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 (link is external) 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.”
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