Neuroscience
The effect of portion size on how much people eat is something of a mystery – why don’t they simply leave what they don’t want, or alternatively, where possible, why not help themselves to more? Andrew Geier and colleagues at the University of Pennsylvania think it has to do with ‘Unit bias’ – “…the sense that a single entity (within a reasonable range of sizes) is the appropriate amount to engage, consume or consider”.
To test this, the researchers left a bowl of M&M sweets in the hallway of an apartment building with a sign that read “Eat Your Fill: please use the spoon to serve yourself”. Some days they left a tablespoon-sized scoop, other days they left a quartercup scoop that was four times as big. Passers-by could obviously help themselves to as little or as much as they wanted regardless of which spoon was provided, but on average, 1.67 times more M&M’s were taken on the days the big scoop was left compared with the tablespoon-sized scoop.
In another experiment, the researchers found that, measured by weight, significantly more pretzels were taken by passers-by when a complimentary bowl of 60 whole pretzels was left in an apartment building, compared with when a bowl of 120 half-pretzels was left. And it was a similar story when either a bowl of 80 small Tootsie rolls (an American snack bar) or a bowl of 20 large Tootsie rolls was left in an office building.
In other words, throughout the study, people took more food when the unit on offer was larger. “Consumption norms promote both the tendency to complete eating a unit and the idea that a single unit is the proper portion”, the researchers said. However, they also acknowledged that other factors must have been at play because the amount of food taken did not vary in direct proportion with the increase in unit size on offer.
The researchers concluded that this ‘unit bias’ applies in other walks of life too – they cited the example of films: “double features are rare, but very long movies are not”, and amusement-park rides: “one ride on a particular attraction is usually enough, whether it takes one or five minutes”.
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Geier, A.B., Rozin, P. & Doros, G. (2006). Unit bias. A new heuristic that helps explain the effect of portion size on food intake. Psychological Science, 17, 521-525.
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.
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Neuroscience
The 'power of one' - why larger portions cause us to eat more
The effect of portion size on how much people eat is something of a mystery – why don’t they simply leave what they don’t want, or alternatively, where possible, why not help themselves to more? Andrew Geier and colleagues at the University of Pennsylvania think it has to do with ‘Unit bias’ – “…the sense that a single entity (within a reasonable range of sizes) is the appropriate amount to engage, consume or consider”.To test this, the researchers left a bowl of M&M sweets in the hallway of an apartment building with a sign that read “Eat Your Fill: please use the spoon to serve yourself”. Some days they left a tablespoon-sized scoop, other days they left a quartercup scoop that was four times as big. Passers-by could obviously help themselves to as little or as much as they wanted regardless of which spoon was provided, but on average, 1.67 times more M&M’s were taken on the days the big scoop was left compared with the tablespoon-sized scoop.
In another experiment, the researchers found that, measured by weight, significantly more pretzels were taken by passers-by when a complimentary bowl of 60 whole pretzels was left in an apartment building, compared with when a bowl of 120 half-pretzels was left. And it was a similar story when either a bowl of 80 small Tootsie rolls (an American snack bar) or a bowl of 20 large Tootsie rolls was left in an office building.
In other words, throughout the study, people took more food when the unit on offer was larger. “Consumption norms promote both the tendency to complete eating a unit and the idea that a single unit is the proper portion”, the researchers said. However, they also acknowledged that other factors must have been at play because the amount of food taken did not vary in direct proportion with the increase in unit size on offer.
The researchers concluded that this ‘unit bias’ applies in other walks of life too – they cited the example of films: “double features are rare, but very long movies are not”, and amusement-park rides: “one ride on a particular attraction is usually enough, whether it takes one or five minutes”.
_________________________________
Geier, A.B., Rozin, P. & Doros, G. (2006). Unit bias. A new heuristic that helps explain the effect of portion size on food intake. Psychological Science, 17, 521-525.
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.
- Diners Order More Food And Drink From Larger Waiters And Waitresses
Psychologists have already identified a multitude of factors – besides actually how hungry we are – that influence the amount we choose to eat, from the size of the portion, to the company we're dining with. To this list, we can now add the weight...
- A Psychological Problem With Snacking In Front Of The Telly
TV snacks are easily forgottenBesides how hungry we feel, all sorts of other factors also affect how much we eat, including portion size and social convention. Another factor is memory for how much we've already eaten. The much-studied amnesic H.M....
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Our bias for the left-hand side of space could be distorting large-scale surveys. Past research has shown that when people are asked to bisect a horizontal line down the centre, most will cross the line too far to the left. This leftward bias is thought...
- Forget Stroop, Here's The Snarc
You’ve probably heard of the Stroop effect (if not, see here), now let me introduce you to the SNARC. The Spatial Numerical Association of Response Codes (SNARC) effect is the observation that people are faster to make a judgment about a number if the...
- Hemispheric Bias Shifts With Tiredness
Normally we have a slight bias to the left-hand side of space. So if we’re asked to mark the centre of a line, for example, we tend to overestimate the length of the left-hand portion. Now Tom Manly (pictured) at the MRC Cognition and Brain Sciences...