Infants' discrimination of heading direction from optic flow

Adults discriminate their direction of motion or heading from optic flow to within 1Ã under many circumstances, but little is known about how heading perception develops early in life. Accordingly, we examined the extent to which 4 to 5 month-old infants could discriminate heading direction from optic flow. Three studies using using a looking time habituation method suggested that 4-month-olds discriminated 180Ã, but not 4Ã, 8Ã, or 16Ã changes in heading. Using a more sensitive forced choice preferential looking (FPL) technique, we estimated that the minimum change in heading angle that 4 to 5 month-olds could discriminate was approximately 22Ã. To determine if infants and adults differed in the extent to which they fixated near the focus of expansion (FOE), we examined the spontaneous fixation patterns made by adults who viewed optic flow displays depicting different directions of heading. Adults fixated within 4 deg of the FOE approximately 70% of the time, but infants did not. When asked to determine whether infants preferred the left, center or right of an optic flow display depicting forward, leftward, or rightward motion, an observer made correct judgments only 40% of the time, a value not significantly different from chance levels of 33%. The combined results indicate that prelocomotor infants do not accurately discriminate direction of heading from optic flow, nor do they systematically fixate near the FOE.