160 Instinct and Intelligence 



produces a visual sensation and impression; 

 the salutation is the result of its action on motor 

 centres plus an intercurrent stream of released 

 psychical nervous force. (See Fig. 14.) It is 

 evident the sensation produced by the external 

 stimulus is not alone a sufficient cause for the 

 salutation, because if in place of a friend we 

 had met someone we disliked we should not 

 have saluted him. It is plain that a latent 

 image of our friend had been re-excited when 

 we met him; a psychical image stored in our 

 brain had been brought into action, and the 

 contents of the idea thus produced has assumed 

 an intelligent form in the association areas of 

 our cerebral cortex, and, guided by the result 

 of experience, is followed by the contraction 

 of definite groups of muscles. 1 



An idea, therefore, means the thing or 

 movement which has produced the sensation, 

 and the contents of the idea consist of energy 

 derived from the characteristic features pos- 

 sessed by the object or movement which has 

 caused the sensation. Latent impressions thus 



1 Introduction to the Study of Physiological Psychology, by 

 Prof. Theodor Ziehen, pp. 20, 285. 



