Babies start using logic years earlier than experts thought

In intriguing research, a team of scientists may have discovered the earliest age at which a person can reason logically: 12 months.

For decades, psychologists have considered language a necessary and essential indicator of inferential thinking — the complex ability to “read between the lines,” to reason one’s way to a correct interpretation of an event when the evidence is not obvious.

As recently as 2014, experiments by prominent developmental psychologists suggested such thinking began from 3 to 5 years of age.

Psychologist Nicolo Cesana-Arlotti, a postdoctoral fellow at Johns Hopkins University, thought the age might be much younger.

“If you have logical reasoning, you can generate conclusions, you can obtain evidence that would be hard to obtain otherwise,” he explained this week.

“It opens you up to much more information. So we were driven by the belief that logical reasoning might play an important role in a full picture” of the infant mind.

He and his colleagues were right.

In a study published this month in the journal Science, Cesana-Arlotti and his colleagues described how they determined infants might have inference-making ability.

Their experiment involved 144 babies, half of them a year old and half 19 months old, but none yet talking.

In the experiment, the children sat in the laps of their silent and impassive mothers, who were blindfolded so the babies would not pick up on any unintentional facial clues.

An animated sequence then played on an individual computer screen.

Each group watched the same animation, which included such virtual objects as an umbrella, flower, smiley face and dinosaur placed in front of a black screen.

The tops of each were drawn to be identical, and when the two objects flew behind the screen — say, the umbrella and the smiley face — only those tops could be seen.

Suddenly, a cup scooped up one of the objects — the baby could not see which — and moved in front of the screen.

Again, just the object’s top was visible within the cup.

At this point, the black screen dropped to reveal the remaining object — let’s assume the umbrella — behind it.

To test the babies’ logical reasoning — their ability to infer through the process of elimination that the smiley face must be in the cup — the researchers pulled a fast one.

Instead of the smiley face, another umbrella appeared in the cup. Each baby, regardless of age group, reacted by looking longer at the cup. There was no difference between the two age groups.

“It’s a classic paradigm,” said Cesana-Arlotti, the study’s lead author. “When something unexpected happens, the infant looks longer because their expectations have been violated.”