Pursuit gain is calculated as the ratio of pursuit velocity to target velocity, where a value of 1.0 indicates perfectly accurate pursuit tracking. With regard to the role of pursuit eye movements in motion parallax, infant studies find that smooth pursuit gain is quite mature as early as 3-months-of-age, which is typically the lower age limit on depth-from-motion studies. Following habituation, infants dishabituated to a depth-phase reversed test trial on average by 16-weeks-of-age. ![]() Infants were habituated to a translating random-dot cinematogram containing a particular phase of depth corrugation specified by motion parallax. Nawrot, Mayo, and Nawrot ( 2009) explored the onset of sensitivity to motion parallax from 8- to 29-weeks-of-age. In a longitudinal study using computer-generated stimuli, E. Two studies using real objects in a motion parallax scenario concluded that infants are sensitive to motion parallax between 3- and 6-months-of-age, based on dishabituation (von Hofsten, Kellman, & Putaansuu, 1992) and preferential reaching measures (Condry & Yonas, 2013). Previous research on the development of infants' sensitivity to depth from motion parallax is limited. Retinal motion in the same direction is perceived farther away than fixation (M. With motion parallax, perceived depth sign relies on the direction of the smooth pursuit eye movement signal: Retinal image motion in the direction opposite the pursuit signal is perceived nearer than fixation (remember that retinal image motion and object motion in the scene are opposite). Smooth pursuit eye movements are used to track a moving stimulus, or a stationary stimulus during observer movement, in order to maintain fixation, minimize blur due to motion, and maximize acuity (Krauzlis, 2004). Nawrot & Joyce, 2006) suggests that the human and primate visual systems use a concomitant smooth pursuit eye movement signal to disambiguate the depth sign in motion parallax. Recent work (Nadler, Nawrot, Angelaki, & DeAngelis, 2009 M. Fortunately, the perception of depth from motion parallax is not depth-sign ambiguous. However, unlike depth from retinal disparity, the retinal image motion information for depth from motion parallax is inherently depth-sign ambiguous (Farber & McConkie, 1979). uncrossed) signals opposite depths relative to fixation. The magnitude of retinal disparity is proportional to the object's depth from the fixation point, and disparity sign (crossed vs. Whereas motion parallax uses retinal motion cues, with binocular stereopsis the cues come from retinal disparity. Motion parallax and binocular stereopsis work in similar ways to provide very similar cues to relative depth. Furthermore, an object's relative velocity is also a cue to relative depth magnitude as objects nearer to the point of gaze move more slowly across the visual field than do objects more distant from the fixation point. Due to the observer translation and compensatory eye movement, objects located nearer than the observer's point of gaze have a relative movement in the opposite direction to the observer's movement, whereas objects located farther away have a relative movement in the same direction as the observer's movement. ![]() ![]() As the observer translates, gaze is maintained on a particular object in the scene through the activity in a number of eye movement systems (Miles, 1998). Motion parallax is monocular depth cue that arises from the relative motion of objects at different distances that is created when an observer translates laterally. Moreover, describing the development of these oculomotor functions in relation to depth perception may aid in the understanding of certain visual dysfunctions. These results suggest that the development of the eye movement system may play a crucial role in the sensitivity to depth from motion parallax in infancy. OFR eye movements also corresponded to both age and smooth pursuit gain, with groups of infants demonstrating asymmetric function in both types of eye movements. The development of smooth pursuit was significantly related to age, as was sensitivity to motion parallax. Infants 8 to 20 weeks of age were presented with three tasks in a single session: depth from motion parallax, smooth pursuit tracking, and OFR to translation. The current study investigates infants' perception of depth from motion parallax and the development of two oculomotor functions, smooth pursuit and the ocular following response (OFR) eye movements. ![]() In adults, and in monkeys, a smooth pursuit eye movement signal is used to disambiguate the depth-sign provided by these relative motion cues. Motion parallax is a motion-based, monocular depth cue that uses an object's relative motion and velocity as a cue to relative depth.
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