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William H. Calvin, "The Mind’s Big Bang and Mirroring." Unpublished manuscript, ©2000.  See also http://WilliamCalvin.com/2000/MirrorNeuronsCommentary.htm.

 
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This 'tree' is really a pyramidal neuron of cerebral cortex.  The axon exiting at bottom goes long distances, eventually splitting up into 10,000 small branchlets to make synapses with other brain cells.
William H. Calvin

University of Washington
Seattle WA 98195-1800 USA


The Mind’s Big Bang and Mirroring

  by William H. Calvin

Mirror neurons in the frontal lobe are an intriguing possibility for explaining the seeming dichotomy between anatomically- and behaviorally-modern Homo sapiens.  They are neurons, located in the monkey’s version of Broca’s area, which might be involved in mirroring, that tendency of two people in conversation to mimic one another’s postures and gestures.  And, as such, candidates for what might be involved in the cultural spread of communicative gestures and perhaps even vocalizations.

The Italian neurophysiologist who discovered the monkey mirror neurons, Giacoma Rizzolatti, does not claim so much.  Indeed, he takes pains to bring flights of fancy back to the more limited hard data.  Every time someone mentions mirror neurons as part of a neural circuitry for “see one, do one” mimicry, Rizzolatti will point out that they could equally be involved in simply understanding.  Just as in language, where we know that there is a big difference between understanding a sentence and being able to construct and pronounce it, so mirror neurons might just be in the understanding business rather than the movement mimicry business.

But it’s an exciting prospect because of the motor theory of speech understanding, put forward by Alvin Liberman back in 1967.  Elaborated by others in the last few decades, it claims that tuning in to a novel speech sound involves subvocal attempts to create the same sound, that our useful memories of a novel speech sound come from our movement system stirring up proprioception from our vocal tract, that our memories are not merely the sound we heard but partial models for how to mimic it.  Mirroring the sound, using real production, might be an infrequently-achieved second stage.  This is why Rizzolatti emphasizes understanding.

The brain has neurons which buzz away during certain actions and not others, say when the monkey picks up an object with its finger tips but not when digging it out of a hole (for which other neurons might buzz away).  Mirror neurons are a subset of these movement-related neurons in premotor cortex area F5 which, in addition, buzz away when the monkey merely sees another monkey (or even human) do the same thing, often only out of the corner of its eye.  It isn’t just the movement which stirs up these neurons; making the grasping gesture in mid-air won’t work.  It seems to require an object as well, much as most verbs require an associated theme to be expressed at the same time.  And object movement alone won’t work, as when the experimenter picks up the object with forceps instead of his fingers.  Sure sounds verb-like to me.

The mirror neurons would seem to be just what you need for mirroring gestures, the confluence of the particular sensory representation and the particular movement production.  And why has this stirred so many of us into enthusiastic extrapolations of Rizzolatti’s data?  Because humans are extraordinary mimics, compared to monkeys and apes, and it surely helps in the cultural spread of language and toolmaking.  Furthermore, for a half century, there has been a big puzzle in human evolution, and we keep trying out ideas for size.  Augmented mirroring is the latest.

The upper Paleolithic art and tools speak, as Richard Leakey said in his 1994 Science Masters book, “of a mental world we readily recognize as our own.”  It bursts on the scene rather suddenly, compared to the infrequent progress in toolmaking over the million years that came before.  As Ian Tattersall said in Becoming Human, “This… stands in dramatic contrast to the relative monotony of human evolution throughout the five million years that preceded it.  For prior to the Cro-Magnons, innovation was… sporadic at best.”

       In general, it is best not to identify innovations with the species that obviously practiced them.  Big innovations (say, upright posture) were likely invented earlier by the predecessor species (Terry Deacon is excellent on this, see his Symbolic Species).  Behavior invents, bones follow (a less elegant way of saying form follows function).  In this view, the bony transitions are merely solidifying progress already achieved by behavioral flexibility and learning abilities, likely including imitation.

