222 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



s 



inferior parietal convolution, the gyrus angularis, contiguous to 

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

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

 independently. It may be imagined that the individual 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 

 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 

 our ability to recog- 

 nize external objects 

 through the senses 



might be affected in other ways than a failure to comprehend the 

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

 wider term agnosia to indicate any failure in the intellectual recog- 

 nition of external objects. From this point of view word-blindness 

 might be designated as visual agnosia, word-deafness as auditory 

 agnosia, and astereognosis as chiefly a tactile agnosia. The exact 

 localization in the cortex of the areas involved in the auditory and 

 visual associations and perceptions connected with speech has not 

 been established definitely. The question is a complex and difficult 

 one, and those who have had the most experience are perhaps the 

 most cautious in referring word-blindness or word-deafness to the 

 lesion of circumscribed areas of the cortex.* It may be said, 

 however, with some certainty, that the phenomena of sensory 

 aphasia in general are connected with lesions involving the area 



* For a general review see Monakow, "Ergebnisse der Physiologic," 1907, 

 p. 334. 



H 



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

 tical area V, damage to which produces "mind-blind- 

 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 . ) 



