Power wheelchairs are controlled by a variety of technologies, from conventional joysticks to head arrays and sip and puff systems. However, little research has been completed on the use or effectiveness of power wheelchair driving controllers, whether conventional or alternative. The first study examines a novel alternative power driving control which interfaces with a manual wheelchair. The subsequent studies explore alternative methods of driving including body-machine interface based on inertial sensors and tongue drive systems. Body-machine interface is a motor learning paradigm in which users reorganize their voluntary movements to accomplish new functional tasks.
Lin et al. (2013) present an alternative controller interface for driving power mobility devices. The study compares two groups, manual wheelchair users (MWCU) who all had a spinal cord injury and non-manual wheelchairs users (NMWCU), who were nondisabled. Performance measures of completion time and speed, and the muscle activation of the wrist and the forearm are tracked during forward propulsion over five meters and turning right and left for both the bimanual gilder (BG) and a conventional joystick. All participants had upper extremity strength graded as ‘good’ by manual muscle testing, and all MWCU had a thoracic spinal level injury with 7/11 being at the level of T11 or 12. Considerations for the impact of this level of strength and ability on the propulsion patterns and therefore the muscle recruitment was not noted in the article.
The authors reported that, based on study results, driving tasks using the BG controller interface took almost twice as long as using the conventional joystick. They also identified that different patterns of muscle recruitment were used for each controller, with the BG requiring less wrist flexion and extension but more triceps activation than the conventional joystick as well as requiring both upper extremities to operate instead of one with the conventional joystick. It is questioned why the authors chose this specific sub-population of people with SCI as they are not likely to use a power add on or alternate drive control interfaces and the injury level that may potentially benefit from this type of device would likely not have intact triceps muscles. The authors identify that study limitations included that the BG was not applied to a power wheelchair and they did not include participants who had experience driving power wheelchairs. Based on the findings in this study, it is difficult to surmise if the BG would be a viable option as an alternate controller interface for people with cervical level injuries or people with thoracic level injury with reduced strength for injury or overuse.
Farshchiansadegh et al. (2014) completed a prospective controlled trial (n=3) to assess a body-machine interface (BMI) ability to operate a computer, power wheelchair and other assistive technologies after cSCI. in this study, subjects performed reaching movements to 24 targets and then completed a typing task. Both groups performed the same list of activities (i.e., reaching, typing, gaming and virtual wheelchair navigation) over five sessions. The study analyzed time to target, Euclidean endpoint error, typing speed, and gaming performance. Both SCI and control subjects continuously reduced the time to target and the Euclidean endpoint error (no p-value provided). The typing performance of the SCI subjects improved at the same rate as the control subjects (no p-value provided). All participants demonstrate increased gaming performance across sessions (no p-value provided).
Kim et al. (2014) completed a pre-post study (n=11) where study subjects received a tongue drive system (TDS) and underwent one personal computer (PC) access and one PWC navigation session each week for 6 weeks; only the latter is presented here. A Tongue Drive System translates specific user defined tongue gestures into application specific commands by detecting the position of a small magnetic tracer on the user’s tongue. The study revealed an increased usability in PWC navigation (no p-value provided). The post-study usability questionnaire showed an ease of use found that TDS received the same scores as sip-and-puff (SnP) systems.
Kim et al. (2015b) completed a prospective controlled trial (n=20) were all participants received a Tongue-Drive System (TDS) piercing and performed several tasks including Fitt’s law tapping, wheelchair driving, phone-dialing, and weight-shifting tasks over five to six consecutive sessions. The study evaluated the completion times of wheelchair diving, phone-dialing, and weight shifting, and throughputs of tapping tasks. The throughputs of the SCI study subjects using TDS for multidirectional tapping tasks were significantly lower than those of the able-bodied participants (p=0.001). The wheelchair driving completion time of both groups improved over the course of the sessions when using the unlatched mode. The wheelchair completion time using the latched strategy for the SCI study subjects continuously decreased until it reached a time similar to that of the able-bodied participants. The SCI study subjects using the semi-proportional strategy took 1.47 times longer to complete the wheelchair driving task compared to the able-bodied participants. The completion time of phone-dialing and weight shifting in SCI study subjects decreased over the course of the sessions.
Laumann et al. (2015) completed a post study (n=13) where study subjects underwent tongue piercing and were fitted with a magnetic barbell linked to the Tongue Drive System (TDS), which was accessed twice weekly for six-eight weeks to perform computer tasks, drive a wheelchair, perform in-chair weight shifts, and dial a phone. The study evaluated symptoms of intraoral dysfunction, change in tongue size, and usability of tongue barbell with TDS, and receiving and wear ability of a tongue barbell. Six of 12 participants reported pain and tongue swelling, and four had difficulty speaking and eating during the first three days after piercing, correlated with a 17% increase in tongue size between days one and two. All participants reported that the TDS was effective for using the computer, driving a powered wheelchair, dialing phone numbers, and doing in-chair weight shifting. Ten participants were found to be more than satisfied with the system and one person was indifferent.
Kim et al. (2013) completed a prospective controlled trial (n=34) with able bodied volunteers who tested the use of a mouse, keypad and Tongue Driving System (TDS) and with individuals injured at the tetraplegia level who were tested thought the use of Sip and Puff device (SnP). The study evaluated the center out tapping, ability for correctly completed commands (CCC%), maze navigation and navigational skills in an obstacle course. Able-bodied individuals rode through the obstacle course using the TDS in 260.7±10.4 seconds during the first session. By the fifth session, the average completion time had shortened to 207.7±8.2 seconds (p<0.001). Performance showed the biggest change between the first and second sessions (p<0.001). The number of navigation errors was 5.5±5.1 during the first session, reaching a low of 2.1±2.5 errors during the fifth session, significant reduction between first and second session (p=0.001). Study subjects with tetraplegia took 253.2±60.9 seconds and 179.9±24.1 seconds to complete the obstacle course using the TDS during the first and 6th sessions (p<0.001). Over the same time, navigation errors dropped from 9.5±6.6 to 1.7±2.0 errors using the TDS. Navigation performance of the SCI injured study participants during the fifth and sixth sessions showed that they did better using the TDS versus a Sip and Puff system (SnP).
There is level 4 evidence (from one repeated measures study by Lin et al. 2013) that a bimanual power wheelchair controller may be an alternative to a power add on for manual wheelchairs.
There is level 2 evidence (from two prospective controlled trials; Kim et al. 2015b; Kim et al. 2013, one pre-post study by Kim et al. 2014, and one post study by Laumann et al. 2015) that the use of a tongue drive system is demonstrating effective and proficient performance in operating of a power wheelchair and other assistive technology devices.
There is limited evidence related to the benefit and use of conventional versus alternative driving controls.