We examined the effects of the gravitational vertical on the perception of reversible figures.
Each reversible figure had two interpretations depending on whether it was viewed vertically
in one orientation or upside down. When it was presented horizontally, the two
interpretations alternated. Subjects were required to indicate which interpretation was
perceived after briefly viewing the horizontal presentation on a head-mounted display. When
the subject was upright, each interpretation occurred by chance. When the subject was lying …