July 1974
A Note on the Relation Between Perceptual and Conceptual Knowledge
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 References to these essays must cite them explicitly as unpublished manuscripts.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.
1. On the perceptual scale of size the environment consists of substances, surfaces, and the medium, not of either tiny particles in space or large bodies in space as it does at the far extremes of the metric scale. Particles, bodies, and space are conceptual entities.
2. On the perceptual scale the earth is flat, not round. The terrestrial earth approximates to a plane; it is only the astronomical earth that approximates to a sphere.
3. At the perceptual level the earth does not move. It is that with reference to which moveable objects move. At this level motion is absolute, not relative. The sun moves across the sky. The opponents of Copernicus should be given their due!
4. At the perceptual level gravity is a force perpendicular to the substratum, downward, not a force of attraction between masses, or even a force toward the center of the earth. The perceptual law of gravity is:Things fall down.
5. At the perceptual level the environment is always upright in the sense that the uprightness or inclination of anything is defined by it. The slope, slant, tilt, etc. of any object or surface must be taken with reference to the absolute substratus in perception. (cf. memo of October 1973 on the optical inversion experiments.)
6. At the perceptual time scale, i.e., at moderate durations, events are specified in the stimulus flux (e.g., oxidation by burning) but on the scale of years or microseconds the stimulus flux is not informative (e.g., oxidation by weathering, or the joining up of two oxygen atoms with a carbon atom).
7. At the perceptual level illumination reaches a steady state instantly, and the speed of light considered as radiant energy is irrelevant. An optical motion (the displacement of a visual solid angle) has no inertia, and is quite unlike a physical motion. The simultaneity of events at this level does not depend on the point of observation.
8. Finally, at the perceptual level there is always awareness of the self, proprioception, or at least it is always possible. At the conceptual level, however, it is usually absent, or at least awareness of the self tends to be avoided. Visualizing can occur either at the perceptual or the conceptual level.
Now, what about the relation of perceptual and conceptual knowledge (or perceptual and conceptual visualizing)? If it is partly a matter of size-scale or level as I have argued note that the difference is not that of a boundary. The difference is not categorical. Perceiving and conceiving are not different in kind as we have been assuming, especially since Immanuel Kant. They are both forms of cognition. There are clearly transitional cases between the two levels. The difference between them is nonetheless real and important. When we talk about the perception of abstract “space” or the perception of “motion” in the sense of Isaac Newton we are confusing the two levels and making the problem of perception insoluble. We get into the dilemma of supposing either that concepts are imposed on sensory data or that concepts are accumulations of sensory data and these suppositions cannot be reconciled. How can we understand the different levels of apprehension without falling into the error of the stale old dichotomy of percept versus concept?