       But in the case that Lascaux and Chauvet illustrate (more generally, see the July 2000 National Geographic), the bony changes seem to be about 100,000 years earlier than the culture manifestations.  So there was behavioral innovation without (as yet) a corresponding change in body proportions and the other tell-tale things that paleo­anthro­pologists focus upon.

       So did we get a lot more mirror neurons 50,000 years ago?  Or did an already augmented human mirroring system merely help spread another biological or cultural invention in a profound way?  The latter would likely suffice because the profound (and perhaps sudden, as halfway steps seem so unlikely) improvement in language concerns structuring, not words or phrases per se.  Mirroring had likely been aiding in the gradual development of novel vocalizations and words for a million years, and likely even short sentences (for which you don’t need structural support).  A great deal of what’s important for language doesn’t involve syntax, but structuring really makes long sentences fly, and likely complicated thoughts as well.  Let me explain.

       There are certainly major predecessors to structured language.  Body postures communicate mood and intention (dogs communicate dozens), and arm or face posture sequences provide even more bandwidth for broadcasting your feelings and intentions.  Species-specific vocalizations get a big addition from culturally-defined “words” (whether signed or spoken) whose learned meaning depends much more on context.  Next comes word combinations, such as short sentences.  So far we’re mostly talking about what Derek Bickerton in 1990 called “protolanguage,” and this unstructured language (you can guess the meaning without any help from word order or inflections) is what you see in toddlers and speakers of pidgins (my halting German similarly lacks grammar).

       Long sentences, however, are too ambiguous without some mutually understood conventions about internal structuring into phrases and clauses.  A clause may be embedded in a phrase, and vice versa, ad infinitum.  Such conventions constitute syntax and each dialect has a different way of doing things.  “Universal grammar” is simply the tendency of all human groups to use a restricted set of structuring possibilities; not every scheme is possible, and that likely has something to do with the way in which the human brain is wired.

       Once you have a syntax (kids pick them up between 18 and 36 months), you can convey complicated thoughts.  And hopefully think them first, so as to avoid that blues lament about when “Your mind is on vacation but your mouth is working overtime.”  It is this last step up to syntax that is the usual candidate for the mind’s big bang, not the language-lower-case stuff that, though essential, falls short of structuring per se.  The British anthropologist Kenneth Oakley suggested in 1951 that the art-and-tools efflorescence might have been when fully modern language appeared on the scene.  To quote Bickerton, “Only language [he means, in this case, syntax] could have broken through the prison of immediate experience in which every other creature is locked, releasing us into infinite freedoms of space and time.”

       And the mental machinery for syntax is likely shared, at least in part, with music beyond rhythm, planning beyond the predictable seasons, and the logical chaining of ideas - all things that involve the novel, not just learned repetitions like singing the national anthem for the Nth time.  Novel structured stuff is what we usually call “higher intellectual function.”  Pay via natural selection for one functionality like planning or language (or maybe even something like precision throwing), and you may get the others mostly “for free.”

       Whatever economist said that “There are no free lunches” obviously didn’t read Darwin and his successors.  There is a great deal of multiple use in evolution and you can see a reminder on many a street corner.  Those curb cuts were paid for by the wheelchair considerations but they are largely used - and for free - by suitcases and skateboards, bicycles and tricycles.  Bickerton and I address some of the possible preadaptations for syntax in our Lingua ex Machina book (MIT Press 2000).

       At the stage of protolanguage, pace Phil Lieberman, the speed of articulation or the duration capacity of the buffer may not be important.  Indeed it is useful to imagine a version of structured thought that is too slow for repartee.  It might be handy when you have time to think about things overnight, and so it can influence agendas and contingent planning - but even if you could speak a novel sentence aloud, no one might be able to interpret it without thinking about it overnight.  Conversational language may not have been the first “killer application” of structured thought, but rather something closer to the contingency or precision aspects of plan-ahead.

