p004fig01.04 (top row) Kanizsa stratification; (botton row) transparency images<BR>||  [top row images] "... are called stratification percepts... This simple percept can ... be perceived either as a white cross in front of a white outline square, or as a white outline square in front of a white cross.  The former percept usually occurs, but the percept can intermittently switch between these two interpretations. ...it is said to be a <I>bistable</i> percept. ..."