Considerations in the Efficacy and Effectiveness of Virtual Reality Interventions for Stroke Rehabilitation: Moving the Field Forward

VR Interventions in Stroke Rehabilitation: Exploratory Phase

Virtual reality technologies have been used as stroke interventions with some success over the past several decades. In stroke rehabilitation, as well as other health behavior–related areas such as diet and exercise, providing an intervention that is motivating and engaging is crucial to patient involvement and participation. Naturally, VR technologies were initially heralded as a potentially successful medium for the delivery of engaging and motivating rehabilitation interventions. A SWOT (strengths, weaknesses, opportunities, and threats) analysis of the field of VR and rehabilitation by Rizzo and Kim⁶ showed that the integration of gaming features into VR applications could enhance motivation. Burke and colleagues²⁰ further explored principles of game design and concluded that both meaningful play and challenge were integral to the use of VR in rehabilitation. Researchers also began to document that the VR applications and interventions needed to have components beyond those related to engagement and enjoyment.²¹

Much of the early research and development of VR systems for rehabilitation focused on large-scale, laboratory-based systems or complex, custom-made, expensive hardware devices.²² Although the development and initial evaluations of these systems were promising, many of these early prototype systems did not make it into the clinical setting. Early work at the beginning of the 2000s using video-capture systems— such as the GestureTek system (GestureTek, Toronto, Ontario, Canada)—for rehabilitation provided much of the groundwork for the low-cost VR systems in development today.²³ The camera-based system captures an image of the user, without the need for cumbersome markers or devices. Although the system was still relatively costly, the camera-based tracking and relative ease of use have allowed greater access to the technology for clinicians.

Initially, researchers used small, exploratory case studies to examine the feasibility of using off-the-shelf games and devices.^24,25 Given that the field was still exploring the motivational and engaging aspects of games and VR interventions, this type of research was appropriate. Within months of the release of the Nintendo Wii console (Nintendo, Redmond, Washington) in 2006, news articles began reporting on the topic of “Wii-hab” in hospitals and nursing homes, and research soon followed. The Nintendo Wii was explored as both an alternative and an adjunct to conventional stroke rehabilitation.^26,27

The release of the Microsoft Kinect (Microsoft Inc, Redmond, Washington) in 2010 stirred up a new wave of development of games for rehabilitation; however, a few lessons had been learned from the previous 4 years of “Wii-hab” excitement. Researchers and nonrehabilitation programmers have been experimenting with methods of utilizing the internal mechanisms of the Microsoft Kinect sensor for the purposes of accurate tracking, providing specific feedback, and collecting and recording meaningful data.^28,29 Lange and colleagues³⁰ have since developed an application for balance using the Kinect camera that has applications for a broad range of populations, including people with stroke. Along with being able to customize gestural input, they have created other features, including a calibration of the Kinect camera to user baseline function, a variety of on-screen user representations, an option for multiple users (using the same Kinect camera and using 2 different cameras in 2 different locations), and recording and quantification of performance.²¹ Other researchers have developed customized games using the Kinect camera, and findings from initial usability studies are positive.^31–36

VR Interventions in Stroke Rehabilitation: Intervention Development and Efficacy

Most of these systems are still in the exploratory phase of research and have not progressed beyond user testing and feasibility and small case studies. Pairing low-cost sensors, such as the Microsoft Kinect sensor, with customized software has allowed researchers to design, describe, and control the active ingredients in VR interventions for stroke rehabilitation. Since 2010, research has circled back around through the phases of research to better understand the mechanisms of impact on people with stroke for both upper limb function and balance and mobility.

