The Treatment of Akinesia using Virtual Images

by Jerrold D. Prothero

Methods for Quantitative Experiment

The quantitative gait analysis, carried out as part of the confirmation phase, took place in the Biomechanics Laboratory at the Department of Rehabilitation Medicine, Health Sciences Building BB828 at the University of Washington. Reflective markers used as video camera targets were positioned over landmarks on the right pelvis and right lower extremities. The subject walked along a 30 foot walkway with a conductive surface which, when used in conjunction with conductive tape applied to the soles of both shoes, provided a gait event marker system for determining the spatial and temporal characteristics of gait. A videotape camera recorded the subject from the waist down. Data were taken at intervals of 40 milliseconds. For a more detailed description of the Biomechanics Laboratory, see Lehmann et al.\ [39].

Four treatment conditions were tried, in the following order: no visual cues (N), following a laser pointer spot (L), a VV Sport display with no image on (G), and a VV Sport display running a simple taped animation moving down the screen at the walking rate (V). One would expect condition G to provide the same or worse treatment value compared to condition N.

Eight trials were run for each condition. The order of the trials was not randomized; all of the trials for one condition were run before the next condition.

Due to the amount of manual labor involved in converting the raw data into analyzable form, only two of the eight trials were examined for each condition. The analyzed trials were chosen to provide uniformity across the four treatment conditions: the trials analyzed had the subject starting with the same foot and stepping on the force plate, instead of to one side of it.

The data analysis for each trial focused on a single representative stride (one step with each foot). The subject's right side, which had the reflective markers, is called the ``affected'' side (A); the other is called the ``unaffected'' side (U).

The data are organized around a series of events. The first is the heel strike of the affected side (AHS), followed by the toe strike of the affected side (ATS), the affected heel lifting off the ground (AHO), the unaffected heel striking the ground (UHS), the affected toe lifting off the ground (ATO), and finally the affected heel striking again (AHS2), to complete the cycle.

The following data were gathered as a function of time: each of the above events; the affected knee angle; distance from the hip to the floor; distance from the hip to the small toe; and horizontal distance from the hip to the small toe.

Other derived data were stride length and a plot comparing the time spent in each of four gait components for the affected and unaffected side. The plot gives one a measure of the symmetry of the subject's gait.

Unfortunately, data collection was centered around a force plate in the walkway which provided a very definite visual cue. It is to be expected that this reduced the apparent relative improvement for the treatment conditions by improving the ``untreated'' condition.