Baby's Brain in Week 39
Think about how complicated learning would be if the human brain didn't allow us to create categories. Take vehicles out on the street—we understand what we see because we automatically put these vehicles into categories: SUVs, sedans, minivans, station wagons, sports cars, and trucks, and so on. If we were not able to categorize, we would need to learn about each vehicle individually, independent of the next one.
Around this age, babies are able to make correct inferences about novel objects, sounds, animals, and people that they have never experienced because they can fit them into categories of events that they've previously experienced. A young child who encounters a cat and learns that it purrs does not need to learn this information about a new cat that she meets. (This ability is sometimes called "generalizing.")
What the Research Shows
Researchers determined that upon seeing pictures of cats, three-month-old babies look reliably longer at a picture of a dog that has been slipped into the group of cat pictures. Staring at this dog indicated to the researchers that child after child knew that it didn't belong with the group of cats.
However, some objects and animals are so similar that it's difficult for babies to separate them into categories. In one research study, seven-month-olds were shown pictures of airplanes and birds. No matter how these objects were pictured, the babies were not surprised or perturbed upon seeing the birds and airplanes mixed together. They couldn't yet decipher airplane and bird categories.
But for babies between nine and 11 months, the categories were clear: Babies at these ages looked reliably longer at the picture of an airplane which had been inserted into a picture of birds, signaling that they were on to the odd card out.