Is language, like food, a basic human need without which a child at a critical period of life can be starved and dam aged? Judging from the drastic experiment of Frederick I in the thirteenth century, it may be. Hoping to discover what language a child would speak if he heard no mother tongue, he told the nurses to keep silent. All the infants died before the first year. But clearly there was more than lack of language here. What was missing was good mothering. Without good mothering, in the first year of life especially, the capacity to survive is seriously affected. Today no such severe lack exists as that ordered by Frederick. Nevertheless, some children are still backward in speaking. Most often the reason for this is that the mother is insensitive to the signals of the infant, whose brain is programmed to learn language rapidly. If these sensitive periods are neglected, the ideal time for acquiring skills passes and they might never be learned so easily again. A bird learns to sing and to fly at the right time, but the process is slew and hard once the critical stage has passed. Experts suggest that speech stages are reached in a fixed sequence and at a constant age, but there are. cases where speech has started late in a child who eventually turns out to be of high IQ. At twelve weeks a baby smiles and makes vowel-like sounds at twelve months he can speak simple words and understand simple commands at eighteen months he has a vocabulary of three to five words. At three he knows about 1,000 words which he can put into sentences, and at four his language differs from that of his parents in style. rather titan grammar. Recent evidence suggests that an infant is born with the capacity to speak. What is special about man's brain, compared with that of the monkey, is the complex system which enables a child to connect the sight and feel of, say, a toy-bear with the sound pattern 'toy bear'. And even more incredible is the young brain's ability to pick out an order in language from the mixture of sound around him, to analyse, to combine and recombine the parts of a language in new ways. But speech has to be induced, and this depends on interaction between the mother and the child, where the mother recognises the signals in the child's babbling(咿哑学语) , grasping and smiling, and responds to them. Insensitivity of the mother to these signals dulls the interaction because the child gets discouraged and sends out only the obvious signals. Sensitivity to the child's non-verbal signals is essential to the growth and development of language. The purpose of Frederick I's experiment was ______.