the methods of constant stimuli, limits, and adjustment can be used to test the participants, but method of limits is most commonly used in research conducted using the rod and frame task. when using the method of limits, the experimenter sets the orientation of the rod and frame separately and then the participant is asked to adjust the rod orientation until they perceive it to be vertical. deviation from true vertical can then be determined. based on which way the frame is tilted, the rod can be viewed as either being tilted in the same direction as the frame (direct effect), or in the opposite direction of the frame (indirect effect).