STUDIES OF CEREBRAL FUNCTION IN LEARNING, VII 43 



specific conduction paths or predetermined localization. In 

 general, these are instances where the reaction is determined 

 not by the stimulation of particular nerve endings, but by 

 the excitation of any receptors so long as a constant pattern 

 or ratio among them is maintained; or where the reaction 

 consists not in the activation of a given group of muscles, 

 but in the movement of any effector in a certain relation to 

 the orientation of the body. I need only cite a few examples 

 in order to show the common occurrence of such reactions. 



Martin ( '22) has pointed out that the character of the vaso7 

 motor reflex is determined by * ^ the total impulse-stream gen- 

 erated within the afferent portion of the nerve trunk in a unit 

 of time," irrespective of the particular fibers stimulated. In 

 the field of vision we have such familiar facts as that two 

 objects of unequal brightness or size may produce a constant 

 differential reaction no matter upon what part of the retina 

 their images are projected, or what angle they subtend. Thus 

 I found for the rat (Lashley, '12) that when trained to choose 

 the larger of two visual patterns, he would continue to choose 

 the larger, even when both exceeded in area the larger with 

 which he had been trained. Kohler ('21) has reported a 

 number of similar observations for the chimpanzee. In the 

 cutaneous field Weber's circles form another familiar example 

 of the same principle. On the motor side we see many in- 

 stances of functional equivalence in the employment of diverse 

 muscle groups. I have reported cases of this sort in the 

 transfer of training to limbs paralyzed during training (Lash- 

 ley, '24 a). Marina's experiments ('15) on interchange of 

 eye muscles are of a similar type, and a familiar example is 

 the common ability to trace script of any size with either 

 hand or foot. 



Among the more complex integrations of man this principle 

 of independence of particulate neurons is even more clearly 

 indicated. Head's analysis of the semantic type of aphasia 

 (Head, '20) is the best recent example. The patients lose 

 the ability to distinguish or think certain relationships, 

 although the words which express these relationships are still 

 retained. 



