Altered foot placement modulation with somatosensory stimulation in people with chronic stroke

Many individuals who experience a stroke exhibit reduced modulation of their mediolateral foot placement, an important gait stabilization strategy. One factor that may contribute to this deficit is altered somatosensory processing, which can be probed by applying vibration to the involved muscles (e.g., the hip abductors). The purpose of this study was to investigate whether appropriately controlled hip abductor vibration can increase foot placement modulation among people with chronic stroke. 40 people with chronic stroke performed a series of treadmill walking trials without vibration and with vibration of either the hip abductors or lateral trunk (a control condition) that scaled with their real-time mediolateral motion. To assess participants' vibration sensitivity, we also measured vibration detection threshold and lateral sway evoked by abductor vibration during quiet standing. As a group, foot placement modulation increased significantly with either hip or trunk vibration, compared to without vibration. However, these changes were quite variable across participants, and were not predicted by either vibration detection threshold or the lateral sway evoked by hip vibration during standing. Overall, we found that somatosensory stimulation had small, positive effects on post-stroke foot placement modulation. Unexpectedly, these effects were observed with both hip abductor and lateral trunk vibration, perhaps indicating that the trunk can also provide useful somatosensory feedback during walking. Future work is needed to determine whether repeated application of such somatosensory stimulation can produce sustained effects on this important gait stabilization strategy.

Extended training improves the accuracy and efficiency of goal-directed reaching guided by supplemental kinesthetic vibrotactile feedback

Prior studies have shown that the accuracy and efficiency of reaching can be improved using novel sensory interfaces to apply task-specific vibrotactile feedback (VTF) during movement. However, those studies have typically evaluated performance after less than 1 h of training using VTF. Here, we tested the effects of extended training using a specific form of vibrotactile cues-supplemental kinesthetic VTF-on the accuracy and temporal efficiency of goal-directed reaching. Healthy young adults performed planar reaching with VTF encoding of the moving hand's instantaneous position, applied to the non-moving arm. We compared target capture errors and movement times before, during, and after approximately 10 h (20 sessions) of training on the VTF-guided reaching task. Initial performance of VTF-guided reaching showed that people were able to use supplemental VTF to improve reaching accuracy. Performance improvements were retained from one training session to the next. After 20 sessions of training, the accuracy and temporal efficiency of VTF-guided reaching were equivalent to or better than reaches performed with only proprioception. However, hand paths during VTF-guided reaching exhibited a persistent strategy where movements were decomposed into discrete sub-movements along the cardinal axes of the VTF display. We also used a dual-task condition to assess the extent to which performance gains in VTF-guided reaching resist dual-task interference. Dual-tasking capability improved over the 20 sessions, such that the primary VTF-guided reaching and a secondary choice reaction time task were performed with increasing concurrency. Thus, VTF-guided reaching is a learnable skill in young adults, who can achieve levels of accuracy and temporal efficiency equaling or exceeding those observed during movements guided only by proprioception. Future studies are warranted to explore learnability in older adults and patients with proprioceptive deficits, who might benefit from using wearable sensory augmentation technologies to enhance control of arm movements.

Effect of vibrotactile stimulation of the hallux nail on segmental coordination: A secondary analysis using uncontrolled manifold analysis

Controlling center of mass (CoM) movement in the mediolateral direction is imperative for stable walking. During walking, CoM movement is adjusted by the coordination of each body segment, which can be evaluated using uncontrolled manifold (UCM) analysis. UCM analysis evaluates segmental coordination by analyzing variablity in motor movement among the different segments of the body. The vibrotactile stimulation of the hallux nail can augment the sensory information of the plantar surface for necessary motor control. This study aims to investigate the effect of the vibrotactile stimulation of the hallux nail on segmental coordination to control CoM movement in the mediolateral direction during walking. Thirteen healthy men participated in the study. A vibrator was attached to each hallux nail, and pressure sensors were placed under the hallux balls. When the hallux ball was in contact with the floor, vibration stimulation was applied. A three-dimensional motion analysis system was used to measure the segment angles during walking, and UCM analysis was used to evaluate kinematic synergy for controlling CoM movement in the mediolateral direction. Subsequently, segment angles were used as an elemental variable. The synergy index and bad variability as motor noise were negatively related to the status without the stimulation. Vibrotactile stimulation in young people was more effective for people with large motor noise and a small synergy index during the single-stance phase. Thus, kinematic synergy can be immediately changed by sensory input using vibrotactile stimulation of the hallux nail, although applying vibration stimulation should be considered in advance.

