Haptics Rendering and Applications

There has been significant progress in haptic technologies but the incorporation of haptics into virtual environments is still in its infancy. A wide range of the new society's human activities including communication, education, art, entertainment, commerce and science would forever change if we learned how to capture, manipulate and reproduce haptic sensory stimuli that are nearly indistinguishable from reality. For the field to move forward, many commercial and technological barriers need to be overcome. By rendering how objects feel through haptic technology, we communicate information that might reflect a desire to speak a physically- based language that has never been explored before. Due to constant improvement in haptics technology and increasing levels of research into and development of haptics-related algorithms, protocols and devices, there is a belief that haptics technology has a promising future

A Systematic Review of Weight Perception in Virtual Reality: Techniques, Challenges, and Road Ahead

Weight is perceived through the combination of multiple sensory systems, and a wide range of factors – including touch, visual, and force senses – can influence the perception of heaviness. There have been remarkable advancements in the development of haptic interfaces throughout the years. However, a number of challenges limit the progression to enable humans to sense the weight in virtual reality (VR). This article presents an overview of the factors that influence how weight is perceived and the phenomenon that contributes to various types of weight illusions. A systematic review has been undertaken to assess the development of weight perception in VR, underlying haptic technology that renders the mass of a virtual object, and the creation of weight perception through pseudo-haptic. We summarize the approaches from the perspective of haptic and pseudo-haptic cues that exhibit the sense of weight such as force, skin deformation, vibration, inertia, control–display ratio, velocity, body gestures, and audio–visual representation. The design challenges are underlined, and research gaps are discussed, including accuracy and precision, weight discrimination, heavyweight rendering, and absolute weight simulation. This article is anticipated to aid in the development of more realistic weight perception in VR and stimulated new research interest in this topic

Motor learning and sensory plasticity in healthy adults and Parkinson's disease

We use multiple sources of sensory information to guide goal-directed movements, such as reaching. When information from multiple modalities (i.e. vision, proprioception) is incongruent, one learns to adapt his or her movements and recalibrate one sense to more closely match the other; simply put, one begins to perceive his/her hand where one sees it. This thesis attempts to better characterize this sensory recalibration (termed 'proprioceptive recalibration') following adaptation to a visuomotor distortion under a variety of contexts, and contributes to the existing literature that describes sensory plasticity associated with motor learning. Specifically, chapter two describes the effect of initial exposure to a visuomotor distortion and the dominance of the hand trained on proprioceptive recalibration. In. this study, participants used their dominant right or non-dominant left hand to reach to targets with visual feedback of hand position that was abruptly rotated clockwise relative to their unseen hand. Proprioceptive recalibration was then assessed and found to be comparable in the two hands and consistent with previous studies employing a gradual perturbation; these findings suggest that neither the initial error signal nor dominance of the hand trained influence recalibration. Chapter three describes how the magnitude of the visuomotor distortion affects the magnitude of recalibration, and how this is related to changes in reach aftereffects. Changes in reach aftereffects and proprioception were measured following adaptation to increasingly misaligned visual hand feedback; these changes were found to increase systematically as a function of the distortion magnitude. However, while these changes were directly correlated with the distortion magnitude, they were not correlated with each other, which suggests that these two processes may be mediated by simultaneous yet separate underlying mechanisms. Chapter four similarly describes how the magnitude of a cross-sensory error signal (generated in the absence of a visuomotor signal derived from goal-directed movement) affects the magnitude of recalibration, and how this is related to changes in reach aftereffects. Participants moved their unseen hand along a grooved path while viewing a cursor that moved towards a target; the position of the path was gradually rotated counter-clockwise with respect to the cursor. Following this cross-sensory adaptation, changes in reach aftereffects and proprioception were both found to saturate at a small distortion as no further changes were observed with training with increasing misalignment. Furthermore, these changes were not correlated with the magnitude of the misalignment. However, in contrast to the findings in chapter three, these changes were correlated with each other, suggesting that the cross-sensory discrepancy drives changes in both reach aftereffects (partially) and proprioception. This study helps to characterize the contribution of different error signals to changes in motor and sensory systems. Lastly, chapter five describes how damage to central nervous system structures integral to sensorimotor integration (i.e. the basal ganglia) affects proprioceptive recalibration. Patients with Parkinson's disease were able to learn to reach to targets with gradually rotated and translated visual feedback of hand positions comparably to healthy older adults. Patients also recalibrated proprioception comparably to healthy older adults, although the trend for greater recalibration in patients suggests that they may depend more on salient visual information of hand position than proprioceptive feedback to guide movement

