the gestural origins of language - uqam€¦ · the gestural origins of language. or, how language...
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Michael Corballis
University of Auckland
The gestural origins of language
Or, how language went fromhand to mouth
Pedigree
Cresollius (1620), Mandeville (1728), Condillac (1746), Rousseau
(1782), Tylor (1868, 1871), Morgan (1877), Wallace (1881),
Romanes (1888), Wundt (1912), Paget (1944), Johanneson (1949,
1950), Hewes (1973), Wescott (1974), Critchley (1975), Steklis &
Harnad (1976), Engelfield (1977), Kimura (1979), Armstrong,
Stokoe & Wilcox (1991), Kendon (1991), Corballis (1991, 1999),
Donald (1991), Allott (1994), Givon (1995), Rizzolatti & Arbib
(1998), Skoyles (1998), Armstrong (1999), Goldin-Meadow &
McNeill (1999), Wells (1999), Place (2000), Arbib (2005), Rizzolatti
& Sinigaglia (2006), Armstrong & Wilcox (2007), Tomasello
(2008)—and more
“What’s the one obvious thing we humans do that [chimps]
don’t do? Chimps can learn sign language, but in the wild, so
far as we know, they are unable to communicate about
things that aren’t present. They can’t teach what happened
100 years ago, except by showing fear in certain places.
They certainly can’t plan for five years ahead. If they could,
they could communicate with each other about what compels
them to indulge in their dramatic displays. To me, it is a
sense of wonder and awe that we share with them. When we
had those feelings, and evolved the ability to talk about
them, we were able to create the early religions”
In conversation with Freddy Gray, on p. 13 of The Spectator of 10 April, 2010.
Jane Goodall on chimps
Or Robert Browning …
! “He said ‘What’s time? Now is for dogs and
apes! Man has forever’”
--from A Grammarian’s Funeral (1855)
Six reasons to believe that languageevolved from manual gestures
"# The hands as a “natural” communication system
$# In great apes, gesture is closer to language than is
vocal communication
%# “Mirror neurons” in primates form a natural platform
for language evolution
&# Signed languages are true languages
'# Handedness and cerebral asymmetry for language
are correlated, suggesting common influence
(# Development of speech depends on a gestural
scaffold
1. Why manualgestures have thedesired properties
The 4D World
! We live in 4D space-time
! Voice conveys information in 1D only
! Gestures convey information in 4D
! Allows iconic representation
! Vision is our dominant mode
! The hands and arms provide the “natural”way to communicate about events in theworld
Visuo-manual action
! Long history in primates
! Arboreal adaptations
! Adaptation of hand for manipulative
activities: fruit-plucking, tool use, grooming,
catching insects, …
! 3D colour vision
! Intentional behaviour
A pitcher is worth a thousand words
2. Great ape gesturesare more language-like than are their
vocalizations
Jane Goodall: Chimp unable to suppress
pant-hoot on discovery of cache of bananas
“The production of sound in the absence
of the appropriate emotional state seems
to be an almost impossible task for a
chimpanzee.”
--The Chimpanzees of Gombe (1986, p. 125)
LACK OF VOLUNTARY VOCAL
CONTROL IN CHIMPS
Flexibility of manual and vocalgestures in great apes
! Manual gestures much
less tied to “typical”
contexts than
facial/vocal gestures in
chimps and bonobos
Pollick, A. S. & de Waal, F.B.M. (2007). PNAS, 104, 8184-8189
Flexibility of manual and vocalgestures in great apes
! Much lower correlations
between groups for manual
than for facial/vocal gesture
Pollick, A. S. & de Waal, F.B.M., (2007). PNAS, 104, 8184-8189
LIMBIC SYSTEM NEOCORTICAL SYSTEM
Ploog, D. (2002). In T. J. Crow (Ed.) The speciation of modern Homo Sapiens. OUP
Two systems of vocal control
Evolved in mammals,
with increasingly
differentiated control
over hands, fingers,
articulators, & vocal folds
Anterior cingulate
Cerebral peduncle
Peri-acqueductal grey
Motor strip
Pyramidal tract
Nucleus ambiguous
Some chimp gestures
Arm-on Arm-raise Back-off
Ball-offer Belly-offer Direct-hand
Foot-stomp Genital-offer Ground-slap
Hand-beg Hand-clap Head-bob
Head-shake Lead Leg-offer
Lip-lock Look-back Point
Poke-at Push-object Raise-object
Reach Rub-chin Shake-object
Spit-at Swagger Throw-stuff
Touch-side Wave-object Wrist-offer
—from Tomasello, Call, Warren, Frost, Carpenter, and Nagell (1997)
Teaching “language” to great apes
! No success in teaching apes to talk
! Moderate success in teaching forms of
signed language
! Washoe
! Kanzi
! Koko
Savage-Rumbaugh, S., Shanker, S.G. and Taylor, T.J. (1998). Apes,
language, and the human mind. New York: Oxford University Press.
