Listen to part of the lecture in a psychology class.

Professor: We're gonna talk today about a couple of experiments related to learning in infants or babies. Those areas are memory and imitation. Memory and imitation. So you read chapter eight of your textbook, right? It deals with these topics. So I'll have some questions for you. Two studies I want to look at, they've been controversial. That's because they show these things happening before earlier than we used to think.

So first, let's look at an experiment by Carolyn Rovee-Collier. She published an important study that looked at the cognitive abilities of infants. What can you tell me about Rovee Collier’s study?

Male student: She had a baby in a crib (婴儿床，剽窃), and above the baby, there was a toy, a mobile hanging above the crib. And a ribbon（丝带） was tied from the mobile to the leg. So when the baby kicked, the mobile moved.

Professor: Uh…there's a picture in your book.

Male student: So. Yeah. When they returned the baby to the crib weeks later, the baby kicked its leg when it saw the mobile again, its foot wasn't tied to the mobile, but it was still kicking.

Female Student: But Rovee-Collier also went on to say that was proof, evidence that the baby had remembered something, had a memory. The baby had kept that Information that kicking moves the mobile.

Professor: Good. In those experiments, he typically had a 2.5 month old infant. The baby kicks and gets to see the mobile move. So Rovee-Collier concludes that very young infants can remember, retain information like this. So what did critics say about her conclusion? Sara?

Female Student: That it wasn't true. It wasn't real memory.

Professor: Yes. Good. Here's a distinction one critic raised. This is, a researcher, a leading expert in the field, said that the baby kicking after seeing the mobile is an example of implicit memory（隐式记忆）. Implicit memory refers to remembering information, but not being consciously aware of remembering. For example, many motor skills. Remember, those are skills involving movement of the body that kind of thing. Motor skills are forms of implicit memory, like knowing how to ride a bike. So the baby's kicking has to do with implicit memory, because it involves perception and motor skills. The baby kicks and sees the mobile move. Now, explicit memory（外显记忆）, on the other hand, is, well, you tell me what is it?

Female Student: And that's where you can remember something, remember it consciously, you can remember what happened in the past. That's what's usually meant by the word memory, I mean real memory.

Professor: Okay. Most researchers, they would say uh that ability in the area of explicit memory, doesn't happen until a baby is 6 months to a year old, later than what Rovee-Collier said. So that distinction between two different kinds of memory is important in this debate about memory in infants.

And then there's another thing, another cognitive ability they test besides memory. They tested imitation. That's like when a parent smiles and the baby smiles back, or the parent opens their mouth, then the baby opens its mouth. Here the researcher was Andrew Meltzoff. Meltzoff has done studies with babies in the first few days after they were born. What did he find in his experiments?

Male student: Yeah. He would do things like stick out his tongue and open his mouth and baby was able to imitate it. He thought imitation was biologically based, I think, and um. That's because.. Wasn't it because they were imitating something right after they've seen it for the first time?

Professor: Yes, that's right. Meltzoff showed that in the first 3 days of life, the babies could do a full imitative response. And he thinks it's biologically based, because this occurs before they have the opportunity to observe other people engage in these behaviors. Like sticking out the tongue.

Here again, other experts disagree. They say that this was just an automatic response of the baby's part, not true imitation. And true imitation doesn't happen until much later they think. Meltzoff also tested something called deferred imitation. It's an imitation that occurs after a time delay of hours or even days. Meltzoff show that 9 month old infants could imitate actions that they'd seen performed 24 hours earlier, like pushing a button on a box that produced a beeping sound. But some experts, like the Piaget believed that deferred imitation doesn't occur until about 18 months of age. So you can see that when some of these things begin, remembering, imitation isn't entirely certain yet. But still, I do think psychologists will eventually find agreement on these issues.