Editing Optical illusion (section)

=== Depth and motion perception ===
[[File:Vertical–horizontal illusion.png|250px|left|thumb|The [[vertical–horizontal illusion]] where the vertical line is thought to be longer than the horizontal]]
[[File:Ponzo illusion.gif|left|thumb|alt=The Yellow lines are the same length. Click on the name at bottom of picture for an explanation.|[[Ponzo illusion]]]]
Illusions can be based on an individual's ability to see in three dimensions even though the image hitting the retina is only two dimensional. The [[Ponzo illusion]] is an example of an illusion which uses monocular cues of depth perception to fool the eye. But even with two-dimensional images, the brain exaggerates vertical distances when compared with horizontal distances, as in the [[vertical–horizontal illusion]] where the two lines are exactly the same length.

In the Ponzo illusion the converging [[Parallel (geometry)|parallel lines]] tell the brain that the image higher in the [[visual field]] is farther away, therefore, the brain perceives the image to be larger, although the two images hitting the [[retina]] are the same size. The optical illusion seen in a [[diorama]]/[[false perspective]] also exploits assumptions based on monocular cues of [[depth perception]]. The [[M.C. Escher]] painting ''[[Waterfall (M. C. Escher)|Waterfall]]'' exploits rules of depth and proximity and our understanding of the physical world to create an illusion. Like [[depth perception]], [[motion perception]] is responsible for a number of sensory illusions. Film [[animation]] is based on the illusion that the brain perceives a series of slightly varied images produced in rapid succession as a moving picture. Likewise, when we are moving, as we would be while riding in a vehicle, stable surrounding objects may appear to move. We may also perceive a large object, like an airplane, to move more slowly than smaller objects, like a car, although the larger object is actually moving faster. The [[phi phenomenon]] is yet another example of how the brain perceives motion, which is most often created by blinking lights in close succession.

The ambiguity of direction of motion due to lack of visual references for depth is shown in [[The Spinning Dancer|the spinning dancer illusion]]. The spinning dancer appears to be moving clockwise or counterclockwise depending on spontaneous activity in the brain where perception is subjective. Recent studies show on the fMRI that there are spontaneous fluctuations in cortical activity while watching this illusion, particularly the parietal lobe because it is involved in perceiving movement.<ref>Bernal, B., Guillen, M., & Marquez, J. (2014). The spinning dancer illusion and spontaneous brain fluctuations: An fMRI study. Neurocase (Psychology Press), 20(6), 627-639.</ref>