The Optical Information for Self-Perception (Gibson, 1979, Chapter 7)

So far we have considered what the world looks like to a point of observation that may or may not be occupied. It was important to Gibson that he establish that the optic array available at such a point is public, not private, and so can be shared across individuals (see Chapter 1 for the problem and 3 for the solution). In this chapter, Gibson asks what is seen by an individual when they occupy a point of observation, and in this case there is some privately available information that specifies things about the self. 

The field of view is the solid angle of the ambient light that can be sampled by an observer. All animals have two such fields of view (one per eye, which occupy slightly different points of observation) and these overlap to varying degrees (a lot in humans, not much in horses). 

The field of view is bounded - there is an occluding edge, but this particular edge is made by the eye socket and the nose. As this edge sweeps across an array, occluding and revealing optical information, there is also information about the head available. Other special surfaces are present - limbs, hands, feet, and more. They are special, in that they are us, but they are not different in kind from all the surfaces and events we have discussed, so the information is of the same kind too. 

There is, of course, non-visual information about the self (from muscles, etc); but there is also a great deal of optical information, and all this information across multiple sources is propriospecific (about the self). Gibson explicitly denies here the notion of specific nerve energies. 

Information about the self co-occurs with information about the environment and events; they define each other in all the usual ways. This provides some useful information about the relations between these things. For example, for distance, if we consider it as sweeping across the ground of an environment (vs a line from a point in space) then that gradient out to the world has a reference point, in the motion parallex of the nose as the closest point to the eye. The motions of the head are not confused with motions of the world, even though they both cause flow on the retina, because they are specified by different information and that relation can be perceived. And the motion of limbs relative to the environment is all specified (supporting 'hand-eye coordination', or, ecologically, the visual control of manipulation).

Gibson then spends some time on the specific case of information for self-motion. Self-motion creates global optic flow, which flows from the focus of expansion (specifying heading) around the moving observer and flows back into the focus of contraction at the opposite pole of a sphere. That flow also contains occlusion information specifying surface layout, and all the rest, revealed by the motion. Again, the information about the self and about the environment co-occur and co-define each other and it is all the same kind of information. (It occurs to me here that the worries some people have about 'retinal flow' being the proximal stimulus that contains ambiguities between self- and world-motion is not as ecological as they tend to say, because the two cases create distinct information).