The Treatment of Akinesia using Virtual Images

by Jerrold D. Prothero

Overview

As mentioned in the introduction, a new head-up display has recently been introduced by Virtual Vision, Inc. The VV Sport display subtends 15 vertically by 22 horizontally of the visual field for one eye. The rest of the visual field is unobstructed, except for a tinted, see-thru visor. The subjective impression is that the image in the display is ``floating'' out in front of the wearer at a distance of approximately ten feet (see Section 1.2).

Since the entire display can be worn like sunglasses and weighs only five ounces, the display itself is quite portable. The display takes NTSC format video input. Depending on how one chooses to provide the image (for instance, an 8mm videotape player), one can anticipate another couple of pounds for a beltpack (including a power supply for the VV Sport).

As pointed out to us by T.R., this display raises the possibility of a new method for treating akinesia: using the display to present a virtual image which would appear to be on the ground and which would be capable of producing kinesia paradoxa. If such a technique worked, it would provide the benefits of tangible cues, with the added advantage of portability and user control.

There are a number of basic questions which this technique raises, which were only partially addressed in this introductory work. These include:

• Is it possible to generate kinesia paradoxa using anything other than tangible objects?

• Assuming that a VV Sport display is used, should the display appear below the dominant or non-dominant eye?

• What are the field-of-view requirements? That is, how much of the patient's field-of-view does the image need to subtend, and where in the field-of-view does the image have to be?

• How important is spatial stabilization? That is, when the patient moves, how accurately do we need to shift the image so as to make it appear fixed at a given spot on the floor? Do we need a gait tracker to provide information on the patient's position, so as to adjust the image correctly?

• Does the image have to appear physically realistic? Are properties such as accurate shadows, perspective, and high resolution important?

• Is there something better than the VV Sport display for providing non-tangible visual cues? For comparison, we also tried a simple laser pointer which provides a dot image on the floor. The laser pointer used was an Americraft Tac Star, model TSP 200. It has a two milliwatt power output and produces a red dot approximately an eighth of an inch in diameter.

The first phase of this study, conducted with one subject, was a rather informal attempt to explore the above issues. The second phase, conducted with a second subject, was intended to confirm our findings from the first phase. The second phase included a quantitative experiment conducted at the Biomechanics Laboratory in the University of Washington's Department of Rehabilitation Medicine.