Can the urban environment cause headaches?

Stripes can be rather a pain for some people...
20 July 2020

Interview with 

Arnold Wilkins, University of Essex


green city


Arnold Wilkins is a psychologist from the University of Essex who’s interested in visual disturbances. Arnold told Katie Haylor that there’s rather a lot of brain devoted to what we see, and that the brain has evolved to process natural images. This, he says, can cause a problem when we’re asked to look at unnatural images - spatially repetitive stripes for instance - which means the brain needs to work a bit harder, maybe a bit too hard, and the resulting headache can be quite a pain...

Arnold - A student of mine took photographs by standing at the side of the curb and aiming the camera across the street, somewhat randomly. We were able to analyse the images, using a computer algorithm written by my colleague Olivier Penacchio, and we were able to predict how uncomfortable people could find these images. All the algorithm did was to measure statistically how unnatural the images were. Some are more unnatural than others, you see. The worst patterns are probably those in the escalator stair treads that you get in department stores and the underground.

Katie - But they're everywhere!

Arnold - They are. Yes. These patterns and stripes are there partly because of the way we build things. So they're a component of modular construction. But they're also there as decoration because designers, for some reason seem to like them. Which is unfortunate. I could give you an example. There was a large brand new bank built. One senior executive at the bank wasn't able to work in the new building that because it was decorated with stripes and she happened to have migraines. And fortunately for her she was sufficiently high up to be able to demand to retain her original office.

Katie - You said repetitive shapes. And you also said stripes. Are those the culprits? Or are there any other defining characteristics that cause a problem?

Arnold - We can define them mathematically using Fourier analysis, which is a bit complicated to explain, but basically looks at the world as if made up of lots of sine waves in different orientations and different wavelengths. And by analysing those, using a simple algorithm, we can predict discomfort. We can explain a surprisingly large proportion of the variance in judgments of discomfort from such a simple algorithm. It's interesting because all the algorithm's doing is effectively saying, "how unnatural is the image?". The images that make the algorithm go off as it were, are particularly stripes, but anything that's spatially repetitive, they don't have to be obvious stripes. If you look at a modern office block, that will easily do it.

Katie - That sounds like quite a big problem, because if you're consciously, visually aware of something that looks uncomfortable, at least you can try and take some sort of action. But what it sounds like you're saying is that you can be unaware.

Arnold - Yes, largely. We're not usually aware of what causes headaches. I did a study a long time ago, which showed that fluorescent lighting caused headaches. And in fact, it doubled the number of headaches that office workers experienced. We compared the flickering type of fluorescent lighting with what was then a modern flicker free type. And none of the participants attributed their headaches to the lighting. But when we changed the lighting the headaches halved. So people really don't know what triggers their headaches. It may well be something visual that they're not aware of.

Katie - Do we know what's going on in the brain to make them uncomfortable? Has anyone stuck someone in an MRI scanner and watched them watching images?

Arnold - Yes. And what you find is you get a very large hemodynamic response. We've done two types of measurement, one using fMRI and one using near infrared spectroscopy. And they both showed the same thing. In the visual part of the brain, you get a lot of activity that you can measure in terms of the blood oxygenation demand from the neural activity. Clear neural correlates of the discomfort people experience.

Katie - And how does that turn into a headache though?

Arnold - How - I'm not sure. We do know that there are substantial changes in oxygenation during a headache. And we know that the sort of visual stimuli that provoke a large hemodynamic response are also those that people say, give them a headache. Quite how the trigger happens, I'm not sure yet.

Arnold explained that there’s huge variation in how susceptible people are to these kinds of headaches, but his previous study found that the more illusions experienced (all sorts, changes in colour, movement etc) when you look at stripes, the more susceptible you seem to be to this stripe-induced headaches. And whatsmore, this may be a particular issue for people who suffer from migraine with aura. As Anna was saying earlier, aura are the squiggly lines of visual disturbance that some ppl experience with a migraine headache.

So what can be done about these stripe-inducing headaches? Because we don’t always have control over what our environments look like. Maybe you can paint your bedroom a different colour if its bothering you, but re-designing local office blocks is a whole other ballgame. Back to Arnold...

Arnold - I think it's fair to say that architects are becoming aware of them now. And interested in them. It is quite unnecessary to decorate buildings with high contrast stripes. And indeed some architects have gone so far as to get gardens to grow up the side of buildings. And that's a very nice way of overcoming some of the aggressive architecture that you otherwise get.

There are things you can do about your susceptibility, other than changing the environment, which is to change your local environment, your vision, by wearing coloured glasses. This may seem very strange -

Katie - It actually doesn't seem strange at all Arnold. Because I have prescription glasses cause I'm too scared to wear contact lenses! But my sunglasses are brown tinted. And I always love the summer because I get to wear my brown tinted glasses. Life looks nicer to be honest through them! But sometimes when my eyes are tired, I wear them inside. And I must look like an idiot, but I do it because when I'm looking at a screen, I feel better. It doesn't seem strange to me.

Arnold - Well, we've just done a study. This was done by Alex Vieira, who was a student of mine. She asked individuals with migraine, with aura, to look at text in an apparatus that I designed a while ago called the Intuitive Colorimeter, which just allows people to change the colour of light falling on the text, and to vary it systematically in a controlled way so that we could overcome the effects of colour adaptation and so on. And the interesting thing was that all of the individuals who had migraine with aura chose a very strongly saturated colour, a very strong colour, very different from one individual to another. But, when we gave them glasses of that colour so that they could get that coloured light under normal illumination, their ability to search for words in text was greatly improved.

When we gave the same task to individuals who didn't have migraine, or had migraine without aura, no such choice of strong colours. Everybody chose the colours they would normally experience in everyday life. So from a yellow, through to a white, through to a bluey-white from the sky. So, there are huge differences in the choice that people with migraine with aura make as compared with migraine without aura or headache-free people. There's a clear link between migraine with aura and colour, which is curious, and we've got to explore it further.

Katie - Do you know what's going on?

Arnold - Well, we know that when people wear a colour they find comfortable for looking at things, the size of the hemodynamic response in the visual cortex is reduced. In migraine, one of the early findings was that people with migraine have an abnormally large hemodynamic response in the cortex. The brain was measured using fMRI, and you look at something called the blood oxygenation level dependent signal. And that was larger than in headache-free individuals, in response to certain patterns. When these individuals with migraine with aura wore coloured spectacles of the choice of colour they found comfortable, that abnormal response was reduced. It was normalised. Whereas when they wore coloured glasses with a different colour, there was no such reduction. So the colour choice is critical. It's only when you get the colour right for the individual that you get these beneficial effects.


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