x THE FORE-BRAIN 629 



of internal speech. " The auditory images," writes Dejerine, " are 

 the first to be formed ; they are the most deeply traced and always 

 control the processes of internal language ; the motor images of 

 articulation next form very rapidly, and unite closely with the 

 auditory images. The union of these two contributes the first 

 and indispensable basis of internal language. At a much later 

 stage the child learns to attach the visual image of words to the 

 auditory and motor images of articulation. . . ." 



In reading the child gradually learns to connect the sounds of 

 the words it already knows with graphic characters, the meaning 

 of which is at first unknown to it. At the same time or shortly 

 after, it learns to write, i.e. to reproduce written or printed 

 characters, which reinforces in its memory the intimate connection 

 between the phonetic images primarily acquired and the newly- 

 learned graphic images which correspond with them. 



Hence in all who are able to read and write, the mechanism of 

 language is more complicated than in the uneducated. It depends 

 on the harmonised activity not only of the auditory and motor 

 word centres, but also of the visual word centre. But, in both 

 educated and uneducated, speech depends essentially upon the 

 co-ordination of word sounds with word motor images; verbal 

 images, even in those whose visual memory is exceptionally 

 developed, only play a subordinate part in speech, in so far as 

 they are intimately connected with phonetic symbols. The 

 scientific proof of this lies in the fact that, while there are 

 numerous clinical cases in which word deafness, from lesions 

 confined to the auditory centre, is associated with loss or disturb- 

 ance of speech, i.e. with aphasia or dysphasia which Wernicke 

 terms sensory to distinguish it from the motor aphasia due to 

 destruction of Broca's centre there are no cases on record of 

 word blindness due to lesions confined to the visual sphere, in 

 which the patient was incapable of speaking. Kussmaul's word 

 blindness is characterised by inability to read and write from 

 dictation, i.e. alexia and agraphia, and is not associated with 

 aphasia or dysphasia if the lesion is limited to the visual sphere. 



This theory of the absolute functional preponderance of the 

 auditory centre in the mechanism of speech is at variance with 

 the view of Charcot, who classed individuals into auditive, visual, 

 and motor, according as they depended chiefly on the auditory 

 word centre, the visual word centre, or the motor word centre in 

 speech. But on Charcot's theory no one can be a visual who is 

 unable to read, and before learning to read it is necessary to 

 be an auditive. We must assume, in order to explain the 

 change into a visual, that the practice of reading intensifies 

 memory of written characters so much that it becomes easier to 

 evoke graphic images than verbal sounds. 



It is more difficult, on this theory, to understand how auditives 



