VR-Balance


Christopher Widdowson ­ widdwsn2
Jatin Ganhotra ­ ganhotr2
Jane Wang ­ jzwang2
David Chen ­ dxchen3

Motivation and Background:
The project uses a virtual reality head-­mounted display (HMD) to investigate the influence of real and virtual height on state anxiety and postural control in older adults. Specifically, data from the HMD’s inertial measurement unit (IMU), including angular velocity, linear acceleration, and magnetic field strength, is assessed in conjunction with data from other external sensors and psychological measures to obtain a fine­-grained assessment of postural control. This project builds on an existing literature in kinesiology, human kinetics, and applied health sciences. However, this approach is novel in that it allows for simulated experimental conditions with older adults that would normally be intractable due to safety and feasibility issues.

Previous Work:
Previous research on this topic has shown a clear relationship between psychological and physiological markers of efficacy and state anxiety on postural control in young and older adults. The results in the initial studies show the potential for additive effects of psychological and physiological factors on the strategies used in postural control. However, across initial studies, the maximum vertical height exposure for an older adult was 160 cm (1.6 m). There is some evidence suggesting that 1.6 m is not a sufficient height difference to elicit a robust fear response (Brown et al., 2006). Indeed, the results Davis et al. (2009) support this notion. In order to circumvent safety issues related to exposing older adults to heights greater than 1.6 m, Cleworth, Horslen, and Carpenter (2012) used a head­mounted virtual reality display to compare the efficacy of real versus virtual height in two height conditions: 0.8 m (low) and 3.2 m (high) above ground. Results showed that COP displacement was greater following changes in height for the real compared to virtual condition. Interestingly, measures of electrodermal activity, anxiety, fear, and COP displacement increased with height irrespective of environment type, while perceived stability, balance confidence, and COP amplitude decreased. Thus, virtual reality is capable of inducing the psychological effects comparable to real­world height manipulations, while avoiding the associated risks to health and safety. For more information on previous studies, please refer to the research paper and the references section.

Description:
The project is centered around studying balance of elderly people while they are interacting in a virtual environment. Different experiences are presented to them, the Oculus Rift will receive data based on their reaction, and that data will then be mined, collected, and evaluated. The project work is divided into several phases where the most important step is to mine the Oculus data from it’s gyroscope (angular velocity (rad/sec)), accelerometer (linear acceleration (m/s^2)), and magnetometer (magnetic field strength (Gauss)) while the user is in VR and map the data collected to specific events in the VR. There are several challenges to the above:

  1. We used Vizard Virtual Reality Software, because the future work involves mining data from additional sensors (e.g.force-plate, electroencephalogram (EEG) cap) that are currently integrated into an existing platform.
  2. The API provided for extracting the required data from the Rift has not been widely used for these specific purposes.
  3. The most crucial step is to map the events from Vizard Virtual environment and the data collected from the Oculus, so that we can analyze the changes in the data based on certain events in the VR.

The first step was to extract the required data from the Rift and apply necessary modifications for matching it with the events data in the VR. The experiments are conducted such that the participant uses the Rift with slight modifications to the virtual environment(e.g. manipulate surface height) after certain time. We record the data from Oculus from the beginning of the experiment till the end and then map the data collected to the various events.

Technical challenges:
There were technical challenges along the way, while building the project. Other than working on a better and richer VR experience which took a considerable chunk of our time, we also faced the following technical challenges:

  • Building an executable that logs all data available from Oculus on-demand
  • Logging all events during the experiment, while the user is in VR
  • Mapping the data gathered from Oculus to a specific event in the VR.

We believe this to be the key technical challenge we faced, since our VR experience was based on Vizard (Python), while our application to capture data from Oculus was built using C++. Other than starting/stopping the Oculus data capture executable on-demand in the VR, the key issue was stitching collected data to various events in the VR.

Future work:
This project is a part of ongoing work with Prof. Hernandez, where we currently gathered data from Oculus. Christopher and Jatin plan to continue working on the project, in terms of gathering data from more sensors available and overall, building a better and richer VR experience for the experiment.

Comfortable VR experience (Human factors):
It is possible that the experimental manipulations may be uncomfortable for some users. Deliberately manipulating vertical height may induce discomfort through perceived depth cues, motion parallax, or a combination of other perceptual cues. Specifically, enabling adjustments to player (camera) height will directly affect the position of the horizon line which may disorient some users during the viewing transformation.

However, in our experience we have tried to strictly follow the Oculus Best Practices Guide in terms of rendering, minimizing latency, optimization, head­tracking / positional tracking, movement speed, degree of stereoscopic depth, and especially health and safety. All virtual reality content was tested multiple times and will be pilot tested for approval before being integrated into the final experiment on elder people.

The course content provided a strong foundation in terms of understanding the bits and pieces of VR and overall, building a comfortable and immersive VR experience. Our experience was different in a way that it’d be used by elder people, so we tried to make sure the after effects are minimal.

REFERENCES

  • Brown, L. A., Melody, A. P., & Doan, J. B. (2006). The effects of anxiety on the regulation of upright standing among younger and older adults. G​ait & Posture, 24,​397­405.
  • Carpenter, M. G., Adkin, A. L., Brawley, L. R. & Frank, J. S. (2006). Postural, physiological and psychological reactions to challenging balance: Does age make a difference? A​ge and Ageing, 35,​ 298­303.
  • Cleworth, T. W., Horslen, B. C., & Carpenter, M. G. (2012). Influence of real and virtual heights on standing balance. G​ait & Posture, 36,​172­176.
  • Davis, J. R., Campbell, A. D., Adkin, A. L. & Carpenter, M. G. (2009). The relationship between fear of falling and human postural control. G​ait & Posture, 29,​275­279.
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