Beloved pediatrician Dr. T. Berry Brazelton, who died recently at the age of 99, established his reputation by arguing that babies are not “lumps of clay,” as was the prevailing view when he entered the medical field in the 1940s, but rather complex expressive beings whose behavior is “purposeful and meaningful.” In the decades since Brazelton first began making a case for the purposefulness of the infant mind, research on infant cognition has demonstrated that it is even more complex than he ever imagined. A new study just published in Science reveals that babies as young as twelve months old are actually capable of syllogistic reasoning.

Cesana-Arlotti et al. conducted a series of experiments to investigate the logical processes behind preverbal infants’ continuous efforts to understand how the world around them works. Beginning with the premise that infants are capable of developing, testing, and adapting hypotheses about uncertain future events, the researchers sought to characterize the “basic logical representations” with which they might formulate such hypotheses, given the fact that they have not yet developed the language skills which are often considered a prerequisite for such logical thinking. In order to identify the framework upon which such baby reasoning is constructed, the researchers focused on “one simple logical representation and rule: disjunction (either A or B) and disjunctive syllogism (not A, therefore B).” In other words, they designed their experiments to see whether or not infants were capable of reasoning through the process of elimination.

Infants of 12 and 19 months of age were presented with computerized vignettes in which two different objects, such as a dinosaur and a flower, were shown being hidden behind a wall. Once the objects were out of sight, a cup entered the picture and scooped up one of the objects and brought it out from behind the wall, but only the top part of the object—identical to the top of the other object—was visible in the cup. Next, the wall was lowered, revealing the object behind it—the object that had not been lifted up by the cup. Finally, the object in the cup emerged and was revealed to be either A) the object that was not behind the wall (as would logically be expected), or B) an object identical to the object behind the wall (a violation of logical expectation). Or, in dinosaur and flower terms, if it was the dinosaur that was scooped up and the flower left behind the wall, in one case, the expected dinosaur would emerge from the cup, and in the other an unexpected replica of the flower would emerge.

Since infants’ visual attention is drawn to whatever they find most interesting at any given moment, the amount of time they spent looking at the different objects was measured to determine whether the unexpected outcome had any effect upon their interest level. As was hypothesized, the infants stared longer at the unexpected outcome than at the expected outcome, indicating that they were aware of what the outcome logically should have been according to the disjunctive syllogism, “not A, therefore B.”

As a test to determine whether inferences were being made by the infants at appropriate stages throughout the vignette, or if they only reacted to a violation of expectation at the big cup reveal at the conclusion, the researchers analyzed their oculomotor responses at stages where inferences were called for. Significantly, the infants’ pupils dilated more when the scene called for an inference than when it did not, indicating increased cognitive activity during these stages.

Even though reasoning through the process of elimination is a rudimentary form of logic, the authors of the paper point out that it is this same form of reasoning that is most favored by the master logician Sherlock Holmes as he undertakes a “case-by-case analysis of different possibilities, excluding alternatives until the culprit is found.” The results of this study suggest that the sort of logical reasoning that astonishes us in a Sherlock Holmes is actually not a rare or even an acquired ability, but rather innate and universal, and that “intuitive and stable logical structures involved in the interpretation of dynamic scenes may be essential parts of the fabric of the mind.”

References

Cesana-Arlotti, Nicoló, et al. “Precursors of Logical Reasoning in Preverbal Human Infants.” Science, American Association for the Advancement of Science, 16 Mar. 2018.

Halberda, Justin. “Logic in Babies.” Science, American Association for the Advancement of Science, 16 Mar. 2018.

Klass, Perri. “How Dr. T. Berry Brazelton Shaped Pediatrics.” The New York Times, The New York Times, 15 Mar. 2018