Communication Method Based on Pupil Diameter Changes for Amyotrophic Lateral Sclerosis (ALS) Patients: A System Designed for Adaptation to Symptom Progression

Patients with severe physical disabilities owing to amyotrophic lateral sclerosis (ALS) typically have normal cognitive function; however, they often experience difficulties with speech, writing, and oculomotor functions as their symptoms progress. There is a need for a consistent communication system that can adapt to these progressing symptoms. The ability to modulate pupil diameter remains intact in patients who experience difficulties with eye movements, speech, and writing owing to ALS. This study focuses on the behavior of changes in pupil diameter when attention is directed to a target with periodic changes in light intensity. The purpose of this study is to develop a communication system that consistently adapts to the progression of symptoms, based not on eye movement but on changes in pupil diameter, enabling patients with severe disabilities due to ALS to communicate daily, even when their eye movement symptoms worsen. Additionally, the study aims to confirm the feasibility of the developed system for communication that reflects the intentions of patients with ALS. We developed a wearable communication system with a head-mounted display (HMD) that can be used in any situation. Users can express “Yes” or “No” to their surroundings without moving their gaze, directing attention solely to the target. Targets are displayed on the HMD and flicker periodically in different phases. The intention-estimation algorithm determines which target the user selects based on the pattern of changes in pupil diameter. To evaluate the system’s performance, an experiment was conducted with one patient with ALS who has difficulty with speech and writing. The results showed that the accuracy of intention estimation for yes/no responses was 100 %, and the average time to estimate the intention was 6.88 s. In conclusion, we confirmed the feasibility of a daily communication system based on pupil diameter for patients with severe disabilities because of ALS.