Page:Popular Science Monthly Volume 41.djvu/799

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Destruction of the motor speech center causes a much more extensive interference with the use of language. The motions of the vocal organs being no longer co-ordinated, an inarticulate jargon, or the senseless repetition of a word or phrase, is all that is left of the power to talk. The ability to write is also lost. Reading aloud is, of course, impossible; but it is also a matter of common observation in such cases that the ability to understand print is lost or greatly impaired. This proves that in most persons direct associations between visual words and ideas, if they exist at all, are too weak to be depended upon. So the understanding of spoken words is the only way of using language that is independent of the motor speech center.

But it is destruction of the auditory center that causes the most extensive loss of language. In such a case words (though they may be heard through the right side of the brain) are not understood. This failure to understand is called word-deafness. But there are other serious defects. Although the vocal apparatus is in perfect order, and there are ideas seeking expression, the words uttered are mutilated, deformed, and often totally different from the ones intended, so that intelligible speech is wellnigh impossible. This shows that in talking the most important association impulses do not go directly from the centers for ideas to the motor speech center, but to the auditory center, which, remembering the sounds, by fresh impulses arouses the motor center to utter them. Writing is still more interfered with, because it depends upon the utterance-memory, which goes astray without the sound-memory.

Does destruction of the auditory center also prevent reading? We should expect it to do so, from the way in which reading is learned, and excellent authorities say that it does. There is not enough simple and direct evidence (consisting of the inability to read during life, followed by the discovery of disease limited to the auditory center after death) to prove this, on account of the small number of available cases and the lack of attention to reading in the observation of many of them. Making allowance, however, for the difficulties in the way of gathering direct evidence on this point, the cases published support the view that in most persons the auditory center is essential to the understanding of what is read. But there is other evidence that is quite convincing. We have seen that in reading the visual center can not, as a rule, call up the ideas, else destruction of the motor speech center could not interfere with reading as it does. Nor is the motor speech center directly connected with the centers for ideas; if it were, destruction of the auditory center could not interfere with talking as it does. This leaves only the auditory center, which is abundantly capable, for the sounds of words readily awaken ideas