Imagine a big slice of your favorite pie. Imagine eating all of it. Your mouth automatically begins salivating, your taste buds begin firing up. Now, imagine eating more pie until you are full…A short while later, you find yourself confronted with the real pie. You might think that this is going to be a problem, but instead, you end up eating less pie.
That’s according to a recent report in Science (10 Dec. 2010) by researchers Moorewedge et al at Carnegie Mellon University. In a series of clever experiments with real and imagined candy (M&Ms) and cubes of cheddar cheese, the researchers revealed a fundamental capacity of the mind/brain — the ability to habituate to a stimulus that is only imagined.
Habituation refers to the decrease in physiological/behavioral responsiveness (the desire to obtain) that comes with repeated exposure to a (liked) stimulus. It’s what makes us stop eating, or thinking about eating. We habitually habituate to many stimuli besides foods, like sunlight, repetitive background noise or simply walking on sand.
The opposite of habituation, in this context, is sensitization, wherein the perception or imagining of a (wanted) stimulus (say, your favorite dessert, or pasta dish) is limited to a single exposure — just enough to whet the appetite and motivate you to obtain it. The researchers make a distinction between these two processes and focused their attention on the mechanics of habituation, that is:
How does the brain get the appetite to stop wanting or seeking out what it craves?
The difference between actual experience and mental representations of experience may be smaller than previously assumed. — authors Morewedge, Huh, and Vosgerau, Thought for Food: Imagined Consumption Reduces Actual Consumption, Science, 10 Dec., 2010.
This work points out the over-lapping nature of perception (seeing/tasting/smelling) and mental imagery (memory based); though seemingly different functions, both can elicit the same emotional states (and even motor responses) and both utilize similar neural pathways. Given this, the team wondered whether imagining that one had already eaten plenty of an imagined stimulus (by imagining eating a food item repeatedly) could actually produce habituation to the real thing.
Would subjects told to imagine eating a whole lot of M&Ms, or another group that was told to imagine eating just a few pieces, eat more or less of the food item when it was actually offered (in the form of a bowl of M&Ms, or, cheddar cheese cubes)?
As a control measure, each subject was first given a control task (such as imagining putting coins into a laundry machine) that was fairly similar to the imagined food task (but did not involve tasting/eating). A point system was later introduced to the subjects, via a computer game, wherein they could trade so many points for a single food item.
To discover the true variance in responses to the food, the researchers sought to construct an index of “change in liking” before and after the imagined eating task. Each experiment was followed by a reinforcement game that established an “index of wanting”. An analysis of variance (ANOVA) was conducted using these two indexes.
The results? Those who imagined eating the most of a given food (e.g., eating 30 pieces instead of 3), showed less motivation to earn points in exchange for the real food, and/or, consumed much less of the food item when it was actually available. The results were object-specific too; the mental simulation did not cause habituation to other foods, only the imagined one.
The researchers also noted that two distinct psychological processes were involved in habituation behaviors: hedonic responses (liking and palatability) and appetitive or motivational responses (wanting). Interestingly, the experiments showed no change in liking (of the food); the significant difference was in the appetitve response. The simulated consumption of the food decreased a subject’s motivation to obtain that food.
Apart from its theoretical importance (i.e., proving that mental imagery is a “top-down” cognitive process, and alone can create behavioral change, like habituation), these results have important implications for other fields, most especially in food and drug addiction therapy and intervention.
In summing up, quoting from the paper: “Rather than increase the likelihood of enacting the simulated behavior (eating), simulation evoked the consequences of the behavior (habituation).”
Image (graph): courtesy of Science/AAAS