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Meaning on the Brain: How Your Mind Organizes Reality

The views expressed are those of the author and are not necessarily those of Scientific American.

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They called him “Diogenes the Cynic,” because “cynic” meant “dog-like,” and he had a habit of basking naked on the lawn while his fellow philosophers talked on the porch. While they debated the mysteries of the cosmos, Diogenes preferred to soak up some rays – some have called him the Jimmy Buffett of ancient Greece.

Anyway, one morning, the great philosopher Plato had a stroke of insight. He caught everyone’s attention, gathered a crowd around him, and announced his deduction: “Man is defined as a hairless, featherless, two-legged animal!” Whereupon Diogenes abruptly leaped up from the lawn, dashed off to the marketplace, and burst back onto the porch carrying a plucked chicken – which he held aloft and shouted, “Behold: I give you… Man!”

I’m sure Plato was less than thrilled at this stunt, but the story reminds us that these early philosophers were still hammering out the most basic tenets of the science we now know as taxonomy: The grouping of objects from the world into abstract categories. This technique of chopping up reality wasn’t invented in ancient Greece, though. In fact, as a recent study shows, it’s fundamental to the way our brains work.

Chunks of reality

At the most basic level, we don’t really perceive separate objects at all – we perceive our nervous systems’ responses to a boundless flow of electromagnetic waves and biochemical reactions. Our brains slot certain neural response patterns into sensory pathways we call “sight,” “smell” and so on – but abilities like synesthesia and echolocation show that even the boundaries between our senses can be blurry.

Semantic Space. Image: Gallant lab, UC Berkeley

Semantic Space. Image: Gallant lab, UC Berkeley

Still, our brains are talented at picking out certain chunks of sensory experience and associating those chunks with other stimuli. For instance, if you hear purring and feel fur rubbing against your leg, your brain knows to associate that sound and feeling with the fluffy four-legged object you see at your feet – and to group that whole multisensory chunk under the heading of “cat.”

What’s more, years of cat experience have taught you that it makes no sense to think of a cat as if it were a piece of furniture, or a truck, or a weather balloon. In other words, an encounter with a cat carries a particular set of meanings for you – and those meanings determine which areas of your brain will perk up in the presence of a feline.

But where’s the category “cat” in the brain? And where’s it situated in relation to, say, “dog” or “giraffe” …or just “mammal?” A team of neuroscientists led by Alexander Huth at UC Berkeley’s Gallant lab decided they’d answer these questions in the most thorough way possible: By capturing brain responses to every kind of object they could dig up.

Chunks in the brain

Those Gallant lab folks are no slouches – you might remember them as the lab that constructed “mind videos” of entire scenes from neural activity in the visual cortex. This time, though, the lab’s ambitions were even broader.

Semantic Map. Image: Gallant lab, UC Berkeley

Semantic Map. Image: Gallant lab, UC Berkeley

A research team led by Alex Huth showed volunteers hours of video footage of thousands of everyday objects and scenes – from cats and birds to cars and thunderstorms – as the subjects sat in an fMRI scanner. Then the researchers matched up the volunteers’ brain activity not only to each object they saw, but also to a whole tree of nested object categories: A taxonomy of the brain’s taxonomy. A vision of a “continuous semantic space,” where thousands of objects and actions are represented in terms of others.

Huth’s team collected volunteers’ reactions to more than 1,300 objects and categories, and arranged these brain responses not only into a tree of object and action categories, but into a map of response gradients across the whole surface of the brain.

And as you can see from the color gradients in that tree diagram to the right (which is also available as an interactive online app), the relationships among our brains’ categories are multidimensional. Objects may be more or less “animal-like,” more or less “man-made,” and so on – and in fact, the researchers say they expect to find more subtle response dimensions that gauge an object’s size and speed.

Association and meaning

All this talk of “dimensions of association” points back to a far more profound idea about how our brains work: We understand the meaning of an object in terms of the meanings of other objects – other chunks of reality to which our brains have assigned certain characteristics. In the brain’s taxonomy, there are no discrete entries or “files” – just associations that are more strongly or more weakly correlated with other associations.

And that idea itself raises deeper quandaries: If associations define what an object or action “is,” as some neuroscientists have argued, then why does the concept of meaning – semantic representation – need to enter the picture at all? Instead of being a special type of mental function, might “meaning” itself simply be another word for “association?”

