A child can learn a language only if he is exposed to the words of this language during a limited critical period. Similar conditions of exposure or non-exposure after this critical period will have little effect on the child’s language acquisition. Furthermore, the phonetic structure of the language that the child hears during the first few years of life will permanently affect the way he/she perceives and produces speech.
Scientific evidence tells us that the influences from the environment are especially important early in life, during a restricted developmental period, during which the neural pathways are highly sensitive to the effects of external stimuli, and a veritable remodelling of the brain is possible. However, the degrees of environment influences vary greatly depending on our age. For example, the environmental stimuli have a far greater impact on the nervous system of a newborn than on that of an adult. That’s why babies take in written (visual) and spoken (auditory) words at a rate that no adult could come close to matching. In fact, babies can learn anything that can be taught to them in a factual and joyous way. As studied by Dr. Glenn Doman, it is easier to teach a five-year-old to read than to a six-year-old, easier at four than at five, easier at three than at four, easier at two than at three, much easier at one than at two, and easiest of all for the baby below one.
Neuroplasticity – the ability of the neurons to modify their connections to make certain neural circuits more efficient is the fundamental characteristic of the human brain that makes learning and memory possible. According to neuroscience, the continuous decline in our ability to remodel our neural connections is probably the basis of the critical periods for learning, though many aspects of the brain remain plastic even into adulthood. More importantly, the malleability of our brain’s synapses constitutes the neurobiological foundation for our ability to learn, and the decline in this malleability with age explains why the early learning is crucial in the earlier stages of life.