Grouping in space and in space-time: An exercise in phenomenological psychophysics

Perceptual organization is difficult to study because it lies on the border between our experience of the world and unconscious perceptual processing. Even the term “perceptual organization” is ambiguous: it means both the outcome of perceptual processes—how things look—and the mechanism that produces it—the psychophysical processes that precede awareness. Perceptual organization is difficult to study for a second reason: because it involves both bottom-up and topdown processes. It is—like respiration—a semi-voluntary process. For example, when we first glance at a Necker cube, we are much more likely to see it as if it were seen from above than from below. Over this response we have no control; it is spontaneous and automatic. But as soon as we see the cube reverse the response appears in some measure to be under our voluntary control.