LEARNING TO SPEAK.
No human being remembers how he learned his mother-tongue in early youth, and the whole human race has forgotten the origin of its articulate speech as well as of its gestures; but every individual passes perceptibly through the stage of learning to speak, so that a patient observer recognizes much as conformable to law.
The acquisition of speech belongs to those physiological problems which can not be solved by the most important means possessed by physiology, vivisection. And the speechless condition in which every human being is born can not be regarded as a disease that may be healed by instruction, as is the case with certain forms of acquired aphasia. A set of other accomplishments, such as swimming, riding, fencing, piano-playing, the acquirement of which is physiological, are learned like articulate speech, and nobody calls the person that can not swim an anomaly on that account. The inability to appropriate to one's self these and other co-ordinated muscular movements, this alone is abnormal. But we can not tell in advance in the case of any new-born child whether he will learn to speak or not, just as in the case of one who has suffered an obstruction of speech or has entirely lost speech, it is not certain whether he will ever recover it.
In this the normal child that does not yet speak perfectly, resembles the diseased adult who, for any cause, no longer has command of language. And to compare these two with each other is the more important, as at present no other empirical way is open to us for investigating the nature of the process of learning to speak; but this way conducts us, fortunately, through pathology, to solid, important physiological conclusions.
[1. Disturbances of Speech in Adults.]
The command of language comprises, on the one hand, the understanding of what is spoken; on the other hand, the utterance of what is thought. It is at the height of its performance in free, intelligible, connected speech. Everything that disturbs the understanding of words heard must be designated disturbance of speech equally with everything that disturbs the production of words and sentences.
By means of excellent investigations made by many persons, especially by Broca, Wernicke, Kussmaul, it has become possible to make a topical division of most of the observed disturbances of speech of both kinds. In the first class, which comprises the impressive processes, we have to consider every functional disturbance of the peripheral ear, of the auditory nerve and of the central ends of the auditory nerve; in the second class, viz., the expressive processes, we consider every functional disturbance of the apparatus required for articulation, including the nerves belonging to this in their whole extent, in particular the hypoglossus, as motor nerve of the tongue, and certain parts of the cerebral hemispheres from which the nerves of speech are excited and to which the sense-impressions from without are so conducted by connecting fibers that they themselves or their memory-images can call forth expressive, i. e., motor processes. The diagram, Fig. 1, illustrates the matter.
Fig. 1.
The peripheral ear o, with the terminations of the auditory nerve, is by means of sensory fibers a, that are connected with the auditory nerve, in connection with the storehouse of sound-impressions, K. This is connected by means of the intercentral paths v with the motor speech-center M. From it go out special fibers of communication, h, to the motor nerves of speech which terminate in the external instruments of articulation, z.