| The flow of visual information on the periphery of the retina is sufficient to generate the illusion of movement even when the self is stationary. Such optic flow information is also crucial for maintenance of postural stability, which in turn is essential for upright locomotion in sighted individuals. Prior research has documented a major developmental shift between 7 and 9 months of age (Bertenthal & Bai, 1989) in sensitivity to peripheral optic flow suggestive of self-motion (assessed by postural sway). Four studies tested the hypothesis that experience with self-produced locomotion, by virtue of exposing infants to a unique form of perceptual input, accounts for the increased sensitivity to peripheral optic flow. Results suggest that development proceeds as a differentiation in the ability to partition the visual field and use smaller portions.;Self-produced locomotion produces a correlation between visual and vestibular input which is not produced by rotation of the head or by movement provided by another's actions. Passive locomotion, such as being carried or pushed in a stroller, allows infants to look away from the direction of locomotion. In contrast, infants beginning to locomote must look in the direction of locomotion, resulting in coordination of peripheral optic flow information with vestibular stimulation specifying self-movement. In this way, self-produced locomotion provides infants with the experience which permits the use of optic flow to perceive self-motion.;Study 1 verified the developmental shift in infants' use of optic flow between 7- and 9-months of age. Study 2 showed that 8-month-olds with self-locomotor experience use portions of the optic flow field not used by prelocomotor infants. Study 3 failed to support the alternative hypothesis that prelocomotor infants could use optic flow information if it were made more conspicuous. Study 4 supported the hypothesis that locomotor experience made no difference in response to an optic flow pattern characteristic of passive locomotion, as one would receive looking out the side of a moving vehicle. The results of these four studies implicated the effects of locomotor experience as the effective factor facilitating the use of peripheral optic flow for postural control, allowing infants to use smaller portions of the visual field. |
