COMMON SENSE (aND SCIENCE) 9 



Electrophysiology of the central nervous system indicates . . . 

 that the brain is continuously active, in all its parts, and an afferent 

 excitation must be superimposed on an already existent excitation. 



Thus any and all "automatic" organizational activity will merge into 

 further activity, at the fringe of consciousness, in which learning is 

 involved. 



We "learn" to use our senses— e.g., to keep our eyes in focus, to 

 run them along the contours that define an object. Beyond this literal 

 aspect of learning lies an equally important figurative aspect. In in- 

 fancy we learn not only control of the musculature of the eye but 

 also the forms or patterns of "things" and "situations." To conceive 

 this learning is difficult: it all takes place without conscious volition 

 in a period lost in the haze of early childhood. Ordinarily we become 

 aware of the function of the learned forms only in cases involving 

 new patterns learned in maturity and, more strikingly, in cases (of 

 illusion) in which the taken-for-granted forms prove insufficient or 

 actively misleading. But our "knowing" always affects our "seeing." 

 We learn not only hoiv to see but also what to see; often we simply 

 don't see anything for which our learning has not, in some sense, pre- 

 pared us. The seaman notes small details in the condition of sea and 

 sky that pass unnoticed by the landlubber. Usually the seaman's 

 vision is no sharper, but he observes, as significant, points the land- 

 lubber could but does not see, because to him they are inconse- 

 quential features of the visual field— taken in by the eye but not by 

 the brain. The seaman possesses a "mental image" (Gestalt, neural 

 pattern, or what you will ) in or against which certain details stand 

 out in bold relief. Consider bird-watching. The old hand's claim to 

 make a valid identification on the basis of a fleeting glimpse aston- 

 ishes the novice, but what stuns him is that the old hand seems to see 

 so much more. Of course the old hand sees more: he is not passively 

 seeing but actively looking, looking for significant similarities and 

 differences in the bird before his eyes and one or several images car- 

 ried in his "mind's eye." 



The ancients supposed that seeing involved a projection of rays 

 from observer to object seen. Today we conceive seeing as the trans- 

 mission or reflection of rays from object to eye. False as a physical 

 mechanism, the ancient view nonetheless symbolizes an important 

 truth. Seeing involves a merging of something from the object, "out- 

 side," with something contributed by the viewer, from inside. Brain 



