An infant receives a buzz to one foot crossed over the other, an experiment that let scientists study how babies experience the world.
Babies’ minds are mysterious. Thoughts might be totally different in a brain that lacks words, and sensations might feel alien in a body so new. Are babies’ perceptions like ours, or are they completely different? Even if babies could talk, words would surely fail to convey what it’s like to experience, oh, every single thing for the first time.
A recent paper offers a sliver of insight into young babies’ inner lives. The study, published October 19 in Current Biology, finds an example in which 4-month-old babies are happily oblivious to the external world.
The research focuses on a perceptual trick that suckers adults and 6-month-old babies alike. When the hands are crossed, people often mistake which hand feels a touch. Let’s say your left hand (now crossed over to the right side of your body) gets a tickle. Your eyes would see a hand on the right side of your body get touched — a place usually claimed by your right hand, but now occupied by your left. Those mismatches between sight, touch and expectation can thwart you from quickly and correctly saying which hand was touched.
Here’s the twist: 4-month-old babies don’t fall for this trick, Andrew Bremner of Goldsmiths, University of London and his colleagues found. In the experiment, a researcher would hold infants’ legs in either a crossed position or straight, while one of two remote-controlled buzzers taped to their feet tickled one foot. The researchers then watched which foot or leg wiggled as a result. If the buzzed foot moved, that meant that the baby got it right.
In either the crossed or straight-legged position, 4-month-old babies moved the tickled foot about 70 percent of the time, the team found. But babies just two months older were fooled by the leg cross, moving the tickled foot in about half the trials.
Bremner interprets the results to mean that young babies don’t link the outside visual world to their own bodies yet. Instead, they exist in a state he calls “tactile solipsism,” in which the only thing young babies know about touch is the sensation on the skin, not who or what is causing it. “Your bodily world would be almost completely separate from your visual world,” he says.
This touch/outer world division may help explain other weird things babies do. As babies first learn to move their arms and legs, they’ll hilariously try to stalk and grab one of their own hands with the other. (My husband and I enjoyed narrating this process David Attenborough–style: “The predatory righthand stalks the elusive left hand prey.”) Young babies seem oblivious to the fact that they own — and can control — their other hand, perhaps because they haven’t yet connected the visual signal coming from the hand to the feeling on their body.
As babies grow and learn more about their world, including the lesson that the things they see are sometimes the things that touch them, their bodies become more integrated with the world. No longer tiny islands, they get better at stitching together sights, sounds, smells and other information into perceptions that make sense.
