A new study reveals that preverbal infants are able to make rational deductions, showing surprise when an outcome does not occur as expected. The results suggest that such reasoning is not necessarily linguistically-based, as some had thought. A disjunctive syllogism is a logical form of thinking where, if only A or B can be true, and A is false, then B must be true. In essence, it’s the ability to conduct the process of elimination. Such ability has been confirmed in toddlers, but not preverbal infants. Here, Nicoló Cesana-Arlotti and colleagues studied 12- and 19-month-old infants while they watched animations.

In the animations, two objects that vary in shape, texture, colour, and category (for example a flower and a dinosaur) are shown but are then hidden behind a barrier. An animated cup scoops up one of the objects, say the dinosaur. The barrier is then removed and either the expected leftover object (flower) is present, or, surprisingly, the removed object (dinosaur) remains behind. The researchers used eye-tracking data to find that infants stared longer at scenes where the unexpected object remained behind the barrier, indicating that they are confused by the outcome and hope to attain more information. Cesana-Arlotti et al. conducted variations of this experiment to confirm that it was indeed the unexpected object that enamoured the infants. As well, the researchers found that the infants’ pupils dilated more when watching movies that required rational deductions, a phenomenon that occurs in adults during deductive reasoning as well. Justin Halberda discusses these findings in a related Perspective.