What is your mind doing when you think about something? For decades, the prevailing wisdom was that when you imagine, say, the scent of a flower or your lover’s perfume, your mind is doing something different from when you actually smell those things. The metaphor was a computer: The hardware for sensing things was distinct from the software for thinking about things.
More recent evidence suggests that the way we understand concepts relies on the sensorimotor system. When you think of the sound of a dripping faucet, the same parts of your brain are activated as when you are actually hearing a faucet dripping. (Computer geeks should see how the computer metaphor breaks down: it’s as if searching a database of images required the server to access its video card.)
But if conceptual thinking requires the sensorimotor system, then thinking about concepts should have the same limitations as our senses. For example, in 2000, Charles Spence, Michael Nicholls, and Jon Driver found that the reaction time for signals was slower after a change of modalities (like touch and hearing) compared to when the modality stayed the same (for example, a visual signal followed by another visual signal).
Diane Pecher, René Zeelenberg, and Lawrence W. Barsalou designed an experiment to see if thinking about different modalities showed the same reaction-time differences. Volunteers were shown a series of simple statements and asked to indicate whether the statements were true or false. The statements all followed the same pattern: OBJECT can be PROPERTY. For example:
BLENDER can be LOUD
TOAST can be WARM
MARBLE can be COOL
BUTTERMILK can be SQUEAKING
Participants rated 300 statements. Pecher’s team was interested specifically in cases where the modality of the property changed. In the list above, Blender-Loud is an auditory property, but Toast-Warm is a touch property—the modality changes. The next transition, to Marble-Cool would be an example where the modality does not change. Buttermilk-Squeaking is a decoy, as were most items on the test, so that participants didn’t catch on to the real goal of the experiment. Here are the results:
Even though participants were engaged in a language task, reaction time was significantly longer when the properties they were considering came from different sensory modalities.
This appears to be compelling evidence that our thought process relies on the sensorimotor system, but the team conducted a second experiment to eliminate an alternate explanation. Perhaps we react faster merely because the words from a particular modality are more closely related linguistically than other words. In the second experiment, the team selected pairs that were very closely related: for example, the words spotless and clean. When used in the form “SHEET can be SPOTLESS” and “AIR can be CLEAN,” these words aren’t related to any specific modality—this is the “related word” condition. A pair such as “SHEET can be SPOTLESS” and “MEAL can be CHEAP” is an example of “unrelated words.” This type of word pair was inserted in to a new experiment that also included same-modality and different-modality pairs. Here are the results:
There was no difference between related and unrelated words, but once again, a significant difference between same-modality and different-modality words was found. Pecher et al. argue that these experiments offer compelling evidence that the way we process concepts is not independent of other systems of the brain; it appears, by contrast, that conceptualization requires the use of the sensorimotor system. Unlike computers, whose highly specialized hardware often performs only a single task, the mind appears to make use of sensory systems not only for sensing, but also for imagining.
Pecher, D., Zeelenberg, R., & Barsalou, L.W. (2003). Verifying different-modality properties for concepts produces switching costs. Psychological Science, 14(2), 119-124.