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New Scientist TV:

Friday Illusion: Move your head to brighten an image

Sandrine Ceurstemont, video producer

Psychologist Alan Stubbs has large prints on his office walls that often catch visitors off guard: by glancing at the images the whole area seems to light up. Now you can experience the same illusion by looking at the video above. As you stare at each image, move your head towards the screen and then back again. The bright spot should appear to spread quite dramatically.

This illusion, discovered by Alan Stubbs at the University of Maine and Simone Gori at the University of Padua, Italy, contradicts the way we typically perceive size and brightness. When we move closer to an object, it appears to be the same size even though the size of the image on our retina has changed. Similarly, the brightness of an object usually remains constant despite changes in illumination. Since we're typically looking around at a 3D environment, our brain automatically makes these adjustments to help us make sense of our surroundings.

So why does this illusion break these rules? Stubbs and Gori noticed that the edges of the bright spot have to be blurry for the effect to occur. "One possible explanation could be that our visual system cannot bring the blurred boundaries into focus and for this reason the correction of the brain for size constancy does not occur," they write. Another possibility is that the brightness gradient suggests to our brain that we are looking at a 3D tunnel, with a light at the end. In this case, it's simply an error of interpretation and our brain is behaving as if it was presented with the actual scenario.

What did you think of the illusion? Perhaps you have some other suggestions for why this effect occurs? Let us know in the Comments section below.

If you enjoyed this illusion, watch how you can colour an image with your eyes, see if you can spot the change in this image or check out our previous Friday Illusions.

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Your pc monitor emits light, the intensity reaching your eye increases by a factor of 10 every time you halve the distance from your eye. This is true across most light sources.


John Doe: If that explained the illusion, why wouldn't that work for every image you look at on the monitor. Move your head closer to this text, and see if it appears to get brighter?


Incidentally, intensity drops as inverse of distance squared, so halving the distance only increases the energy received by a factor of four. (As Colin says, this has nothing to do with the illusion anyway.)


That worked better than I thought. What was really good is that the bright area became larger as I mived quickly toward it, and abruptly shrank at the moment I stopped moving. Cool!


Colin.. it does! however text is normally black and blocks the light output from the monitor. So the effect of black text is the reverse(making it appear dark).


try printing it


IMO it works with LCD monitors only. The tilting of monitor is enough for generation of this "illusion".


John Doe and Zephir you are both clearly wrong, it works perfectly also printed on paper. Regarding John Doe... OK it is clear that vision science is not your cup of tea that it is perfectly fine unless you are writing wrong comments like that without any knowledge on the topic but a lot of arrogance.... You maybe miss all the picture but if you check on pubmed (did you know that pubmed even exist?) you can see that this illusion produced several international peer reviewed scientific papers (any idea what is the meaning of that?) that are way more controlled then internet blogs and there are controlled by experts in the topic (then.. not you...), please, go to do your "keyboard warrior job" somewhere else and read the scientific papers before talk (or write), you will gain much more respect... By the way, a possible explanation is given by Anstis et al. 2007 in Perception (checked on pubmed...) and it is regarding the superimposition of the afterimage on the physical stimulus during the dynamical viewing, don't forget to check before talk (or write) sir...


I'll go with the blurry interpretation, sort of the brain needs time to refocus when you move closer and so thats why the brightness (or most stimulating component) is blurry and bigger before the visual system adapts.


Wrong.. I did not get a word of that!.. But hey .ho. someday I will see the light too(maybe even brighter if I move my head).


Maybe it's a physiological response. The light source in the illusion emulates the sun and our eyes adjust for darker areas when the sun is in our vision. Because our pupils are more dilated than when actually looking at the sun, the sun then appears brighter.


I got a slight effect on the first, and a good effect on the last.. but nothing for any of the others.


It doesn't work for any of them as long as you don't look at the center of the image.


IveGotAPwner, you are correct, your observation supports the afterimage interpretation!


This is really astounding. How-ever, contrary to the text, the mosaic works the same way (for me).


For me it works on the peripheral vision as well. I had problems reading the text because of the perceived "brightness" of the first illustration! :-)




Yes Cahaba but the effect changes: if, for example, you look on the far right of the page and you move closer to the screen the white spot will move from right to left (the contrary if you move away from the screen) and the motion will not be radial anymore (as it was with central fixation), this supports the afterimage explanation


I can see the expansion in the Stubbs-Gori illusion alright, but I also see it in the third pattern, which follows the one with the squares in the background, where it is said that the illusion does not work. In this (the third) pattern, the paracentral circular boundary appears to expand as well, although it is crisp (not blurred) and of high contrast. Furthermore, sitting in front of my monitor and bobbing to and fro, I experience an expansion of the dark frame surrounding the screen, albeit not as strongly. Thus, the statement "When we move closer to an object, it appears to be the same size even though the size of the image on our retina has changed" does not seem to hold under these circumstances. Am I missing something?

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