A series of studies on the development of depth perception investigated the effects of age from birth and age from conception on the frequency of defensive blinking at an approaching object. The initial study found that at 10 weeks after birth preterm infants respond less frequently to an approaching object than full-term and postterm infants. When preterm infants were tested at the same age from conception as a group of full-term infants, response rates were equal. In a second study, postterm infants at 6 weeks after birth blinked at the approaching object more frequently than 6-week-old full-term infants; this finding was replicated in a subsequent study. In a final experiment with 8-week-old full-term infants, we found that the individual infant tested on two successive days was highly consistent in his or her level of responding. These results argue that maturation plays an important role in the development of responsiveness to spatial information.