evidence which Kepes provides in The Language of Vision  is very 
much needed. In fact, the two-dimensional is the opposite of 
inert, as Georg von Békésy discovered in the study of hearing. 
For dynamic simultaneity is the effect of the two-dimensional, 
and inert homogeneity the effect of three-dimensionality. Kepes 
explains (p. 96):

     Early medieval painters often repeated the main figure 
     many times in the same picture. Their purpose was to 
     represent all possible relationships that affected him, and 
     they recognized this could be done only by a 
     simultaneous description of various actions. This 
     connectedness in meaning, rather than the mechanical 
     logic of geometrical optics, is the essential task of 
     representation.