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JOURNAL JNER 9:20 2012, Rehabilitation NeuroEngineering Journal al. AND http://www.jneuroengrehab.com/content/9/1/20 E Rachel Recent REVIEWOpenAccess Benjamin L Michael M Mary Chan4, Leighton J David surveys paper participation. prevents fully case worst difficult more desired participation maximal makes Loss Abstract during observed drawing recent theme underlying Europe. sites industrial academic * benefit. widespread examples limbs aids, Wheelchairs, mobility. improve impaired, function struc
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  Cowan et al. Journal of NeuroEngineering and Rehabilitation 2012, 9:20 JNERJNERJOURNAL OF NEUROENGINEERING http://www.jneuroengrehab.com/content/9/1/20 AND REHABILITATION REVIEWOpenAccessRecent trends in assistive technology for mobility Rachel E Cowan1*, Benjamin J Fregly2, Michael L Boninger3,8, Leighton Chan4, Mary M Rodgers5,6 and David J Reinkensmeyer7 Abstract Loss of physical mobility makes maximal participation in desired activities more difficult and in the worst case fully prevents participation. This paper surveys recent work in assistive technology to improve mobility for persons with a disability, drawing on examples observed during a tour of academic and industrial research sites in Europe. The underlying theme of this recent work is a more seamless integration of the capabilities of the user and the assistive technology. This improved integration spans diverse technologies, including powered wheelchairs, prosthetic limbs, functional electrical stimulation, and wearable exoskeletons. Improved integration is being accomplished in three ways: 1) improving the assistive technology mechanics; 2) improving the user-technology physical interface; and 3) sharing of control between the user and the technology. We provide an overview of these improvements in user-technology integration and discuss whether such improvements have the potential to be transformative for people with mobility impairments. Keywords: Disability, Assistive technology, Robotics Introduction Mobility encompasses an individualÕs ability to move his or her body within an environment or between environments and the ability to manipulate objects. Collectively, these activities enable the individual to pursue life activities of their choosing. An individualÕsability to perform any mobility task can be compromised by impaired body functions or structures. Impairments can onset gradually, as occurs with multiple sclerosis, or they can begin instantly, as occurs with traumatic spinal cord injury, cerebral vascular accidents, and limb amputations. The link between impairment and restricted mobility is evident for amputations and spinal cord injury. However, mobility is also affected by less obvious impairments. For example, the pain associated with knee osteoarthritis can significantly affect walking ability. Persons with reduced heat tolerance, such as those with multiple sclerosis, experience decreased endurance and increased fatigue as ambient temperature increases [1]. Regardless of which body structure or function is impaired, technology can improve mobility. Wheelchairs, walking aids, and prosthetic limbs are examples of technologies that have provided widespread benefit. * Correspondence: rcowan@med.miami.edu 1Department of Neurological Surgery, The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, 1095 NW 14th Terrace, Miami, FL 33136, USA Full list of author information is available at the end of the article To identify new opportunities for improving assistive technologies for persons with a mobility impairment, the National Science Foundation initiated a study using the World Technology Evaluation Center. A scientific panel of national experts was formed and charged with gathering information about research trends in technology that could transform mobility for people with mobility disabilities. Information gathering involved a 5-day visit by two teams to several of the leading European laboratories working in this area. Given the many pathways by which disability can impact mobility, and given the large number of possible technological solutions, the panel focused on seven mobility-based tasks: posture, balance and transfers, manipulation, walking, stair climbing, other locomotion tasks, and using transportation. Even within this limited scope, the technologies reviewed were not exhaustive, but they did provide insight into some important themes in assistive technology research. Before describing these trends, we briefly discuss a framework for understanding different types of assistive technology. Although there are several frameworks that conceptualize disability [2], the international standard is the World Health OrganizationÕs International Classification of Functioning, Disability and Health (ICF) framework (Figure 1). Like other frameworks, the ICF framework acknowledges that ÕdisabilityÕ results from the dynamic © 2012 Cowan et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited.  Cowan et al. Journal of NeuroEngineering and Rehabilitation 2012, 9:20 Page 2 of 8 http://www.jneuroengrehab.com/content/9/1/20 HealthConditionBodyStructures&FunctionsUpper&LowerLimbsMotorcontrolSensoryFeedba ckMuscularstrength&enduranceActivityMobilityParticipationEnvironmentalFactorsPhysicalEnvironmentTechnologyPersonalFactorsContextual Factors ICF Figure 1 ICF Framework: Body functions are physiological functions of body systems (including psychological functions). Body structures are anatomical parts of the body such as organs, limbs, and their components. Impairments are significant deviations from normal or loss of body function or structures. An activity is the execution of a task or action by an individual. Participation is involvement in a life situation. Activity limitations are difficulties an individual has in executing activities. Participation restrictions are problems an individual experiences in involvement in life situations. Environmental factors make up the physical, social, and attitudinal environment in