The answer to that question won’t be a simple one to find, at least for the foreseeable future. “I don’t think it’s possible to make a conclusive claim about that from fMRI data,” says Jack Gallant, the lab’s director; “and anyone who tells you otherwise is mistaken.”

A single three-dimensional pixel – an fMRI voxel – represents the activity of around one million neurons, Gallant explains; and at that resolution, it’s impossible to say what exactly the neural activity is encoding. Meaning could depend on association, association might depend on semantic coding, or the relationship between the two might be more nuanced than we can conceive right now.

Whatever that relationship turns out to be, the implication remains: In our brains, meaning and association go hand-in-hand. In the brain, even our most abstract concepts depend on our own  real-world experiences. That’s an idea that’s infuriated Plato and his followers far more than Diogenes’ plucked chicken – but as Diogenes demonstrated on that long-ago morning, real-world evidence trumps speculation in the end.


Ben Thomas About the Author: Ben Thomas is an author, journalist, inventor and independent researcher who studies consciousness and the brain. A lifelong lover of all things mysterious and unexplained, he weaves tales from the frontiers of science into videos, podcasts and unique multimedia events. Lots more of his work is available at Follow on Twitter @theconnectome.

The views expressed are those of the author and are not necessarily those of Scientific American.

Comments 11 Comments

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  1. 1. Torbjörn Larsson, OM 11:50 am 12/26/2012

    This is interesting to me since I’m vaguely homing in on an analogous situation in science.

    Before I get there, I have to describe my understanding of “association” here. As the article shows, the analysis is founded in the theoretical (I would think, having a neuronal template)and observed phenomena of spatial location in the brain. Associations are more than transitory correlations, they are likely maps of symbolic processing. [ ]

    “Rougier et al. demonstrate how a specific network architecture – modeled loosely on what is known about dopaminergic projections from the ventral tegmental area and the basal ganglia to prefrontal cortex – can capture both generalization and symbol-like processing,”.

    The evolutionary advantage of a cortex (vertebrates) or mushroom bodies (invertebrates) can be predicted to be a learning process that can’t be overtrained. Which is what is observed.

    So we have symbolic-like processing involved in associative learning. What does “meaning” mean in relation to that?

    The analogous situation is observed in science. Computer science has cleanly posed a model system, which computer scientist Scott Aaronson describes in a seminar. [ ]

    When we “prove and verify” mathematical observations, it is now done on a zero-knowledge basis of a mathematical process of posing and verifying sequences of symbols. This is analogous to science theories and testing.

    Aaronson asks if we can ever have a similar mechanistic account of “explaining and understanding”.

    My take on this is that theories, while being zero-knowledge in the sense of symbols, are “explanations” in their ability to predict testable phenomena.

    But we have also an overarching, less well understood process of elimination testing on theories to converge on absolute knowledge, despite our resources being finite in the face of possibly infinite sets of pathways. For example, with the Higgs field we have now in the words of physicists Sean Carroll “a complete knowledge of the laws underlying everyday physics” which isn’t likely to be rejected later. This is then, no doubts, understanding.

    My notion of meaning is then that it is only partial understanding, but it is (or starts with) the process of posing associations between symbols. At the same time these symbols are derived by associations between them and between observations (“a boundless flow of electromagnetic waves and biochemical reactions”).

    The world of these unobserved, hidden symbols is in humans mapped to explicit and observable symbols of language and language assisted thinking, but that is not much different in quality in the sense of symbols.

    Is this notion predictive? Well, it predicts that all we will observe is that ““meaning” itself simply be another word for “association””, pretty much.*

    * When I started this analysis, I didn’t expect to agree with that! It is educational, even meaningful, to read science blogs. :-)

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  2. 2. Torbjörn Larsson, OM 12:10 pm 12/26/2012

    “My take on this is that theories, while being zero-knowledge in the sense of symbols, are “explanations” in their ability to predict testable phenomena.”

    I should also add in this context that theories are, because they are constrained in the same sense as observations made in some experiment, an observation of a process. More involved than observations of individual events, but the same in spirit.

