Can You See Your Own Brain Waves?

By Neuroskeptic | August 21, 2013 12:32 pm

An intriguing new paper in the Journal of Neuroscience introduces a new optical illusion – and, potentially, a new way to see ones own brain activity.

The article is called The Flickering Wheel Illusion: When Alpha Rhythms Make a Static Wheel Flicker by Sokoliuk and VanRullen.

Here’s the illusion:

It’s a simple black and white “wheel” with 32 spokes.

To see the illusion, get the wheel in your peripheral vision. Look around the edge of your screen and maybe a bit beyond – you should find a ‘sweet spot’ at which the center of the wheel starts to ‘flicker’ on and off like a strobe light.

Remarkably, it even works as an afterimage. Find a ‘sweet spot’, stare at that spot for a minute, then look at a blank white wall. You should briefly see a (color-reversed) image of the wheel and it flickers like the real one (I can confirm it works for me).

By itself, this is just a cool illusion. There are lots of those around. What makes it neuroscientifically interesting is that – according to Sokoliuk and VanRullen – that flickering reflects brain alpha waves.

First some background. Alpha waves are rhythmical electrical fields generated in the brain. They cycle with a frequency of about 10 Hz (ten times per second) and are strongest when you have your eyes closed, but are still present whenever you’re awake.

When Hans Berger invented the electroencephalograph (EEG) and hooked it up to the first subjects in 1924, these waves were the first thing he noticed – hence, “alpha”. They’re noticable because they’re both strong and consistent. They’re buzzing through your brain right now.

But there’s a mystery – why don’t we see them?

Alpha waves are generated by rhythmical changes in neuronal activity, mainly centered on the occipital cortex. Occipital activity is what makes us see things. So why don’t we see something roughly 10 times every second?

It’s hard to say what we ‘ought’ to see – perhaps flashing lights, or colors, or patterns – but it is rather interesting that we don’t see (or feel or hear) anything at alpha frequency.

Or do we? Sokoliuk and VanRullen argue that the flickering of the wheel is related in some intimate way to alpha. They offer two lines of evidence here.

Firstly, in a task in which people had to compare the illusionary flicker against a wheel that was actually flickering at different frequencies, the most popular frequency perceived as matching the illusion was 9.1 Hz – i.e. a typical alpha wave one.

But there was a lot of variability:

Secondly, the authors say that perceiving the illusion (not just seeing the physical wheel) causes increased alpha waves:

How could this happen? The authors speculate that there’s a:

Correspondence between the spatial organization of visual cortex (retinotopy, cortical magnification, lateral connections) and the temporal dynamics of neuronal information propagation (neuronal time constants, conduction delays)…

Once alpha activity reaches a critical threshold, the rapid alternation of favorable and less favorable phases for sensory processing produces a “pulsed-inhibition” that can become visible as a regular flicker in the center of the wheel.

This is an extremely cool set of experiments, but to my mind they haven’t yet shown a ‘smoking gun’ which proves that the flicker really is alpha, as opposed to being something that happens to provoke alpha, and be of roughly alpha frequency.

Perhaps a smoking gun would be to show a correlation between an individual’s own alpha frequency (these, we know, differ between people, but are very stable for each individual) and that person’s perceived flicker rate.

ResearchBlogging.orgSokoliuk R, & Vanrullen R (2013). The Flickering Wheel Illusion: When Alpha Rhythms Make a Static Wheel Flicker. The Journal of Neuroscience, 33 (33), 13498-504 PMID: 23946408

CATEGORIZED UNDER: EEG, papers, select, Top Posts, you
  • Jona Sassenhagen

    VanRullen has also claimed that the continuous-wheel illusion, where a fast car wheel seems to revolve in the “wrong” direction, is due to alpha.

    I’ve listened to a talk by Tony Bell online where he says that the flicker of a blank white wall you sometimes see when the night’s been long, the morning close and you’re pretty much done, that’s alpha. You can literally see your own alpha when you get tired and look at a white wall. I believe it, too.

    “why don’t we see something roughly 10 times every second?” <- Poeppel and Pöppel would probably say that in perception, we integrate over temporal windows of some length (possibly even because that's the length of an oscillatory cycle). I think that's also VanRullen's idea, 100-msec windows of perceptual integration.

    "the authors say that perceiving the illusion (not just seeing the physical wheel) causes increased alpha waves" <- Well, rhythmic visual stimuli with a presentation rate near alpha do entrain alpha. Also, visual impulses of course induce a visual ERP complex, which looks so much like alpha that so far, nobody really knows how to tell them apart. But the question of what causes what, even what IS what, cannot be solved. Yet.

