Today I heard about the following experiment. Subjects were given a number to memorize. Half of the subjects were given 7 digit numbers and half were given 2 digit numbers. The subjects were asked to walk across a hallway to another room and report the number to the person waiting there. If they reported the correct number they were going to earn some money. On the way, there was a cart with coupons available that could be redeemed for a snack. There were coupons for chocolate cake and coupons for fruit salad. Subjects could take only one or the other before proceeding to the end of the corridor and completing their participation in the experiment.
63% of the subjects memorizing 7 digit numbers picked the chocolate cake.
Only 49% of the subjects memorizing 2 digit numbers picked the chocolate cake.
I can see two possible explanations of this. One is very interesting one is more prosaic. What’s your explanation? I will post mine, and more information tomorrow.
Update: The experiment is in the paper “Heart and Mind in Conflict: The Interplay of Affect and Cognition in Consumer Decision Making” by Shiv and Fedorikhin. Unfortunately I cannot find an ungated version. It is published in the Journal of Consumer Research 1999. I heard about the experiment from a seminar given by David Levine. Here is the paper he presented which is partially motivated by this and other experiments.
Our interpretations are similar. The interesting interpretation is that we have an impulse to pick the chocolate cake and we moderate that impulse with a part of the brain which is also typically engaged in conscious high-level thinking. When it is occuppied by memorizing 7 digit numbers the impulse runs wild.
The less interesting interpretation is that when we dont have the capacity to think about what to choose we just choose whatever catches our attention first or most prominently, independent of how “tempting” it is. One aspect of the study which raises suspicion is the following. In the main treatment, the coupons were on a table where threre was displayed an actual piece of chocolate cake and and a bowl of fruit salad. This treatment gave the results I quoted above. In a separate treatment, there was just a photograph of the two. In that treatment the number of digits being memorized made no difference in the coupon taken.
The authors explain this by saying that the actual cake is more tempting than a picture. That’s plausible, but it would be nice to have something more convincing. Would we get the same result as in the main treatment if instead of chocolate cake and fruit salad we had yogurt and fruit salad?
Cheap Talk 
9 comments
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May 13, 2009 at 9:16 pm
Sam
1) When your concentrating on something hard you don’t have the spare capacity to assess the implications of your decision and therefore you choose instinctively the delicious chocolate cake rather than the healthy fruit.
2) When your doing a hard task you feel justified in rewarding yourself with the delicious chocolate cake instead of the healthy fruit.
May 13, 2009 at 9:33 pm
mad
3) You become hungrier from thinking more, and desire the more substantial form of replenishment.
May 13, 2009 at 9:45 pm
mad
4) And I suppose the phone number hint implies that the other explanation is that the 7 digits primes you to think more socially; about all the different people you could by the cake for.
May 13, 2009 at 10:09 pm
Jonathan Berman
I imagine that the conventional reason is the same reason why they put candy bars at the checkout of supermarkets. When you spend cognitive energy, you become exhausted and your “will power” is weakened. After spending a half hour shopping for groceries, you’re tired and you give in to temptation that is the candy bar at the checkout counter.
May 13, 2009 at 10:28 pm
jeff
actually, i thought the reason for that is that it empowers your kids to whine and threaten to annoy all of the other shoppers in line unless you give in and buy them the candy. notice that the displays are all at kids-eye-level.
May 14, 2009 at 12:06 am
Vinnie
I think the explanations Sam and Jonathan mentioned above are the most plausible. Another to consider: The chocolate cake is more uniform in color, flavor, and texture. Instinctively, we recognize the fruit salad as more mentally stimulating. We tend to interact more with foods of disparate parts, which could be enough to shove some of the digits out of memory. Say the fruit salad has oranges slices, grapes, watermelon, honeydew, strawberries, and banana slices. That’s six distinctly different colors, textures, and flavors. Add that to the seven digits, and your mind is occupied by 25 disparate parts. In the process, you’ve also activated the sight, taste, and feel sensory regions of the brain to a much greater extent than if you’d chosen the more homogeneous cake. Sensory overload compromises short-term memory.
May 14, 2009 at 8:28 am
Ben
I think most of the reasons posted are better, but here is another alternative:
1) People feel smarter / focus more on their intelligence when being forced to remember the 7-digit number. This builds their confidence, which makes them more likely to choose to cake since dieting could sometimes be associated with a lack of confidence about weight.
May 14, 2009 at 12:52 pm
Thomas Schminke
I would be interested in knowing if all of the participants actually took the coupons, or if those that were trying to keep memorized the more complex number simply by-passed the coupon table more often.
This would tip the results only to those that really wanted some particular coupon over the other … so-as where the general population was 50-50, the strong desire sub-group was 2-1 for cake.
My general interpretation is like the others here though, cognitive overload causes the impulsive portions of the brain to have a stronger say in the 7-digit case, and the impulsive parts of the brain want cake.
May 14, 2009 at 11:34 pm
jeff
yes this is a good question. right now i am traveling and i cant get access to the paper, but i will check when i can.