Recent feasibility trials using the Nintendo Wii have reached similar conclusions: the most effective types of games, the most effective dose, and the most effective level of clinician interaction need to be further explored.^37,38 Saposnik and colleagues³⁹ presented the design and pilot data for a randomized clinical trial using the Nintendo Wii as an intervention for stroke (Effectiveness of Virtual Reality Exercises in STroke Rehabilitation [EVREST]) compared with an equal amount (total time) of recreation therapy (playing cards, Bingo, or Jenga). Their findings were presented in a subsequent article that reported significant unadjusted differences in motor function (as assessed with the Wolf Motor Function Test) between the experimental and control groups in favor of the Wii intervention used in the experimental group.⁴⁰ It should be noted that this was a pilot clinical trial that was not powered to detect differences. Furthermore, there was little explanation on the part of the authors as to the mechanism for change through playing the Wii games. A similarly designed RCT exploring the efficacy of the PlayStation EyeToy (Sony Computer Entertainment America LLC, San Mateo, California) for people with subacute stroke demonstrated that participants improved in self-care ability but not in Brunnström states for the hand and upper extremity.⁴¹ Some of the major limitations mentioned in both studies^40,41 included limited evidence for intervention dosing, choice of outcome measures, and comparison groups.

It also is difficult to obtain meaningful data from the game systems beyond time spent playing and game scores, and even with a variety of measures included in the study, it is difficult to determine the level (body structures and functions, activity performance, or activity participation) on which the intervention had an impact. Variables such as amount of movement, intensity of movement, and amount of clinician input are all being explored.^41–45 The results from several studies were promising and included benefits for people with stroke, including increased participation in activities of daily living, improvement in upper extremity movement, and improvement in static standing balance.^8,46–52

VR Interventions for Stroke Rehabilitation: Moving to Scale-up Evaluation?

As research moves more boldly into the intervention efficacy phase and eventually into the scale-up evaluation phase, choosing appropriate outcome measures and dosing will be crucial. The need for validated outcome measures and specific definitions of intervention dosage was echoed in the extensive Cochrane review by Laver and colleagues⁵³ in 2012. The review identified a number of shortcomings in trials of VR interventions and suggested that research exploring the characteristics of VR (eg, presence, immersion, engagement) will be a crucial component of identifying active ingredients in future studies and will assist researchers in constructing comparison interventions and study design. With the valuable time spent in the early phases of research, researchers will be well positioned to make informed and suitable choices.

Although previous research has provided promising results for the use of VR technologies to improve stroke rehabilitation outcomes, there are still a number of major questions and issues that need to be resolved before larger trials are implemented. A recent review by Fluet and Deutsch⁵⁴ called for both efficacy trials and comparative effectiveness trials of VR interventions for sensorimotor rehabilitation poststroke. Researchers should be cautious in choosing comparison interventions. Rehabilitation interventions are mostly behavioral in nature and are a complex interaction of many factors, including the inherent influence of the person receiving the intervention; one size may not fit all. A match of dose, duration, and frequency of the intervention active ingredients can help minimize the “challenge of making groups equivalent.”⁵³ This challenge stems from the nature of VR interventions. Virtual environments potentially offer scenarios and interactions that are impossible in the real world. Real-world environments, objects, and scenarios can be modeled in a virtual setting. Feedback and rewards can be structured in the virtual environment and affect the performance of the person with stroke. The various tracking and input devices can help the VR intervention mimic real-world environments; however, the perceptions, movements, and subjective experience of the person in the virtual environment may be slightly altered.⁵⁵ These devices also offer methods of measuring outcomes that have been previously unavailable or available only in a laboratory setting.

Utilizing Advances in Measurement Technology

Understanding and measuring what the user is doing during an intervention is only one piece of the equation when it comes to demonstrating the efficacy of rehabilitation interventions for motor impairments in stroke. One of the unique and exciting features of using VR technology in the rehabilitation setting is the capability of these systems to record and analyze the user's performance quantitatively. This is a feature that is lacking with many standard treatment tools used within the clinic setting. The Microsoft Kinect offers the potential as both an input device for the control of a VR intervention by the end user and a device to record kinematic data of the end user.

