Feb. 19, 2003 -- Playing peek-a-boo with an infant is a classic little game. Turns out, it's also an important visual lesson for infants.
A new study looks at this issue, the development of a child's visual system. As early as 4 months old, and certainly by 6 months, infants have learned the concept of perceptual continuity, or knowing when an object is or isn't there, writes lead researcher Scott P. Johnson, PhD, a psychologist at Cornell University in Ithaca, N.Y.
By observing infants at 2, 4, and 6 months of age, Johnson and his colleagues discovered this window of learning. "Filling in the gaps in what we see is a fundamental perceptual skill -- one that we had to learn to perform subconsciously or we wouldn't have time for anything else," Johnson says in a news release.
In his study, Johnson performed three different experiments involving 60 infants. As the babies sat on their mothers' laps, they were shown computer-generated images of a green ball as it moved back and forth, disappearing from view for a short time behind a screen -- then reappearing. Sometimes, the ball disappeared behind a blue box then reappeared. Sometimes it simply rolled continuously.
Infants watched the rolling ball until they lost interest, then they were shown two new displays. At each point, researchers measured the attention time that babies gave to the ball.
None of the 2-month-olds could follow a ball that was partially blocked. But by 6 months of age, almost all the infants could follow a visually blocked ball for about 2/3 of a second. Four-month-olds could go either way -- perceiving the visually blocked ball either accurately or inaccurately, depending on how long the ball was out of sight.
This discovery uncovers a "learning window" -- when nerve connections in a normally developing child's visual system are branching, connecting and "talking" among themselves, writes Johnson. The neural circuits established around the fourth month enable accurate visual perception for the rest of a child's life -- barring traumatic brain damage, disease, or old-age deterioration.
It's a natural development, and parents need not do anything special to make it happen, Johnson adds. "Just sit back and watch, which is exactly what the babies are doing. Newborns are avid learners, but that doesn't mean they're born knowing a lot. The youngest only respond to the visual portions of their world, so they don't perceive what they can't see. Then, around 2 to 4 months of age, they learn to connect the bits and pieces of the visible world, to form mental representations," he says.