Savage-Rumbaugh, S., Wamba, K., Wamba, P., and Wamba, N. (2007).
Applied Animal Science, 10, 7-19.
Kanzi (a bonobo) has quiteextensive visual language
3. Mirror neurons
Mirror neurons
! First discovered in Area F5 in the monkey
! Fire when the animal makes a grasping movement, and also when itobserves the same movement made by another
! Maps observation onto execution
Variety of mirror neurons
! Some respond to relatively precise
correspondence between actual
and observed movements (e.g.,
precision grip)
! Others respond if the movements
are different but the goal is the
same (e.g., grasping with normal or
reversed pliers)
“Mirror neurons will do for psychology what DNA has done for biology”!V.S. Ramachandran
Object-related activity
! In monkey,mirror neuronresponds only ifthere’s an actualobject …
! …even if it’shidden but themonkey knowsit’s there
Object-related action is termed transitive
Transitive and intransitive action inhumans
! Mu rhythmsuppression indexesmirror neuronresponse
! Suppressiongreatest for grip(transitive)
! Less for flat handand grip form(intransitive) but stillsignificant
Muthukumaraswamy SD et al. (2004) Cognitive Brain Research, 19, 195-201
Flat hand Grip form Grip
Homologous areas in monkey andhuman brain
! Primary motor
cortex
! Premotor
cortex
! Mirror neuron
area. In
humans this is
also Broca’s
area
The extended mirror system inprimates
From Rizzolatti G, Sinigaglia C. (2010) Nature Reviews Neuroscience, 11, 264-274
Parietal mirror
neurons
STS neurons
respond to
perception of
biological motion,
but not to actionFrontal mirror neurons
Essential overlap between mirrorsystem and language system
Mirror system in monkeys Language network in human
Language is incorporated in the human mirror system,
predominantly in the left hemisphere
Mirror neurons in primates respond toaction-related sound, but not to primatecalls
Note mirror neurons don’t really mirror; they map visual or auditory
stimuli onto the actions that produce them
Kohler, E., et al. (2002). Science, 297, 846-848.
Changes required for language
! Mirror system responds to intransitive as well astransitive actions. This allows the system tomove beyond understanding of object-graspingto use of gesture in symbolic communication(e.g., mime, and eventually speech)
! More complex programming to supportgrammar? (Arbib, 2005)
! … and for speech, vocalization was incorporated(and biased the system to the left hemisphere)
Arbib, M.A. (2005). Behavioral & Brain Sciences, 28, 105-168.
4. Signed languages
Properties of signed languages
! Have all the linguistic sophistication ofspoken language
! Arise spontaneously in deaf communities
! Emerge as pantomime but becomeincreasingly conventionalized andgrammaticalized
! Depend on same brain areas as spokenlanguages (“sign language aphasia”)
Bellugi, U., & Klima, E.S. (1976) Annals of NYAS, 280,, 14-538
Signs are not mutually transparentbetween different sign languages
Different signs
for “tree”
5. Handedness andcerebral asymmetry
The right-shift theory
! ~88% of human population are right-
handed
! ~ 91% of human population are left-brain-
dominant for language (spoken or signed)
! These asymmetries are correlated
! Both influenced by the same “right-shift”
gene (Annett, 2002)
Annett, M. (2002). Handedness and brain asymmetry: The right shift theory. Psychology Press.
How two alleles of the RS geneinfluence handedness
I I I I I I l
-2 -1 0 1 2 3
RS--
RS+-
RS++
R-L (in standard deviations)
Problem
! How to explain the higher incidence
of left-cerebral language dominance
than of right-handedness?
Annett’s “right shift” theory
Left-handed Right-handed
Right Left Hemisphere dominant for language
RS+
RS-
RS++
RS+-
RS--
Dominant-recessive
influence in
cerebral asymmetry
Additive influence
in handedness
An alternative version
Left-handed Right-handed
Right Left Hemisphere dominant for language
RS++RS--
RS++
RS+-
RS--
Additive model for
both cerebral
asymmetry and
handedness, with
reduced environ-
mental influence
for cerebral
asymmetry
RS+-
6. The gesturalscaffold for speech
development
Volterra, V., Caselli, M.C., Capirci,O., Pizzuto, E. (2005). Gesture and the emergence and development of language . In M. Tomasello and
D. Slobin, (Eds.) Beyond Nature-Nurture. Essays in Honor of Elizabeth Bates. (pp. 3-40) Mahwah, N.J.: Lawrence Erlbaum Associates.
