Why does the professor mention the expressions "mother tongue" and "motherese"?

Do you think we’re born with the skills to learn a language, or do you believe that we develop language skills through social interaction? You’ve read ... at least I hope you’ve read the reading assignment Language and the Mind by Noam Chomsky. So you’re familiar with his argument that we’re born with a device that helps us acquire a language intuitively. He calls it a language acquisition device, or LAD, for short. But psychologists like Jerome Bruner are highly critical of his theory, so today we’re going to examine both sides of the debate.
    In reality, the dispute is connected to the broader debate of nature versus nurture. What do I mean by nature and nurture? Well, let me ask it this way. Is language development controlled by biology, or do we learn from our social environment? Think about these questions and then I’ll ask your opinion again at the end of the lecture, okay? But before examining Chomksy’s theory, I need to clarify one point first. Our discussion today will focus on the acquisition of a child’s first language, or mother tongue, as it is sometimes called. And more about that term later, let’s begin by discussing what Mr. Chomsky has to say about language development.
    Well, his language acquisition device or LAD theory is based on three key assumptions about the process. The first assumption is that children have an innate ability for language development. In other words, they’re born with a set of skills that allows them to intuitively comprehend language. In fact, Chomsky claims that their brains are preprogrammed with what he calls a ’universal grammar.’ And that device allows them to understand the   =~ structure and grammar of a language just by being exposed to it. Let me elaborate on this point. From Chomsky’s perspective, a child’s brain is like a computer. It has already been wired to process and store different kinds of information. Do you see what I mean? Yes? Good! Now this hypothesis leads us to the second assumption: young children can acquire their first language skills independently. That is to say, they don’t have to rely on parents or the social environment to teach them the grammar and structure of their language; they simply use the LAD to figure it out for themselves. The third assumption is that the LAD makes it easy for young children to learn a language.
    However, Chomsky does admit that there’s a small window of opportunity for language development. He thinks, or rather he refers to this short time period as the ’critical period.’ And a recent study of language development in feral children--the children who’ve grown up in extreme isolation from humans--has provided persuasive evidence of the notion of a critical period. For example, when they were found, feral children couldn’t speak at all. In fact, they could only make grunting noises like animals. That’s why they’re called ’feral’. It literally means untamed or wild. In any case, researchers discovered that when these children returned to normal living conditions, they had great difficulty acquiring language unless they were exposed to language before the age of twelve. The argument was that the brains of these abused children hadn’t developed neurologically, so the LAD couldn’t function properly. You can read about the actual feral experiences of a young girl in the book, Genie: A Scientific Tragedy. But getting back to the issue at hand, as you can see from this discussion, Chomksy’s LAD theory leans heavily toward the nature side of the debate. In other words, he and other linguists who support this theory believe that biology predetermines our ability to acquire language. And you’ll notice that the LAD theory focuses on acquiring language, not learning it. But psychologists like Jerome Brunet argue that language development is also a learning process.
    So what’s the difference between acquiring a language and learning it? Well, for one thing, learning a language requires ongoing social interaction, and that assumption forms the basis of Bruner’s theory of the ’language acquisition support system’, or LASS, for short. You see, according to Bruner, some type of LAD may exist, but parents and siblings also play a key role in a child’s language development. How? By involving young children in routine behaviors like saying ’hello’ and ’goodbye’ and daily rituals like meal times and bath times. So it’s probably no surprise that the expression ’mother tongue’ evolved. After all, we all remember listening to the familiar sounds and repetitive phrases our mothers used when we were young. In fact, a researcher named Moerk nicknamed this type of language modeling as ’motherese.’ The second assumption of Bruner’s theory is that language learning is developmental. In other words, parents or siblings create a learning environment that supports the child as he or she builds language skills. So in the beginning, they are quite vocal and the child is rather passive. But as children develop the language skills, they become more active. From this perspective, language learning is more a process of discovery, and children learn to construct new ideas by linking it with previous knowledge and experiences. Therefore, it’s evident that Bruner’s theory strongly supports the notion that nurture is as essential as nature in language development. Now based on what you’ve heard today, where do you stand?
    P And a recent study of language development in feral children--the children who’ve grown up in extreme isolation from humans--has provided persuasive evidence of the notion of a critical period.
    What does the professor imply about the idea of a critical period?