CHAPTER XII 



Some Aspects of Attention 



The student absorbed in reading "does not hear" an ap- 

 proaching footstep. That is, a stimulus which would under 

 other circumstances produce an effect loses a great part of 

 its influence because of the fact that a,nother stimulus is al- 

 ready upon the field. This other stimulus need not be more 

 intense, that is, need not involve more physical energy, 

 than the one which is ignored. It does not win the victory 

 by a mere swamping of its rival through its superior quan- 

 tity. A man may walk along city streets, his eyes and ears 

 bombarded with brilliant lights and loud sounds, and yet 

 ' the centre of his consciousness may be a train of ideas, 

 representing in their physical accompaniment in his cortex 

 a quantity of energy insignificant compared with that of the 

 external stimuli pouring in upon him. Psychologists com- 

 monly express this fact by sajdng that while the strength of 

 a stimulus conditions the intensity of the mental process 

 accompanying it, the clearness of that process depends 

 upon attention. 



§ 8i. The Interference oj Stimuli 



Attention, then, is the name given to a device, whatever 

 its nature, whereby one stimulus has its effectiveness in- 

 creased over that of another whose physical energy may 

 be greater. What happens in the simpler forms of animal 

 life when two stimuli, requiring different reactions, operate 



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