Merging familiar and new senses to perceive and act in space

Our experience of the world seems to unfold seamlessly in a unitary 3D space. For this to be possible, the brain has to merge many disparate cognitive representations and sensory inputs. How does it do so? I discuss work on two key combination problems: coordinating multiple frames of reference (e.g. egocentric and allocentric), and coordinating multiple sensory signals (e.g. visual and proprioceptive). I focus on two populations whose spatial processing we can observe at a crucial stage of being configured and optimised: children, whose spatial abilities are still developing significantly, and naïve adults learning new spatial skills, such as sensing distance using auditory cues. The work uses a model-based approach to compare participants’ behaviour with the predictions of alternative information processing models. This lets us see when and how—during development, and with experience—the perceptual-cognitive computations underpinning our experiences in space change. I discuss progress on understanding the limits of effective spatial computation for perception and action, and how lessons from the developing spatial cognitive system can inform approaches to augmenting human abilities with new sensory signals provided by technology.

Sonification of combined action observation and motor imagery: Effects on corticospinal excitability

Action observation and motor imagery are valuable strategies for motor learning. Their simultaneous use (AOMI) increases neural activity, with related benefits for motor learning, compared to the two strategies alone. In this study, we explored how sonification influences AOMI. Twenty-five participants completed a practice block based on AOMI, motor imagery and physical execution of the same action. Participants were divided into two groups: An experimental group that practiced with sonification during AOMI (sAOMI), and a control group, which did not receive any extrinsic feedback. Corticospinal excitability at rest and during action observation and AOMI was assessed before and after practice, with and without sonification sound, to test the development of an audiomotor association. The practice block increased corticospinal excitability in all testing conditions, but sonification did not affect this. In addition, we found no differences in action observation and AOMI, irrespective of sonification. These results suggest that, at least for simple tasks, sonification of AOMI does not influence corticospinal excitability; In these conditions, sonification may have acted as a distractor. Future studies should further explore the relationship between task complexity, value of auditory information and action, to establish whether sAOMI is a valuable for motor learning.

Does sonification of action simulation training impact corticospinal excitability and audiomotor plasticity?

Sonification is a sensory augmentation strategy whereby a sound is associated with, and modulated by, movement. Evidence suggests that sonification could be a viable strategy to maximize learning and rehabilitation. Recent studies investigated sonification of action observation, reporting beneficial effects, especially in Parkinson's disease. However, research on simulation training-a training regime based on action observation and motor imagery, in which actions are internally simulated, without physical execution-suggest that action observation alone is suboptimal, compared to the combined use of action observation and motor imagery. In this study, we explored the effects of sonified action observation and motor imagery on corticospinal excitability, as well as to evaluate the extent of practice-dependent plasticity induced by this training. Nineteen participants were recruited to complete a practice session based on combined and congruent action observation and motor imagery (AOMI) and physical imitation of the same action. Prior to the beginning, participants were randomly assigned to one of two groups, one group (nine participants) completed the practice block with sonified AOMI, while the other group (ten participants) completed the practice without extrinsic auditory information and served as control group. To investigate practice-induced plasticity, participants completed two auditory paired associative stimulation (aPAS) protocols, one completed after the practice block, and another one completed alone, without additional interventions, at least 7 days before the practice. After the practice block, both groups significantly increased their corticospinal excitability, but sonification did not exert additional benefits, compared to non-sonified conditions. In addition, aPAS significantly increased corticospinal excitability when completed alone, but when it was primed by a practice block, no modulatory effects on corticospinal excitability were found. It is possible that sonification of combined action observation and motor imagery may not be a useful strategy to improve corticospinal, but further studies are needed to explore its relationship with performance improvements. We also confirm the neuromodulatory effect of aPAS, but its interaction with audiomotor practice remain unclear.

Characteristics of improvements in balance control using vibro-tactile biofeedback of trunk sway for multiple sclerosis patients

BACKGROUND AND AIMS

Previously, we determined that training with vibrotactile feedback (VTfb) of trunk sway improves MS patients' balance impairment. Here, we posed 5 questions: 1) How many weeks of VTfb training are required to obtain the best short-term carry over effect (CoE) with VTfb? 2) How long does the CoE last once VTfb training terminates? 3) Is the benefit similar for stance and gait? 4) Is position or velocity based VTfb more effective in reducing trunk sway? 5) Do patients' subjective assessments of balance control improve?

METHODS

Balance control of 16 MS patients was measured with gyroscopes at the lower trunk. The gyroscopes drove directionally active VTfb in a head-band. Patients trained twice per week with VTfb for 4 weeks to determine when balance control with and without VTfb stopped improving. Thereafter, weekly assessments without VTfb over 4 weeks and at 6 months determined when CoEs ended.

