Eye movement influences on coupled and decoupled eye-hand coordination tasks.

Visually guided reaching precision and accuracy depend on the level of coupling between movements of the eyes and hand. In the present study, participants performed central fixations and either saccadic or smooth pursuit eye movements during fast and accurate reaching tasks involving eye-hand coupling and decoupling to better understand type of eye movement influence over upper limb control. Some eye-hand coupling and decoupling tasks also included hand reversals, where the hand moves away from the target to direct a cursor toward the target to account for various levels of hand-cursor and eye-cursor coupling. Regardless of eye-movement type, eye-hand-cursor coupling produced an endpoint accuracy advantage over decoupling. Use of hand reversal decreased peak speed and increased response time of the hand, whether considering fixation or a given eye movement. Use of smooth pursuit slowed hand movements relative to saccades, yet improved endpoint accuracy. Compared to central fixations, using smooth pursuit also slowed hand movements, while using saccades decreased, thus improved, hand reaction times. Data suggest an advantage, when using smooth pursuit to track the hand movement for the greatest endpoint accuracy, an advantage when using saccades for the fastest movements, and an eye-hand coupling advantage when using saccades for the shortest reactions. Researchers should provide clear eye-movement instructions for participants and/or monitor the eyes when assessing similar upper limb control to account for possible differences in eye movements used. Moreover, the type of eye movement chosen for participants should correspond to the primary goal of the task.