Speech development
All animals communicate in some way, but only humans speak. Speech is but one of the forms by which men communicate, and it is different from language, that may be not spoken as in the case of body language. When speaking, men produce sounds (words and sentences) that encode meaning. It requires little thought, being a completely automatic process. Once the person has codified his thoughts into words, the speaking process begins, its various stages starting each one a little later than the previous one.
The brain areas involved in the speech mechanism are located in the left hemisphere for the most part of right-handed people, although left-handed and ambidextrous people may equally well use the right hemisphere for this function. Wernicke's area, which receives audible and visible signals, is in charge of speech recognition and expression. The control of vocalization is located at Broca's area. From the brain several nerves carry signals to specific muscles in the larynx and the mouth, once the central coordination process has taken place.
While the result of the operation of the speech mechanism is a continuous acoustic signal, to be understood it must be perceived as a sequence of sounds. The smallest, meaningful, perceived sound in speech is called 'phoneme.' Words that sound different are constituted by different phonemes. When perceiving a speech signal, a person tries to categorize it into segments and to arrange segments into a hierarchy. Phonemes are compounded to give syllables, and syllables stringed together to form words.
Some syllables may be more stressed than others. This is important in recognition as each word has its particular stress pattern. Words, in turn, have their own stress variations that have an important influence on the interpretation of the utterance. Stress is produced by various devices, such as changes in vocal intensity and pitch. Syllables can be lengthened to stress them. Variations in pitch during a sentence's production produce an 'intonation contour' that signals different meanings. The most familiar contour is the rising pitch at the end of questions.
Speech development, i.e., how human beings acquire the use of speech, is a very complex process and has attracted the interest of thinkers since many centuries ago. It is deceiving because it normally goes smoothly and without much attention, however the questions it poses are very hard to answer. The reason of its passing so unnoticed is that evolution has made it a nearly fail-proof process because of its importance to survival.
A baby of two weeks of age can already tell the human voice from other sounds, and when he is of a month can distinguish segments such as "pa" and "ba." It is generally believed by parents that by the age of one and a half year, when the child utters his first words, he is able to comprehend speech. This is not universally supported by research. Another common belief, that precocity in speaking is a predictor of adult intelligence, does not hold either.
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