Likewise the experience of movement and colour in the visual field also develop in stages. The primitive visual field may contain only pure motion, usually rotary. Colours appear first as space and film colours. These only later enter their objects. Objects are often seen first as parts (e.g. the handle only of a teacup) that join up together later.
All this complexity may readily be explained on the grounds that we are observing the successive stages of recovery of an image-constructing representative mechanism that has several different basic parts (one for motion, one for colour and one for shape). It is difficult, for me at least, to think of it as representing the gradual recovery of the direct awareness of external objects that naïve realism supposes. How can a film colour be regarded as ‘the way we see” the colour located on the surface of e.g. a rose?
So, this data suggests that, topologically, the basic visual field is a pure formless expanse of nothing. Formal geometrical shapes (lines, curves, triangles, etc) only develop later. So what else can we say about its topology? In my book “Analysis of Perception” I described how fact that the boundary of an ordinary after-image forms a Jordan curve (that separates the whole of introspectable visual space into one ‘inside’ and one ‘outside’) can be used to define a basic topological property of visual space. However, no entire visual field itself (including that of Poppelreuter’s stage 1) forms a Jordan curve, as there is no ‘outside’. So can we say that in imagination a patient could “draw” a visual image of a Jordan curve somewhere on the P. stage1 primitive visual field, as we can on a normal visual field? It is difficult to say. No experiments, as far as I know, have been done to determine what visual imagery is available to patients in Poppelreuter’s stage 1. However, as we know that visual imagery uses the same brain mechanisms as are used in vision, it seems unlikely that such patients posses the required imagery. So can a formless spatial expanse be said to possess any kind of topology? If so, what? More clinical investigations of Poppelreuter’s stage 1 patients might yield some interesting results. It is also possible that the development of vision in very early infancy may follow a similar course but this would be difficult to determine.
There is, however, another topological relation that may be relevant. We can ask if visual space, however primitive and so long as it is ontologically a basic ‘given’ (i.e. a real space), is topologically ‘inside’ or ‘outside’ physical space (as an entirety), or any part of physical space (e.g. brain space). To this question naïve realism, the Identity Theory, and material dualism give different, but definite, answers. So perhaps that gives us a clue as to the basic topology of visual space? Not which answer is true, but that such a question can be asked at all.