  • Enzo Tagliazucchi

    well, showing that there is a frequency correspondence does not suffice, one would need to know that the flickering and alpha are phase locked, altough I am not sure how one could do such thing

    • Jona Sassenhagen

      More or less impossible.

      From a Popperian perspective, what you’re saying doesn’t mean so much; yes, the theory would predict that the illusion and alpha should be phase locked. If we find it phase locked, that doesn’t mean the theory is true, but if we don’t find them phase locked, that would be a successful falsification. But since we can’t test that, it’s not relevant. However, they’re also doing a bunch of others things, such as showing that alpha power is higher while you’re perceiving the illusion.
      And they have a strong model, too. One may go so far as to say that since alpha is the one thing that we know to happen in the brain at that frequency range, associating the illusion with alpha is the null model, unless anybody comes up with a simpler explanation.

      • Jona Sassenhagen

        I somehow missed this part of the article: “Over the group of 10 subjects for whom we could reliably determine both the individual alpha frequency and the individual frequency of maximal modulation by the illusory flicker, we found a strongly significant correlation between the two measures (p = 0.004, r = 0.813).” Though really, I’m getting a bit suspicious at an r of .8, and only 10 data points.

        • marcia

          well, I saw an spiral with many colors underneath the picture… while watching it it moved in spiral waves

          • agnes debinski

            I always appreciate updates on how exactly our brain works, especially in regard to brain functions and their impact on other parts of our body, such as e.g. our eyes and thus our eyesight. To be able to turn it all upside down and to show our eyes how our brain works – now that´s creative! I truly relished this article!

  • http://blogs.discovermagazine.com Jay Bingham

    Observing this got me to wondering what would happen if you put two or more of these side by side then let your eyes defocus, like what you do when you look at a stereogram, creating an additional phantom disk. So I did it, first with just two disks then with four disks. With two disks, when my eyes defocused and three disks in view, the pulsing occurred in the center disk. With four disks, when my eyes defocused, there were five disks in view. In this configuration the disk that I was ‘looking’ at would pulse. With the two disk configuration it is certain that the center disk was the phantom created by combining images of the two actual disks so in fact I was not actually ‘looking’ at that disk and the two actual disks were in my peripheral vision. I assume that with four disks I was never actually looking at an actual disk but at a phantom one created from two adjacent disks.

  • finny21

    Tried really hard to see this illusion … nothing :(

    • Buddy199

      Maybe you’re not an alpha male.

      • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

        I lied when I said that alpha waves were named for being the first to be discovered. They are actually called that because of all the neural oscillations, they have the most game.

        • Buddy199

          Los wavos mas macho

    • LZT1

      You;re probably seeing it but not realizing it is what they are saying. Trying looking away from it, a little bit to the sides.

      Also, if you look directly at it, you get a different illusion – the red circles running around the center.

      • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

        Red, eh? To me, looking an directly at it causes the white sections to “sparkle” with faint colors – but not red. They’re mainly green or blue. Interesting individual differences.

    • agnes debinski

      I could swear I´ve experienced this illusion before – while having had an eye doc appointment. Doing it on purpose requires a lot of will power. I had to struggle with myself quite a bit to get there.

    • Agnes Debinski

      That´s interesting, because it worked out for me very well. I suppose it´s a bit of a “you have to believe it to see it” kind of phenomenon….

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  • Keith D.

    I would control for the subtle movements of the eye before making any claim of being linked to alpha waves. They’re constantly flicking to and fro unconsciously and that combined with persistence of vision and the nature of the disc could explain the effect.

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  • Mados

    When I saw the image in my Feedly reader, it stood out amongst all the other articles and images as a strong, flickering, pulsing visual “explosion” coming right at me – extremely uncomfortable to look at so I immediately put a hand over it and still felt uncomfortable an estimated 30 – 40 seconds later. A little while after I tried again and managed to read the article (holding a hand over the image where the text was around it) and realised that it is a static image… And now I can look directly at it and see it as a static image (albeit not entirely still) but when I don’t concentrate then it begins to flickr violently and make me feel dizzy and uncomfortable, also after not looking at it any more. In fact I still feel uncomfortable, dizzy and nauseous right now which is more than a minute after I looked at it last, so I won’t do it again… ever. Very strange effect!

