[[File:Example of Perceived Vertical.jpg|thumb|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.]]
The frame of reference with respect to studies of the [[visual system]] refers to perceived reference axes. In the rod and frame illusion there are a number of things that can influence one’s frame of reference. Past research has found that one reason people experience the rod and frame illusion is due to visual-vestibular interactions.<ref name=Spinelli>Spinelli, Antonicci, Daini, and Zoccolotti, 1995</ref> For instance, when a participant is viewing the rod and frame task while physically tilted, the participant acts as though they are tilted opposite of the orientation of the frame. 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. Other evidence proposed by researchers that is consistent with this is that when participants are put on their sides to view the rod and frame task, they rely on their vision when their [[vestibular system|vestibular]] and [[proprioceptive]] senses are incongruent with those of their visual senses.<ref name=Corbett/> These findingfindings suggest that the rod and frame illusion is processed in a type of hierarchy, where visual input is at the top, then vestibular cues, and finally proprioceptive cues.
In 2010, Lipshits found that, along with this hierarchy of processing, that proprioceptive information, as opposed to gravity, is used by the body to determine which way is vertical.<ref name=Lipshits>Lipshits, 2010</ref> TheLipshits researcher mentionssays that, when we are not able to use vision to determine which way is vertical, peoplewe use other cues based on the axis of theirour head and body.