Da Gama and colleagues⁵⁶ explored the capabilities of the Kinect to detect correct (within specified parameters) movements and provide feedback to the player. Using vectors and angles, computations can be made for a particular movement to help the system determine if it is being performed correctly—something that is typically done by a rehabilitation clinician. They tested this application with clinicians, adults with no disabilities, and older adults in a physical therapy program, and it was able to detect correct movements with high fidelity.⁵⁶

Along with tracking and movement recognition, researchers have explored other components of the Kinect, such as depth sensing. When compared with laser scanning, the point cloud property (depth) does not contain large systematic errors.⁵⁷ As an option for measuring joint angles, the Kinect has a 10% error rate, similar to the error rate demonstrated by clinicians trained in goniometer-based range-of-motion testing. The advantage of the Kinect is the ability to obtain those measurements with a similar error rate throughout an entire intervention session.⁵⁸

Advances in neuroimaging have progressed our understanding about what is occurring at a structural level in the nervous system. A consideration of how a player processes the virtual environment is a crucial piece of understanding how VR interventions affect the nervous system, the “mind-body connection.” Using functional magnetic resonance imaging (fMRI), researchers have shown that the brain views virtual avatars, or representations of the player's own body parts, as embodied “extensions” of the body.⁵⁹ Furthermore, activations are seen in areas of the brain that are associated with a sense of agency.⁵⁹ Adamovich and colleagues⁵⁹ pioneered the use of a virtual avatar in combination with real-time tracking of participant movements and were able to investigate the specific areas of the brain involved with agency through including a temporal delay between the movement and the feedback provided to the participant.

Not only is the virtual avatar embodied, but activation can be seen in areas that are involved in motor preparation, including the anterior intraparietal area and the supplementary motor area, when simply viewing a virtual avatar making a movement.⁶⁰ The simplicity of this experiment allowed the researchers to see the activation in these areas. They also showed that these areas are activated when the person makes a similar real movement.⁶⁰

The use of fMRI as a pretest-posttest measure gained momentum in the early and middle parts of the last decade. Results from several studies showed reorganization of the cortex in people with motor impairments (stroke, cerebral palsy). Both increased areas of activation and decreased or focused areas of activation were shown following VR interventions.⁶¹ In studies that explored activation relative to the paretic side of the body, results demonstrated reorganization and increased activation in the ipsilesional motor cortices.^62,63 The results from the fMRI studies in VR should be interpreted with caution. It is unclear whether the changes in brain structures can be attributed to true recovery of motor function or simply changes in activation in the brain because the person was moving more. Critiques of non-VR motor interventions, such as constraint-induced movement therapy, have alluded to this point.⁶⁴ If the active ingredients in the VR interventions are poorly defined, the findings from fMRI studies lend little support. However, if trends in the VR field move toward a better understanding of the active ingredients in the interventions, particularly those that can be well controlled by a clinician (ie, customized), the findings from associated fMRI studies offer a glimpse into the structural changes that affect behavior and function.

Accessing “Big Data”

Clinical trials, specifically RCTs, are the gold standard in the medical field, including stroke rehabilitation trials. This type of trial falls under the intervention efficacy phase discussed earlier. It is in this phase that researchers attempt to show that the developed VR intervention or technology has the potential to produce a significant change in outcomes for people with stroke. The cost of an RCT is continuing to rise, with a reported 7.5% annual increase in study costs above and beyond the rate of inflation.⁶⁵ Studies involving behavioral interventions, such as rehabilitation interventions for stroke, often incur increased costs due to the need for multiple study participant visits, clinician time for assessments and interventions, and large, complex data sets that need to be managed efficiently. Given the advances in the technologies used for stroke VR interventions, data from these systems can be effectively harnessed and utilized to maximize the efficiency of trial design and facilitate a smoother transition to real-world implementation or scale-up phase trials.