    • Mados

      (Ps. I am not taking any drugs or anything like that, in case someone would get that idea. Upon rereading my own comment I can see that it may sound a bit psychedelic, but it isn’t)

      • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

        Do you suffer from migraines? Patterns like this are known to be unpleasant for people who do.

        • Irina

          Also for people with epilepsy, or who are (even ever so slightly) autistic/

  • George Hampshire

    It flickers even if i directly look at at center.

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  • KA

    Flickering looks like it’s due to microsaccades, and it’s possible those movements are correlated with alpha amplitude in some way.

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      In the paper, they discuss the eye-movement theory and say that while eye movements do seem to enhance the illusion, they’re not responsible for it. For instance they point to the fact that it also works as an afterimage, yet the afterimage can’t be affected by movements…

      • KA

        Maybe I’m just an old curmudgeon, but visually perceiving your own alpha activity doesn’t seem like a reasonable hypothesis to me.

        First off, I’d be more convinced if the authors used their eye tracking data to show that there isn’t a relationship (frequency and/or occurrence) between saccades and the flickering.

        As to the afterimage, it could be affected (downstream from the retina) by movements. I’m not sure that you can see afterimages very well when your eyes are moving. Another possible explanation is that there is some kind of motion aftereffect creating the flicker in the afterimage…

        • Wouter

          “Another possible explanation is that there is some kind of motion aftereffect creating the flicker in the afterimage…”

          This is actually a very decent alternative explanation. If the flicker is caused by eye movements, then the flicker is nothing more than moving contrast changes on the retina (which logically peaks at the stimulus point where spatial frequency is highest: the middle). If so, then the flicker is stimulus movement (on the retina, not in visual space) and can, thus, create a motion-after effect.

          The authors really need eye-tracking information, to rule out this option.

          • Jona Sassenhagen

            I don’t know much about microsaccades, but according to the papers (Martinez-Conde 2009 TiNS, Engbert 2011 PNAS) I just skimmed, their frequency is on the order of 1, 2 hz, so the flicker is unlikely to directly reflect the individual saccades. However, I think this is not what you’re saying, but rather that the spatial pattern is perceived as a temporal pattern due to microsaccades?
            Note that eye tracking was conducted, but they mainly use it to exclude trials with larger (>3°) saccades.

          • Wouter

            I agree that the illusion is not likely caused by eye movements. When participants are asked to fixate, they usually do a fine job, but more importantly they do not go around making approximately 10 saccades per second, let alone in recurrent opposite directions. That would nauseate any healthy human being. However, it should have been put to test of course. A simple frequency analysis of micro saccades would have sufficed.

          • Jona Sassenhagen

            Note that here, participants were engaged in smooth pursuit around the circle.

            But you’re right, they could have correlated flicker intensity with microsaccade density or something like that.

          • KA

            During attempted fixation, the eyes of healthy human beings are constantly moving. Without this movement, we would all be functionally blind.

          • Wouter

            That’s nice, but the rate of involuntary micro-saccades isn’t anywhere near 10 Hz.

            Check out this article for comparisons between multiple fixation stimuli:
            http://www.sciencedirect.com/science/article/pii/S0042698912003380

      • Maciej_Kosilo

        “yet the afterimage can’t be affected by movements…” – I’m not so sure about that- in fact, afterimage can enable you to see your own microsaccades. See Fig 3. in Rolf’s review on microsaccades to experience that (really cool paper btw):

        http://www.martinrolfs.de/Rolfs_MicrosaccadeReview.pdf

    • Jona Sassenhagen

      Relevant:
      Dimigen, O., Valsecchi, M., Sommer, W., & Kliegl, R. (2009). Human Microsaccade-Related Visual Brain Responses. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29(39), 12321–12331. doi:10.1523/JNEUROSCI.0911-09.2009

  • Wouter

    Too bad the authors don’t discuss, why the illusion mainly occurs when the figure is present in the periphery of the visual field. Alpha waves are not confined to peripheral visual field representations. Thus, an explanation based solely on alpha band oscillation is insufficient.

    • Jona Sassenhagen

      Alpha is not confined to representations in the first place.
      I also don’t think anybody would propose an explanation “solely on alpha”. The main claim is: the flicker IS alpha. You still need a lot of stuff around that.
      Ad-hoc hypothesis: temporal integration windows work differently between the periphery and the fovea. Or maybe it’s just that the periphery is generally physiologically more sensitive to motion, so more inclined to interpret something as changing. How do the parvo- and magnocellular pathways relate to alpha on one hand, and sensitivity to periphery/fovea on the other hand?

      Certainly an interesting point.