which people live and conduct their lives. interaction of the user, technology, and the environment. When environmental demands exceed an individualÕsmobility resources, participation may be restricted. Technology can facilitate participation by indirectly (via treatment or therapy) or directly (via physical assistance) enhancing and individualÕs mobility such that their mobility capacity meets or exceeds the demand of the environment (Figure 2). Indirect, or therapeutic, technologies enhance mobility by reducing impairments at the body structure/function level by helping the body in repairing or redressing the body structure impairment, or by supporting rehabilitation of the impaired body function (Figure 2, black arrows). Baclofen pumps are an example of an indirect approach because they facilitate mobility by allowing a person to control his or her spasticity. Robotic therapy devices are another example of an indirect approach because they allow people to reduce impairment through repetitive movement training. Therapeutic technologies typically require clinical oversight to be set-up and operated, are one modality in an overall rehabilitation plan, and are typically not designed to be used to execute daily activities outside the clinic. A companion article reviews recent advances in therapeutic technologies [4]. On the other hand, direct, or assistive, technologies (AT) enhance mobility without altering the impaired body structure/function (Figure 2, grey arrow). Wheelchairs and walkers are prime examples; they enhance mobility, but they do not alter the impairment underlying the mobility loss. Direct technological approaches can augment or support impaired body structure or function, as in the case of a cane or walker, or they can replace the missing or impaired body structure or function, as in the case of a prosthetic limb. In contrast to therapeutic technologies, assistive technologies are operated by the user rather than a clinician and they are designed to be used to execute functional activities in the home and community. The focus of this article is on recent trends in direct technology or AT approaches to enhancing mobility. Recent trends in assistive technology for mobility: improved user-technology integration As stated in the abstract, the unifying theme or trend of the research we observed is a more seamless integration of the capabilities of the user and the assistive technologies. The observed approaches to enhance integration can be broadly classed into three non-mutually exclusive areas; 1) improvements to the assistive technology mechanics; 2) improvements to the user-technology physical interface; and 3) improved shared control between the user and the technology. Improvements in thetechnologymechanics includehardwareand software advances. Improvements to the physical interface  Cowan et al. Journal of NeuroEngineering and Rehabilitation 2012, 9:20 Page 3 of 8 http://www.jneuroengrehab.com/content/9/1/20 BodyStructures&FunctionsUpper&LowerLimbsMotorcontrolSensoryFeedbackMuscularstren gth&enduranceActivityMobility1.ÒMovingwithinanenvironmentÓ2.ÒMovingbetweenenvironmentsÓ3.ÒManipulatingobjectsÓEnvironmentalFactorsTechnologyContextual Factors Figure 2 Simplified ICF framework demonstrating indirect (therapeutic) pathways (black arrows) and direct (assistive) pathways (light arrow) by which technology can improve mobility. (Modified from World Health Organization model [3]). typically focused on better leveraging the capabilities of user to operate the technology and providing more intuitive device control. The panel observed a trend toward better user-technology integration in four key technologies: powered wheelchairs, prosthetics, functional electrical stimulation, and robotic exoskeletons. Power wheelchair based mobility Power wheelchairs are traditionally operated by a joystick and one or more switches which change the function that is being controlled by the joystick. These functions include wheelchair movement, seat tilt, backrest recline, footrest elevation, and seat elevation. Not all persons who could experience increased mobility by using a powered wheelchair possess the necessary cognitive and neuromuscular capacity needed to navigate a dynamic environment with a joystick. For these users, a ÒsharedÓ control approach coupled with an alternative interface is indicated. Shared control has been considered before for powered wheelchair mobility [5]. In a traditional shared control system, the assistive technology ÔassistsÕ the user in path navigation. Shared control systems typically have several modes that vary the assistance provided (i.e., user autonomy) and movement algorithms. Millan et al. suggest shared control approaches can be classified in two ways: 1) mode changes triggered by the user via a button or trigger or 2) mode changes hard-coded to occur when specific conditions are detected [5]. Both approaches have potential problems. Requiring the user to trigger mode changes imparts a substantial mental load, can be tiring, increases complexity, and decreases user-friendliness. Hard coding mode changes may not allow customization to the individual and their specific abilities. Dr. Etienne BurdetÕs Human Robotics research group at Imperial College, in collaboration with the National University of Singapore, has developed a low cost power wheelchair shared control system based on path guidance that provides a third way to address shared control. The target population for the collaborative wheelchair assistant (CWA) is Òpeople who find it difficult or impossible to use a standard power wheelchair but have sufficient sensory abilities to detect when stopping is necessary,Ó such as persons with cerebral palsy, traumatic brain injury, or locked-in individuals [6]. The CWA guides the user along previously programmed paths between specific destinations. Paths are programmed by a ÒhelperÓ who walks the chair through the desired pathway while the chair records the path. The user controls speed, starts, and stops, as well as any deviations required to avoid obstacles that