When you tickle a baby’s foot, the infant might wiggle her toes, but she doesn’t necessarily know where the sensation is coming from. A new study in the journal Current Biology finds that for the first four months of infants’ lives, they don’t really understand how tactile sensations relate to the larger, outside world. 

To test how babies perceive being touched, researchers hooked their feet up to remote-controlled stimuli that buzzed. When adults cross their hands or feet and someone touches them, they often mistake which limb the sensation is coming from, because of confusion between the visual and tactile senses. The researchers found that 6-month-old babies also got confused by being touched while their feet were crossed, only identifying the correct origin of the sensation 50 percent of the time. However, when 4-month-old babies had their crossed feet touch, they could usually correctly identify where the sensation came from, suggesting that at that age, babies aren’t computing how the sensation relates to the visual input of watching someone touch them. 


An infant receiving tactile buzzes to the feet. Image Credit: Jannath Begum Ali

“These striking findings indicate that, early in the first year, human infants exist in a state of tactile solipsism,” the researchers write, referring to the philosophical theory that existence is limited to one’s own self. Young infants perceive touch only in reference to their own bodies, not in terms of what’s going on in the outside world to cause them to feel that sensation. Around six months of age, babies begin to develop this wider view of the world, no doubt helping them to better understand their environments.

"Our argument is that for young babies, touches are just perceived as touches on the body; they're not perceived as being related to what they are seeing or hearing, or perhaps even smelling," study co-author Andrew Bremner of Goldsmiths, University of London explains in a press release. "They're not related to objects perceived in vision. To me this sounds like quite an alien sensory world to live in—the tactile world being quite separate from the other sensory worlds."