Functional Size Perception

In an ambiguous world, it is comforting to think we all share a few common, objective realities. If two people look at the same Granny Smith apple, they are essentially seeing the same thing, right?

Not really. Our unconscious brain is constantly adjusting and manipulating what we see based on an ever-changing personal hierarchy of internal needs. One of the most easily measured proofs of this is something called ‘functional size perception’ or ‘biased size perception’.

The phenomena was first measured in the 1940s by American psychologist J.S. (Jerome) Bruner. He had subjects measure coins and circles of paper using an iris diaphragm, a device that works a bit like the focus ring on a camera. Even though the objects were the exact same size, subjects always saw the coins as bigger. Bruner then ran the experiment with a mix of wealthy and poor subjects judging the size of identical coins, and this time the poor people saw the coins as significantly bigger. The theory was that no matter how covetous the rich might be, because money was existentially important to poor people their brains enhanced the size of the coins to make them more identifiable. This mechanism might be a vestige from our evolutionary past when it would be easier for a hungry hunter to spot a larger prey.

In recent years, this effect has been reproduced in dramatic fashion: thirsty people see glasses of water as much as six centimetres taller than their slaked co-subjects; nicotine-fiending smokers judge cigarettes to be longer; and obese patients greatly overstate the size of cakes.

The reason for this burst of fresh interest in functional size perception is actually quite curious : behavioural psychologists who are learning to manipulate the unconscious brain are seeking ways to measure the true impact of their manipulations. (A quick refresher on the unconscious brain: at any given moment, we are bombarded by far more stimuli – smells, sounds, sights, noises – than our conscious brain can handle, so the vast majority of this information is processed by our unconscious brain.) Over the past 10 years, neuroscientists and behavioural psychologists have been learning to pull triggers in the unconscious brain to alter people’s behaviour and make them do everything from eat less to clean more. The problem is that after manipulating a subject unconsciously, you have to rely on conscious standards of measurement. For example, if you unconsciously manipulated a person to reject fatty foods, you then had to place a bunch of people at a snack bar and see if the test subjects gorged less. A helpful gauge, but hardly an air-tight measurement. Which brings us back to functional size perception: how better to measure unconscious changes than through our unconscious eyes?

This idea was the brainchild of Henk Aarts, the director of the GoalLab at Utrecht University, one of the world’s leading research centres on the unconscious brain. I was speaking to him recently for an essay I was writing on the human unconscious for Ode Magazine, and like so many scientists, he couldn’t repress his enthusiasm for his latest research.

“This is incredible,” he told me, “this is really … “

Aarts then used an expletive. “Wait -you aren’t going to use that, are you? It’s hard to keep a sober tone about this.”

Here’s what made Aarts professional demeanour crumble. He and his GoalLab colleagues Martin Veltkamp and Ruud Custers had primed the concept of gardening in the unconscious brains of subjects by presenting them with a series of word associations where gardening was always linked to positive images. Sure enough, in the following exercise, these subjects then saw shovels and hoes as substantially bigger than the test subjects who hadn’t been primed. Proof that the unconscious manipulation had succeeded in changing the person’s unconscious brain.

“From my scientist’s perspective, this is very exciting, this gives me many possibilities of new experiments to measure environmental stimuli on the unconscious,” says Aarts. “But sometimes, walking down the street, you have to turn that part off or you just get overwhelmed trying to understand why you’re seeing what you’re seeing.”

About Jeremy Mercer

Jeremy Mercer is an author and translator who lives in in the Luberon with his fiancée, two children, five cats, two chickens, ten fish, and one pregnant dog. He is currently on the market for a cheap horse. More at
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One Response to Functional Size Perception

  1. tim says:

    During a break in a life drawing class for which I was the model and looking at various students renditions of their perception of my naked form I was struck by the fact that none of the pictures appeared to me to be remotely like I imagine myself. This is perhaps not surprising. I would imagine that, being vain, of all things that I perceive, my subconscious deludes my conscious mind most about what I look like naked. Therefore any truth in the drawings could easily be disregarded in favour of my own preconceived self-image. My own perception aside however, it was interesting to note that the object of greatest variation from the various points of view represented in the drawings was the size of my penis.

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