Rod and frame test

It relies on the use of a rod and frame apparatus which uses a rotating rod set inside an individually rotatable drum, allowing an experimenter to vary the participant's frame of reference and thus test for their perception of vertical.

Past research has found that one reason people experience the rod and frame illusion is due to visual-vestibular interactions.

This suggests that the illusion, in part, is due to the person compensating for their perceived vertical in the direction that is opposite of the frame.

In 2010, Lipshits found that, along with this hierarchy of processing, proprioceptive information, as opposed to gravity, is used by the body to determine which way is vertical.

[4] Lipshits says that, when we are not able to use vision to determine which way is vertical, we use other cues based on the axis of our head and body.

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.
Picture 2. An image showing a 10-degree frame angle and a 7-degree rod angle. Observers using the apparatus see the rod as vertically oriented. The frame of the page, image border, etc. make it appear tilted here.