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Jeffrey B. Mulligan, Scott B. Stevenson; No role for visual motion in manual tracking. Journal of Vision 2009;9(14):67. doi: 10.1167/9.14.67.
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It is believed that visual motion (“retinal slip”) is one of the primary drivers of smooth pursuit eye movements. By introducing artificial delays in the visual consequences of eye movements via transient stabilization, spontaneous oscillations of the eye can be observed, with the period of oscillation varying as a linear function of the delay. Velocity- and position-based control of eye acceleration predict period-vs-delay slopes of 4 and 1 (respectively). We have previously (VSS ′07) reported slopes close to 1.5 for human observers, suggesting that smooth pursuit utilizes a combination of inputs based on both position and velocity errors. Here we extend the delayed feedback paradigm to manual tracking of a moving target using a joystick or mouse. Unlike the case of oculomotor tracking, manual tracking exhibits period-versus-delay slopes close to 2, consistent with hand "saccades" in which position is controlled by a mechanism driven purely by position errors.
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