The role of learning in 3-D form perception

A mechanism for incrementally advancing continuous paper forms comprising a pair of opposing cams which drive said forms therebetween, each said cam having a plurality of camming surfaces whose phase relative to the other said cam may be manually varied. For each rotation of said pair of cams, said forms are incremented a number of times equal to the total number of camming surfaces per one said cam where an increment is phase dependent.