Is language, like food, a basic human need? Judging from the result of the violent experiment by a German king, Frederick II's, in the 13th century, it may be. Hoping to discover what language a child would speak if they heard no mother tongue, he told the nurses to keep silent. All the babies died before the first year. But clearly there was more than language deprivation 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 violent deprivation exists as what's ordered by Frederick. Nevertheless, some children are still backward in speaking. Most often the reason for this is that the mother is insensitive (不敏感的) to the signals of the baby, whose brain is programmed to map up language rapidly. There are critical times, it seems, when children learn more readily. If these sensitive periods are neglected (忽视), the ideal time for gaining language skills passes and they might never be learned so easily again. Linguists (语言学家) suggest that speech stages are reached in a fixed sequence (顺序) 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. Recent facts suggest that baby is born with the capacity to speak. What is special about Man's brain, compared with that of the monkeys, is the complex system which enables a child to connect the sight and feel of, say, a teddy-bear (玩具熊) with the sound pattern 'teddy-bear'. But speech has to be stimulated (刺激), and this depends on interaction between the mother and the child, where the mother recognizes the signals in the child's babbling (牙牙学语), grasping, crying and smiling, and responds to them. Insensitivity (不敏感) of the mother to these signals dulls (使迟钝) 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. Frederick II's experiment was violent because ______.