188 THE HUMAN BODY 



stimulus of the word mother, heard when she is present or when 

 she is indicated in some way. In course of time this particular 

 succession of syllables is included as part of the concept. Several 

 years later the group of written symbols making up the word 

 mother is included in the same concept. Thus language, spoken 

 and written, becomes indissolubly included in our whole mental 

 equipment. 



It is a curious fact that in man the use of language seems to be 

 not optional, but a necessary factor in his mental development. 

 Two lines of evidence favor this view. The first is the common 

 experience of all of us that we are incapable of thought except 

 in terms of words; coupled with the observation that no race of 

 men exists or is known to have existed without some form of lan- 

 guage. The second, and more striking, fact is that certain regions 

 in the association areas of the cerebrum are specially devoted to 

 language associations. Four such regions are known, having 

 been revealed by the physiological effects of their impairment 

 through accident or disease. Two of these areas have to do with 

 spoken, and two with written, language. One of the two areas 

 for each form of language is sensory and the other motor. An 

 interesting thing about these language association areas is that 

 they seem to be confined to one of the cerebral hemispheres; in 

 right-handed people the left hemisphere contains them, and in 

 left-handed people they occur in the right hemisphere. It has 

 been observed, moreover, that the development of right or left- 

 handedness in infants is coincident with their learning to use 

 language. Just what the relationship between the two properties 

 may be is not clear. 



Impairment of a sensory language area results in word-deafness 

 or word-blindness; the sounds are heard, or the words are seen, 

 but they are without meaning because the power to associate 

 language with concepts is affected. When motor language areas 

 are injured the power of expression is lost. The commonest of all 

 these abnormalities is the loss of power to use spoken language, a 

 condition known as motor aphasia. The sufferer from this con- 

 dition knows what he wants to say but is unable to recall the 

 words by which to express his ideas. Embarrassment often gives 

 rise to a momentary inhibition of the motor aphasia region, re- 

 sulting in the same inability to recall the needful words. 



