THE OPTICAL INFORMATION FOR SELF-PERCEPTION
It has frequently been assumed in previous chapters that the point of observation for an ambient optic array is not occupied. The point has been thought of as a position at which observation could be made, a position that could be occupied but need not be. Such a position could just as well be occupied by another observer and, since all positions can be occupied by any observer, the invariants of the array under locomotion can be shared by all observers. It was important to establish this principle that the point of observation is public, not private, but now we must consider the other side of the coin. When a point of observation is occupied, there is also optical information to specify the observer himself, and this information cannot be shared by other observers. For the body of the animal who is observing temporarily conceals some portion of the environment in a way that is unique to that animal. I call this information propriospecific as distinguished from exterospecific, meaning that it specifies the self as distinguished from the environment.
The field of view of an animal, as I will use the term, is the solid angle of the ambient light that can be registered by its ocular system. The field of view, unlike the ambient array, is bounded; it is a sort of sample of the whole sphere. The angular scope of the field of view depends on the placement of the eyes in the head, some animals having lateral eyes and a nearly panoramic field of view and others having frontal eyes and a roughly hemispherical field of view ( Walls, 1942, Ch. 10). Horses belong to the first group and humans to the second. In both ocular systems, the separate fields of view of the two eyes overlap in front, but the amount of overlap is very much greater in humans than it is in animals with semipanoramic vision. By the field of view, I mean the combined fields of view of the two eyes.