Infants Experience Touch Differently Than Adults

Experts in early childhood development often tell parents to engage with a newborn through gentle touch and play. Studies find physical interaction with adults facilitates neurodevelopment, and the opposite may cause developmental delays. But it turns out that babies may not experience this type of bonding quite as we were led to believe.

New research suggests newborns 4 months old and younger don’t connect the physical sensation of being tickled to the adult who is doing the tickling, a phenomenon the researchers refer to as a “tactile localization deficit.”

For the study published Monday in Current Biology, the researchers tickled 4-month-old and 6-month-old infants with small vibrating devices. The researchers say that touches on the body are just perceived by infants as touches. The sensation isn’t associated with the things they may be seeing or hearing, such as a doting parent.

But they also found out something else interesting about how infants experience tickling: It turns out that babies in the first four months of life are much more accurate than adults at identifying where the sensation of touch may be on the body—and they appear to get worse at the task as they get older.

A large number of temporal order judgment studies have been conducted to understand spatial recognition in adults. In a typical experiment, a subject would be asked to cross his or her hands or feet, and then identify the site of physical sensation. With limbs crossed, a person is more likely to get it wrong, which suggests that the brain “remaps” the body. Spatial recognition studies on adults also demonstrate this phenomenon. In one study, people were asked to hold different objects in each hand, either with arms crossed or not. When arms weren’t crossed, participants were able to correctly answer the question about which hand was holding an item within 34 milliseconds. With arms crossed, participants needed up to 124 milliseconds to answer accurately.

After trying a similar experiment with the feet of the infants crossed and uncrossed, the authors of the recent Current Biology study found that the 4-month-old infants moved their tickled foot 70 percent of the time regardless of whether both feet were crossed or uncrossed. Though the 6-month-olds were correct 70 percent of the time with uncrossed feet, they were only correct 50 percent of the time when their feet were crossed, which the researchers say is an accuracy level equivalent to pure chance.

An infant’s senses begin to develop in utero,  but it is only when they leave the womb that newborns develop vision skills—such as the ability to focus the eyes and move them together. In their first few months of life, infants simultaneously learn to process visual information, walk and talk, integrating their senses as they develop into a fully formed child.

The difference between the spatial recognition of a 4-month-old and that of a 6-month-old may have a lot to do with this developing sense of sight. The younger infants don’t know how to integrate senses; in particular, they can’t yet process the visual information that is directly linked to touch. So, they feel the tickle but don’t know it’s from the person standing in front of them. But once they have a more fully developed sense of vision, they also begin to map how their body fits into the world. As the infant develops, it will no longer process each sense separately.

The authors modeled their study after one involving congenitally blind adults. That study looked at adults who were born blind versus those who lost their sight after birth—even very early on in life. The study found adults who were born without vision were able to identify the location of touch, regardless of whether their hands were crossed or not. However, those who lost sight over time didn’t demonstrate the same level of ability. In essence, those who had always been blind were simply relying on physical sensation, whereas those who had once been able to see their body in the physical world were experiencing sensory touch through a previous, visually mapped framework.

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