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 between 3 and 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 Thursday 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."
But Lisa Oakes, a psychologist at the Center for Mind and Brain at the University of California at Davis, wonders if there could be an alternate explanation.
Perhaps the infants held their gaze longer on the cup simply because they were watching two different items emerge from behind the screen.
"These events are very complicated," she said, "and it would be difficult for an infant to keep track of the sequence of actions and maintain the information in working memory over the entire event. It is possible that the interpretation by the authors is correct, but their interpretation is not the only one."
Additional evidence for their theory, the researchers claim, can be found in the measurements they recorded of each baby's pupil dilation throughout the experiment.
In the time between when the two objects emerged from behind the screen and the contents of the cup were revealed, they discovered that the infant's pupils dilated, and their attention tended to shift toward the cup.
Both the dilation and attention orientation seemed to support the idea of inferential thinking, they concluded.
Susan Hespos, principal investigator at the Infant Cognition Lab at Northwestern University, calls the research "an elegant series of experiments," noting that "infants, toddlers and adults all show similar dilation patterns."
Her takeaway: "These data provide evidence that some of the human characteristics that make us so smart are evident in primitive form early in development. Finding logic abilities in infants as young as 1 year of age suggests that these abilities might be continuous over development."
In a commentary that accompanied the study, Justin Halberda, director of the Johns Hopkins Laboratory for Child Development and the Vision and Cognition Lab, noted the emerging field that is studying the "foundations of logical abilities" and the contribution this latest research might make.
"It is thrilling for us as scientists - using logical reasoning to understand how we reason logically," Halberda said.
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