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The baby emerges from the darkness of the womb with a rudimentary sense of vision —it would be rated about 20/500, or "legally blind," as one expert puts it, but eyesight develops rapidly. Newborns start by looking at the edges of things, exploring. Even when the lights are turned out, as infra-red cameras show, an infant's eyes open wide to carry on its investigation of its surroundings. At eight weeks, it can differentiate between shapes of objects as well as colors (generally preferring red, then blue); at three months, it begins to develop stereoscopic vision.
Testing such perceptions can be complicated. At M.I.T.'s Infant Laboratory, for example, University of Tokyo Graduate Student Shinsuke Shimojo has programmed a computer to check whether seven-month-old Whitney Warren can differentiate between a straight bar and a slightly indented bar. The computer makes the indented portion of the second bar move slightly. If Whitney can see the indentation, he will see its movement, and Shimojo, crouching behind the computer screen, can see his eyes move. Most babies spot the movement easily.
Despite their esoteric quality, such experiments can have an immediate practical value: some infants suffer from eye ailments, such as cataracts, severe astigmatism and strabismus, which benefit from treatment much earlier than would once have been possible. No less important, the new research has demonstrated that an impairment of infant vision can damage those parts of the rapidly growing brain that rely on visual information. That brain damage can be permanent unless the eye impairment is treated early.
Unlike the eyes, the baby's ears have been functioning even before birth, and the newborn arrives with a whole set of auditory reactions. As early as the 1960s, tests indicated that babies go to sleep faster to the recorded sound of a human heartbeat or any similarly rhythmic sound. More recent studies indicate that by the time they are born, babies already prefer female voices; within a few weeks, they recognize the sound of their mother's speech.
Many mothers believe they can understand different kinds of crying by their babies (a controlled experiment in 1973 showed they could not), and they believe even more strongly that their babies can understand a parent's murmurings. And perhaps they can. Though children do not ordinarily say anything very elaborate before the age of one year, Psychologist Peter Eimas of Brown University has demonstrated that infants as young as one month can differentiate between sounds in virtually any language. They also have a "very sophisticated" ability to organize sounds into various categories. "A baby already knows which sounds communicate," says Eimas. "I've never heard a baby imitate the sound of a refrigerator, for example. So a child can put all of his energy into learning how to use the rules of the language."
Pursuing the origins of language back into earliest babyhood is an interesting approach to understanding the infant intellect. No less so is the discovery that this intellect is at work long before any language is