PHWSIOLOGICAL INTERPRETATIONS 89 



this interplay is in patterns quite different from those of the stable, 

 locally differentiated centers and tracts. It is more labile, and the 

 patterns of performance are not stereotyped. Nevertheless, these 

 fields are not structurally identical, and each one has distinctive 

 physiological properties correlated with these histological differences. 



Each field of neuropil differs from others in internal texture, in the 

 source of afferent fibers, and in the distribution of efferents. A local 

 field may be sharply segregated, as in the ventrolateral neuropil of 

 the peduncle and the ventral interpeduncular neuropil, or it may 

 interpenetrate tissue of the specific localized systems, as in the corpus 

 striatum and optic tectum. The pattern of this localization is differ- 

 ent structurally and physiologically from that of the specific systems 

 of cells and fibers, and the two patterns of localization may both be 

 present in the same block of tissue in primitive brains. In higher 

 vertebrates these local differences are accentuated, the segregation 

 of the synthetic apparatus is carried further, and its tissue is locally 

 differentiated in a radically different way from that of the analytic 

 apparatus, as is best exhibited in the associational tissue of the hu- 

 man cerebral cortex. 



The "field" concept has been much exploited of late in several con- 

 texts, and it is fruitful, as applied, for instance, by Weiss ('39, p. 289) 

 in general embryology and by Agar ('43, chap, ii) in general biology. 

 As applied psychologically in Gestalt it has been difficult for the 

 structurally minded neurologist to transfer the dynamic formula- 

 tions into the biological frame of reference; but there is a structural 

 "ground" within which every "configuration" of experience is set, 

 and the primitive neuropil, together with its specialized derivatives, 

 is one important component of the organic substrate of the "gestalt 

 qualities." The "field" as here conceived is an organized living struc- 

 ture in action, some components of which we recognize as stable 

 architecture and some as fluctuations in the excitatory state of the 

 structural fabric. This structure has visible organization, and its 

 properties are open to investigation anatomically and physiologically 

 ('34a; '42, p. 293). 



TWO CONCEPTS OF LOCALIZATION 



The two kinds of structure which have just been considered per- 

 form functions which are localized according to different principles, 

 a distinction which has been generally ignored. The specialized ana- 

 lytic structures have stable arrangement in space, and their functions 

 have corresponding localization in three-dimensional mosaic pat- 

 terns. The functions of the generalized structures are, in the main, 



