Infant sensitivity to radial optic flow fields during the first months of life.

Little is known about the development of the sensitivity for "optic flow," a large-scale pattern perceived during locomotion. The present study aimed to examine infants' coherence thresholds to radial optic flow motion during the first months of life. Using a forced-choice preferential looking technique, infants' sensitivities were measured with a moving radial stimulus varying in coherence on one side and a corresponding non-directional radial noise pattern on the other. Coherence thresholds for 11 infants from each of 2, 4, 6, 8, and 10 months of age groups were studied by a constant stimuli method. In the second experiment, seven infants were followed longitudinally (tested at 2, 4, 6, and 8 months) using the same stimuli. Results of both studies demonstrated significant improvement for the sensitivity of expanding radial motion during the first months of life. Finally, the 2 directions of radial motion were tested (expanding and contracting) for participants followed longitudinally (from 2 to 8 months). Data showed superior sensitivity for expansion versus contraction direction of motion. This dissociation may suggest that sensitivity to direction corresponding with forward locomotion (expansion) develops at a faster rate than the opposite direction encountered when moving backwards (contraction). The sensitivity improvement for expanding patterns likely reflects the maturation of cerebral areas subtending motion integration in infancy.