The role of phenomenal displacement on the perception of the visual upright

Tilt invariably involves the factor of displacement. A clockwise rotation of a rod, for example, results in the top being displaced to the right and the bottom to the left. The question was raised as to which is primary, displacement or tilt. Through a series of experiments, apparent tilt was found to be the perceptual outcome of phenomenal displacement. In addition, gravity seemed to play no significant role in determining the visual upright. Therefore, the conventionally accepted field theory of apparent verticality was rejected and the visual upright was interpreted according to principles which govern the perception of motion and radial direction.