786 THE SENSORIAL CORTICAL CENTERS. 



of Landois, psyckosensorial centers. Total destruction of such a center 

 abolishes conscious perception on the part of the organ of special sense 

 in question. On partial destruction of such a center, the mechanism 

 of sense-activity may remain intact, but the mental connection is want- 

 ing. A dog with such injured centers, it is true, sees, hears, and smells, 

 but he no longer recognizes what he sees, hears, and smells. The centers 

 are to a certain degree the repositories for experiences gained through 

 the special senses. Irritation of these areas may give rise to movements 

 such as occur when sudden, intense sense-impressions are produced; 

 these movements are, therefore, reflex. In this group belongs also dila- 

 tation of the pupil and of the palpebral fissure, as well as lateral move- 

 ment of the eyeball. It appears, however, that, in addition, each cen- 

 ter possesses its own motor apparatus, by means of which the movements 

 of the related organ of special sense are executed. 



FIG. 259. The Psycho-optic and Psycho-auditory Centers and the Sensory Sphere of the Dog's Brain 



(after H. Munk). 



The psycho-optic center or the visual sphere comprises, according to Munk, 

 the portion of the occipital lobe in the dog marked " Seeing " (Fig. 259). If this 

 region is completely destroyed, the dog becomes permanently almost totally 

 blind in the opposite eye cortical blindness. If, however, only the more cen- 

 trally situated portion (with circular outline) is destroyed, there will be loss 

 of conscious sensation of vision on the opposite side, and this may be desig- 

 nated mind-blindness or optic amnesia. Tt is a remarkable fact that destruction 

 of this area on one side is soon followed by compensation. It appears that other 

 adjacent cortical areas of the visual sphere are capable of assuming the function of 

 the injured portion. Under these circumstances it will be found that the animals 

 with the affected eye must to a certain extent again learn to see as in earliest 

 youth. Destruction of the entire center on each side causes total blindness on 

 both sides, while that of the central (shaded) portions alone in the dog causes 

 mind-blindness on both sides. 



A psycho-optic center is observed first in birds, the optic nerve terminating 

 m the midbrain in the lower vertebrates. In accordance with the extent of the 

 decussation of the optic nerves in different animals the psycho-optic center is 

 related to the retinas. 



Munk determined in the dog, further, that both retinas are connected with 

 each psycho-optic cortical center, and in such a manner that each retina receives 



