[[File:Rod and Frame Apparatus.png|thumb|Picture 1. A picture taken of the Rod and Frame apparatus originally sold by the Stoelting company, and now owned by the Rochester Institute of Technology.]]
RodThe rod and frame illusion occurs because of the effect of the orientation of the frame on the rod. In the simplest example of the rod and frame illusion, the illusion will cause the participant to perceive the rod to be oriented [[Congruence (geometry)|congruent]] with the orientation of the frame.<ref name=Corbett>{{Cite journal | last1 = Corbett | first1 = J. | last2 = Enns | first2 = J. | year = 2006 | title = Observer pitch and roll influence: The rod and frame illusion | journal = Psychonomic Bulletin & Review | volume = 13 | issue = 1 | pages = 160–165 | doi = 10.3758/bf03193828| pmid = 16724784 | doi-access = free }}</ref> When the participant is viewing the rod and frame that are both positioned at 0 degrees (or vertical), they perceive the rod as vertical with perfect accuracy. However, when the frame is tilted away from vertical, the participant's perception of vertical is affected. The participant tends to perceive the rod to be tilted in the same direction as the frame is oriented (e.g., if the frame is tilted in the counterclockwise direction, the rod will also be perceived as being tilted counterclockwise). As the tilt of the frame increases, the participants' perceived vertical increasingly deviates from true vertical.
