Your Child's Brain in Week 76
In trying to make sense of his ever-widening world, your toddler relies on his developing categorization and imitation skills. By now, you know he can remember and imitate the things he sees you do even days later; he can use your description of his environment to categorize the things in it. He's becoming much better at sorting objects into categories, both mentally and in his playroom.
Now, those skills are deepening: At about 18 months, your toddler can watch you use an object and will not only remember how you used it days or weeks later, but will also have developed a category for it that encompasses similar objects and generalizes its purpose—that is, he can apply the use from one object to another.
For example, let's say one morning your child closely observes you making coffee: You pour water into the back of the coffee maker, place a filter in the basket, scoop grounds into the filter, turn the machine on. He hears the machine working, smells the coffee brewing, and watches as you pour the contents of the now-full carafe into a mug to drink.
The next day you go to a neighbor's house, and she's making coffee. Although her coffee maker is different than yours and your neighbor is obviously a different person than you, your child realizes what the neighbor is doing. Your toddler has categorized the machine as a coffee maker and generalized what it's for, all based on her earlier experiences with you in your kitchen. Likely, she'll also know that you and the neighbor will drink the contents, as you had the previous morning.
What the Research Shows
In a one study, 18-months-olds watched as a researcher put one of two puppets on his hand: A gray mouse who wore on a gray mitten on one of its paws or a pink rabbit wearing a pink mitten on one of its paws. Then the researcher took the mitten off the puppet's hand and shook it, which rang a bell that was sewn inside the mitten. Finally, he replaced the mitten back on the puppet's hand. (The children were not given the opportunity to play with the puppets themselves during this session.)
The next day the children returned to the laboratory. If they had seen the gray mouse used the day before, they were now handed the pink rabbit (and vice-versa). Most of the children not only remembered most of what the experimenter had done with the puppet the day before —removed the mitten, shook it to ring the bell, replaced the mitten—but also were able to apply the actions to the different-colored and different-looking puppet who wore a different-colored mitten than what they'd previously seen. (This remembering-and-mimicking skill, you might recall, is referred to as "deferred imitation.")
In the same study, 12-month-olds were able to perform the three targeted actions only when the puppet was the same as the one they'd seen the experimenter use the day before, but not when it was different. The ability to categorize the different-looking puppets and imitate ringing the mitten bell was simply not in place until about 18 months.