Rehabilitation Outcome Following Acute Stroke: Considering Ideomotor Apraxia

Stroke is a leading cause of death and the leading cause of adult disability in the United States affecting approximately 795,000 people yearly. Stroke sequelae often span multiple domains, including motor, cognitive, and sensory subsystems. Impairments can contribute to difficulty participating in activities of daily living (ADLs) and translate into disability - a concern for patients and occupational therapists alike. The role of ideomotor apraxia (IMA) in stroke rehabilitation is unclear. Thus, the purpose of these two studies is to investigate stroke rehabilitation outcome while considering the presence of ideomotor apraxia. Stroke causes dysfunctional movement patterns arising from an array of potential etiologies. Agreement exists that understanding the patient's functioning serves as the basis for the rehabilitation process and it is insufficient for clinicians simply to determine functional movement problems without knowing how underlying impairments contribute. Stroke-induced paresis is a prevalent impairment and frequent target of traditional rehabilitation. Stroke rehabilitation often addresses paresis narrowly with little consideration for other stroke consequences. Ideomotor apraxia is one such disorder after stroke that could conceivably limit rehabilitation benefit of otherwise efficacious treatment interventions aimed at remediating paresis. This led us to an initial study of a subject who experienced a single left, ischemic stroke with paresis of his right upper extremity and comorbid ideomotor apraxia. The subject participated in combined physical and mental practice for six consecutive weeks to improve use of his right arm. After intervention, the subject demonstrated clinically significant improvements in functional performance of his more-affected right upper extremity and reported greater self-perception of performance. The subject continued to demonstrate improvements after four weeks with no intervention and despite persistent IMA. This single case report highlights the importance of recognizing that ideomotor apraxia does present after stroke, and traditional stroke rehabilitation efforts directed at paresis can be efficacious for subjects with IMA. Traditional beliefs suggested that ideomotor apraxia does not translate to disability in everyday life and that IMA resolves spontaneously. Despite accumulating evidence of the influence of IMA on functional ability, this topic remains relatively neglected. It is unclear how ideomotor apraxia affects the rehabilitation process. The second study reports rehabilitation outcomes of a group of subjects following acute stroke. The Florida Apraxia Battery gesture-to-verbal command test was used to detect IMA in subjects. Level of independence with a set of ADLs and motor impairment of the more-affected upper extremity was documented at admission and discharge. Study subjects participated in standard of care stroke rehabilitation in the inpatient rehabilitation units. A total of fifteen subjects who sustained a left hemisphere stroke participated in this study - ten with IMA and five without IMA. After rehabilitation, subjects with IMA improved ADL independence and displayed decreased motor impairment of their right upper extremity. Subjects with and without IMA exhibited comparable improvements in ADL independence, but subjects with IMA exhibited less ADL independence upon when compared to subjects without IMA. Additional findings suggested that subjects with IMA were not different with respect to motor impairments and length of stay; however, additional studies with larger sample sizes are needed. In summary, these two studies aid to elucidate the implications of ideomotor apraxia on traditional stroke rehabilitation efforts. Study subjects with ideomotor apraxia after acute stroke still derive benefit from traditional rehabilitation. Because traditional rehabilitation interventions narrowly target motor impairment, these findings support the need for considering IMA as a factor in developing interventions tailored to patients with IMA and possibly as a specific focus for interventions. A step toward addressing this need is to assess whether IMA is present after stroke on a regular basis. This work provides a framework for researchers and clinicians to investigate further how ideomotor apraxia translates into disability. These findings are important since consideration of ideomotor apraxia could influence selection and design of rehabilitation interventions to optimize patient daily functioning after stroke

Influence of Gaze Position on Grasp Parameters For Reaches to Visible and Remembered Stimuli

In order to pick up or manipulate a seen object, one must use visual signals to aim and transport the hand to the object’s location (reach), and configure the digits to the shape of the object (grasp). It has been shown that reach and grasp are controlled by separate neural pathways. In real world conditions, however, all of these signals (gaze, reach, grasp) must interact to provide accurate eye-hand coordination. The interactions between gaze, reach, and grasp parameters have not been comprehensively studied in humans. The purpose of the study was to investigate 1) the effect of gaze and target positions on grasp location, amplitude, and orientation, and 2) the influence of visual feedback of the hand and target on the final grasp components and on the spatial deviations associated with gaze direction and target position. Seven subjects reached to grasp a rectangular “virtual” target presented at three orientations, three locations, and with three gaze fixation positions during open- and closed-loop conditions. Participants showed gaze- and target-dependent deviations in grasp parameters that could not be predicted from previous studies. Our results showed that both reach- and grasp-related deviations were affected by stimulus position. The interaction effects of gaze and reach position revealed complex mechanisms, and their impacts were different in each grasp parameter. The impacts of gaze direction on grasp deviation were dependent on target position in space, especially for grasp location and amplitude. Gaze direction had little impact on grasp orientation. Visual feedback about the hand and target modulated the reach- and gaze- related impacts. The results suggest that the brain uses both control signal interactions and sensorimotor strategies to control and plan reach-and-grasp movements

