ABSTRACT

The facts of occlusion have been described in Chapter 5. They are part of ecological optics. But they were not recognized as facts until observations and experiments made them compelling. The experiments described in the last two chapters about surfaces, layout, change, and kinesthesis were radical enough, but they culminated in the most radical of all, in what I can only call the discovery of the occluding edge. This discovery is radical for the following reason. If it is true that there are places where opaque surfaces are seen one behind another, if it is true that one can perceive a hidden surface, a paradox arises. For we are not now allowed to say that a hidden surface is perceived; we can only say that it is remembered. To be perceived, a thing must be "present to the senses"; it must be stimulating receptors. If it is not, it can only be experienced by means of an image; it can be recalled, imagined, conceived, or perhaps known, but not perceived. Such is the accepted doctrine, the theory of sensation-based perception. If an occluded surface is perceived, the doctrine is upset.