Effects of Task Type and Task Duration on Visual Fatigue on Smartphones at Different Ages

This study investigated the effects of task type and task duration on visual fatigue on smartphones at different ages. A total of 24 young adults (21–29 years old) and 24 older adults (63–77 years old) participated in an experiment with two different tasks (reading and searching) on smartphones, where each task lasted 1 h. The change in critical fusion frequency (CFF) and the subjective visual fatigue score were used as physiological and subjective indices, respectively, to measure visual fatigue. The results showed that the participants experienced more severe visual fatigue in the reading task than in the searching task on smartphones. Both changes in CFF and increases in subject visual fatigue occurred earlier in the reading task than in the searching task. The participants' visual fatigue increased as the task duration increased, and physiological visual fatigue occurred significantly earlier than did subjective visual fatigue. Compared with younger adults, older adults experienced more subjective visual fatigue when the task complexity was higher and more physiological visual fatigue as task duration increased. Different arrangements of breaks should be considered according to different task types on smartphones to alleviate visual fatigue, and a short break interval every 15 min during the reading task and every 30 min during the searching task is recommended. Older adults not only need to avoid prolonged visual tasks on smartphones more but also should refrain from persisting in continuous visual work. They are in greater need of suspending visual tasks promptly as soon as they initially feel visual fatigue. In addition, designers and developers need to reduce the cognitive load brought by task complexity on smartphones to alleviate the perception of visual fatigue among older adults.