The new draft now includes the following text:

3.5 Perception Outside the Visual Field

The Gestalt Bubble model has another unusual property not normally encountered in models of vision. In most models the processing of the visual input is confined to the area of the input itself, just as in image processing. In this model however the purpose of visual processing is defined as a reification or completion of a percept of the complete local environment surrounding the observer, filling-in features that are outside of the visual field by extrapolation in exactly the same way that amodal completion interpolates edges that pass behind an occluder. In other words, the head is treated as an occluder of the world behind the head, and the final percept is of a spherical world surrounding the body, only part of which corresponds to the visual field. This is shown in Figure 17 (E) (reproduced below, where the shaded portion represents the occluded visual world behind the head, and the faded lines in that region represent spatial edges and surfaces extrapolated from the visible portion of the representation.

This raises the question whether the world behind the head is actually perceived visually at all. Although the world behind the head is clearly not seen with the same vivid sensation of color and form as the world within the visual field, there is nevertheless a percept of space behind the body, as can be demonstrated by the fact that it is possible to take a step or two backwards without stumbling. A step (whether forwards or backwards) requires an exact knowledge of the height and orientation of the ground at the point of contact. This becomes evident whenever a step encounters an unexpected change in surface height or orientation, even of as little as an inch or two, which inevitably results in a This raises the question whether the world behind the head is actually perceived visually at all. Although the world behind the head is clearly not seen with the same vivid sensation of color and form as the world within the visual field, there is nevertheless a percept of space behind the body, as can be demonstrated by the fact that it is possible to take a step or two backwards without stumbling. A step (whether forwards or backwards) requires an exact knowledge of the height and orientation of the ground at the point of contact. This becomes evident whenever a step encounters an unexpected change in surface height or orientation, even of as little as an inch or two, which inevitably results in a stumble. A backwards step without a stumble therefore indicates that the stepper has knowledge of these parameters within about an inch or two. Whether such information must necesssarily be consid ered visual information is irrelevant at this point, since this model is advanced as a perceptual model in which visual, auditory, somatosensory, and other information are unified in a single coupled system, which is why a representation of the body percept is included at the center of the structure, whose pos tural configuration would be updated both visually, and from somatosensory and kinesthetic informa tion. This model suggests that surfaces in the scene are extrapolated from their visible portions in the visual field into the unseen portion of the perceptual field. For example the walls and ceilings of a hall way would be completed perceptually behind the observer, as would such regular features as a hand rail. This explains how it is possible to accurately grab a handrail, pole, or surface at a point well outside of the visual field while viewing only the visible portion of the object within the visual field. Like the backwards step, this performance clearly demonstrates the availability of high resolution spatial information about objects outside of the visual field. Both Gibson and the Gestaltists fully appreciated the significance of this aspect of amodal perception (Reed 1988, Kanizsa 1979, Tampiere 1956).

Now, to return to the reviewer's comment about the illuminant, it too is often up outside the field of view. How ever it is easy to point back up at an unseen illumination source without looking, and even to say whether it is point-like or diffuse, and what color it is. This shows that we have information about its position and structure from the illumination profile in the visual field. I propose that that information is spatial information, and that it is encoded in the same coordinate system as our perceptual space, i.e. that it is perceived amodally, like any other object in the occluded world behind the head. Furthermore, the view within our visual field influences our per ception of the illuminant, just as our assumption of the nature of the illuminant influences our interpretation of the scene in the visual field. There is therefore a bidirectional influence between the appearence of the visual field and the percept of the illuminant, which is the point I was making with the model.