This can be readily explained by a review of what occurs in answering a simple question. When you answer a question, the following processes have taken place: 1. You have heard the words of the question. 2. The words have been recognized as known words, and have awakened a corresponding concept. 3. The concept has started a train of thought which has led you to a conclusion. 4. You have formulated your conclusion in words. 5. You have voluntarily set in motion a mechanism consisting of your throat, lips, and tongue, to speak the words. 6. This mechanism has responded to the effort, and has produced the sound of your reply. Now, any one of these processes may be interfered with, in which case you will not answer the question. If you are deaf, you may not hear it. If it is spoken in a language which you do not understand, the words will fail to be recognized, as the sounds will not awaken any memory or concept.
But the words addressed to a child are at first mere sounds to him, and it is only by repeated reiteration of the word in connection with the object or act indicated by it that the child has acquired a knowledge of its meaning. If these acquired bits of knowledge stored up in the memory in childhood are blotted out, the meaning of the word will be lost, and the effect will be the same as if the word had never been learned, or as if it were spoken in an unknown language. This is the condition known as word-deafness, or loss of memory of the sound and meaning of words. It is not an uncommon form of brain-disease, and the symptom and the location of the disease have been connected in so many cases that it is now possible to state that in right-handed persons such a condition is due to disease of the left temporal region, and in left-handed persons to disease in the right temporal region. But such a defect will not only prevent one from recognizing a word when spoken, it will blot out the memory of words, and the power of recalling the words which you desire to use. Therefore you will be unable to answer the question, not only because you do not understand it, but because, if you did understand it—as you might be made to do by appropriate gestures—you could not find words in which to reply. Here, then, another special class of memories, to the exclusion of all others, is blotted out by a localized disease.
But let us follow the process a little further. Suppose you have heard the question, and understood its import, and the concept awakened has set in motion a train of thought which has led you to a proper conclusion, since it is to be supposed that you are neither an idiot nor insane, both of which conditions might interfere with this part of the process; and suppose that your conclusion is formulated in words in your mind. You have still to speak the words before your reply is heard. We will pass by a paralysis of the muscles of the throat or tongue, which would, of course, prevent your speaking, and consider the process of setting in action the voluntary centers which govern speech. You have learned to speak by repeated efforts,
