Field-of-View and Cuing Requirements

As described above, our best results in the first portion of the study were a series of initiation steps, rather than smooth, sustained ambulation. As we had suspected would be the case ahead of time, the limited vertical field-of-view seemed to cause problems.

To determine the field-of-view requirements for initiating and sustaining ambulation, we went back to using a row of playing cards spaced about 26 inches apart, viewed directly. We used the visor of a welder's helmet to block off parts of the subject's field-of-view.

The region beyond three paces ahead does not seem to be required for initiating or sustaining ambulation, at least for normal indoor walking rates. As T.R. had indicated before arriving for the study, during initiation he looks for a cue at his feet. During sustained ambulation, he is looking at cues two to three paces forward. Blocking off the region beyond one pace forward did not prevent him from initiating. However, blocking off the region from the plane of his body up to one pace forward appeared to prevent him from sustaining ambulation. Apparently the peripherally-viewed cue in this region is important.

As mentioned previously, the vertical field-of-view of the VV Sport display is 15. The region from two to three paces forward subtends about 10. Therefore, the VV Sport is adequate to provide the two fovealy-viewed cues needed for sustained ambulation. It is not, however, adequate to provide the peripherally-viewed cue at about one pace forward as well.

A second problem associated with the limited vertical field-of-view of the VV Sport display is the awkward transition from initiation to sustained ambulation. To initiate one has to tilt one's head forward, so that the VV Sport can provide a cue at one's feet. To sustain, one has to tilt one's head backward, to provide a cue two to three paces forward. This is a clumsy maneuver, which makes it difficult to reach sustained ambulation.

To deal with the second problem, we decided to use the VV Sport display only to sustain ambulation, while some other method was used to initiate. We experimented with three initiation methods.

The first method used was a physical playing card, placed at the subject's feet. This was the most reliable of the three methods, but also the least convenient.

The second method was to have T.R. imagine the squares in the VV Sport display continuing off the bottom of the display until they reached his feet, but without actually looking down to see them. He would step forward when he imagined the cue reaching his feet. This was more effective than using the VV Sport display for both initiating and sustaining ambulation, but was more difficult to maintain, perhaps because it involved a greater cognitive load.

The third method tried was to use the spot from the laser pointer for the initiating cue. This also worked, and was quite convenient.