Babies left tickled pink as scientists try to isolate sensory experiences
New born babies feel tickles without making any connection between the sensation and the tickler, research has shown.
They only associate touch with the outside world after around four months of age, scientists have learned.
Lead researcher Professor Andrew Bremner, from Goldsmiths, University of London, said: "Our findings are really the first to address what is quite a fundamental question about our sensory experience in early life. When young babies feel a touch on their hand, can they appreciate where that touch is in the outside world?
"We think .. that at four months of age, human babies perceive touches just on their bodies, and not in the external world.
"If one tries to imagine what this must be like, it's a bit of a dizzying idea."
The scientists conducted an experiment in which a mechanical "tickler" was used to tickle the feet of four and six-month-old babies.
In some sessions, the infants' feet were crossed and in others uncrossed.
Adults are known to get in a muddle when touched with their hands or feet crossed. As their brains try to decode where the sensation is coming from, they are likely to make mistakes when asked to identify its location.
Six-month-old infants can be confused the same way, the researchers found, but those in the younger age group seemed instinctively to know which foot was being tickled.
The four-month-old babies wiggled the foot that was tickled 70% of the time, and it made no difference if their legs were crossed or uncrossed.
Six-month-olds moved the correct foot on only 50% of occasions with their legs crossed - no better than by chance.
Other research has shown that adults who are born blind share the ability of four-month-old infants to localise touches equally well with limbs crossed or uncrossed.
"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," said Prof Bremner.
"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."
The findings are reported in the journal Current Biology.