Development of the Auditory-Verbal Mode of Communication

All biologic systems have the ability to exchange information. This exchange may take place between parts of a system or between the system and its environment. The most basic communication is found within the system, whether the system is that of an amoeba or a human being. Even within the system there is a wide range in the complexity of the messages sent and received. The act of speaking would be one of the more complex intersystem communications, which also display a wide range of complexity, since they are geared to the environmental controlling needs of the species. For example, the chipmunk has a language made up of sounds of varying pitch, rate, time, and intensity. When the female is "in season," she stretches out on a log or branch and forcefully "bangs" her chest against the log, thus emitting a sharp, staccato chirp. Four weeks prior to delivering her young, she informs the male that he must leave the nest. She does this by a sharp, rapid chattering. After the young have arrived, and with the male still banished, the mother sings to the young with a range of trills that sound like the singing of a nightingale. There are sharp sounds for alarm as well as for anger. Appropriate responses to taped sounds can be obtained. This auditory input communication system is similar to that of the human being. An olfactory system or visual input communication systems, such as those seen in the firefly, are used by various species to meet their environmental and procreation needs. Although we know that other animals, such as the porpoise, have complicated communication systems that could be classified as a language, only humans have developed it to such a finite degree. Because these differences in communication ability exist, we are interested in understanding what anatomic, histologic, biochemical, and electrophysical basis there is for human language development. In addition, we should begin to understand where environmental factors enter into the growth pattern. The receptor segment of the neural system involved in communicative activity is critical for the development of language and speech, as is evidenced by the communication difficulties of the deaf. However, the receptor segment is not the decisive factor between human and nonhuman communication systems. Many lower animals have receptor systems as complete as or more complex than those of human beings. The difference, then, lies above the receptor system and involves the decoding, processing, and transferring of information to the appropriate primary sensory area of the cerebral hemisphere. Geschwind (1974) proposes that the evolution of a new association structure in the human brain, which allows for the mixing of information from each of the