For some individuals who control their assistive technology using a single switch, operation using foot extension may provide the best performance. This paper reviews the design of a wheelchair footrest switch for an individual with cerebral palsy. The switch was used for control of an augmentative and alternative communication (AAC) system. Performance using the footrest switch was measured and compared to performance using the original head-activated switch. Improvements in performance resulted in enhanced quality of life.
selection technique, switch, outcomes, AAC, communication rate
Assistive technology can be controlled using various methods. Generally, direct selection offers higher performance than other methods. However, some people do not have the physical ability to use a keyboard or other pointing system. In such cases, alternative methods must be used. One alternative selection technique is row-column scanning using a single switch.
For people who use AAC, optimizing communication rate is generally highly valued. Since selection rate directly affects communication rate, selection rate must also be optimized. Evidence-based practice (EBP) requires the measurement of performance. Selection techniques can be chosen on the basis of measured performance.
The individual for whom this work was done was an 8 year-old female with cerebral palsy who used a single switch to control an AAC system. The switch was being activated using the head. Parents believed that the subject could have better control using the foot and the author was asked to design and fabricate a foot-activated switch.
Resources available included materials and tools in the maintenance shop at an Easter Seals Camp and the local small town business community. The footplate was secured to the wheelchair with an adjustable angle fitting located under the ankle area of the foot. This placement was advantageous in that downward forces through the lower leg would produce little or no torque. By loosening the adjustment clamp, the footplate could swivel on the mounting rod. A system of limiting the rotation was implemented and a switch was added.
Figure 1. d (Click image for larger view)
Subjective and anecdotal evidence indicated that the footrest switch performed significantly better than the head-switch. Objective evidence was obtained using the Single Switch Performance Test. This software (1, 2) was used by the family to measure the performance using both the original head-switch and the footrest switch. Figure 1 shows that performance using the footrest switch was close to twice as fast as that using the original head-switch.
Parents reported that the subject experienced significantly better quality of life as a result of this enhancement to her selection system. She performed better in school. She was more successful in other pursuits such as writing to family members and using the computer for other activities.
It may be noted that the release time parameter for the original head-switch is faster than for the footrest switch. The AAC system was not configured to make use of the switch release, although that was likely possible. However, the speed of the release time for the head-switch was a result of an involuntary reflex, which was not usable for control.
Figure 2. d (Click image for larger view)
Several months following this work, the family contacted the author again. The footrest switch continued to perform well. A new wheelchair was being procured and a new footrest switch was needed. With the availability of enhanced resources and time, the second switch was designed in a manner to be more readily replicable and less dependent on a specific footrest mounting system. Principles proven in the first effort were maintained in the second design. In addition, a compression spring feature was added to provide for adjustable activation torque.
Figure 2 is a photograph of the second footrest switch with the protective cover removed, labeled to show various elements.
Barry Romich, P.E.
1022 Heyl Road
Wooster, OH 44691-9786
Tel: 330-262-1984 x211
This should be in the right column.