      • Wouter

        “The main claim is: the flicker IS alpha.”

        And that’s what my previous post was about; if the flicker is alpha, why only see it when the figure is present in the periphery of the visual field?

        Your post-hoc hypotheses could be viable answers to this issue, but I would like to have heard this issue being discussed by the authors before them claiming that flicker is alpha.

        • Jona Sassenhagen

          “And that’s what my previous post was about; if the flicker is alpha, why only see it when the figure is present in the periphery of the visual field?” <- I don't think they necessarily need to be able to answer that question while providing some interesting EEG evidence for their model. Right now I think, a theory doesn't need to be able to explain everything; it needs to make interesting predictions, and we need to test these, and that the flicker rate is near alpha, and that alpha power is high while the illusion is perceived are such findings.

        • Mixie

          If our alpha waves are creating some kind of noise to our eyes/brain system (and normally any EM activity does so to its surroundings), then maybe our brain has an anti-noise system to combat that (which would prevent us from seeing flashes or any other kind of neuro/electric/etc garbage non-stop).
          If such noise-filtering system exists, it would make sense to expect it to be the strongest at our eyes’ focus, right – to make us capable of properly seeing the visual info coming from the outside world.
          While possibly our periphery can “escape” brain’s control a bit easier. Off course, I’m just brainstorming. No hard evidence behind it. :)

          And it would be ‘easy’ for the brain to have such anti-noise functionality, since every brain would actually know at what frequency it’s operating in each moment so it would know what frequencies to filter..

    • tgoyer

      I would wager to guess that it’s because objects in the periphery aren’t as crystal clear as objects in the center of our eyesight.

      Since our brains are hard-wired to make sense of randomness, it kicks into overdrive trying to make sense of something it can’t quite visualize clearly. This may lead to a spike in alpha wave intensity and thus our ability to consciously perceive it.

      That is all conjecture, of course, but it may explain it.

  • jlo5440

    The center flickers for me whether I look at it directly or off center, but I was unable to get the afterimage thing to work for me. I do get migraines, so I wonder how that can affect this… very interesting though!

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  • http://blogs.discovermagazine.com Brian Crawford

    I don’t have to look away, the center is flickering all the time. I guess it’s about 12hz. Now I wonder what my alpha rate is.

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  • Trick Heilman

    Try Scrolling up and down as you look directly at the image.

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      Those effects are likely down to your web browser or your monitor, rather than your brain. Scrolling causes your computer to display the image wrong. I think, in an attempt to “smooth” the scrolling – it works for most images, but not something as black and white as this.

      EDIT: Wait a minute… maybe I’m wrong. I just tried sticking my face right in front of the screen, and the weird scrolling effects disappear… which implies they are not entirely monitor-based.

  • Trick Heilman

    For me it flaps, changes diameter and the distance between lines increases when I scroll the image up and down while looking at it.

  • Anna O

    Hi Neuroskeptic … This is off topic – but just wanted to alert you to the fact that your feed is not working (http://feeds.feedburner.com/neuro-skeptic).

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      Whoa, that’s not good. Thanks for the heads up.

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  • Ohan Barsoumian

    Very easy to see the illusion/flickr

  • Michael Chernik

    i got an erection…was that supposed to happen?

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

      Did it oscillate 10 times per second?

      • David A. Carlson

        If so, his girl should be one happy lady.

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  • http://robinnixon.com/ Robin Nixon

    More likely a result of the moire effect between the radial stripes of the image and the linear layout of the visual cortex.

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  • David A. Carlson

    I dont see a flicker, I just see it pulsing. Unless I want it to stop pulsing, then I make it stop pulsing.

    • David A. Carlson

      What does that mean?

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  • Alaine Pakkala

    Can’t see it. Would a closed head injury be responsible

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  • James Davis
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  • Rod Schmidt

    Why don’t we see our brainwaves in daily life?

    I DID see this once! (recently) I was resting in bed, listening to a Silva recording, trying to max my alpha brainwaves. I opened my eyes, looking at a white wall and ceiling – room was dimly lit – everything was flashing! (something like 10 Hz, maybe faster) At first I thought the light outside was flashing, but no. In about a quarter of a second it damped down and there was no flashing. I closed eyes again, waited, then opened and saw same effect again, but not so strong.

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  • A. K. McCoy

    I see the flickering immediately but not in peripheral, would the fact that I have had cataract surgery in both eyes make a difference? Can’t spend too much time on this at the moment as I am at work but will try again this evening

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Neuroskeptic

No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.

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