Evidence for mental subdivision of space by infants: 3- to 4-month-olds spontaneously bisect a small-scale area into left and right categories.

Young infants have been shown to represent the left versus right spatial category relations of a target object and a vertical referent bar. In the present study, we examined whether infants would represent left versus right when the vertical bar was removed from the stimulus display. In Experiment 1, 3- to 4-month-olds who had been familiarized with stimuli depicting a diamond appearing in different locations to the left or right of the vertical midline displayed a mean novel category preference for a stimulus depicting the diamond on the opposite side of the midline. In Experiment 2, another group of 3- to 4-month-olds discriminated the within-category position changes of the diamond as it appeared to the left or right of the vertical midline. The results indicate that young infants can mentally bisect small-scale space into left versus right categories.