RESULTS

A 20% improvement in balance to normal levels occurred with VTfb. Short term CoEs improved from 15 to 20% (p ≤ 0.001). Medium term (1-4 weeks) CoEs were constant at 19% (p ≤ 0.001). At 6 months improvement was not significant, 9%. Most improvement was for lateral sway. Equal improvement occurred when angle position or velocity drove VTfb. Subjectively, balance improvements peaked after 3 weeks of training (32%, p ≤ 0.05).

CONCLUSIONS

3-4 weeks VTfb training yields clinically relevant sway reductions and subjective improvements for MS patients during stance and gait. The CoEs lasted at least 1 month. Velocity-based VTfb was equally effective as position-based VTfb.

The effect of tactile augmentation on manipulation and grip force control during force-field adaptation

Background

When exposed to a novel dynamic perturbation, participants adapt by changing their movements’ dynamics. This adaptation is achieved by constructing an internal representation of the perturbation, which allows for applying forces that compensate for the novel external conditions. To form an internal representation, the sensorimotor system gathers and integrates sensory inputs, including kinesthetic and tactile information about the external load. The relative contribution of the kinesthetic and tactile information in force-field adaptation is poorly understood.

Methods

In this study, we set out to establish the effect of augmented tactile information on adaptation to force-field. Two groups of participants received a velocity-dependent tangential skin deformation from a custom-built skin-stretch device together with a velocity-dependent force-field from a kinesthetic haptic device. One group experienced a skin deformation in the same direction of the force, and the other in the opposite direction. A third group received only the velocity-dependent force-field.

Results

We found that adding a skin deformation did not affect the kinematics of the movement during adaptation. However, participants who received skin deformation in the opposite direction adapted their manipulation forces faster and to a greater extent than those who received skin deformation in the same direction of the force. In addition, we found that skin deformation in the same direction to the force-field caused an increase in the applied grip-force per amount of load force, both in response and in anticipation of the stretch, compared to the other two groups.

Conclusions

Augmented tactile information affects the internal representations for the control of manipulation and grip forces, and these internal representations are likely updated via distinct mechanisms. We discuss the implications of these results for assistive and rehabilitation devices.

The role of sensory augmentation for people with vestibular deficits: Real-time balance aid and/or rehabilitation device?

This narrative review highlights findings from the sensory augmentation field for people with vestibular deficits and addresses the outstanding questions that are critical to the translation of this technology into clinical and/or personal use. Prior research has demonstrated that the real-time use of visual, vibrotactile, auditory, and multimodal sensory augmentation technologies can improve balance during static and dynamic stance tasks within a laboratory setting. However, its application in improving gait requires additional investigation, as does its efficacy as a rehabilitation device for people with vestibular deficits. In some locomotor studies involving sensory augmentation, gait velocity decreased and secondary task performance worsened, and subjects negatively altered their segmental control strategies when cues were provided following short training sessions. A further question is whether the retention and/or carry-over effects of training with a sensory augmentation technology exceed the retention and/or carry-over effects of training alone, thereby supporting its use as a rehabilitation device. Preliminary results suggest that there are short-term improvements in balance performance following a small number of training sessions with a sensory augmentation device. Long-term clinical and home-based controlled training studies are needed. It is hypothesized that sensory augmentation provides people with vestibular deficits with additional sensory input to promote central compensation during a specific exercise/activity; however, research is needed to substantiate this theory. Major obstacles standing in the way of its use for these critical applications include determining exercise/activity specific feedback parameters and dosage strategies. This paper summarizes the reported findings that support sensory augmentation as a balance aid and rehabilitation device, but does not critically examine efficacy or the quality of the research methods used in the reviewed studies.

Effects of long-term balance training with vibrotactile sensory augmentation among community-dwelling healthy older adults: a randomized preliminary study

Background

Sensory augmentation has been shown to improve postural stability during real-time balance applications. Limited long-term controlled studies have examined retention of balance improvements in healthy older adults after training with sensory augmentation has ceased. This pilot study aimed to assess the efficacy of long-term balance training with and without sensory augmentation among community-dwelling healthy older adults.

Methods

Twelve participants (four males, eight females; 75.6 ± 4.9 yrs) were randomly assigned to the experimental group (n = 6) or control group (n = 6). Participants trained in their homes for eight weeks, completing three 45-min exercise sessions per week using smart phone balance trainers that provided written, graphic, and video guidance, and monitored trunk sway. During each session, participants performed six repetitions of six exercises selected from five categories (static standing, compliant surface standing, weight shifting, modified center of gravity, and gait). The experimental group received vibrotactile sensory augmentation for four of the six repetitions per exercise via the smart phone balance trainers, while the control group performed exercises without sensory augmentation. The smart phone balance trainers sent exercise performance data to a physical therapist, who recommended exercises on a weekly basis. Balance performance was assessed using a battery of clinical balance tests (Activity Balance Confidence Scale, Sensory Organization Test, Mini Balance Evaluation Systems Test, Five Times Sit to Stand Test, Four Square Step Test, Functional Reach Test, Gait Speed Test, Timed Up and Go, and Timed Up and Go with Cognitive Task) before training, after four weeks of training, and after eight weeks of training.

