x THE FORE-BRAIN 609 



Against Henschen's localisation, Monakow brought out the fact 

 that in cases of blindness acquired in infancy, with total degenera- 

 tion of the optic nerves, the cortex of the calcarine fissures does 

 not suffer a greater reduction of volume than the cortex of the 

 external convolutions of the occipital lobe. 



Henschen tried to adapt Munk's theory of retinal projection 

 to the visual sphere. According to Henschen the upper quadrants 

 of the retina are represented in the upper border of the calcarine 

 fissure, the lower quadrants in its lower border. Against this 

 view it may be observed with Monakow that in cases of bilateral 

 hemianopsia of cortical origin in man, there is persistence of 

 central or macular vision even when the calcarine region as well 

 as the introflexed cortex in this fissure are affected. This proves 

 that the focus of distinct central vision cannot be limited to 

 a restricted cortical area. Both Sachs and Bernheimer reject the 

 theory of Munk and Henschen that the macula lutea is repre- 

 sented in a circumscribed area of the visual sphere. 



Lesions of the occipital lobes not only produce hemianopsia, 

 but may also be associated with special psychical disorders, 

 characterised by alterations of the visual representations. These 

 disturbances differ in form and degree, from a slight difficulty in 

 rightly interpreting visual images to genuine psychical blindness 

 similar to that observed in monkeys after removal of both occipital 

 lobes, which when the symptoms of blindness and amblyopia have 

 passed, recover vision completely, but continue incapable of 

 recognising the objects which they see. The symptoms which 

 characterise psychical blindness in monkeys may be illustrated by 

 the following experiment : if some grapes or bits of dried fig are 

 scattered on the table with lumps of cork of the same size, the 

 ape which has lost both its visual spheres is incapable of dis- 

 tinguishing them by vision ; it picks them up indifferently, one 

 after the other, but retains the grapes, while it rejects the cork 

 directly it is taken into the mouth. 



The same obtains in typical cases ot psychical blindness in 

 man. Although the individual sees to a certain extent, and 

 stereognostic vision is preserved, he is not capable of identifying 

 the objects he sees, even when familiar in everyday life. Psychical 

 blindness is a very complex disturbance, which depends on various 

 components. It is not exclusively dependent on the partial lesion 

 of the visual sphere, but may occur when some of the association 

 paths by which the visual cortex is brought into relation with 

 other cortical regions are interrupted. 



A special form of incomplete psychical blindness seen in man 

 is the so-called word blindness which was first reported by 

 Kussmaul (1877). It is characterised by inability to comprehend 

 the significance of printed or written words, although the power of 

 expressing ideas in speech or writing is retained. The individual 



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