Babies show eye for object lessons

Between 4 months and 6 months of age, babies parlay their visual experience into the insight that objects exist as permanent entities, even when hidden from view, a new study finds.

BALL GAME. When shown a ball disappearing behind the box, 4-month-old babies can learn to expect the ball’s reemergence. Johnson/PNAS

The results challenge the influential notion that such knowledge is innate. Advocates of the innateness hypothesis argue that babies up to 6 months old can’t systematically track objects with their eyes, even though babies of that age do realize that, say, a ball that rolls behind a screen should be visible when the screen is removed.

According to Scott P. Johnson of New York University and his colleagues, however, 4-month-olds indeed monitor moving objects and learn from these experiences to expect that moving objects will emerge from behind barriers.

The researchers tested 48 4-month-olds and 32 6-month-olds. Each child sat in a parent’s lap and watched an animated computer scene as an infrared camera tracked the baby’s eye movements. On the screen, a green ball moved horizontally, periodically disappearing behind a blue box and then reemerging.

Although 6-month-olds frequently looked at the box’s opposite side in expectation that the ball would reappear there, 4-month-olds rarely did so, at least at first.

If allowed to watch a ball move across an otherwise clear screen for a few minutes, 4-month-olds subsequently shown the scene with the blue box often looked to where the hidden ball was about to emerge. This tactic hastened the process of learning about the permanence of objects for younger infants, Johnson and his coworkers propose in the Sept. 2 Proceedings of the National Academy of Sciences.

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Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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