Using unconstrained tongue motion as an alternative control mechanism for wheeled mobility

Abstract

Tongue drive system (TDS) is a tongue-operated, minimally invasive, unobtrusive, noncontact, and wireless assistive technology that infers users' intentions by detecting and classifying their voluntary tongue motions, and translating them to user-defined commands. We have developed customized interface circuitry between an external TDS (eTDS) prototype and a commercial powered wheelchair (PWC) as well as three control strategies to evaluate the tongue motion as an alternative control input for wheeled mobility. We tested the eTDS performance in driving PWCs on 12 able-bodied human subjects, of which 11 were novice. The results showed that all subjects could complete navigation tasks by operating the PWC using their tongue motions. Despite little prior experience, the average time using the eTDS and the tongue was only approximately three times longer than using a joystick and the fingers. Navigation time was strongly dependant on the number of issued commands, which reduced by gaining experience. Particularly, the unintended issued commands (the Midas touch problem) were rare, demonstrating the effectiveness of the tongue tracking and external magnetic field cancellation algorithms as well as the safety of the TDS for wheeled mobility.

Figures

Fig. 1

eTDS prototype.

Fig. 2

Block diagram and signal flow graph of the TDS–PWC interface circuitry.

Fig. 3

GUIs for the TDS–PWC control interface in LabVIEW environment. (a) GUI designed for the discrete and continuous control strategies. (b) GUI for the gearshift control strategy.

Fig. 4

Plan of the obstacle course used in the PWC navigation human trials, using the TDS, showing the dimensions and approximate PWC trajectory.

Fig. 5

eTDS prototype worn by an able-bodied subject to wirelessly control a PWC. eTDS is wirelessly connected to the laptop under the seat, which is connected to the TDS–PWC interface circuitry through a USB port.

Fig. 6

PWC navigation experimental results using eTDS with different control strategies. (a) Average navigation time. (b) Number of collisions. (c) NICs. The mean values along with their 95% confidence interval are shown for each variable.

Fig. 7

Subjective rating of three PWC control strategies using tongue motions: discrete, continuous, and gearshift based on a questionnaire filled by subjects after the trials.

Fig. 8

Average NIC versus the trial number for each control strategy. The learning effect in discrete control strategy is quite evident from the early trials. However, the other two strategies, which are relatively more complicated, require more trials to show the effects of learning.