Upper limb exoskeletons (ULEs) are robotic devices that can mobilize a severely disabled individual's arm and help the user perform some activities of daily living independently. Despite advancement in the mechanical design of ULEs, a versatile control interface that enables full and continuous control of a ULE with multiple degrees of freedom for a user with disability in both arms and legs (tetraplegia) still requires further research and development. In this study, ten individuals with tetraplegia used a tongue-based interface to fully control a five degrees of freedom ULE for a drinking and a snacking task. This required moving the ULE hand from a wheelchair armrest position to grasp an object (bottle or strawberry) placed on a table in front of the participant, moving the object towards them until it touched a face shield, and placing the object on the table. All participants successfully controlled the exoskeleton and completed the tasks. The drinking task lasted 149.6 s on the first day and 122.9 s (median) on the second day of using the exoskeleton. The participants performed the snacking task only on the first day of ULE use and achieved a median task time of 167.0 s. The study showed that the tongue interface could provide effective, efficient, and safe control of the exoskeleton.

Tongue-computer interfaces have shown the potential to control assistive devices developed for individuals with severe disabilities. However, current efficient tongue-computer interfaces require invasive methods for attaching the sensor activation units to the tongue, such as piercing. In this study, we propose a noninvasive tongue-computer interface to avoid the requirement of invasive activation unit attachment methods. We developed the noninvasive tongue-computer interface by integrating an activation unit on a frame, and mounting the frame on an inductive tongue-computer interface (ITCI). Thus, the users are able to activate the inductive sensors on the interface by positioning the activation unit with their tongue. They also do not need to remount the activation unit before each use. We performed pointing tests for controlling a computer cursor and number typing tests with two able-bodied participants, where one of them was experienced with using invasive tongue-computer interfaces and other one had no experience. We measured throughput and movement error for pointing tasks, and speed and accuracy for number typing tasks for the evaluation of the feasibility and performance of the developed noninvasive system. Results show that the inexperienced participant achieved similar results with the developed noninvasive tongue-computer interface compared to the current invasive version of the ITCI, while the experienced participant performed better with the invasive tongue-computer interface.

People with complete tetraplegia who are paralyzed from the neck down require alternative computer and robot interfaces based on the remaining functionalities. The inductive tongue-computer interface (ITCI) consists of two small touchpads that are manipulated by the tongue and can provide individuals with tetraplegia the possibility to control computers, robots, and other electronic devices. The tongue gesture can be used to expand the vocabulary of the ITCI and provide more control commands. In this study for the first time, a tongue gesture recognition method was introduced that can identify a set of six gestures with 94.3% accuracy and a set of 23 gestures with 72.3% accuracy. Furthermore, a robot interface was developed using the tongue gestures and it was compared with a previously tested method based on soft buttons on the ITCI. Four able-bodied participants performed a pouring water task with the two control methods when visual feedback from the interface was presented on a screen and then without the visual feedback. Task completion time for the gesture-based control and the button-based control did not differ. However, gesture-based control provides more control commands that can be used for interfacing other systems.

Intraoral target (typing) and on-screen target (pointing/tracking) selection tasks were performed by 10 participants during 3 consecutive day sessions. Tasks were performed using 2 different intraoral sensor layouts. Reduction of undesired sensor activations while speaking as well as the influence of intraoral temperature variation on the signals of the intraoral interface was investigated. Results showed that intraoral target selection tasks were performed better when the respective sensor was located in the anterior area of the palate, reaching 78 and 16 activations per minute for repetitive and “unordered” sequences, respectively. Virtual target pointing and tracking tasks, of circles of 50, 70, and 100 pixels diameter, showed no significant difference in performance, reaching average pointing throughputs of 0.62 to 0.72 bits per second and relative time on target of 34% to 60%. Speaking tasks caused an average of 10 to 31 involuntary activations per minute in the anterior part of the palate. Intraoral temperature variation between 11.87 °C and 51.37 °C affected the sensor signal baseline in a range from –25.34% to 48.31%. Results from this study provide key design considerations to further increase the efficiency of tongue–computer interfaces for individuals with upper-limb mobility impairments.