    So explanations and hence meaning and associations are still observations, albeit at a higher level.* A brain is at its basics, when it isn’t busy inventing myths, understandable as an evolutionary advantageous trait.

    * And analogously absolute knowledge is observation at the most general (universal) level.

    Ouch! If it looks too neat, it is likely not correct. At least it is something to test.

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  3. 3. elemswee 12:47 pm 12/26/2012

    …might “meaning” itself simply be another word for “association?”…
    And this is expressed in a language(another man-made tool) isn’t it…how cool could the human brain be!! :)

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  4. 4. Dr.d 4:13 pm 12/26/2012

    Dr.diogenes suggested :-) : “real-world evidence trumps speculation in the end.” If we limit ‘evidence’ to falsifiable, measured/experienced objects and/or events as witnessed by human beings, then it must happen in a living brain. This I call the physical and phenomenological ontology ‘territory’ to distinguish it from the non-physical, epistemological ‘map’ abstraction made possible by metaphysical logic representation of the same territory for communication purposes. If the reported fMRI study had been recorded from controlled (inbred, environment)subhuman brains, then, the 3-d pixels would likely be almost identical. But in humans, as has been suggested: “In the brain, even our most abstract concepts depend on our own real-world experiences…” but IMHO they would significantly reflect the individualistic variations in genetic and memetic content. This would even be true for the majority of healthy, mentally stable normal humans living peacefully. Now, if the study were made with that 1% of the educated population able to appreciate that beyond the phenomenologically obvious, all humans experience falsifiable ‘feelings’ that resist the classical scientific ‘descriptions’ because they are outside the sensory threshold of human ontological, physical detection(either end of the phenomenological spectrum) then epistemological metaphysical logic explanations need to feel the existential reality gap, and the fMRI would reflect it. Enter epistemontological BPS hybrid model reflecting the brain dynamics of introspective self awareness denied subhuman species. We need these fMRI studies in individuals acting against self interests, in response to higher abstract goals. Hope you can find them. :-) Merry Xmas. Dr.d

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  5. 5. Dr.d 6:20 pm 12/26/2012

    My webhost4life provider has ruined my w-site so I cannot provide a free access to the references and content to sustain my brain farts, so go here and buy…if it’s worth your while….sorry.

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  6. 6. MikeB 11:31 am 12/27/2012

    It would be interesting to see if these same neural taxonomic classifications hold for different ethnic and/or linguistic groups. A confirmed Whorfian myself, I’d bet not.

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  7. 7. dant1 9:25 pm 12/27/2012

    My notion of meaning is that it is likely to be only partial understanding.

    You say; “At the same time these symbols are derived by associations between them and between observations (“a boundless flow of electromagnetic waves and biochemical reactions”).
    The world of these unobserved hidden symbols is, in humans, mapped to explicit and observable symbols of language and language assisted thinking, but that is not much different in quality in the sense of symbols”.

    What do you mean by “but that is not much different in quality in the sense of symbols”.

    I presume it will all finish up based on a collection of zero knowledge based axioms.

    Link to this
  8. 8. dant1 9:27 pm 12/27/2012

    My comment was addressed to Torbjörn Larsson, OM. I thought I was linked to this!

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  9. 9. ronyrao 2:41 am 12/29/2012

    At the same time these symbols are derived by associations between them and between observations.

    Link to this
  10. 10. jgrosay 8:21 am 01/2/2013

    The specific behavior that lead to the condemnation of the “Cynic philosophers” in the Bible, that praises those “Who do not seat in the meeting of Cynics”, was that Cynics had sex with their spouses in front of everybody, as dogs do. While in the USA, the word “cynicism” may refer to an skeptic person that has an ample experience in mundane subjects, and may have made a lot of travels to places with other cultures, in places such as in Spain, being called “Cynic=cínico” is one of the strongest insults somebody may receive.

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  11. 11. rharkn 6:12 pm 01/2/2013


    You wrote: “…non-physical, epistemological ‘map’ abstraction…”

    Careful about equating “non-physical” with “abstraction.” Lots of people make this mistake. There’s no such thing as “NON-physical” (other than the term itself). Everything that exists can be traced back to its physical basis. The mind is a physical process carried on by the brain, and an abstraction exists physically in the brain as a configuration of neurons–as does the word “non-physical”(an unfortunate oxymoron).

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