New evidence that metaphor touches the brain directly?

A small new brain study adds some evidence to the “direct sensory input” side of the hypothesis that metaphors are an important part of our cognitive machinery.

The study’s results suggest that metaphors are linked to the physical sensations they represent, rather than being just culturally derived.

Many neuroscientists accept that metaphors have direct sensory links, and that metaphor performs major rational functions. But how human thought is grounded in metaphor remains a hot question, as evidenced by the dispute between George Lakoff and Steven Pinker, both of whom studied linguistics with Noam Chomsky, over whether metaphor is the basis for rational thought (Lakoff) or one of the tools used by already-rational brains (Pinker).

The new study, reported by Science NOW on February 7th, doesn’t resolve this issue, but it does show that there is an explicit neurophysical link between tactile metaphors and brain areas associated with touch.

In the study, subjects were scanned while listening to statements that were alternatively tactile-rich (“This is a hairy situation”) and tactile-neutral (“This is a precarious situation”). The results show that tactile-rich metaphors activate the parietal operculum, a brain area associated with touch. The tactile-neutral metaphors didn’t activate this brain area.

These results suggest that we understand metaphors physically as well as rationally. Our most powerful and common metaphors appear to be enhanced by their association with direct physical contact with the world.

Another article, at PsychCentral, reports the results with more details. For example, Simon Lacey, one author of the study, notes that “visual cortical regions were not activated by textural metaphors, which fits with other evidence for the primacy of touch in texture perception.”

And, the article reports,  “researchers did not find metaphor-specific differences in cortical regions well known to be involved in generating and processing language, such as Broca’s or Wernicke’s areas.”

These two findings seem to indicate that vision and language, two candidates for the primary source of sense-based metaphorical thought, are not dominant, at least when it comes to tactile metaphors. Specific sensory areas of the brain appear to respond to different kinds of sensory imagery.

The study’s senior author is quick to stress that the results do not support a mechanistic, “this part of the brain does that” view of cognition. Dr. Krish Sathian says “I don’t think that there’s only one area responsible for metaphor processing. Actually, several recent lines of research indicate that engagement with abstract concepts is distributed around the brain.”

Sathian continues: “I think our research highlights the role of neural networks, rather than a single area of the brain, in these processes. What could be happening is that the brain is conducting an internal simulation as a way to understand the metaphor, and that’s why the regions associated with touch get involved.”

While the tactile study by Sathian, et al., downplays the role of the brain’s language centres in processing metaphors, the authors of another study, published in December, argue that their results show that sound sequences are processed as abstractions, rather than as merely streams of sensory input.

In this study, subjects were scanned while they watched a video presentation of different sound sequences. By mixing correct and incorrect visual representations of the pronunciation of these sounds, the researchers were able to separate the sensory and abstract portions of the sequences. As a result, the researchers concluded “that two areas of known left-hemisphere speech-processing regions, namely, pars opercularis and planum polare coded speech at an abstract level.”

In an online article reporting the study, “Lead researcher Steven Small says that the new findings suggest that the understanding of speech does not just emerge from lower-level processing of speech sounds, but involves a specialized perceptual region.”

Combining these studies could be taken to suggest that there is a direct sensory connection to metaphors, but that there are “higher” brain regions that play a role in processing the brain’s representations of these inputs.

Two small fMRI studies don’t resolve the issues around the role of base-level sensations in rational thought. Rather, they reinforce how complicated this research area is — and how far we are from figuring it all out.

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