The Leaning Tower of Pisa effect: An illusion mediated by colour, brightness, and motion

We report a novel, easily observed, and extraordinarily striking optical il lusion mediated by interactions of colour, brightness, form, and motion per ception-the Leaning Tower of Pisa (LTOP) illusion. Under some circumstances , the perception of orientation of coloured forms is radically altered by r otary movement. We demonstrate that this kinetic effect-easily reproduced w ith a common record turntable-is optimised by particular colour and brightn ess differences between foreground and background with an illusory tilt of 8 degrees and more. The described illusions can be easily studied at home b y downloading the colour figures from www.percepiionweb.com/perc1000/ ditzi nger, printing them on a common colour printer and placing them on a rotati ng record turntable.