Exploratory experiments on the stimulus conditions for the perception of a visual surface.

It is possible that the simplest visual perceptions are those of surface and edge (1). These impressions can be obtained when the eyes are fixated, i.e., without having to consider the effect of the succession of overlapping retinal images normally obtained when the visual environment is scanned. They can probably be explained without reference to the stimulation arising from the posture and the movements of the eyes, head, and body—the factor of equilibrium and orientation in space perception. The vestibular-kinesthetic-tactual complex of stimuli has to be considered, of course, but the visual stimulus might be considered first. This approach to space perception is simplified above all by deferring consideration of the meaning of percepts until their psychophysical basis has been established. The question to which this approach leads, then, is what are the proximal stimuli, in terms of image-variables, for the "elementary impressions" of surface and edge? A phenomenal surface has the