610 PHYSIOLOGY CHAP. 



affected with word blindness sees the letters and words, and can 

 even copy them ; but he is incapable of reading them, combining 

 them together, or understanding them. In cases in which the 

 visual field is examined by the perimeter, it is found that word 

 blindness is sometimes independent . of any change in the field, 

 and at other times is associated with a concentric contraction 

 of the field, or with hemianopsia. 



Word blindness leads us to assume that, there is in the brain a 

 region for the perception of the graphic signs of speech and the 

 memory of them, which are necessary to the understanding of 

 their significance. But in which part of the brain is this special 

 centre for the visual perception of words located ? The fact that 

 word blindness can exist independently of any alteration in the 

 visual field, shows that the centre for verbal visual perceptions 

 lies beyond the sphere of vision properly so called. But the fact 

 that it may be associated with hemianopsia, or a concentric 

 restriction of the visual field, leads us to conclude that this centre 

 must lie contiguous to the centre of vision proper. There are 

 cases of word blindness on record in which the post-mortem 

 examination showed a lesion of the second left parietal convolu- 

 tion; this includes the angular gyrus, which in our opinion 

 represents the anterior portion of the visual area of man. 



XII. Less experimental work has been done on the localisa- 

 tion of the auditory area, no doubt because the sense of hearing is 

 less easy to examine in animals than vision. 



Ferrier (1875) was the first to point out that the centre of 

 auditory sensation is represented in the ape by the cortex of the 

 first temporal convolution, and by the corresponding region of the 

 third external convolution in dogs (cf. points 14, 15, Figs. 275, 

 276). In fact, this part of the temporal lobe alone responds to 

 electrical stimulation by very definite reactions : by movements of 

 the ear muscles on the opposite side, while the eyes open widely, the 

 pupils dilate, and the eyes and head are suddenly turned to the 

 opposite side, as if the animal were surprised by some unexpected 

 sound on that side. To confirm this interpretation Ferrier 

 cauterised the temporal convolution. If the lesion was confined 

 to one side, the monkey continued to react to auditory sensations, 

 by moving its head if any one called it, but if the ear of the 

 operated side were plugged with wool, it seemed no longer aware 

 of sounds. After bilateral lesions of the upper temporal con- 

 volution the monkey no longer reacted to certain auditory stimuli 

 which under normal conditions excite attention. The deafness 

 assumed by Ferrier is obviously an erroneous interpretation of the 

 symptom. All subsequent investigation has shown unmistakably 

 that the auditory centre is not confined to the area indicated by 

 Ferrier, but its focal area is probably represented by that centre. 



H. Munk (1878-81) stated that when area B of the temporal 



