CHAPTER LI 



SENSATION 



BEFORE passing to the study of the various special senses, there are 

 a number of general considerations in connection with the subject of 

 sensation that demand our attention. 



The psychologist divides the mental phenomena, which the 

 physiologist localises in the brain, into three main categories : 



1. Intellectual : perceiving, remembering, reasoning, etc. 



2. Emotional : joy, love, hate, anger, etc. 



3. Volitional : purposing, deliberating, doing. 



These are all closely connected together, and are all present in 

 each healthy brain ; but according as one or other may predominate, 

 we speak of intellectual, emotional, or strong-willed individuals. 

 The connection is especially close between intellect and will, which 

 represent as it were the two sides of what we may call a conscious 

 reflex action; the intellect gives the reason or stimulus for the 

 exercise of the volitional power. The emotions are more complex, 

 and we shall not discuss them ; they are elaborate mental processes, 

 in which sensations predominate. 



The intellectual faculties are derived from the senses ; sensations 

 form the materials for intellect ; in other words, we know and learn 

 from what we see, feel, hear, taste, and smell. People born blind or 

 deaf thus labour under the great disadvantage of having one or the 

 other channel of knowledge closed ; they can, however, make up for 

 this in some measure by an education, and consequent increased 

 sensitiveness of the channels that remain open. 



The simplest mental operation is a sensation that is, the 

 conscious reception of an impression from the external world. For 

 this the following things are necessary : 



1. A stimulus. 



2. A nerve-ending to receive it. 



3. A path to the brain. 



4. A part of the brain to receive the impulse. 



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