Results

Participants in the experimental group were able to use vibrotactile sensory augmentation independently in their homes. After training, the experimental group had significantly greater improvements in Sensory Organization Test and Mini Balance Evaluation Systems Test scores than the control group. Significant improvement was also observed for Five Times Sit to Stand Test duration within the experimental group, but not in the control group. No significant improvements between the two groups were observed in the remaining clinical outcome measures.

Conclusion

The findings of this study support the use of sensory augmentation devices by community-dwelling healthy older adults as balance rehabilitation tools, and indicate feasibility of telerehabilitation therapy with reduced input from clinicians.

Supplemental vibrotactile feedback control of stabilization and reaching actions of the arm using limb state and position error encodings

Background

Deficits of kinesthesia (limb position and movement sensation) commonly limit sensorimotor function and its recovery after neuromotor injury. Sensory substitution technologies providing synthetic kinesthetic feedback might re-establish or enhance closed-loop control of goal-directed behaviors in people with impaired kinesthesia.

Methods

As a first step toward this goal, we evaluated the ability of unimpaired people to use vibrotactile sensory substitution to enhance stabilization and reaching tasks. Through two experiments, we compared the objective and subjective utility of two forms of supplemental feedback – limb state information or hand position error – to eliminate hand position drift, which develops naturally during stabilization tasks after removing visual feedback.

Results

Experiment 1 optimized the encoding of limb state feedback; the best form included hand position and velocity information, but was weighted much more heavily toward position feedback. Upon comparing optimal limb state feedback vs. hand position error feedback in Experiment 2, we found both encoding schemes capable of enhancing stabilization and reach performance in the absence of vision. However, error encoding yielded superior outcomes - objective and subjective - due to the additional task-relevant information it contains.

Conclusions

The results of this study have established the immediate utility and relative merits of two forms of vibrotactile kinesthetic feedback in enhancing stabilization and reaching actions performed with the arm and hand in neurotypical people. These findings can guide future development of vibrotactile sensory substitution technologies for improving sensorimotor function after neuromotor injury in survivors who retain motor capacity, but lack proprioceptive integrity in their more affected arm.

Electronic supplementary material

The online version of this article (doi:10.1186/s12984-017-0248-8) contains supplementary material, which is available to authorized users.

Improving training for sensory augmentation using the science of expertise

Sensory substitution and augmentation devices (SSADs) allow users to perceive information about their environment that is usually beyond their sensory capabilities. Despite an extensive history, SSADs are arguably not used to their fullest, both as assistive technology for people with sensory impairment or as research tools in the psychology and neuroscience of sensory perception. Studies of the non-use of other assistive technologies suggest one factor is the balance of benefits gained against the costs incurred. We argue that improving the learning experience would improve this balance, suggest three ways in which it can be improved by leveraging existing cognitive science findings on expertise and skill development, and acknowledge limitations and relevant concerns. We encourage the systematic evaluation of learning programs, and suggest that a more effective learning process for SSADs could reduce the barrier to uptake and allow users to reach higher levels of overall capacity.

The experience of new sensorimotor contingencies by sensory augmentation

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We investigate learning of sensorimotor contingencies by sensory augmentation.

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The sensory device maps information of magnetic north to vibrotactile stimulation.

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Active training with the device leads to marked changes in perception of space.

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The device facilitates navigation and alters navigational strategies.

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The device gives subjects a strong feeling of security and of “never get lost”.

Embedded in the paradigm of embodied cognition, the theory of sensorimotor contingencies (SMCs) proposes that motor actions and associated sensory stimulations are tied together by lawful relations termed SMCs. We aimed to investigate whether SMCs can be learned by means of sensory augmentation. Therefore we focused on related perceptual changes. Subjects trained for 7 weeks with the feelSpace belt mapping information of the magnetic north to vibrotactile stimulation around the waist. They experienced substantial changes in their space perception. The belt facilitated navigation and stimulated the usage of new navigation strategies. The belt’s vibrating signal changed to a kind of spatial information over time while the belt’s appeal and perceived usability increased. The belt also induced certain emotional states. Overall, the results show that learning new SMCs with this relatively small and usable device leads to profound perceptual and emotional changes, which are fully compatible with embodied theories of cognition.