Stages of Smooth Pursuit
Pursuit eye movement can be divided into two stages: open loop pursuit and closed loop pursuit. Open loop pursuit is the visual system's first response to a moving object we want to track and typically lasts ~100 ms. Meaning that this stage is ballistic: visual signals have not yet had time to correct the ongoing pursuit velocity or direction. The second stage of pursuit is called closed-loop pursuit. This stage lasts from 100 ms after the initiation of pursuit until the pursuit movement has ceased. This stage is characterized by the online correction of pursuit velocity to compensate for retinal slip. In other words, the pursuit system tries to null retinal velocity of the object of interest. This is achieved at the end of the open-loop phase. Pursuit gain in the closed-loop phase, i.e. the ratio of eye angular velocity and target angular velocity, is near to 1.
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