IMAGINATION. 73 



ideational and sensorial centres are locally distinct appears 

 to be supported by no facts drawn from the observation of 

 human beings. After occipital destruction, the hemianop- 

 sia which results in man is sensorial blindness, not mere 

 loss of optical ideas. Were there centres for crude optical 

 sensation below the cortex, the patients in these cases 

 would still feel light and darkness. Since they do not pre- 

 serve even this impression on the lost half of the field, we 

 must suppose that there are no centres for vision of any 

 sort whatever below the cortex, and that the corpora quadri- 

 gemina and other lower optical ganglia are organs for reflex 

 movement of eye-muscles and not for conscious sight. 

 Moreover there are no facts which oblige us to think that, 

 within the occipital cortex, one part is connected with sen- 

 sation and another with mere ideation or imagination. The 

 pathological cases assumed to prove this are all better ex- 

 plained by disturbances of conduction between the optical 

 and other centres (see p. 50). In bad cases of hemianopsia 

 the patient's images depart from him together with his sen- 

 sibility to light. They depart so completely that he does not 

 even know what is the matter with him. To perceive that 

 one is blind to the right half of the field of view one must 

 have an idea of that part of the field's possible existence. 

 But the defect in these patients has to be revealed to them 

 by the doctor, they themselves only knowing that there is 

 * something wrong ' with their eyes. What you have no idea 

 of you cannot miss ; and their not definitely missing this 

 great region out of their sight seems due to the fact that their 

 very idea and memory of it is lost along with the sensation. 

 A man blind of his eyes merely, sees darkness. A man blind 

 of his visual brain-centres can no more see darkness out of 

 the parts of his retina which are connected with the brain- 

 lesion than he can see it out of the skin of his back. He 

 cannot see at all in that part of the field ; and he cannot 

 think of the light which he ought to be feeling tliere, for the 

 very notion of the existence of that particular ' there ' is 

 cut out of his mind.* 



* See an important article by Binet io the Revue Philosopbique, xxvi. 

 481 (1888) ; also Diifour, in Revne Med. de la Suisse Romaude, 1889, No, 

 8. cited in the Neuroloo-ischcs Coiitralblatt, 1890, p. 48. 



