group (n ϭ 8) received only one unannounced slip on the same slippery floor (V-C). Results demonstrated that the incidence of balance loss and fall on V-T was comparable to that on S-24. In both trials, fall and balance-loss incidence was significantly reduced in comparison with that on S-1 or on V-C, resulting from significant improvements in the COM state stability. The observed generalization indicates that the control of COM stability can be optimally acquired to accommodate alterations in environmental constraints, and it may be broadly coded and easily modifiable within the CNS. Because of such mechanisms, it is possible that the locomotor-balance skills acquired with the aid of low-friction moveable platforms can translate into resisting falls encountered in daily living.
Stability improvements made in a single acquisition session with merely five slips in walking are... more Stability improvements made in a single acquisition session with merely five slips in walking are sufficient to prevent backward balance loss (BLOB) at the end of session, but not after 12 mo. The purpose of this study was to determine whether the effect of an enhanced single acquisition session would be retainable if tested sooner, at intervals of Յ4 mo. Twentyfour young subjects were exposed to blocks of slip, nonslip, and both types of trials during walking at their preferred speed in the acquisition session. In each of the four follow-up sessions around 1 wk, 2 wk, 1 mo, and 4 mo later, these same subjects experienced only a single slip after eight to 13 unperturbed walking trials in an otherwise identical setup. Gait stability was obtained as the shortest distance between the measured center of mass (COM) state (position and velocity) and the mathematically predicted threshold for BLOB at preand postslip, corresponding to the instants of touchdown of the slipping limb and liftoff of the contralateral limb, respectively. During the acquisition session, pre-and postslip stability improved significantly, resulting in a reduction of BLOB from 100% in the first slip (S1) to 0% in the last slip (S24), with improvements converging to a steady state, that enabled all of the subjects to avoid BLOB, regardless of whether a slip occurred. During retest sessions, subjects' preslip stability was not different from that in S24, but was greater than that in S1. Their postslip stability was also greater than that in S1 but less than that in S24, resulting in BLOB at a 40% level. No difference was found in any of these aspects between each follow-up session. These adaptive changes were associated with a range of individual differences, varying from no detectable deterioration in all aspects (n ϭ 8) to a consistent BLOB in all follow-ups (n ϭ 3). Our findings demonstrated the extent of plasticity of the CNS, characterized by rapid acquisition of a stable COM state under unpredictable slip conditions and retention of such improvements for months, resulting in a reduced occurrence of unintended backward falling.
Page 1. WE2A-5 Performance Analysis of the Detector for the Structured Irregular LDPC Coded MIMO-... more Page 1. WE2A-5 Performance Analysis of the Detector for the Structured Irregular LDPC Coded MIMO-OFDM System Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving, TX 75039 Email: {Kyeong. ...
Abstract. The paper presents a dynamic data-driven mixed reality en-vironment to complement a ful... more Abstract. The paper presents a dynamic data-driven mixed reality en-vironment to complement a full-scale bio-terror preparedness exercise. The environment consists of a simulation of the virtual geographic loca-tions involved in the exercise scenario, along with an artificially ...
The Purdue Homeland Security Institute assisted in a live bioterrorism response exercise organize... more The Purdue Homeland Security Institute assisted in a live bioterrorism response exercise organized by the Indiana Department of Homeland Security and Jennings County at the Muscatatuck Urban Training Center. A simulation environment is developed to comple-ment the live ...
Page 1. Efficient Linear Equalization for High Data Rate Downlink CDhlA Signaling Jianzhong Zhang... more Page 1. Efficient Linear Equalization for High Data Rate Downlink CDhlA Signaling Jianzhong Zhang. Tejas Bhatt and Giridhar klandyam cliarliezhang, tejasbhatt, giridliar.rnandyamQnokia.com Nokia Research Center, Irving, TX 75039 ...
Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving,... more Kyeong Jin Kim, Tejas Bhatt, Victor Stolpman Nokia Research Center 6000 Connection Drive, Irving, TX 75039 Email: [email protected] ... Ronald A. Iltis Department of Electrical and Computer Engineering University of California Santa Barbara, California 93106 ...
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