Data-driven health care utilizes patient-oriented data to adjust intervention and treatments in an effort to maximize positive health outcomes.⁶⁶ Electronic medical and health records are only a small piece of data-driven health care. It is through analyzing and interpreting patient data, followed by implementing changes or making treatment decisions, that the power of the data is finally realized. With regard to VR intervention for stroke, large amounts of data collected can be utilized to create highly customized interventions. Virtual reality technologies and systems have the potential to incorporate in vivo assessments of performance. The data can then be used to make minute adjustments to the level of challenge in the game so that the person with stroke remains at that just-right level of challenge. The data also can be analyzed remotely by a therapist who can then make appropriate, informed decisions about patient progress.

The implications for trial design go beyond treatment decisions. Telerehabilitation can provide an efficient vehicle for therapist interactions, and in vivo assessments using the technology and automatic uploading to a database can lessen the burden on bioinformatics and biostatistics personnel. Trials can be done in the home or community for those who have limited transportation, lessening the burden on the study budget. A constant stream of data can help investigators identify outliers or nonresponders more rapidly and adjust the trial design or increase the sample size to ensure sufficient power. Utilizing big data in VR intervention trials for stroke rehabilitation has the potential to shift the structure of clinical trials in rehabilitation and the nature of traditional interventions for stroke rehabilitation. Researchers are encouraged to maximize their approach to using data in trial and intervention design through VR technologies.

Precision Adjustment of Gameplay

Constant monitoring and analysis of data also can be utilized to create VR interventions that are motivating and engaging for the person with stroke. Components of engagement, motivation, and self-efficacy ought to be defined and integrated into the VR intervention tasks. Much of the research by Lewthwaite and Wulf⁶⁷ is changing the way the field thinks about motor learning and practice. The basic concepts of self-determination theory, autonomy, competence, and relatedness are all vital to creating learning within a game-based or VR structure.⁶⁸ Both competence and relatedness have unique effects on game performance and task satisfaction, whereas autonomy is a moderator of one of the other concepts.⁶⁹ Autonomy also is important when considered in conjunction with player typologies. Assessing and integrating player typologies into a VR intervention for stroke can allow for the game tasks to be adjusted to the most precise level of challenge for the player and provide continual, player-specific adjustments according to the individual's typology (eg, wanderer versus conqueror).⁷⁰ For example, assessment tools, such as questionnaires or cognitive measures, can be integrated into a game, and the next set of game tasks can be structured according to the finding of the assessment tool. A player with an explorer typology might enjoy tasks that involve games taking place at multiple locations on a map, whereas a player who is a conqueror might enjoy games that allow him or her to obtain a certain number of items or prizes. Both players might do the same physical or cognitive task; however, the reward structure will look different. Additionally, feedback can be timed appropriately by considering both player typologies and self-determination theory to deliver a satisfying, motivating, and effective VR intervention for stroke.

Moving Forward

The technologies behind VR interventions and measurement tools have progressed, and we now have the components for moving through the phases of research in a thorough and step-wise fashion. Much of the research with the new technologies in the field is still in the intervention development phase, and we will begin to see intervention efficacy studies followed by larger scale-up evaluations in the next several years. We challenge researchers to be thorough in their early stages and clearly define the active ingredients of their VR interventions. This challenge includes clearly defining parameters such as dosing, frequency of intervention, number of repetitions, intensity, and so on. Managing and utilizing extracted data from the VR technologies are keys to defining these parameters. Clinicians and engineers/programmers can have a better sense of what components of the intervention are most related to patient performance. With the level of customization available through the Kinect sensor, defining the intervention parameters is no longer a time-intensive task.

With advances in neuroimaging and other methods of measurement (eg, motion capture), we can begin to understand how manipulating motivation, engagement, and self-efficacy in VR interventions affects motor performance. Imaging also can help to identify responders and nonresponders for VR interventions as well those who might respond better to virtual environments. As researchers move into the intervention efficacy phase, choosing measurement tools will be a much easier process if the active ingredients of the VR intervention are well defined in the prior phases.⁷¹