The University of Queensland

Spatio-Temporal Rivalry
When you play the video below you should fixate the central cross hair.
You should intermittently see two illusions.
1) An illusory static green ring
2) An illusory entirely red rotating windmill

These should intermittently appear, disappear and reappear for as long as you view the movie.

(WARNING: This demonstration will only work if the video plays smoothly).
Explanation:
Human vision relies on different types of cell that are specialised for encoding different types of information.
Some are specialised for encoding movement, but these have poor spatial resolution.
Some are specialised for encoding static spatial form, but these can encode moving form as blur.

Usually, the different types of cell cooperate to deliver a stable and coherent impression of the world.
This illusion is an exception. Cells specialised for encoding movement are signalling the presence of a
rotating windmill, but due to their poor spatial resolution they average across green segments
and signal that the windmill is entirely red.

Cells specialised for encoding static form are sensitive to the thin green arcs, but they average input
over time, and therefore signal that the green sections are blurred to the point that they are joined
together to form an illusory static green ring.

Instead of deciding which interpretation of the input is correct, your brain intermittently switches
between these illusions. In this instance, your brain cannot make up its mind.

Arnold, D.H., Erskine, H., Roseboom, W. & Wallis, T.S.A. (2010). Spatio-temporal rivalry: A perceptual conflict involving illusory static and moving forms. Psychological Science 21: 692 - 699.


Motion-Induced Spatial Conflict (The MISC Illusion)
When you play the video below you should fixate the central cross hair.
You will see red squares with central bars moving across the screen.
Don't look at the squares, keep looking at the central cross hair.
The central bars will change from being black, to bright green, then
back to black, and so on. When the bars are darker or brighter than the
red squares they should seem to move smoothly. However, for brief intervals
when the bars are nearly as bright as the red squares, they should seem to jitter
(or flicker) as they move.

(WARNING: This demonstration will only work if the video plays smoothly).
Explanation:
Human motion perception relies on mechanisms that detect differences in brightness.
When there is little or no difference in brightness (i.e. when the green bars are equally bright
relative to the red squares) your motion detecting mechanisms fail to promote a smooth sense of
movement. Instead, you experience the positions of the zero brightness movement (the green
bars) as intermittently jumping along, creating a sense of jitter. The jump frequency is not
driven by the stimulus. It is driven by processes in your brain.

This was the first illusion to be discovered where a rapid but intermittent rate of change is
experienced which is driven entirely by processes in your brain (as opposed to the jitter rate
being driven by characteristics of the stimulus).

Arnold,D.H., & Johnston, A. (2003). Motion induced spatial conflict. Nature 425, 181 - 184.


The Missing Arc Illusion
When you play the video below you should fixate the central red dot.
The video consists of rotating white discs, but these should look mishappen.
Specifically, while fixating each of the rotating discs should appear to have
a misshapen trailing edge. These may appear flat or concave, making each dot
look a little like an arrow (pointing in the direction it is rotating) or a bullet
with a round leading edge but a flat trailing edge.

(WARNING: This demonstration will only work if the video plays smoothly).
Explanation:
Human vision averages information about inputs over time. So, moving forms can be
encoded as blur. There are processes that target the trailing edges of movement for
suppression, to help eliminate perception of blur signals.

In this animation, the trailing edges of the rotating discs are positioned where the leading edges
were 60ms before. They therefore get caught up by de-blurring processes and get targeted for
suppression. This leaves you with an impression that the rotating discs are misshapen at trailing edges.

TIP: If you track any of the rotating discs with your eyes (and stop it moving across your retinae)
you will see that it is circular. Discs will only look misshapen if you fixate and let the images of the
discs move across your retinae.

Marinovic, W. & Arnold, D.H. (2013). Motion deblurring in human vision results in an illusory distortion of moving form. Vision Research 88: 47 - 54.