William H. Calvin, "Corticocortical Coherence as an Enabling Step for Fluent Nested Embedding." See also http://WilliamCalvin.com/2000/ParisEvolLanguage.htm.
conference: T H E E V O L U T I O N O F L A N G U A G E
Paris April 3-6, 2000
Ecole Nationale Supérieure des Télécommunications
Paris - France
Webbed Preprint Collection|
William H. Calvin
University of Washington
Corticocortical Coherence as an
William H. Calvin
The cognitive categories needed for keeping track of "Who
owes what to whom" (evolved for minimizing the freeloader problem in
reciprocal altruism) are a nice setup for the agent-theme-goal role tags so
useful for quickly communicating "Who did what to whom."
The prefrontal-premotor circuitry needed for planning novel throwing
and hammering movements looks a lot like the binary trees of phrase structure.
repeated payoffs of even more altruism, or even more accurate throwing, seem
capable of adapting brain circuitry that could be occasionally borrowed for
The cortical "plainchant
choirs" needed for preprogramming accurate throws can, when extensive
enough, make the long corticocortical paths (corpus callosum and such)
temporarily coherent, overcoming the usual blur and jumble.
Coherence would permit the various phrases and clauses to be located at
diverse cortical sites, yet still "sing
as a unified choir" as alternative sentence interpretations compete with
threshold for coherence provides a "capstone"
candidate for fluent structured thought and talk -- something that might have
triggered the flowering of art and technology seen late in hominid evolution,
after brain size itself had stopped growing.
Since corticocortical coherence is the one that builds atop the other
two, and is the one that might have had a sudden emergence (the others look
like gradual carryover so far, perhaps for millions of years), let me start by
briefly explaining the first two pre-syntax "stones" of this arch
so that the "capstone" role in enabling fluent syntax can be appreciated.
of Argument Structure.
Bickerton's preadaptation is from reciprocal altruism.
What pays for the improvements in abstract cognitive categories for
actor, recipient, and action are that they help keep track of who owes what to
is not only handy for minimizing the cheater problem, telling the individuals
possessing such cognitive traits when they ought to find a partner more likely
to reciprocate occasionally, but it aids the furtherance of coalitions between
Bickerton's idea is that,
once you have the cognitive categories for keeping track of "Who
owes what to whom," you can start communicating "Who
did what to whom" -- and have a syntax-ready recipient with the preformed mental
categories needed for disambiguating the longer utterances.
You get the essentials of argument structure (categories for agent,
goal, and theme) from the payoffs of ever more cooperation.
You may further improve the underlying neuroanatomy with new payoffs
from language itself, but the foundations came "free," paid for via the prior cooperation/altruism use.
Conversions of function are a familiar story in evolutionary theory
(Darwin spoke of them before introducing his example of the fish swim bladder
converting into an amphibian lung).
And any conversion goes through an intermediate phase of
our mapmaking tendencies that lead us into erroneously assuming one region,
one function (it's another instance of the reification fallacy), cortical regions are
While a region may have a specialization that is essential (you can't
do the function without it, as seen in the stroke and cortical surface
stimulation results), the region may participate in other functions (as seen
via its increase in blood flow when performing nonspecialist tasks).
Even the common strokes illustrate the multifunctionality: most aphasic
patients also suffer from hand-arm apraxia, suggesting a core of neural
machinery for novel sequencing that is shared by novel hand-arm and
of Phrase Structure.
The other common way
of disambiguating a long string of words is what, in pre-minimalist days,
was called phrase structure.
The nested embedding of phrases and clauses, one within another, is
strongly reminiscent of the structured planning needed for planning
multi-joint ballistic movements during "get
The hand movement is embedded in the elbow rotation which is embedded
in the shoulder rotation which is embedded in the body's
Planning involves getting the whole thing right; there may be dozens of
ways to hit the target, but they're hidden in a sea of millions of wrong
solutions, ones that would cause dinner to run away.
What pays for planning improvements is aimed throwing for hunting and precision hammering for toolmaking; when novel sequences of hand-arm movement are not being planned, such neural machinery may be available for structured planning of other things, such as long utterances or agendas. Again, once structured language pays for further improvements, it may in passing improve aimed throwing or precision hammering, to the extent that they continue to share neural machinery.
important feature of ballistic planning is its use of cortex for novel
sequences (i.e., not standardized target distances as in darts and basketball
free-throws, where subcortical circuits probably take over) with demanding
requirements for timing precision (small targets have very brief "launch
windows" and so timing jitter must be minimized).
Coherence for Fluent Structured Thought.
I recently refined Hebb's 1949 notion of a cell-assembly
whose spatiotemporal firing pattern (think of a short song) represents a
concept, relationship, action -- or a phrase or a clause.
