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Abstract:
Adults discriminate their direction of motion or heading from
optic flow to within 1 deg by engaging motion processing circuits
in extrastriate cortex. Little is known about how heading
perception or the cortical circuits associated with it develop
early in life. Using an established psychophysical method, we
estimated that the minimum change in heading angle that 4 to
5-month-olds could discriminate was approximately 22 deg. To
determine if infants and adults differ in the extent to which they
fixate near the focus of expansion (FOE), we examined the
spontaneous fixation patterns made by adults who viewed displays
depicting different directions of heading. Adults fixated within 4
deg of the FOE 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
results indicate that prelocomotor infants do not accurately
discriminate their direction of heading from optic flow, nor do
they systematically fixate near the FOE. The results imply that
adult-like spatial processing capacities associated with dorsal
stream cortical systems do not emerge early in life but instead
undergo considerable postnatal development.
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