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There are some questions here about various optical illusions. I stumbled upon this one and would like to find out where does it belong. Wikipedia has a page about illusory motion that mentions several types; peripheral drift seems to be closest, but I am not sure about it.

enter image description here

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  • $\begingroup$ Are you referring to the apparent motion of the blue center ring when you move your gaze around the image? $\endgroup$
    – AliceD ♦
    Mar 22, 2022 at 16:35
  • $\begingroup$ @AliceD Sorry, it did not occur to me that perhaps it is not perceived by everybody - when I just stare at any place in the image, it appears that the central dark area is expanding. $\endgroup$
    – მამუკა ჯიბლაძე
    Mar 22, 2022 at 17:08
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    $\begingroup$ @ARogueAnt. Interesting, for me I need eye movement to do the trick. Once I steady my gaze the movement stops, although microsaccades seem to cause a tiny bit residual movement nonetheless. The type of computer screen, screen settings, screen size, distance from the screen and other variables like color blindness may play a role too. $\endgroup$
    – AliceD ♦
    Mar 22, 2022 at 19:59
  • $\begingroup$ @ARogueAnt. Thanks for the link! This is incredible - I do observe very strong effect. $\endgroup$
    – მამუკა ჯიბლაძე
    Mar 22, 2022 at 20:56

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Peripheral drift illusions, as their name suggests, create the illusion of motion in the periphery of the visual field. Similar images that generate illusory motion in the center of the visual field have been termed central drift illusions. Both of these types of illusions use high contrast "luminance gratings" - repeating patterns of high and low brightness - to generate illusory motion.

Peripheral drift illusions can be used to generate an illusion of expansion, as demonstrated by the "Active Volcano" image (a) below (from Seno, Kitaoka, & Palmisano, 2013):

enter image description here

The control image (b) does not generate the illusion. The only difference between the images is their luminance grating pattern.

Many examples of expansion (and contraction) illusions can be found here. Here is a particularly powerful example called Fujiwara's black hole illusion:

enter image description here

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  • $\begingroup$ Thanks, this is informative enough, so I accept your answer. One question though - do you know anything about individual variations? Before my question was migrated I learned from a comment that at least one user does not experience this illusion from my image. Also for me your (a) only has very weak effect. $\endgroup$
    – მამუკა ჯიბლაძე
    Apr 1, 2022 at 9:46
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    $\begingroup$ @მამუკაჯიბლაძე Good question. Research is still ongoing about the cognitive cause of the illusion (good summary), and several possible factors have been proposed. I am not aware of any study actually looking at individual differences, but presumably differences in the factors (saccades, latencies, processing, etc) could account for such variation. $\endgroup$
    – Arnon Weinberg ♦
    Apr 1, 2022 at 17:10
  • $\begingroup$ More details on peripheral drift illusions in my answer to: What's the explanation of this optical illusion where many coloured arcs radiate from a central point? $\endgroup$
    – Arnon Weinberg ♦
    Aug 14, 2022 at 0:31

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