...low-cost
Less than $1000 U.S.
...display
A head-up display is one in which information is viewed superimposed on the outside world (as by displaying on a windscreen or visor) so that the information can be read with the head erect and with the outside world always in the field of view [2].
...cues
Other depth cues include interposition (blocking of one object by another), linear and size perspective, texture gradients, distribution of shadows and illumination, motion parallax, and stereoscopic cues related to comparing the retinal images to the two eyes [32].
...collimating
``Collimation'' refers to changing a divergent beam of light (from a point source) into a parallel beam, or (in our case) a near-parallel beam.
...dyskinesia)
``A nervous condition marked by involuntary muscular twitching of the limbs or facial muscles'' [78].
...dystonia
``Impaired or disordered tonicity, esp. muscle tone'' [78].
...myoclonus
``Twitching or clonic spasm of a muscle or group of muscles'' [78].
...disease
Tremor, rigidity, and akinesia.
...survivors
Survivors of a viral epidemic active between 1916 and 1927.
...`on-off'
Fluctuations between akinetic and ``normal'' periods.
...floor
As the study actually developed, we first used the laser pointer as an initiation cue, and only later as a full-fledged cue.
...hip
Greater trochanter.
...toe
Metatarsal.
...length
A stride is one step with each foot.
...screen
Assuming the subject to be looking two to three paces forward, as is true for T.R. in sustained ambulation, the optimal angle is probably around 4015#15.
...effect
This is interesting, since a superficially similar use of the laser pointer did work, as discussed below.
...subject
As discussed in the next section, this appears to be the region in which T.R. is looking during sustained ambulation.
...stabilization
Precise space stabilization could be achieved by using a gait tracker and possibly a head tracker to drive the animation.
...display
In a similar way, T.R. has indicated that when walking on a gravel road he can adjust his stride length by looking for cues at the desired stride length apart.
...either
One animation, running in the plane of the screen (and therefore appearing to be moving sharply into the ground as seen in the Virtual Vision display looking two to three paces forward), was nearly as effective as another animation running nearly parallel to the ground as seen under the same conditions. The difference in effectiveness appeared to be related more to the relative speeds than to the relative angles. The angle will probably be significant for sustained ambulation.
...cues
While the observable results with the T.R. trials were better with the laser pointer than the VV Sport display, T.R. believes that the mode in which he is chasing the laser spot is fundamentally different cognitively from either stepping over tangible cues, stepping over the laser spot, or stepping over the apparent images in the VV Sport display. He believes that the VV Sport display is therapeutically far more significant than the laser pointer. This is discussed in Subsection 6.4.1.
...display
Again, the reader is referred to Subsection 6.4.1 for a comparision of the VV Sport display to the laser pointer.
...5.2)
Recall from Section 4.3 that the ``affected'' side is the side with the reflective markers (right side).
...pointer
Both T.R. and D.L. bought laser pointers immediately after the trials.
...solution
A laser spot which was clearly visible outside on a bright day might pose safety concerns.
...display
As mentioned above, stepping over the laser spot does function as a robust external cue. However, this leads to two problems: one is that the spot appears on top of the foot, breaking the spatial illusion. This can be handled by turning the laser pointer off at the appropriate moment; in some ways this is less serious than the corresponding difficulty with the VV Sport display, in which one ideally has to make the image disappear as the foot passes over it. The second problem is that, unlike the VV Sport display, the laser pointer has to be redirected after each step, thus preventing smooth motion for seriously akinetic patients. Possibly this problem could be dealt with by developing a laser pointer with several dots which was waist-mounted and which swiveled appropriately as the patient walked.
...representation
A ``polygonal representation'' represents an object as one or more 2-D surfaces built up out of polygons. By contrast, a ``voxel representation'' consists of a set of 3-D components.
...anatomy''
In the interest of openness and avoiding confusion, I should mention that my father John and brother Jeff are both members of the Digital Anatomist Program.

Clarence Smith Jr.
Tue Sep 12 12:45:35 PDT 1995