Research
About our Research
Infant Categorization Development
What have we learned about babies’ categories?Imagine how hard it would be to think about every dog you encountered as a separate individual—without recognizing that all dogs have some features in common. By grouping dogs together, we know that we can call them all using the same label (dog), that they can eat the same food, and that they might jump up when excited. Categories, such as dog, shoe, and cup, are especially important for babies. As infants learn about and remember objects, grouping those objects will help them learn the objects’ names, what to do with those objects, and how the objects will react. We have discovered babies have amazing abilities to group objects. By 4 months, babies can group dogs together and recognize that a cat is not the same sort of thing as a dog. This is remarkable when you consider that at 4 months babies don’t know the words “dog” or “cat”, and that dogs and cat are very similar—they have four legs, tails, fur, etc. It might be tempting to say that babies “know” the category of cat or dog by 4 months. However, babies only notice such categories under some circumstances. For example, younger infants group together dogs that look alike, but not dogs that look more different from one another. In addition, young babies are more likely to form a group of “dog” if they see different dogs together than if they see those dogs one at a time—probably because they can compare the dogs and see how they are similar and different without having to remember one of them. This kind of research is important for making sense of how infants organize and remember the objects they encounter—which is important for uncovering the origins of language and conceptual understanding.
Four-
to 6-month-old infants presented with two pictures of different items
form more exclusive categories (e.g., a category of dog that does not
include cats). Infants presented with two identical pictures form more
general categories (e.g., one that includes both dogs and cats).
Infants appear to have difficulty noticing how objects are similar when
objects are presented one at a time.
Older infants (10 to 13 months of age) also form more exclusive categories when presented with actual objects to play with when they are given two different objects at one time. When given two identical items at one time, infants form more general categories.
Infant Memory Development
What have we discovered about babies’ short-term memory?
Short-term memory is the kind of memory we use when we recognize that an object that is briefly out of sight is the same when it reappears—for example recognizing that a ball that rolls under the couch is the same ball that emerges from the other side (at least if it’s the same color, shape, and size). This kind of memory is critical to see the visual world as unchanging as we blink and move our eyes around. This kind of memory is important for babies—they need to track objects (such as balls and cats) as they move behind furniture and other objects, and they need to be able to connect what they see before and after they blink. In fact, we have discovered that by 4 months babies have this kind of memory—they notice when something changes after it has been out of view momentarily. But, the number of things they can remember this way is extremely limited. We found that 4- and 6-month-old babies remember only one thing. By 10 months, babies remember several things, suggesting that their short-term memory develops extremely rapidly in the first year of life. In general, we have discovered that although short-term memory emerges early in life, it rapidly develops between 4 and 10 months of age. These early limits on short-term memory might be especially important for helping young babies deal with the overwhelming amount of new information they encounter each day.
If infants can store the colors of the squares in memory, they should notice the color changes and look longer at the changing displays. We measure how much infants can remember by varying the number of squares on the screen. We have found that 4- to 6-month-old infants seem to be able to remember only 1 square, whereas 10- to 13-month-old infants seem to be able to remember 3 or 4 items, which is close to the adult capacity.
Infant Visual Perception Development
What have we learned about babies’ visual perception?
One important feature infants must perceive is object boundaries or edges. This may seem trivial—as you look at your desk or around the room, you easily detect the edge of your notepad, your coffee cup, and the chair across the table. But, in fact, figuring out where one object ends and the next one begins isn’t that easy—the visual system needs to consider changes in texture, depth, and shape. We have been studying how the developing visual system solves this very complicated problem by examining infants’ perception of an extremely simple visual scene—one that has just two shapes that are adjacent, so they share a single edge. We have found that infants’ perception of this edge—that is, whether they perceive it as the edge of one object but not the other—changes at about 6 months of age.
If the edge divides the image into a top half and a bottom half, adults perceive the shared contour as the edge of the bottom half, and perceive the bottom region as in front of the top region. If the edge has the same contour as the outside edge of one region, that region is symmetrical, and adults perceive the edge as belonging to that part of the display. Again, the symmetrical shape is seen as closer than the other shape. Infants’ perception of the bottom or symmetrical part of these kinds of displays changes dramatically at about 6 months of age—perhaps as infants learn to sit upright and begin reaching for objects. At this time, seeing the edges of objects has a whole new meaning for the infant.
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