THE AUDITORY, GUSTATORY, AND OLFACTORY CENTRES. 713 



IV. The sensory regions are those areas in which conscious perceptions of 

 the sensory impressions are accomplished. Perhaps they are the substratum of 

 sensory perceptions, and of the memory of sensory impressions. 



1. The visual centre, according to Munk, includes the occipital lobes (fig. 484, 

 1 , 2 , 3 ), while, according to Ferrier, it also includes the angular gyrus. Huguenin 

 observed, in a case of long-standing blindness, consecutive disappearance of the 

 occipital convolutions on both sides of the parieto-occipital fissure, while Giovanardi, 

 in a case of congenital absence of the eyes, observed atrophy of the occipital lobes, 

 which were separated by a deep furrow from the rest of the brain. Stimulation of 

 the centre gives rise to the phenomena of light and colour. Injury causes disturb- 

 ance of vision, especially hemiopia of the same side ( 344 Westphal). When 

 one centre is the seat of irritation, there is photopsia of the same halves of both 

 eyes (Charcot). Stimulation of both centres causes the occurrence of the phenomena 

 of light or colour, or visual hallucinations in the entire field of vision. Cases of 

 injury to the brain, where the sensations of light and space are quite intact, and 

 where the colour sense alone is abolished, seem to indicate that the colour sense 

 centre must be specially localised in the visual centre (Samelsohn). After injury of 

 certain parts, especially of the lower parietal lobe, "psychical blindness " may occur. 

 A special form of this condition is known as " word-blindness " or alexia 

 (Coecitas verbalis), which consists in this that the patient is no longer able to 

 recognise ordinary written or printed characters (p. 711). 



Charcot records an interesting case of psj^chical blindness. After a violent paroxysm of rage, 

 an intelligent man suddenly lost the memory of visual impressions ; all objects (persons, streets, 

 houses) which were well known to him appeared to be quite strange, so that he did not even 

 recognise himself in a mirror. Visual perceptions were entirely absent from his dreams. 



Clinical observations on hemianopia ( 344) show that the field of vision of each eye is 

 divided into a larger outer and a smaller inner portion, separated from each other by a vertical 

 line passing through the macula lutea. Each right or left half of both visual fields is related 

 to one hemisphere ; both left halves are projected upon the left occipital lobes, and both right 

 upon the right occipital lobes (fig. 487). Thus, in binocular vision, every picture (when not 

 too small) must be seen in two halves ; the left half by the left, the right half by the right 

 hemisphere ( Wernicke). 



As a result of pathological stimulation of the visual centre, especially in the insane, visual 

 spectres may be produced. Pick observed a case where the hallucinations were confiued to the 

 right eye. Celebrated examples of ocular spectra occurred in Cardanus, Swedenborg, Nicolai, 

 J. Kerner, and Holderlin. 



After degeneration of the cortical centre, the fibres which connect the occipital lobes with the 

 external geniculate body, the anterior corpora quadrigemina, pulvinar, these structures them- 

 selves, and the origin of the optic tract undergo degeneration {v. Monakow). 



2. The auditory centre lies on both sides (crossed) in the temporo-sphenoidai 

 lobes [according to Ferrier in the superior temporal convolution] ; when it is com- 

 pletely removed, deafness results, while partial (left side) injury causes psychical 

 deafness. [See p. 704 for contradictory results.] Amongst the phenomena caused 

 by partial injury is surditas verbalis (word-deafness), which may occur alone or in 

 conjunction with coecitas verbalis. Wernicke found in all cases of word-deafness 

 softening of the first left temporo-sphenoidai convolution (p. 704). In left-handed 

 persons, the centre lies perhaps in the right temporo-sphenoidai lobes ( Westphal). 



Clinical. We may refer word-blindness and word-deafness to the aphataxic group of diseases, 

 in so far as they resemble the amnesic form. A person word-blind or word-deaf resembles one 

 who in early youth has learned a foreign tongue, which he has completely forgotten at a later 

 period. He hears or reads the words and written characters ; he can even repeat or write the 

 words, but he has completely lost the significance of the signs. While an amnesic aphasic 

 person has only lost the key to open his vocal treasure, in a person who is word-blind or word- 

 deaf even this is gone. From a case of recovery it is known that to the patient the words sound 

 like a confused noise. Huguenin found atrophy of the temporo-sphenoidai lobes after long- 

 continued deafness. 



3. Gustatory and Olfactory Centre. In the uncinate gyrus on the inner side 

 of the temporo-sphenoidai lobe (especially on the inner side of that marked U in 



