328 RESEARCHES ON CORTICAL LOCALISATION AND 



normal functions of the cerebrum, that deprivation of one or both 

 of these senses in congenital or early cases grossly modifies, and in 

 adult cases necessitates an entire readjustment of, the associa- 

 tional processes which constitute the physical basis of the psychic 

 functions. 



In cases of deafness or blindness in which the deprivation is 

 congenital or is acquired in early life, the psychic functions are 

 either very imperfectly evolved, or are performed in an entirely 

 abnormal manner. In early or congenital deafness, the complex 

 mechanism for the reception, storage, and reproduction of lan- 

 guage, or the symbolic representation of the results of sensorial 

 excitation and of psychic association, is incapable of evolution, 

 unless the patients are laboriously educated through other avenues 

 of sensation. It is hardly necessary to add that mutism is a 

 necessary consequence of this disability, though a considerable 

 development of lip-language can often be induced by education. 

 Such patients, in fact, unless educated by special methods, would 

 necessarily possess mental functions relatively little removed from 

 those of the lower primates. On the other hand, the congenital 

 or early blind can obtain a large and important part of their mental 

 content by means of the sense of hearing, just as do ordinary un- 

 educated (i.e. non-reading and non-writing) individuals. That 

 the former can supplement their methods for the acquisition and 

 communication of information by means of the deaf and dumb 

 alphabet, &c., and the latter by means of the tactile motor sense, 

 does not affect the fundamental difference between them, which 

 is based on the fact that a highly important part of the mental 

 content is normally (in the uneducated) acquired by means of the 

 sense of hearing and not by that of sight. 



In such cases deafness is therefore a more serious deprivation 

 than blindness, as, for the evolution of the functional activity of 

 the cerebrum, an entirely new development of associational spheres, 

 to replace those normally employed for auditory and spoken lan- 

 guage, has to be acquired. In the case of congenital or early 

 acquired blindness, on the other hand, the complex sphere of 

 language, with all its psychic components, can be employed in a 

 perfectly normal manner, and almost exactly as it is brought into 

 use in the case of persons who neither read nor write. 



Deprivation of sight or hearing, when occurring later in life, 

 results, in the educated, in relatively less cerebral disability, and 



