Quantitative and comparative assessment of learning in a tongue-operated computer input device--part II: navigation tasks

Abstract

Tongue drive system (TDS) is a novel tongue-operated assistive technology (AT) for the mobility impaired, to empower them to access computers and drive powered wheelchairs (PWC) using their free voluntary tongue motion. We have evaluated the TDS performance in five sessions over 5-8 weeks to study the learning process in different tasks of computer access and PWC navigation on nine able-bodied subjects who already had tongue piercing and used our magnetic tongue studs throughout the trial. Computer access tasks included on-screen maze navigation and issuing random commands to measure the TDS information transfer rate. PWC navigation included driving through a ~50-m obstacle course using three control strategies. Some of the qualitative aspects of using the TDS were also evaluated based on the two Likert scale questionnaires, one of which was short (eight questions) and asked at the end of each session and the other one (46 questions) at the end of the trial. Included in this study was also a task to measure the tongue fatigue as a result of using the TDS continuously for a few hours. All performance measures showed significant improvement from the first to the second session as well as further gradual improvements throughout the rest of the sessions, suggesting a rapid learning process.

Figures

Fig 1

(a) eTDS prototype used in this study consists of a headgear (b) with an array of three-axial magnetic sensors (c) mounted on a pair of goosenecks and a wireless control unit. (d) Wireless receiver USB dongle is used for delivering data to a PC. (e) Custom-designed interface connects the PC to powered wheelchairs via a standard nine-pin connector. (f) eTDS detects the position of a small permanent magnetic tracer that is embedded in the upper ball of a titanium tongue stud.

Fig 2

(a) On-screen maze navigation task. (b) Recommended tongue positions for six TDS tongue commands plus the tongue resting position, which is considered neutral. (c) Designated keys on the keypad to resemble the TDS commands positions.

Fig 3

Portion of the maze and two typical cursor paths from segment 1 to segment 2. SoD is the sum of all deviations from the track. When the path is around the outer corner of the track, deviation is also measured over the extensions of segments.

Fig 4

GUI screen for timed randomly selected commands task from which the TDS ITR can be derived: (a) indicating the random command and being ready, (b) selecting the tongue command and staying there until the blue bar is filled before returning back to neutral.

Fig 5

(a) Typical tongue rapid movement waveform and (b) its spectrum derived by FFT. Units are in microtesla because the amplitudes are directly derived from magnetic sensor outputs.

Fig 6

(a) TDS-PWC interface attached to a Pride Q6000 enhanced display [also see Fig. 1(e)]. (b) Experimental setup for the PWC driving part of each session. An operator walked behind the subject with an emergency stop button in hand as a safety measure. (c) Plan of the obstacle course showing its dimensions, obstacle locations, and driving trajectory.

Fig 7

Cursor path of a subject navigating through one of the maze designs with TDS in the (a) first session (SoD = 8.54, TCT = 18.8 s) and (b) fifth session (SoD = 1.33, TCT = 13.3 s) (c) TCT and (d) SoD for all subjects in the maze navigation task.

Fig 8

(a) Percentage of CCC% and (b) ITR using TDS in timed randomly selected commands task.

Fig 9

(a) Obstacle course PWC CT and the PPR for various PWC control strategies. (b) Sum of the two types of NEs (collisions and out-of-tracks).

Fig 10

(a) Sample of PCA space for four-command training in the first session with FOM1 = 48.3 and FOM2 = 32.1. (b) PCA space for the same subject in the fifth session with FOM1 = 681.7 and FOM2 = 67.1.

Fig 11

(a) MR in Hertz. (b) CVs of movement times (MV). (c) Maximum amplitude of the signal FFT (MA).

Fig 12

Results of the short questionnaire asked at the end of each session for subjective evaluation of the TDS.

Fig 13

Preferred PWC driving strategy throughout the five sessions.