214 HUMAN PHYSIOLOGY. 



Sensor Centers. These are the centers in which the afferent im- 

 pulses are translated into conscious sensations. The most im- 

 portant are : 



The visual center, located in the occipital lobe and especially in 

 the cuneus. Unilateral destruction of this area results in hemianopsia, 

 or blindness of the corresponding halves of the two retinae. Destruc- 

 tion of both occipital lobes in man results in total blindness. Stimu- 

 lation or irritation of the visual center causes photopsia, or hallucina- 

 tions of sight, in corresponding halves of the retinae. There have 

 been instances of injury of these parts when sensations of color 

 were abolished with preservation of those of space and light, thus 

 showing a special localization of the color center. Recent experi- 

 ments show that the centers of the two hemispheres are united, as 

 ocular fatigue of an unused eye was found to be proportional to the 

 fatigue of the exercised one. 



The auditory centers are located in the temporosphenoid lobes. 

 Word-deafness is associated with softening of these parts, and their 

 complete removal results in deafness. 



The gustatory and olfactory centers are located in the uncinate 

 gyrus, on the inner side of the temporosphenoid lobes. There does 

 not seem to be any differentiation, up to this time, of these two 

 centers. 



The center for tactile impressions was located by Ferrier in the 

 hippocampal region. Horsley and Schafer found that destructive 

 lesions of the gyrus fornicatus were followed by hemianesthesia of 

 the opposite side of the body, which was more or less marked and 

 persistent. These observers conclude that the limbic lobe " is 

 largely, if not exclusively, concerned in the appreciation of sensa- 

 tions, painful and tactile." 



The superior and middle frontal convolutions appear to be the 

 seats of the reason, intelligence, and will. Destruction of these parts 

 is followed by proportional hebetude, without any impairment of 

 sensation or motion. 



