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smooth pursuit
Smooth pursuit eye movements allow the eyes to closely follow a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit is asymmetric: most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making ''catch-up saccades''. Most humans are also better at downward than upward pursuit.〔Grasse KL, Lisberger SG. Analysis of a naturally occurring asymmetry in vertical smooth pursuit eye movements in a monkey.'' J Neurophysiology'' 1992 Jan;67(1):164-79. PMID 1552317〕 Pursuit is modified by ongoing visual feedback.
==Measurement==
There are two basic methods for recording smooth pursuit eye movements, and eye movement in general. The first is with a search coil. This technique is most common in primate research, and is extremely accurate. An eye movement shifts the orientation of the coil to induce an electric current, which is translated into horizontal and vertical eye position. The second technique is an eye tracker. This device, while somewhat more noisy, is non-invasive and is often used in human psychophysics and recently also in instructional psychology. It relies on the infrared illumination of the pupil to track eye position with a camera.
During oculomotor experiments, it is often important to ensure that no saccades occurred when the subject was supposed to be smoothly pursuing a target. Such eye movements are called catch-up saccades and are more common when pursuing at high speeds. Researchers are able to discard portions of eye movement recordings that contain saccades, in order to analyze the two components separately. Saccadic eye movements differ from the smooth pursuit component by their very high initial acceleration and deceleration, and peak velocity.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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