Smooth Pursuit - Measurement

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 electrical 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.