Perception of impending collision in 3-to 6-week-old human infants

The ability of 3- to 6-week-old infants to distinguish between shadow-cast stimuli specifying the presence or absence of optical collision was tested under the following experimental conditions: (a) rapid versus slow visual display expansion and contraction; (b) figure-ground contrast reversal of the display; (c) rapid change in illumination without display expansion or contraction. Rapid and slow expansions of a dark display on a light background elicited significantly more defensive behavior (blinking and backward head movements) than their contractions. This was not the case for expansion versus contraction of a display lighter than its background. A sudden brightening of the screen did not elicit differences in blinking or backward head movements relative to a sudden darkening. Infants as young as 3 to 6 weeks of age perceive optical collision and respond defensively if the expanding display is darker than its background.