       Now let me briefly address Steven Mithen’s notion in The Prehistory of the Mind of connecting compartments as a source of the mind’s big bang.  Let me quote Rama Ramachandran on Steven:  “[Mithen] claims that before the big bang there were three different brain modules in the human brain that were specialized for ‘social or machiavellian intelligence,’ for ‘mechanical intelligence’ or tool use, and for ‘natural history’ (a propensity to classify).  These three modules remained isolated from each other but around 50,000 years ago some genetic change in the brain suddenly allowed them to communicate with each other, resulting in the enormous flexibility and versatility of human consciousness.”

       As the proprietor of about the only neural-circuits theory for how novel long-distance cortical interconnections might improve dramatically (and without any further brain enlargement or reorganization, at that), I find Mithen’s notion appealing and like to think that he might have read the second half of my book, The Cerebral Code (MIT Press 1996, and just out in German translation).  It addresses the subject of rapid, on-the-fly communications between distant cortical areas.  The problem is how to do it without a slow learning procedure for each new novel combination.  I suggest that the improved interconnections between areas occur when the anatomically-incoherent corticocortical interconnections (lots of jumble and blur) finally become temporarily coherent via a physiological workaround involving sufficient redundancy.  With such a plainchant chorus of sufficient size, you can recover a novel spatiotemporal firing pattern at the other end and pass it on (see chapter 7 of Cerebral Code) to a third cortical area, also unaltered.  That ability to routinely handle novelty, dependent on finally reaching a critical mass that allows recovery of the original pattern from the blur and jumble, might well have contributed to the aforementioned Big Step Up.

       I trust, by the way, that we’re all talking about “compartments/modules” as merely a convenient bit of jargon for a functional specialization, with no notion of exclusivity.  The flip side of all those blood-flow maps, from which people often infer specialization, is multiple use; just look at a given region and notice how many different tasks all activate it.  Regions just don’t stay dark during other tasks, unless someone thresholds the data.  Our tendency to give a functional name, based on the first use discovered, constantly leads us into reification fallacies.  As the linguist Liz Bates likes to point out, all of the “language” areas of brain seem “to have kept their day job” and that’s pretty likely for Mithen’s compartments too.  (This is an American idiom referring to amateurs who are not ready to turn pro, the advice being that they “shouldn’t give up their day jobs” just yet.  One suspects that this applies with particular force to our amateur performances in the area of logical chains of reasoning, that maybe we aren’t yet ready for prime time.)

       So what does the mirror neurons concept add to all this?  Certainly the prospect of finding a physiological basis for “See one, do one” imitation is exciting.  But, for starters, I worry that the mirror neurons simply represent a form of visual association learning.  If you’ve ever seen yourself perform the movement, you could have matched up what you saw with the associated movement program that you sent to your muscles.  Ditto the monkey, long before the recording session; the “mirror neurons” of premotor cortex would just be those now activated by either the sensory pattern or the movement program.  And then maybe you generalize the association to the similar movements of others.  (Yes, there are some innate exceptions, like infant facial expression imitation, where learning doesn’t seem to be required - and not leaving something to learning is often an indication of how important it has become.)  But sensory-motor association of modular movements, and their novel chaining - now that combination might turn out to be pretty powerful.

       So I think that it is the higher intellectual functions that emerged so dramatically 50,000 years ago, not just syntax or augmented mirroring.  But mirroring novel sequences, as in learning how to dance, may have been the key to spreading it around the world so quickly as a cultural conquest.

 


William H. Calvin is a theoretical neurobiologist, Affiliate Professor of Psychiatry and Behavioral Sciences at the University of Washington in Seattle.  He is the author of ten books, mostly for general readers, about brains and evolution.  The most recent is his book with Derek Bickerton, Lingua ex Machina: Reconciling Darwin and Chomsky with the Human Brain (MIT Press, 2000).  His web site starts at faculty.washington.edu/wcalvin.

 

 


Related books and their amazon.com links:

William H. Calvin, The Cerebral Code (1996)

William H. Calvin and Derek Bickerton,
  Lingua ex Machina: Reconciling Darwin and Chomsky with the Human Brain  
(MIT Press, 2000).

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