Logic in babies.

Halberda does a commentary on work of Cesana-Arlotti et al. showing that one essential form of logical inference, process of elimination, is with the toolkit of 12 month old infants. They used that fact that visual behaviors - such as a shift in one's gaze or a prolonged stare - can be diagnostic of internal thoughts to demonstrate that preverbal infants can formulate a logical structure called a disjunctive syllogism. That is, if A or B is true, and A is false, then B must be true. Presenting infants with scenes where the outcome revealed B to be false evoked looks of surprise:

Cesana-Arlotti et al. asked whether prelinguistic 12- and 19-month-old infants would spontaneously reason using process of elimination. This is a form of inference also known as disjunctive syllogism or modus tollendo ponens—it is any argument of the form: A or B, not A, therefore B. Cesana-Arlotti et al. relied on one of the few behaviors babies voluntarily engage in—looking at whatever they find most interesting. They measured infants' looking at computerized vignettes in which two different objects (A and B) were shown being hidden behind a wall. Infants watched as a cup scooped one of the objects from behind the wall, and then came to rest next to the wall—critically, only the topmost edge of the contained object could be seen peeking out of the cup, such that infants could not tell for sure whether the object was A or B. At this moment, infants could have formed a disjunctive thought—for example, “either the object in the cup is object A or it is object B.” Next, this ambiguity was resolved: The wall dropped to reveal that object A was behind the wall, but the contents of the cup remained hidden. This is the moment of potential elimination, and an opportunity for infants to draw a key inference—“because object A is not in the cup, object B must be in the cup.” Finally, infants' expectations for the cup's contents were tested: Either the expected object (object B) or, surprisingly, another object A emerged from the cup. Infants looked longer at the surprising outcome—an indication that their expectations were violated and a hint that they were seeking further information to resolve the conflict.