What Does the Size of a Pizza Slice Teach Us?

Have you seen this video that went viral a few weeks ago?

If not have a look now before reading further.

It is tempting to judge harshly. It is obvious to the watching outsider, it makes no difference how many slices there are … it is still the same pizza.

Well, technically yes.

But that is not  how our minds work. That is not how we perceive what is going on around us.

Look at the following image.

imageWhich red circle is bigger?

Go one measure them.

They are the same size.

We think in relative terms. We compare constantly. We see an object in relation to the environment it is in. If the other circles are larger, then the red circle appears smaller. If the other circles are smaller than the red circle appears larger.

The girlfriend in the video is comparing the number of slices. At this level of comparison she is correct. Eight slices is less than 12 slices.

The assumption in the video is that she will eat all 12 slices. If you eat all 12 there is no difference to eating the 8.

However 5 slices feels like a lot, even if 5 smaller slices is less than 4 larger slices. We can feel full, even if we have put less into our body.

You can use this logic in your favor. Look at the picture below and imagine the blue circle is your dinner plate. Would you feel more satisfied with the plate on the left or the right?


Chances are you would prefer the plate on the left. The plate looks fuller, and therefore as if there is more food. It is not. The portion sizes are the same.

If you were dishing up the plate on the right you might feel sorely tempted to put more food on the plate. The portion in relation to the rest of the plate looks measly. This is one of the simple ways we end up eating too much.

These kinds of comparisons are everywhere. They trick us. But we can also use them to our advantage if we stop laughing and realize what is going on.

I often prefer to have many smaller slices of something than fewer large slices.

hiddenbrain_deepbluereverse2_sq-d4dc2bc0fb94c4fa0074fb7ab2e1b681e6245d7a-s400-c85This quote from the Stopwatch Science segment on the Hidden Brain podcast from NPR sums it up nicely.

You may have heard that smaller portions can help you eat fewer calories. That’s true. But what about larger tables? Researchers Brennan Davis, Collin Payne and My Bui hypothesized that one of the ways smaller food units lead us to eat less is by playing with our perception. They tested this with pizza and found that while study participants tended to eat more small slices, they consumed fewer calories overall because it seemed like they were eating more. The researchers tried to distort people’s perception even further by making the smaller slices seem bigger by putting them on a bigger table. What they found is that even hungry college students ate fewer calories of (free) pizza when it was chopped into tiny slices and put on a big table.

* Emphasis is mine

Here is a few more pictures for you to look at and consider what your mind is doing.

Which line is longer?

Which bar is the largest?


You should know by now that all of those bars are the same size.

Don’t believe me?

Go on measure them.

We are easily deceived.

This can work for us, or against us.

For some reason I was thinking about the pizza video over the weekend. I realised that while we all want to laugh, she is more ‘right’ than we think. She is doing what we all do.

Maybe we are laughing because of that discrepancy. We know deep down we could easily make the same mistake. Maybe we can sense part of our mind telling us she is right, and when we sense that we realise the cognitive effort required to counteract that impulse.

I found this quote in a National Geographic article I read while working on this post.

Even when we intellectually accept these precepts of science, we subconsciously cling to our intuitions—what researchers call our naive beliefs. A recent study by Andrew Shtulman of Occidental College showed that even students with an advanced science education had a hitch in their mental gait when asked to affirm or deny that humans are descended from sea animals or that Earth goes around the sun. Both truths are counterintuitive. The students, even those who correctly marked “true,” were slower to answer those questions than questions about whether humans are descended from tree-dwelling creatures (also true but easier to grasp) or whether the moon goes around the Earth (also true but intuitive). Shtulman’s research indicates that as we become scientifically literate, we repress our naive beliefs but never eliminate them entirely. They lurk in our brains, chirping at us as we try to make sense of the world.

Why Do Many Reasonable People Doubt Science? 

By Joel Achenbach

* Emphasis is mine

Laugh all you want. This is real. We all do it.

The quote above makes the point that even seasoned professionals struggle to overcome the impulse of our subconscious mind. It requires effort.

To overcome this tendency you need to acknowledge it exists. Hopefully I have done enough here to help you out.

Once you acknowledge it exists you need to learn to see the world around you. To truly see all everything as it really is, not as your mind perceives it.

Artists are good at this. It is one of the key skills. They are less likely to be fooled by the above illusions because they are trained to see the world as it is.

The follow on from this is to pay attention to context.

Context isn’t everything, but it is a lot of things.

In many ways we are our environment, our situation, more than we are ourselves.

(Listen to this podcast for more on that last thought Invisibilia: Is Your Personality Fixed, Or Can You Change Who You Are?)