VALIDATION OF A MODEL OF SENSORIMOTOR INTEGRATION WITH CLINICAL BENEFITS

Healthy sensorimotor integration – or how our touch influences our movements – is critical to efficiently interact with our environment. Yet, many aspects of this process are still poorly understood. Importantly, several movement disorders are often considered as originating from purely motor impairments, while a sensory origin could also lead to a similar set of symptoms. To alleviate these issues, we hereby propose a novel biologically-based model of the sensorimotor loop, known as the SMILE model. After describing both the functional, and the corresponding neuroanatomical versions of the SMILE, we tested several aspects of its motor component through functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS). Both experimental studies resulted in coherent outcomes with respect to the SMILE predictions, but they also provided novel scientific outcomes about such broad topics as the sub-phases of motor imagery, the neural processing of bodily representations, or the extend of the role of the extrastriate body area. In the final sections of this manuscript, we describe some potential clinical application of the SMILE. The first one presents the identification of plausible neuroanatomical origins for focal hand dystonia, a yet poorly understood sensorimotor disorder. The last chapter then covers possible improvements on brain-machine interfaces, driven by a better understanding of the sensorimotor system. -- La façon dont votre sens du toucher et vos mouvements interagissent est connue sous le nom d’intégration sensorimotrice. Ce procédé est essentiel pour une interaction normale avec tout ce qui nous entoure. Cependant, plusieurs aspects de ce processus sont encore méconnus. Plus important encore, l’origine de certaines déficiences motrices encore trop peu comprises sont parfois considérées comme purement motrice, alors qu’une origine sensorielle pourrait mener à un même ensemble de symptômes. Afin d’améliorer cette situation, nous proposons ici un nouveau modèle d’intégration sensorimotrice, dénommé « SMILE », basé sur les connaissances de neurobiologie actuelles. Dans ce manuscrit, nous commençons par décrire les caractéristiques fonctionnelles et neuroanatomiques du SMILE. Plusieurs expériences sont ensuite effectuées, via l’imagerie par résonance magnétique fonctionnelle (IRMf), et la stimulation magnétique transcranienne (SMT), afin de tester différents aspects de la composante motrice du SMILE. Si les résultats de ces expériences corroborent les prédictions du SMILE, elles ont aussi mis en évidences d’autres résultats scientifiques intéressants et novateurs, dans des domaines aussi divers que les sous-phases de l’imagination motrice, les processus cérébraux liés aux représentations corporelles, ou encore l’extension du rôle de l’extrastriate body area. Dans les dernières parties de ce manuscrit, nous dévoilons quelques applications cliniques potentielles de notre modèle. Nous utilisons le SMILE afin de proposer deux origines cérébrales plausibles de la dystonie focale de la main. Le dernier chapitre présente comment certaines technologies existantes, telles que les interfaces cerveaux-machines, pourraient bénéficier d’une meilleure compréhension du système sensorimoteur

A Literature Review and Introductory Pediatric Aquatic Therapy Manual

Aquatic therapy continues to grow as an acceptable and often times preferable means of achieving therapeutic goals across a variety of patient populations: pediatric to geriatric, orthopedic to neurologic. The unique properties of water allow people to exercise and to recover in a safe and relaxing environment that promotes similar goals to those on land. However, land exercises can not simply be performed in water due to the water\u27s unique properties. Similarly, exercises for adults do not work as effectively for children. Many physical therapy programs across the nation provide only minimal instruction on aquatic or pediatric therapy as a part of the core curriculum. The purpose of this literature review and the accompanying manual are to provide a review of the unique characteristics of water and to introduce pediatric aquatic activities to physical therapy professionals and students. The review of literature focuses on the physical properties of water, thermal considerations, advantages of aquatic therapy, and precautions. The manual includes a variety of recreational and therapeutic activities to be utilized by a physical therapist in a therapeutic pool. The activities are categorized based upon their primary therapeutic objective. The result of this project is an overview of aquatic therapy and the properties of water. In addition, the beginning aquatic physical therapist and physical therapy student are provided with ideas to facilitate their own creativity in designing individual pediatric aquatic therapy treatment plans