A NEW TWIST ON THE ROTATING-TRAPEZOID ILLUSION - EVIDENCE FOR NEURAL-ADAPTATION EFFECTS

In a series of experiments, the selective-adaptation paradigm was appl ied to the rotating-trapezoid illusion in an effort to demonstrate neu ral-adaptation effects in the figural reversal of this classic illusio n. Prior to viewing the standard trapezoid, the observer adapted to a rectangle rotating unambiguously in the same direction as the trapezoi d or in the opposite direction. In accordance with the neural hypothes is, illusion strength was greatest when the two figures rotated in the same direction and weakest when the two figures rotated in opposite d irections. Results were confirmed with two separate dependent variable s: the observer's 'first look' at the illusion after adaptation and th e observer's reversal rate during a test period. These findings were d iscussed in terms of (a) the basic similarity of results for the rotat ing trapezoid and reversible figures such as the Necker cube and (b) t he need for a multiprocess model of both classes of illusions which em phasizes bottom-up and top-down processes.