1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 193 



speaks for a certain presen'ation of "spatial" relations even beyond 

 the striate area. 



That a fixed projection of the retina upon the geniculate body 

 exists has been shown by the experiments of Brouwer-Zeeman and of 

 Overbosch. The work of Overbosch especially demonstrates a surpris- 

 ing-ly sharp projection of small retinal segments upon small segments 

 of the external geniculate body in the cat. Less definiteness in pro- 

 jection in the corresponding portions of the ^^sual system can hardly 

 be expected in primates. These studies together with those of Min- 

 kowski (1913, 1914), Ronne (1914), Putnam, Brouwer, Heuven, et al, 

 and with the present investigations besides numberless clinical obser- 

 vations, definiteh^ prove the essence of Henschen's and Wilbrand's 

 conception of the organization of the entire afferent visual system 

 according to the "principle of localization." If there are statements 

 contradictor^^ to this ^^ew it is now defensible to regard them as 

 surely owing to errors in obser^^ation, technique, or interjDretation. 



Still another result follows from our statements. Since it has been 

 found that the striate area alone and no other region of the hemisphere 

 is the terminal cortical area of the central visual path, it is logical to 

 conclude that all cortico-petal visual impulses will reach the striate 

 area no matter what their special quality is. Thus various color 

 impulses will also enter the striate area and not perhaps a separate 

 cytoarchitectural area outside it. Moreover, because each small seg- 

 ment or "elementars' unit" of the visual cortex has its own indepen- 

 dent afferent connection wath one, single, independent, peripheral 

 "receptor unit" in the retina, each such cortical unit must be capable 

 of reacting to all forms of light stimuli. In other words, each of the 

 elementary visual units including their correlated cortical units, the 

 latter composing the "mosaic" of the visual cortex, will respond to 

 all differences in the length and in the number of light waves. Since 

 all receptive, conducting, and cortical elementary units are equally 

 organized, the response to equal stimuli wiU be the same. The unequal 

 combination of stimuli vdW necessarily produce an unequal response 

 of cortical units. But such an equivalent organization exists, it must 

 be assumed, only in a. portion of the visual system, in that which 

 corresponds to the macula lutea and probably also to that of its next 

 proximity. The remaining portion corresponding to the extramacular 

 retina, less perfectly organized, will react to a smaller number of 

 light stimuli, and its "spatial" discrimination will be less efficient. 

 But taking a given small portion of that extramacular visual sj'stem. 



