254 BRAINS OF RATS AND MEN 



Now let us suppose that these primitive associa- 

 tion centers are enlarged so that their interrelation- 

 ships are much closer and there is a broader area of 

 overlap, as illustrated in Figure 52. The associations 

 may be more intimate and more complex. There is a 

 cortical field of overlap, D, which is common to all 

 of them. This field must not be thought of as local- 

 ized in some particular spot as drawn, but as repre- 

 senting a more complex type of interrelationship of 

 primitive associational fields. The field D is not domi- 

 nated by any single sensory system. It is frequently 

 activated in complex situations where Ay B, and C 

 are simultaneously excited, and any features which 

 are common to all of these experiences will affect the 

 field D in each case. 



With the further separation in space of these fields 

 and the interpolation of still other hierarchies of asso- 

 ciational centers between them we reach the stage of 

 organization of the human brain which may be 

 crudely diagramed as in Figure 53. Here the associa- 

 tion center D may be conceived as modified by fea- 

 tures common to a large number of different complex 

 experiences. This, again, is an enduring change in the 

 structural configuration or "set" of the apparatus. 

 Whether a psychological "image" is involved is not 

 a relevant matter from the present point of view. 

 The significant thing is that the associational com- 

 plexes thus fabricated are not bound to particular 

 sensori-motor experiences; they are free from specific 



