Today, me and one of my favourite science Youtubers, Alie Astrocyte from Neurotransmissions,
Alie: "Hey there!", are going to talk to you about a small portion of the fascinating world
of visual illusions. Specifically, about some which can trick your brain to prevent overeating.
[INTRO by Caro Waro & Cristina de Manuel]
Inés: Look at the yellow dot. It looks like the circle in the middle is changing size,
even though it isn’t – only the ones surrounding it are. This is the dynamic version of the
Ebbinghaus or Titchener illusion, and it actually won illusion of the year in 2014. But what
is it about it that tricks us into believing that the middle circle is changing size?
Alie: The reason it looks like it's changing size is due to its context. The size of the
central circle is judged relative to the size of the surrounding circles. Another illusion
which follows a similar principle is the Ponzo illusion – although both lines are the same
length on your screen, the top line looks much longer because our brain takes the angled
lines as a guideline for perspective.
Inés: Basically, the way our brain processes the images that enter our eyes has a lot to
do with why we fall for visual illusions – they show ways in which our perception is a little
bit distorted or less accurate in some manner, but in general they do help us perceive the
general picture in some way. Now most of the time, optical illusions are just a little
bit of fun play and don't really have much of an impact on our lives, but the Delbouef
illusion is one that begs to differ.
Alie: The Delbouef illusion is believed to operate in a similar fashion to the Ebbinghaus
and Ponzo illusion. The larger the proportion of the diameter of the inner circle to the
outer circle, the larger the interior circle appears to be – even if as is the case here,
they are both the same size. This effect leads to unexpected perceptual differences, such
as overdrilling during dentistry procedures.
Inés: It sounds unlikely – but there are plenty of studies out there showing that dentists
are more likely to drill larger holes than necessary when treating cavities and root
canal surgeries, and it's almost certainly driven by the Delbouef illusion.
However, whilst dentistry procedures are more than likely to take your appetite away, there
is another real life application to this illusion, reducing portion sizes!
Alie: As the saying goes, our eyes are generally bigger than our belly, and indeed we do use
our eyes to estimate how much we should serve ourselves. Unfortunately, we’re not very
good at estimating how much food we need, and instead, we tend to fill the plate until
it “looks right” to us. A study has shown that the average size of the dinner plate
in the West has increased from an average of 23cm to 30cm in diameter over the past
100 years. If you do the maths, that’s almost twice the surface area, and therefore, could
equate to twice or even more of the amount of calories depending on whether you pile
the food on or distribute it evenly. In fact, they often recommend people trying to reduce
their portion sizes to serve them on smaller plates.
Inés: It really does make a difference doesn’t it?
The difference in the way that we serve the food is due to two effects: contrast and assimilation.
Basically, what this means is when you have a portion of food on a larger dinner plate
it will highlight the gap between the food and the edges of the plate, and the brain
will perceive them as two different entities, and will contrast them, making the portion
seem smaller than it is. On the other hand, on a smaller plate, as the edges of the food
are closer to the edges of the plate, the brain is more likely to assimilate and merge
both edges together, perceiving the portion as being larger. We know that the contrast
effect is strongest when the diameter ratio between the two circles is close to a third,
whereas the assimilation effect occurs when the diameter ratio between the two circles
is above two thirds.
Alie: The irony of both of these effects is that when people were asked to serve themselves
a targeted portion size onto plates of various sizes, they actively avoided the effects of
contrast and assimilation when serving themselves. Those serving onto large plates were more
likely to overserve themselves, whereas those serving onto small plates were likely to underserve
themselves. Even when people were told about the effects
of the Delboeuf visual illusion and whether they would be likely to over- or underserve
themselves, they still did so even if to a lesser degree, which shows just how strong
the effect of this visual illusion is!
Inés: So are there any better ways to trick your brain into nailing the correct serving
size? The researchers of this study also decided to play around with contrast, that is, varying
the colour of the plates and the colour of the tablecloths they were on and the results
were very interesting. When people were asked to serve themselves on white plates that were
on dark tablecloths, or that is, a high contrast situation, they underserved themselves even
more than average on small plates, and would still overserve themselves on larger plates.
However, when serving in low contrast conditions, that is, white plates on white tablecloths
– the overserving disappeared altogether although people did continue to somewhat underserve
themselves.
Alie: Even more surprisingly the opposite effect is observed when playing with the contrast
of the food and the plate! When your food doesn’t stand out from your plate, you’re
likely to overserve yourself even more on larger plates, and underserve on smaller plates
Inés: So to sum up – the well-regarded famous advice of eating off small plates is
in fact, well-supported by science if you're looking to lose a few kilos.
Alie: And if you’re unable to get your hands on any small plates, then make sure your plates
blend into your tablecloth and try serving food that stands out on it! This will help
you serve yourself smaller portions, and prevent overeating. Thanks so much for having me on,
Inés! This was a lot of fun! [Thanks for joining me in this video! ^_^
Inés: So there you go – if you’ve got too much on your plate you now know you can
use science and visual illusions to prevent overeating. And don't go just yet! This is
a collaboration video which means that there's another video over on Neurotransmissions.
It's about the neuroscience of Tourette's, which I think is a video topic made in heaven,
because in case you didn't know, Alie is a neuroscientist and I have Tourette's syndrome,
which is very interesting to talk about it.
If you're here from Alie's channel, then hi and welcome to Draw Curiosity and feel free
to check out any of the other science videos I've made - and as always, thank you so much
for watching us and I'll see you in the next one, bye!
[ART & ANIMATION: Caro Waro & Cristina de Manuel]
[MUSIC: Thastor & CryoSleepKitten]
[HOSTING: Alie Astrocyte & Inés Dawson]
[SCRIPTING & EDITING: Inés Dawson]
[Translated by {your name} into {language}]