Eyes-Free Tongue Gesture and Tongue Joystick Control of a Five DOF Upper-Limb Exoskeleton for Severely Disabled Individuals

Mostafa Mohammadi; Hendrik Knoche; Mikkel Thøgersen; Stefan Hein Bengtson; Muhammad Ahsan Gull; Bo Bentsen; Michael Gaihede; Kåre Eg Severinsen; Lotte N S Andreasen Struijk

doi:10.3389/fnins.2021.739279

Eyes-Free Tongue Gesture and Tongue Joystick Control of a Five DOF Upper-Limb Exoskeleton for Severely Disabled Individuals

Front Neurosci. 2021 Dec 17:15:739279. doi: 10.3389/fnins.2021.739279. eCollection 2021.

Authors

Mostafa Mohammadi¹, Hendrik Knoche², Mikkel Thøgersen¹, Stefan Hein Bengtson², Muhammad Ahsan Gull³, Bo Bentsen¹, Michael Gaihede⁴, Kåre Eg Severinsen⁵, Lotte N S Andreasen Struijk¹

Affiliations

¹ Neurorehabilitation Robotics and Engineering, Center for Rehabilitation Robotics, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
² Human Machine Interaction, Department of Architecture, Design and Media Technology, Aalborg University, Aalborg, Denmark.
³ Department of Materials and Production, Aalborg University, Aalborg, Denmark.
⁴ Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
⁵ Department of Neurology, Aarhus University Hospital, Aarhus, Denmark.

Abstract

Spinal cord injury can leave the affected individual severely disabled with a low level of independence and quality of life. Assistive upper-limb exoskeletons are one of the solutions that can enable an individual with tetraplegia (paralysis in both arms and legs) to perform simple activities of daily living by mobilizing the arm. Providing an efficient user interface that can provide full continuous control of such a device-safely and intuitively-with multiple degrees of freedom (DOFs) still remains a challenge. In this study, a control interface for an assistive upper-limb exoskeleton with five DOFs based on an intraoral tongue-computer interface (ITCI) for individuals with tetraplegia was proposed. Furthermore, we evaluated eyes-free use of the ITCI for the first time and compared two tongue-operated control methods, one based on tongue gestures and the other based on dynamic virtual buttons and a joystick-like control. Ten able-bodied participants tongue controlled the exoskeleton for a drinking task with and without visual feedback on a screen in three experimental sessions. As a baseline, the participants performed the drinking task with a standard gamepad. The results showed that it was possible to control the exoskeleton with the tongue even without visual feedback and to perform the drinking task at 65.1% of the speed of the gamepad. In a clinical case study, an individual with tetraplegia further succeeded to fully control the exoskeleton and perform the drinking task only 5.6% slower than the able-bodied group. This study demonstrated the first single-modal control interface that can enable individuals with complete tetraplegia to fully and continuously control a five-DOF upper limb exoskeleton and perform a drinking task after only 2 h of training. The interface was used both with and without visual feedback.

Keywords: assistive devices; disabled individuals; human-robot interaction; rehabilitation robotics; tetraplegia; tongue computer interface; upper-limb exoskeleton.