SENSE AREAS AND ASSOCIATION AREAS. 



219 



Conditions of this kind have been referred to lesions in the cortex 

 of the temporal or temporo-parietal region {H and V, Fig. 97), 

 and, as in the case of motor aphasia, the lesion is usually on the 

 left side. Since the cortical centers for hearing and seeing are 

 situated in distinct parts of the brain, we should expect that the 

 mechanism for the association, in one case of visual memories of 

 verbal symbols with certain concepts, and in the other case, of 

 auditory memories, should also be located in separate regions. 

 Inability to understand spoken language, or word-deafness, is, in 

 fact, usually attributed to a lesion involving the superior or middle 

 temporal convolution contiguous to the cortical sense of hearing 

 {H, Fig. 97), while loss of power to understand written or printed 

 language, word-blindness (alexia), is traced to lesions involving the 

 inferior parietal convolution, the gyrus angularis, contiguous to 

 the occipital visual center (F, Fig. 97). These two conditions 

 may occur together, but cases are recorded in which they existed 

 independently. It may be imagined that the incUvidual suffering 

 from word-blindness alone is essentially in the condition of one 

 who attempts to read a foreign language. The power of vision 

 exists, but the verbal symbols have no associations, therefore no 

 meaning. So one who is word-deaf alone may be compared to the 

 normal individual who is spoken to in a foreign tongue. The words 

 are heard, but they 

 have no associations \m 



with past experience. 

 Sensory aphasia may 

 be complete or incom- 

 plete. In the com- 

 plete form there is 

 word-deafness as well 

 as word-blindness, and 

 there may be difficul- 

 ties as well in the pow- 

 er of articulate speech. 

 In the incomplete type 

 these symptoms are 

 exhibited in milder 

 and varying form. 

 One may imagine that 

 inabihty to recognize 

 external objects 

 through the senses 



might be expressed in other ways than by a failure to comprehend 

 the visual or auditory symbols, and some writers, therefore, employ 

 the wider term "agnosia" to indicate an}' defect in the intellectual 



Fig. 97.— Lateral view of a human hemisphere; cor 

 tical area V, damage to which produces "mind-bUnd' 

 ness" (word-blindness); cortical area H, damage to which 

 produces "mind-deafness" (word-deafness); cortical area 

 <S, damage to which causes the loss of articulate speech; 

 cortical area W, damage to which abolishes the power of 

 writing. — (Donaldson.) 



