CHAPTER XIII 

 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 another 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 gnored. It does not win the victory 

 by a mere swamping of its rival through its superior quantity. 

 A man may walk along city streets, his eyes and ears bom- 

 barded with brilliant lights and loud sounds, and yet the 

 centre of his consciousness may be a train of ideas, repre- 

 senting 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 saying that while the strength of 

 a stimulus conditions the intensity of the mental process ac- 

 companying it, the clearness of that process depends upon 

 attention. 



96. The Interference of 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 simultaneously? We may quote from Jennings the 



