This is an animated GIF free zone... Illusory Motion
Did you ever wonder why you see motion in images where nothing is moving??+david pinto
shared a post by +Celina Angel
), which got me tagged into a conversation on how the illusory motion demos work, so I thought I'd share that conversation with others since these are among the coolest and most effective illusions around.Before going any further, in this case, size really does matter, so it's best to view each of these full size for the full effect.
In illusions of this sort, the sense of motion is thought to be linked to eye movements, and in particular to microsaccades.
These are very tiny but rapid eye movements that we make all the time, but of which we are not consciously aware. They are important for our perception of the world because if we kept our eyes perfectly still, the stabilized images on the retina would fade - and, obviously, the goal of vision is to see the world, so it's to our advantage to have the tiny eye movements going on behind the scene. +Michael Bach
has a nice discussion of the role of eye movements in a related illusion (the rotating snake) on his demo site: http://www.michaelbach.de/ot/mot_rotsnake/
and he also has an interactive demo for a version of the green and purple star image, where you can experiment yourself
with the various stimulus attributes to see their effect on motion.
The general idea is that as the eyes move around ever so slightly, the luminance steps (changes from bright to dark or vice versa) simulate what one would expect if an object were moving in the real world - where different luminances would hit the same part of the eye at different times, and so the motion detection system treats the image as a moving object. As Bach points out, different people will have different strengths and frequency of microsaccades, and so different people will see these illusions stronger or weaker.
A recent paper published in The Journal of Neuroscience looked at the issue directly and supported the idea that transient events like microsaccades and even blinks are linked to the perception of motion in these types of illusions. Jotero-Millan, +Stephen Macknik
, and Martinez-Conde (2012) Microsaccades and Blinks Trigger Illusory Rotation in the “Rotating Snakes” Illusion: http://m.jneurosci.org/content/32/17/6043
One other thing that is interesting to me about the particular image I was brought into discuss (the orange and blur "spinning" vortex in the images I've shared) is that in addition to the illusory motion, it also shows an example of ambiguous figure/ground organization. We can see the vertical middle part out front as figure with the sides looping behind as background or we can see the two side parts as sort of worms looking at each other as figure with the vertical middle part behind as the ground - sort of like Rubin's face/vase illusion: http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/figure_ground.html
We are doing some work in my lab on the effects of aging on both motion perception and figure/ground, so it's a particularly meaningful illusion for me ;) #ScienceSunday
(curated by me, +Robby Bowles
, +Rajini Rao
, +Chad Haney
, and +Buddhini Samarasinghe
-- image sources:Spinning Vortex
by Beau Deeley http://goo.gl/PzJjAzTime Tunnel Show
and Baby Turtles Lightened By Moonlight
by +Akiyoshi Kitaoka http://goo.gl/a7XQfX
- this is a terrific place to view myriad amazing illusions that Kitoaka has created, along with some information about how they work.Psychedelic Star
by Ophtasurf http://goo.gl/OCLCTt