For Gibson, invariants in the structure of light reaching the eye correspond to the stable features of the real world: the surfaces and edges of objects, ... the texture of the ground that grows more dense with distance. In spite of the fact that the image of an object on the retina may shrink in size as it recedes, the image is invariant with respect to the texture of its surroundings. (205)
No less than the privileging of hard-edged surfaces and objects, the liberal deployment of textural surfaces in VEs testifies to the effort to capitalize on Gibson's theory; indeed, both cases betray the same underlying logic: that building such visual invariants into artificial environments will function to attract the attention of our evolutionarily-attuned brains.
In his criticism of this strategy, Hillis accuses VR researchers of, in effect, misapplying Gibson's theory. Although innate perceptual invariants like texture gradients function, within Gibson's theory, as enabling constraints on how we perceive the environment, carried over into VEs they become the mechanism for an unhindered and limitless potential for visual interface with any environment imaginable (and, no doubt, many not yet imaginable). It is as if the simple presence of icons or representations of perceptual invariants (hard edges, texture gradients) within an environment were enough to transform it into a world not simply visually apprehensible to us, but rather one in which we can feel at home. What such logic ignores is the deep correlation of our visual system with other, nonvisual perceptual systems—a correlation that is, incidentally, foregrounded at each stage of Gibson's career.vii
If perceptual invariants do in fact exist and if they serve to inform us about the world, they do so only in conjunction with the panoply of perceptual processes constitutive of the kinds of beings we are. This means that the appropriation of Gibson does not pay sufficient heed to the evolutionary basis of his theory. Thus, although VR technology might well “permit users to see like birds" (or like anything whatsoever), a VE constructed on the basis of perceptual invariants “may confuse users precisely because they have not been hardwired' by evolution to fly like birds" (130). In sum: whereas Gibson's theory of perception (including the role played by perceptual invariants) is a holist one that encompasses (and is constrained by) the range of perceptual processes constitutive of our evolutionarily robust embodied being, its deployment in VE design is piecemeal and premised on an unthematized, and I think, wholly implausible, hope that vision can by itself reconstitute the richness of human perceptual function.
EMBODYING VIRTUAL REALITY
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