June 1963
Outline of Present Evidence for a Stimulus-Information Theory of the Perception of the Environment and for the Control of Locomotion in an Environment
J. J. Gibson, Cornell University
The World Wide Web distribution of James Gibson’s “Purple Perils” is for scholarly use with the understanding that Gibson did not intend them for publication. References to these essays must cite them explicitly as unpublished manuscripts. Copies may be circulated if this statement is included on each copy.
(Evidence must show, first, that the information is available in the ordinary flowing stimulus-array and, second, that it can be registered by individuals.)
1. The specifying of a surface in the world by a textured area in the optic array, and of “nothing” in the world by a textureless area of the array.
Hence the appearance of terrain and sky over the ages of evolution.
Hence the observations on optical support (the need for a textured array under the feet).
Hence animals will move into a textureless patch but not into a textured patch (observations of deer, birds, etc.)
Hence the placing response of animals (e.g., kittens).
Hence the laboratory results on surfaceness and filminess as in Metzger and Katz. (Waddell?)
Difficulty: The puzzles of the figure-ground phenomenon. A closed contour (pictorially) seems to induce the experience of a solid object, but optically it does not always specify it. (Apertures and windows.) The puzzle of the modes of color perception, and aperture-perception.
2. The specifying of an edge in the world (jump in depth by a step-wise increase in one or both of the variables of optical texture in an array: (a) density: (b) increased paralytic motion or “shear”. (There is also increased binocular disparity for some animals, but this requires a dual array.)
— Consider here some of the results of the parallax experiments (Gibson, Smith, and Flock).
a. The specifying of depth downward at an edge (a cliff) by a horizontal line of increased density or notility in the array.
Hence the results of Gibson and Walk with the “visual” cliff.
b. The specifying of one surface behind another (transparency) in the parallax experiments.
3. The specifying of the recession of a surface (slack in the layout) by a continuous increase (gradient) in texture density, or notility, or disparity. (What about “one way compression”?)
Hence the optical tunnel results when the texture became dense
Hence the results of Dibble, Waddell, Carroll, Flock, and the parallax experiments. (Discuss problems of slant and shape.)
a. The specifying of a change in the rate of recession of a surface by a change in the gradient of density (notility, disparity) of optical texture.
Illustrations but no experiments.
b. The specifying of a horizon in the world by “vanishing” values of texture elements, and of parallax. The imitation of a horizon in pictorially mediated perception.
Examples only.
4. The specifying of subjective movement in (i.e. locomotion through) the environment by a continuous transformation of structure of the array (motion perspective), and of staying in the same placeby a continuing non-transformation of the array (not counting blue sky).
Hence cinerama observations.
Hence the striped cylinder observation.
Hence the behavior of birds and fish in a flowing medium.
-Evidence from aircraft-landing studies (e.g. Gibson, Olum, and Rosenblatt).
5. The specifying of objective motion in the environment by the transformation of an edge-bounded figure in the optic array.
Hence results with shadow-transformations in various experiments.
Hence some of the observations in the “law of common fate” and some of the results of Johansson.
The question of whether the laboratory experiments using motion in a window, and pictorial motion, agree with this hypothesis.
a. The specifying of rigid object-motion in the environment by a perspective transformation of a bounded figure in the optic array, and of elastic (viscous) object-motion by a non-perspectivetransformation.
Experimental results for perception are not wholly predicted by this formula. The hypothesis may be inadequate. Some confirmation in Fieandt’s experiment, and those of Johansson (and Reynolds).
6. The specifying of one surface going behind another by the optical event of “being wiped”. (This is related to the optical facts of occlusion, being “hidden,” or “disappearing,” and to the general phenomenon of edge-depth). Wiping is a special transformation describable as a progressive line of disappearance of texture for an edge-bound figure.
Hence Michotte’s results on the “tunnel phenomenon” and the “rabbit-hole” phenomenon, and the seeming paradox of an invisible phenomenal object.
7. The specifying of the approach of an environmental object by the centrifugal magnification of a figure in the array without centrifugal flow of the remainder; and of approach to an object by centrifugal magnification of the figure with accompanying flow of the rest of the array.
Hence results with the shadow-apparatus yielding approach of an approach object.
8. The specifying of imminent collision with an environmental object or surface by optical looming (the terminal magnification of any figure in the array approaching the 180 degree limit of magnification).
Hence the results of Schiff’s recent experiments with animals, and the precursors with human observers, using the shadow-projection apparatus.