have entered the pre-programmed path. However, the burden of navigation falls on the wheelchair, which adheres to the programmed path until the user initiates a deviation. During the deviation, the chair acts like a mass-spring-damper system being pushed away from the pre-programmed path by the user. The  Cowan et al. Journal of NeuroEngineering and Rehabilitation 2012, 9:20 Page 4 of 8 http://www.jneuroengrehab.com/content/9/1/20 wheelchair thus returns to the path once the user relinquishes control. The benefit of this approach is that the cognitive load of navigation and path-planning is not born by the user. The user only needs to focus on obstacle avoidance and speed control. Before users navigate new environments, new paths must be created. It is envisioned that new Ôpath librariesÕ could be automatically generatedfrombuildingplans.Thissharedapproach does not fit into the categories defined by Millan et al. [5] as there are no mode changes triggered by the user or via automatic sensing; it is rather an approach that more seamlessly integrates the user and machine. Other approaches toward improving powered mobility are seeking to exploit better the userÕs inherent capabilities for controlling the chair through better input devices. One approach is to design an interface that can be operated by an alternate body part. An example of this approach is the development of tongue based control interfaces, such as that developed by the Sensory Motor Interaction (SMI) center of the department of health science and technology at Aalborg University. It is an inductive system relying on a ferromagnetic tongue piercing and an intraoral device embedded with 18 sensors. Ten sensors are dedicated to a keyboard and eight to joystick control. It has been designed to interface with most power wheelchairs that can be controlled by traditional joysticks [7]. In a related approach, a group at Georgia Institute of Technology (USA) has developed a tongue interface that is not dependent on a physical interface between the tongue and sensors. Instead, sensors external to the oral cavity wirelessly track tongue position via a tongue-mounted magnetic sensor. This interface has been tested in 13 persons with high cervical spinal cord injuries [8]. Other related work has explored how information from sensors placed anywhere on the body can be automatically mapped to wheelchair control signals, again allowing a person to use the parts of the body that they are capable of moving well to control the wheelchair [9]. Another way to better make use of a userÕs inherent capabilities is to use a brain computer interface (BCI) to detect, decode, and communicate intended movements from brain electrical activity. A previous NSF study examined recent progress in BCI technology [10] in detail, so we only summarize a few important points here. Current noninvasive BCI technology is characterized by a low information transfer rate (low bandwidth), which is a challenge for real-time wheelchair navigation. Low bandwidths can result in substantial delays between when a user initiates a maneuver and when the wheelchair responds, introducing a potential safety hazard [11]. In addition, BCI driven wheelchair navigation typically requires extensive training, imposes a substantial cognitive load, and can be very tiring. If BCIs are to mature into a realistic option to control power wheelchairs, these issues must be resolved in a cost-effective manner. Dr. BurdetÕs Imperial College group has developed a possible solution to these challenges using the shared control system described previously. The computer ÒdrivesÓ the chair between destinations using pre-programmed paths while the user monitors the pathways for unexpected obstacles. A slow BCI is used for selecting among the destinations and a ÒfastÓ one is used for emergency stopping. This approach removes the cognitive load of navigation, preventing the inevitable fatigue, and does not require extensive training, but it limits use of the system to known environments and programmed destinations [11]. Prosthetic limb control Prosthetic development challenges include replacing both the efferent nervous system (i.e., movement) and the afferent nervous system (i.e., sensory feedback). Adequate prosthetic limb control will be achieved when both efferent and afferent systems are adequately replaced. Three novel approaches were observed in Europe for better interfacing the user and their prosthetic: 1) computer-vision enhanced control, which is an example of improving both the device and the shared control system, 2) peripheral nervous system interfaces, an example of improved interfaces, and 3) kinematic/kinetic based control, a strategy which improves the mechanics of the limb through software and provides a better interface. The first two approaches target upper limb prosthetic control and the third targets lower limb. Computer-vision enhanced control When an individual reaches to grab an object, the hand assumes a given orientation and opens to accommodate the object. Typically, prosthetic hand control has a high mental burden, as the user must plan the grasp and generate step by step commands to position and shape the hand. Although a high degree of control can be achieved by this method, users prefer intuitive controls requiring less conscious involvement. In pursuit of a less demanding control strategy, researchers at the University of Aalborg have developed a camera-based shared control system that uses image recognition to autonomously select the proper hand orientation, grasp shape, and grasp size based on images of the object being manipulated [12]. The user is responsible for aiming, triggering, and orienting the hand, while the camera-based control selects and implements grasp type and size. By increasing the autonomy of the prostheses, user burden is lessened. The system was successfully tested in 13 non-disabled subjects who used it to control an artificial hand [13]. Once refined, this system is targeted for application with the Pisa
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