Quantitative and comparative assessment of learning in a tongue-operated computer input device

Abstract

Tongue drive system (TDS) is a wireless, wearable assistive technology that enables individuals with severe motor impairments to access computers, drive wheelchairs, and control their environments using tongue motion. In this paper, we have evaluated the TDS performance as a computer input device in four tasks, commonly known as horizontal, vertical, center-out, and multidirectional rapid tapping, based on Fitts' law and ISO9241-9 Standard. Nine able-bodied subjects, who already had tongue piercing, participated in this trial over five sessions during 5 weeks, allowing us to study the TDS learning process and its current limiting factors. Subjects wore tongue rings made of titanium in the form of a barbell with a small rare-earth magnetic tracer hermetically sealed inside the upper ball. Participants performed the same tasks with a mouse (only in the first session) as a reference as well as a standard keypad for benchmarking. Six performance measures were considered, including throughput, error rate, and reaction time, all of these improved significantly from the first to the last session, and some of these plateaued over the course of the experiment. The comparison between tongue-TDS versus index-finger-keypad provides valuable insights into tongue human factors, which can lead the way in improving the usability of the TDS and similar tongue-operated assistive technologies.

Figures

Fig. 1

(a) TDS prototype comprised of a headgear with an array of lateral magnetic sensors, a wireless control unit, a USB receiver dongle, and a small magnetic tracer embedded in a titanium tongue stud with M&M-shaped upper ball. (b) Experimental setup with the subject sitting 1 m away from a 22″ LCD monitor, performing the multidirectional tapping task.

Fig. 2

GUI screen for (a) horizontal and vertical unidirectional tappings, (b) center-out tapping with all 48 possible target conditions on the right panel, and (c) multidirectional tapping with all 45 possible target conditions and their sequential order of tapping on the right panel.

Fig. 3

(a) Recommended tongue positions for six TDS tongue commands plus the tongue resting position, which is considered neutral. (b) Designated keys on the keypad to resemble the TDS commands' positions.

Fig. 4

Unidirectional tapping tasks: (a) throughput, (b) error rate, and (c) task completion time of horizontal tapping and (d) throughput, (e) error rate, and (f) task completion time of vertical tapping.

Fig. 5

Center-out tapping task: (a) throughput, (b) error rate, (c) task completion time, (d) path efficiency, (e) deviation from optimum number of movements, and (f) reaction time.

Fig. 6

Multidirectional tapping task: (a) throughput, (b) error rate, (c) task completion time, (d) path efficiency, and (e) deviation from optimum number of movement.

Fig. 7

Sample cursor traces of one subject in the center-out tapping task with (a) TDS in the first session (TP = 0.91 bits/s, error rate = 12.5%, TCT = 7.4 min, PE = 72.30%, DONM = 1.59, and RT = 0.64 s); (b) TDS in the fifth session (TP = 1.87 bits/s, error rate = 15.97%, TCT = 5.3 min, PE = 84.40%, DONM = 0.19, and RT = 0.61 s); (c) keypad in the fifth session (TP = 2.10 bits/s, error rate = 7.64%, TCT = 5.2 min, PE = 85.70%, DONM = 0.01, and RT = 0.53 s); and (d) mouse in the first session (TP = 3.88 bits/s, error rate = 1.39%, TCT = 2.1 min, PE = 65.70%, DONM = 0.09, and RT = 0.10 s).

Fig. 8

Comparison between the TDS and the keypad in the fifth session in terms of (a) effective distance, (b) effective width, (c) movement time in the center-out task, and (d) movement time in the horizontal tapping task.

Fig. 9

Comparison between the TDS and the keypad in the fifth session of the center-out task in terms of movement time MT versus effective index of difficulty IDe and their regression models based on Fitts' law.