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Inferring Our Desires
Related: Cached Selves, The Neuroscience of Desire
You don't know your own mind.
- Jonathan Swift, Polite Conversation
Researchers showed subjects two female faces for a few seconds and asked which face was more attractive. Researchers then placed the photos face down and handed subjects the face they had chosen, asking them to explain the motives behind their choice. But sometimes, researchers used a sleight-of-hand trick to switch the photos, showing viewers the face they had not chosen. Very few subjects noticed the face they were given was not the one they had chosen. Moreover, they happily explained why they preferred the face they had actually rejected, inventing reasons like "I like her smile" even though they had actually chosen the solemn-faced picture.1
The idea that we lack good introspective access to our own desires - that we often have no idea what we want2 - is a key lemma in naturalistic metaethics, so it seems worth a post to collect the science by which we know that.
Early warnings came from split-brain research, which identified an 'interpreter' in the left hemisphere that invents reasons for beliefs and actions. When the command 'walk' was flashed to split-brain subjects' right hemispheres, they got up from their chairs and start walking away. When asked why they suddenly started walking away, they replied (for example) that they got up because they wanted a Coke.3
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The Neuroscience of Desire
Who knows what I want to do? Who knows what anyone wants to do? How can you be sure about something like that? Isn’t it all a question of brain chemistry, signals going back and forth, electrical energy in the cortex? How do you know whether something is really what you want to do or just some kind of nerve impulse in the brain? Some minor little activity takes place somewhere in this unimportant place in one of the brain hemispheres and suddenly I want to go to Montana or I don’t want to go to Montana.
- Don DeLillo, White Noise
Winning at life means achieving your goals — that is, satisfying your desires. As such, it will help to understand how our desires work. (I was tempted to title this article The Hidden Complexity of Wishes: Science Edition!)
Previously, I introduced readers to the neuroscience of emotion (affective neuroscience), and explained that the reward system in the brain has three major components: liking, wanting, and learning. That post discussed 'liking' or pleasure. Today we discuss 'wanting' or desire.
The birth of neuroeconomics
Much work has been done on the affective neuroscience of desire,1 but I am less interested with desire as an emotion than I am with desire as a cause of decisions under uncertainty. This latter aspect of desire is mostly studied by neuroeconomics,2 not affective neuroscience.
From about 1880-1960, neoclassical economics proposed simple, axiomatic models of human choice-making focused on the idea that agents make rational decisions aimed at maximizing expected utility. In the 1950s and 60s, however, economists discovered some paradoxes of human behavior that violated the axioms of these models.3 In the 70s and 80s, psychology launched an even broader attack on these models. For example, while economists assumed that choices among objects should not depend on how they are described ('descriptive invariance'), psychologists discovered powerful framing effects.4
In response, the field of behavioral economics began to offer models of human choice-making that fit the experimental data better than simple models of neoclassical economics did.5 Behavioral economists often proposed models that could be thought of as information-processing algorithms, so neuroscientists began looking for evidence of these algorithms in the human brain, and neuroeconomics was born.
(Warning: the rest of this post assumes some familiarity with microeconomics.)
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