Even the complete sentence should have one, if it is to compete with
This firing pattern would be a "code" for the concept, but one would expect the code for, say, comb
to be different in visual association cortex than near auditory or motor
uniform-across-the-cortex code would be powerful but, for the same reasons as
it took Europeans so long to invent the Euro, it isn't
a default solution.
The corticocortical connection from concept-laden temporal lobe to
movement-schema-laden frontal lobe via the arcuate fasciculus (second only the
corpus callosum in size) is surely jumbled (neighboring axons may not remain
neighbors at the other end) and the fanout of connections guarantees blur.
So a different code arrives, equally good in most respects (just like
changing money when border crossing) but when it gets sent back to the
originating cortex, it is doubly distorted.
For frequently used concepts, of course, an identity relation can soon
when novel messages are being sent around ("'A
square green tomato' -- anyone recognize this phrase?"), it runs into the same problem
as trying to get moneychangers to recognize a wooden nickel.
You can't get the
virtues of a universal code for novel on-the-fly concepts without the
equivalent of a coherent corticocortical connection.
What I demonstrated
in Chapter 7 of The Cerebral Code was that enough clones of the code in
the sending cortex (think of a plainchant choir recruiting additional members
from neighboring cortex, all singing the same song) would suffice to create a
small choir singing the same song at the destination. (Such choirs are needed for reducing jitter and are also an
outcome of a Darwinian copying competition for achieving quality on-the-fly.)
This allows novel codes to be passed
back and forth without slowly learned identities.
While handy for association tasks in general, the role of
corticocortical coherence in nested embedding is where the common code really
shines. It seems capable of making syntax an everyday, subconscious
task that operates in seconds.
"meaning of the sentence"
is, in this model, an abstract cerebral code which competes for territory with
codes for alternative interpretations, often in the manner of a Darwinian
Phrases and clauses require coherent corticocortical links to
contributing territories, having their own competitions and tendencies to die
out if not reinforced by backprojecting codes.
It starts to look like a choral work of many voices, each singing a different tune but with the requirement that it mesh well with all the others. Indeed, the symphonic metaphor might be appropriate for the more complex sentences that we can generate and understand. Certainly the reverse-order analogy to Benjamin Britten's Young Person's Guide to the Orchestra, the all-together version being succeeded by the various voices playing separately, is the best metaphor I know for the read-out process that converts the parallel-structured plan into serial-ordered speech.
Syntax Back to Protolanguage.
Consider the implications of efficiently linking the concept-filled
temporal lobe with the prepare-for-action frontal lobe, with a common code
replacing the degenerate codes -- and then dropping back to the old system, with
now-incoherent paths forcing a reliance on slowly established identities.
Without coherence, you'd still have a vocabulary (the temporal lobe still
still be able to plan some nonlanguage actions (you'd pass many of the
neuropsychological tests for frontal lobe functioning), but your ability to
quickly invent new trial run associations would suffer.
only couldn't you form up a syntactic sentence to speak (except for stock phrases),
but you couldn't judge sentences
that you heard someone else speak because you could no longer judge the quality
of your trial interpretations, whether they were nonsense, good guesses, or sure
quality associations would be too slow for the windows of opportunity, and the
results would be of poor quality because not shaped up very far by Darwinian
copying competitions in the brain.
And so your performance on language tasks would drop back to something
like protolanguage, a wide choice of words but with novel sentences limited to
just a few words to avoid ambiguity.
Big Step Up: Homo
sapiens and Structured Thought.
reciprocal altruism's cognitive categories and ballistic movement's planning
circuits are both compatible with slow language improvement over a few million
corticocortical coherence should have a threshold (the size of the plainchant
choir, achieved mostly by temporarily borrowing neighboring cortex, not via
brain size increases).
borrowing abilities cross the coherence threshold, structured thought and talk
would have become far more fluent -- and
thus a capstone candidate for what triggered the flowering of art and technology
seen late in hominid evolution, after brain size itself had stopped growing.
A proper lingua ex machina would be a language machine capable of
nesting phrases and clauses inside one another, complete with evolutionary
circuitry for structured thought might also facilitate creative shaping up of
quality (figuring out what to do with the leftovers in the refrigerator),
contingency planning, procedural games, logic, and even music.
And enhancing structured thought might give intelligence a big boost.
Solve the cerebral circuitry for syntax, and you might solve them all.
None of us are there yet, but this "three-stone archway" provides an illustration of how our big
questions -- what, how, and why
might hang together.
I thank Derek Bickerton for
persistently steering me in this direction, and the Rockefeller and Mathers
Foundations for provocative venues.
Hebb, The Organization of Behavior (Wiley 1949), p.62.
William H. Calvin, The Cerebral Code (1996)
William H. Calvin and Derek Bickerton,