Controlling an effector with eye movements: The effect of entangled sensory and motor responsibilities

Abstract

Restoring arm and hand function has been indicated by individuals with tetraplegia as one of the most important factors for regaining independence. The overall goal of our research is to develop assistive technologies that allow individuals with tetraplegia to control functional reaching movements. This study served as an initial step toward our overall goal by assessing the feasibility of using eye movements to control the motion of an effector in an experimental environment. We aimed to understand how additional motor requirements placed on the eyes affected eye-hand coordination during functional reaching. We were particularly interested in how eye fixation error was affected when the sensory and motor functions of the eyes were entangled due to the additional motor responsibility. We recorded participants’ eye and hand movements while they reached for targets on a monitor. We presented a cursor at the participant’s point of gaze position which can be thought of as being similar to the control of an assistive robot arm. To measure eye fixation error, we used an offline filter to extract eye fixations from the raw eye movement data. We compared the fixations to the locations of the targets presented on the monitor. The results show that not only are humans able to use eye movements to direct the cursor to a desired location (1.04 ± 0.15 cm), but they can do so with error similar to that of the hand (0.84 ± 0.05 cm). In other words, despite the additional motor responsibility placed on the eyes during direct eye-movement control of an effector, the ability to coordinate functional reaching movements was unaffected. The outcomes of this study support the efficacy of using the eyes as a direct command input for controlling movement.

Oculomotor behavior can be adjusted on the basis of artificial feedback signals indicating externally caused errors

“…Further, they indicate that adaptive changes to the gaze behavior can be induced by artificial post-saccadic feedback signals. The results of the current study also add to the research stating that eye movements are a suitable means to communicate action intentions to a human machine interface and thus could be used as input to assistive devices for patients with motor impairment [36,37] as the participants in our study learned to successfully communicate their intended object with their gaze. Overall, our results suggest that artificial and externally attributed post-saccadic feedback signals can be used to adapt oculomotor behavior to task demands.…”

“…The modulation of gaze behavior based on artificial feedback has a major application in human-computer interaction and assistive technology. Individuals with severe motor impairments, such as spinal cord injury, could use gaze to communicate action intentions to a human-machine interface that controls, for example, a robotic arm, a wheelchair or even an exoskeleton [ 36 , 37 ]. Such an assistive device could replace the motor function of paralyzed limbs and initiate intended actions such as reaching for a target object, thereby improving the users’ independence.…”