Page:Principles of Psychology (1890) v1.djvu/70

50 cases of extensive injury about the fronto-temporal regions, as a complication of aphasic disease. Nothnagel suggests that whilst the cuneus is the seat of optical sensations, the other parts of the occipital lobe may be the field of optical memories and ideas, from the loss of which mental blindness should ensue. In fact, all the medical authors speak of mental blindness as if it must consist in the loss of visual images from the memory. It seems to me, however, that this is a psychological misapprehension. A man whose power of visual imagination has decayed (no unusual phenomenon in its lighter grades) is not mentally blind in the least, for he recognizes perfectly all that he sees. On the other hand, he may be mentally blind, with his optical imagination well preserved; as in the interesting case published by Wilbrand in 1887. In the still more interesting case of mental blindness recently published by Lissauer, though the patient made the most ludicrous mistakes, calling for instance a clothes-brush a pair of spectacles, an umbrella a plant with flowers, an apple a portrait of a lady, etc. etc., he seemed, according to the reporter, to have his mental images fairly well preserved. It is in fact the momentary loss of our non-optical images which makes us mentally blind, just as it is that of our non-auditory images which makes us mentally deaf. I am mentally deaf if, hearing a bell, I can't recall how it looks; and mentally blind if, seeing it, I can't recall its sound or its name. As a matter of fact, I should have to be not merely mentally blind, but stone-blind, if all my visual images were lost. For although I am blind to the right half of the field of view if my left occipital region is injured, and to the left half if my right region is injured, such hemianopsia does not deprive me of visual images, experience seeming to show that the unaffected hemisphere is always sufficient for production of these. To abolish them entirely I should have to be deprived of both occipital lobes, and that would deprive me not only of my inward images of sight, but of my