Cognitive vigilance in power wheelchair driver training often relies upon verbal cuing.This pilot study investigated using auditory feedback from a wheelchair mounted obstacle sensing device as an alternative to verbal cuing. Three subjects with documented histories of driving challenges due to impaired vigilance participated.The protocol included an initial evaluation, training and post evaluations along prescribed driving paths.Results showed auditory feedback increased attention to task for all subjects. One subject demonstrated improved driving performance after training. The evaluation path may have lacked sufficient challenge for the other 2 subjects to demonstrate improvement. Future studies should use a more appropriate obstacle sensing device and use evaluation paths of varying difficulty.
Power wheelchair training, obstacle sensing
Pediatric powered mobility training entails teaching a child to integrate the physical, cognitive and behavioral skills necessary to become effectively mobile. The ultimate goals are increased independence and environmental interaction which in turn facilitate cognitive, perceptual, spatial and social development.A number of strategies and guidelines for training children appear in the literature (1). Cognitive vigilance and attention to task is a skill that is difficult to teach and yet is essential for safe and consistent driving. A common training objective is to reduce the subject’s reliance on verbal cuing while simultaneously increasing his/her reliance on external environmental cues. Training persons with cognitive and perceptual impairments such as delayed initiation and/or distractibility is particularly challenging. The Massachusetts Hospital School (MHS) provides medical, rehabilitative, recreational and educational services to children and young adults who are physically disabled and assists them in achieving their maximum level of independence in all aspects of life. Many MHS therapists provide power mobility training to their patients. However, the protocols are generally not standardized and many of the techniques used are intuitive. Several of the patients have histories of power mobility challenges due in part to a lack of cognitive vigilance. This study had 3 objectives. First, to determine if an obstacle sensing device mounted on a powered wheelchair could provide useful auditory feedback to persons with cognitive and perceptual impairments. Second, to determine if training with such a device would improve the subject’s functional mobility skills and third, to observe if there was an internalization of the auditory cues such that mobility skills remained improved upon removal of the device.
Three subjects were chosen for the study based upon qualifying criteria. First, the subjects had to own their power wheelchair (with individually prescribed seating systems) and be able to operate the chair without assistance. Second, the subjects must have had a documented history of power mobility challenges due to cognitive or perceptual impairments such as delayed initiation, distractibility or diminished vigilance. Finally, the subjects had to be generally responsive to verbal cuing for redirection and have shown the capability of integrating new learning. This study was approved by the MHS Committee for Human Studies. Written consent was obtained from the parent/guardian of each participant prior to his/her participation in the study.
The study consisted of 3 phases; pre-training evaluation of the subject’s mobility skills, a period of training with the obstacle sensing device and finally a post training evaluation both with and without the device. Post testing with and without the device allowed observation as to whether the subject had internalized environmental cues provided by the device (2). The pre- and post-training evaluations required each subject to drive his/her wheelchair along a prescribed outdoor path while trained observers collected objective measures without offering any verbal cuing or corrective intervention. The path required driving parallel to a railing, both right and left 90o turns, and stopping in front of an object. Objective measures included: the time to complete the route, the number of contacts with objects and the number of device activations. Brief training took place on similar but different paths under the direction of the subject’s individual therapist. Therapists created logs of all activities (2). It was anticipated that 6-9 training sessions would be conducted over a 2 week period.
Obstacle sensing systems that provide auditory feedback when activated are readily available for applications such as reverse sensing in motor vehicles. In the interest of proceeding expeditiously, it was decided to adapt a commercially available obstacle sensing system produced for automobiles (3). A single sensor was mounted beneath the center of the center of the pre-existing laptray. To avoid unnecessary activations, metal shields were placed over a portion of the sensor face. When the wheelchair approached an object, the sensor would emit an audible, intermittent beep. After activation the frequency of the beeping increases and becomes a continuous tone as the object is approached. The continuous tone occurred at approximately 2 feet in the frontal direction and 6-8 inches perpendicular to the sides of the wheelchair. Beeping was initiated at approximately twice these distances.
During implementation of the training protocol, unanticipated factors such as subject’s limited availability and wheelchair servicing resulted in some changes. Only 3-5 training sessions were conducted over a period of 2-7 weeks. In the post-training evaluations, all 3 subjects took more time to travel the path with the device than without it. Thus the device was clearly successful in alerting each subject to a potential problem and causing them to slow or stop to evaluate the situation (Table 1). There was little change between the pre-training time and the post-training time without the device for subjects 1 and 2, indicating that training with the device had little effect. In contrast, subject 3 improved her travel time by 19% and thus seemed to benefit from training with the device. Subjects 1 and 2 did not exhibit any contacts during the evaluations, while subject 3 exhibited one contact in the pre-training and one in the post-training without the device. Qualitative comments from the therapists indicated a lack of change in the driving behaviors of subjects 1 and 2 and an improved attention to task for subject 3.
Time to Travel the Evaluation Path (min:sec) |
||||
|---|---|---|---|---|
Subject |
Number of Training Sessions |
Pre-Training |
Post-Training without device |
Post-training with device |
1 |
5 |
2:49 |
2:43 |
3:55 |
2 |
3 |
3:23 |
3:35 |
4:20 |
3 |
4 |
13:05 |
10:37 |
11:39 |
Overall, this pilot study demonstrated that an obstacle sensing device, which provides auditory feedback, has the potential to be effective in the powered mobility training of children who demonstrate impaired cognitive vigilance. Wheelchair training is a multivariate process that involves individual, environmental and task-related characteristics (4). Thus the main outcomes of a pilot study will primarily address improvements and refinements for future studies. While an effective pre-training, training, and post-training mobility training protocol was developed, the objective metrics of number of contacts and number device activations were not useful for determining improvement in mobility. Only subject 3 had any contacts. The range at which the sensing device began beeping was longer than necessary and may have been more distracting to the user than the continuous tone.However, the device was able to provide useful feedback to subject 3 and appeared to serve as a tool for increasing attention to task for both subjects 1 and 2.This study revealed the need to make further refinements in selection of the evaluation path and in device hardware. The path used in this study was effective for measuring basic wheelchair skills but did not require complex maneuvering skills. The path minimized the number of distractions and may not have been sufficiently challenging for subjects 1 and 2. Since each subject serves as his/her own control, future studies should consider having evaluation paths of varying difficultly available so as to more closely match the existing skill level of each subject.An ideal sensing device would activate when an obstacle is approximately 3 feet in front of the wheelchair and then only with a continuous tone. When traveling parallel to an obstacle (for example a wall) the sensor should activate at a distance of 6-8 inches. Conducting a more longitudinal and less intense training protocol should also be considered (4).
We would like to thank the subjects and therapists from the Massachusetts Hospital School who participated in this study and Jerry Potter of Rostra Controls Inc. for donating the obstacle sensing system.
Allen H. Hoffman, PhD
Mechanical Engineering Department
Worcester Polytechnic Institute
100 Institute Road
Worcester, MA 01609-2280
Office Phone (508) 831-5217
email: ahoffman@wpi.edu
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