The Conditions for the Perception of the Covering and Uncovering of a Line.

It is shown that a line of changing length is generally perceived as a line of constant length undergoing covering or uncovering when stimulus information (or the perception of objects to which such information gives rise) is compatible with that 'inference,' namely, that the line is contiguous with a phenomenally opaque object large enough to cover its disappearing portion. Otherwise, the line tends to be seen as of changing length. However, there is a preference for the constancy solution, so that a tendency toward perceptual rationalization occurs when the sensory information does not support that solution.