Most people would agree that babies are cute, with their funny hair and chubby cheeks, but that's just what's on the outside. What, if anything, is going on inside their little heads? As it turns out, there's probably a lot more going on than you think!
The predominant view of the infant mind over the last, well, three or so centuries, is that babies are born without any knowledge about the world (Baird & Kaufman, 2008). At most, they are born with a couple very basic, very general processes that allow them to build knowledge from their experiences (Pavlov, 1927/1960). Indeed, the "father of psychology", William James, is well known as stating that infants' experience of the world is "one great blooming, buzzing confusion" (p442, Principles of Psychology, 1890).
Recent research, however, seems to have turned this classic empiricist view of infant cognition on its head. Not only do infants have knowledge of the world, at least in a few core domains, but their knowledge appears to be quite sophisticated and principled. The benefit of having such cognitive structures in place at birth or soon thereafter (i.e., within the first year) is that it allows infants to make sense of what they hear, see, and feel. Without principles to guide their attention and the acquisition of knowledge, the world really would seem a "blooming, buzzing confusion"!
The view that infants are endowed with "core knowledge" is the product of scores of studies performed over the last three decades, many using what are known as "looking time" techniques. Such techniques capitalize on the tendency of even very young infants to look longer at events that do not accord with their expectations. These methods are a vast improvement over previous methods that usually depended on the infant making motor responses (e.g., reaching for an object, or crawling to a location), which we know are poorly developed early in life for reasons having to do with immature brain maturation, not immature cognitive abilities.
That's all well and good, you may say, but, "Where's the beef? What exactly do infants know?" Perhaps surprisingly, one domain in which they seem to know quite a lot is physics! They make a categorical distinction, for example, between objects and non-solid substances (i.e., water or sand).
In fact, the ontological distinction between "things" and "stuff" has been of central importance not only to psychologists, but also to linguists who study grammatical differences in object and substance names (Link, 1983), and to philosophers who study the metaphysical importance of separable and non-separable entities (Sattig, 2010).
We now know that infants have different expectations for objects and non-solid substances. For example, they expect objects, but not substances, to maintain cohesion. Building this into the system makes sense, given that objects generally do not fall apart when moved, while substances do. If one plans to reach for a toy in the bathtub or for the water, it would be useful to know what to expect from each type of entity so that the appropriate motor plan can be initiated (i.e., grasping for objects, but not substances).
Cohesion is one way in which objects and substances differ. They are alike however, in their adherence to the principles of solidity and continuity. Neither type of entity can blink in or out of existence, and neither can pass through a solid surface (e.g., salt in a shaker). Infants are savvy to this, too, and are surprised (i.e., look longer) when shown events in which either an object or a substance appears to pass through a solid wall.
Another aspect of physics that infants appear to know about early on is gravity. Unlike other types of physical knowledge though, infants understanding is skeletal at first, and gets enriched with age and experience. Initially, infants understand only that an object must be in contact with another surface in order to be supported (i.e., not fall). In a couple months' time, infants expect an object to fall unless it rests on top of a surface. And in another couple months, they understand how much of an object must be on top, and finally, by about one year of age, can take the shape and likely weight distribution of the object into account when predicting when it should fall.
These kinds of findings reveal the rich and sophisticated knowledge that infants seem to have about the physical world from a very young age, before they've had a chance to have gained much experience with seeing, let alone manipulating, objects and substances in the world.
Interested readers can read more about the amazing minds of babies in a review of these and other findings by Susan Hespos (Northwestern University) and myself published recently in WIREs Cognitive Science. Or, feel free to visit our websites where you can find out more about infant research and download articles reporting related findings with infants. Hespos Infant Cognition Lab and vanMarle Developmental Cognition Lab.