3o6 The Animal Mind 



have a practical use ; the dogs rolling over and over each 

 other are nearly as absorbed in each other's movements 

 as if they were in deadly combat. 



That relief from practical necessity which will serve the 

 purpose we are considering is to be found not in play, but 

 in infancy. If a creature spends the period during which 

 its nervous system is undergoing most rapid development 

 in a state of complete shelter and protection from external 

 danger, with all its vital needs supplied, then the nervous 

 energy which under other conditions would be expended 

 in the processes underlying attention to external stimuli 

 is free to be so devoted that attention will be directed 

 toward the creature's inner experiences. The human 

 baby, while he may be interested in lights and sounds, in 

 external impressions, does not need to be alert and watchful 

 lest he miss his dinner or be dined on himself ; his atten- 

 tion is free to be expended on his own movement experiences 

 as well as on anything else. That young children do go 

 through a stage of intense interest in the sensations result- 

 ing from their own movements is a fact made clear from 

 many observations. The curious period of "self -imita- 

 tion" in the child when it repeats for an indefinite period 

 the same movement or sound, over and over again (14), 

 is very likely a period of vivid attention to movement sen- 

 sations. 



That the prolonged period of human infancy is of advan- 

 tage to the intellectual life of man because it means .plas- 

 ticity, the absen£e of fixed instincts that would take the 

 place of acquisition by individual experience, was first 

 pointed out by Fiske (227). But quite as important is 

 the fact that in prolonged infancy we have the opportunity 

 for acquiring the habit of that attention to our own move- 

 ments which is the prerequisite for anticipated movements. 



