SOME ASPECTS OF STEREOPSIS 95 



ganism and formed, possibly before, possibly after birth, indepen- 

 dently of any experience, or whether they are somehow due to con- 

 ditioning. 



Whatever may be the nature of a given perception, therefore, the 

 perception of a disjunction implies a neural disjunction of some sort, 

 whereas the localization of the disjoined elements within a field of 

 relations implies the presence of interconnections of some sort be- 

 tween nervous elements involved in the perception of these elements, 

 whether these interconnections were previously functional, or only 

 became functional as a result of the perception itself. And while 

 there may be no unique structure of nervous interconnections capable 

 of yielding the system of relations as perceived — the solution of the in- 

 verse problem of neural nets is not necessarily unique — nevertheless 

 there are limitations, and empirical anatomical data may serve, in 

 time, to complete the characterization. 



The problem we wish to consider is the following. By whatever 

 means it is acquired, the normal human adult does possess a percep- 

 tual space within which he locates the objects of his perception. With 

 objects some distance away from him, visual cues are the chief, and 

 frequently they are the only, means available to him for the localiza- 

 tion of these objects within this space. In these cases, where the 

 visual cues are the only ones, how is the localization effected? That 

 is, what kinds of cues can be provided by the eyes alone, which, to- 

 gether with past associations (but not the memory of a previous lo- 

 calization), may serve the subject in localizing the object within his 

 perceptual space If the eyes themselves provide several, more or less 

 independent, cues for localizing the same object— and they certainly 

 do— then the final localization must come as a kind of resultant of 

 all of these. Under normal conditions these cues would doubtless act 

 in harmony and reinforce one another, thus providing a fairly ac- 

 curate judgment. But under abnormal conditions due to pathology 

 or instrumentation, the normal harmony would be disrupted, making 

 the perceived relations a bizarre distortion of the true ones. In fact, 

 it is by considering the nature and occurrence of these distortions 

 when the cues are in disharmony that we might hope to get our best 

 information as to their separate modes of operation. 



In the system of spatial relations among disjoint elements, per- 

 haps the simplest and most primitive, beyond, of course, the mere 

 fact of separation, is the amount of separation. This is easily under- 

 stood in terms of kinaesthesis. Greater separation requires more 

 movement for crossing it, a more intense kinaesthetic sensation, and 

 in these terms our discussion of the discrimination of intensities may 

 find an application here. With reference to visually perceived extent 



