178 THE MECHANISM OF LIFE 



changes occurring in the cells of the visual, cortical area might be 

 the sensible object of investigation, while to an optician the 

 crystalline lens of the eye and the muscles of accommodation 

 would be the significant things. 



The Kinds o£ Perception. — The above discussion suggests, 

 then, that a perception is the prolongation into action of some 

 kind, or into virtual, or nascent, or contemplated action, of a 

 sensory process : it is an actual or potential sensori-motor process. 

 Now it may be pure (in Bergson's terminology) when it is un- 

 accompanied by the exercise of memory, or it may be mixed 

 when memory is a factor in the prolongation of the sensation into 

 action. We may act in many ways — reflexly, instinctively, 

 automatically, or habitually, as well as deliberately. In reflex 

 actions the unconsciousness of the outer event, or stimulus, that 

 initiates the acting may be complete, and obviously a man may 

 do very difficult (but learned) things without thinking about what 

 he is doing. May we say that automatic or habitual activity is 

 unconscious, or that there is some kind of mental or psychical 

 accompaniment — subconsciousness it may be called — and that 

 this is pure perception ? There does not seem to be any reason 

 why we should not say so. A man may do some skilled work in 

 a shop, for instance, filled with the continual noise of machinery, 

 and he may think all the time about something quite different. 

 He may not be conscious (in the usual sense of the word) of the 

 noise of the machines, but he will certainly note the cessation 

 of the latter, or even a change in the rhythm. At any moment, 

 also, during the performance of the " automatic " work on which 

 he is engaged, some slight deviation from the usual course of 

 things may compel the attention to it, so that, although he was 

 not conscious of his own activities in the sense that he deliberated 

 them, some kind of psychical processes certainly was their 

 accompaniment. 



When the work is unfamiliar or difficult, or when we act in 

 circumstances that are unusual, then full and vivid consciousness 

 of what we are doing accompanies sensori-motor activity. Thus 

 a skilled musician may play a scale with complete mental detach- 

 ment from the sensations of musical intervals, but he will attend 

 to the latter with the greatest care if he is playing a composition 

 for the first time. Deliberated and unfamiliar action therefore 

 involves perception that must be distinguished from that which ac- 

 companies reflex, instinctive, or habitual sensori-motor activities. 



