Motion Popout in Selective Visual Orienting at 4.5 But Not at 2 Months in Human Infants

The effect of element density on selective orienting was examined in 2 experiments with 2and 4.5-month-old infants. Selective visual orienting to a singleton oscillating target that appeared with other static bars was used to study the effects of element density. Increasing the set size and density of the static bars decreased selective orienting to the moving target in the 2-month-old infants, but it increased selective orienting in the 4.5-month-olds despite the fact that the overall levels of correct orienting to the target were titrated to be the same at the 2 ages. Thus, density affected the selectivity of visual orienting to movement at these 2 ages differently with popout being evident at the older age. In the 2nd experiment, motion popout for the 4.5-month-old infants was replicated using oscillating targets that had the same peak and mean speeds but different temporal frequencies and amplitudes of oscillation. Increases in the efficiency of perceptual grouping of similar elements between 2 and 4.5 months of age could overcome the lateral masking effects of increasing element density seen at the lower end of this age range.