Em
erg
ence
of
language
Emergence ofintentional
communication
Manual components(gestures)
Vocal components(words)
Bimodal period
Two-wordstage
9 ……………………… 14 ……………..….. 24Months
Em
erg
ence
of
language
Emergence ofintentional
communication
Manual components(gestures)
Vocal components(words)
Bimodal period
Two-wordstage
9 ……………………… 14 ……………..….. 24Months
How did the switchoccur?
Neuron discharge
during grasping
with the mouth.
Neuron discharge
during grasping with
the contralateralhand
Neuron discharge
during grasping
with the ipsilateral
hand
Rizzolatti, G., et al. (1988) Exp. Brain Res. 71, 491-507.
Recordings from area F5 in
the monkey brain
Link between hand and mouth inprimates
Gentilucci, M., et al. (2004). European Journal of Neuroscience, 19, 190-202.
Also in humans: Vocalization changesdepending on action
A Subject says “ba”
B Subject vocalizes
nonlinguistic sound
C Observation of
action
D Pantomime of
action
E Nonbiological arm
cherry
apple
*
* *
Subjects say “ba” while watching a persongrasping cherry or apple
Gentilucci, M., et al. (2004). Neuropsychologia 42, 1554-1567.
C = children
A = adults
The switch was gradual
! Probably from hands to face to vocal tract
! Speech is facial gesture half-swallowed, butwith vocal accompaniment
! Vocalization allows internal gestures(tongue, velum, larynx) to be accessible
! Control of the vocalization was the last step,involving changes to vocal tract, breathing,tongue control, and control of the larynx
Speech itself is a gestural system, notan acoustic one
! Mirror system already preadapted for either
visual or acoustic input
! These are mapped onto gestures
! Language is an embodied system—we
communicate using our bodies
Motor theory of speech perception
! Lack of invariance in acoustic signal
! Invariance lies in production (or gesture)
! Hence all language, spoken or signed (or both), maps onto gestures
Articulatory phonology
! Speech conceived as gestures of the lips,
the velum, the larynx, and the blade, body,
and root of the tongue
! Perception of speech involves recovery of
gestures, not acoustic analysis
! These gestures are partly visible
(lipreading, McGurk effect, …)
Why the switch?
Speech frees the hands
! Allows development of manufacture
! Also allows the development of pedagogy, sothat manual activities (e.g., making and usingtools, cooking lessons, etc) can bedemonstrated and verbally described at thesame time.
! Speech is much less demanding of energyresources
! Speech is miniaturization
• Does not work in the dark, or when obstacles intervene.
• “[African languages are not elaborate enough] to enable
a native to state his exact thought. Some of them are very
dependent upon gesture. When I was with the Fans they
frequently said "We will go to the fire so that we can see
what they say", when any question had to be decided
after dark, and the inhabitants of Fernando Po, the Bubis,
are quite unable to converse with each other unless they
have sufficient light to see the accompanying gestures of
the conversation.” —Mary Kingsley, Travels in West Africa, 1897,
reprinted 1965, p.504
Gesture needs light
When did the switchoccur ?
Speech may have become dominantwith H. sapiens
! This could explain the rise of “modernity”
from around 90,000 years ago
! More sophisticated manufacture
! Cave art, sculpture, bodily embellishment
! Burial rites
! FOXP2 mutation
Changes for speech occurred late inevolution of Homo
! Lowering of larynx
! Lengthening of
tongue and neck
! Flattening of face
! These changes
not complete even
in Neanderthal,
30,000 years
ago?
Orangutan Chimp Human
Human Neanderthal
An extreme conclusion?
! “… fully human speech anatomy first
appears in the fossil record in the Upper
Paleolithic (about 50,000 years ago) and is
absent in both Neanderthals and earlier
humans” (Lieberman, 2007, p. 39)
—Lieberman, P. (2007) The evolution of
human speech. Current Anthropology, 48, 39-46
The FOXP2 gene
! KE family: deficits in speech due to mutation on
the FOXP2 gene on chromosome 7
! The primary deficit is oro-facial movement*
! Affected members of the KE family don’t show
activation of Broca’s area when generating verbs
! FOXP2 gene responsible for introducing articulate
vocalization to the mirror system?
*Watkins, K.E., et al. (2002). Brain, 125, 452-464.
FOXP2 and the MirrorSystem
! Unaffected KE members show activation ofBroca’s area when generating verbs
! Affected members show bilateral activationexcluding Broca’s area
! Could FOXP2 have assimilatedorofacial/vocal control into Broca’s area,and the mirror system?
Liégeois, F. et al., Nature Neuroscience, 2002, 11, 1230-1237
Evolution of the FOXP2 gene
! FOXP2 underwent 2 mutations in hominins afterthe split from the apes
! The more recent occurred not later than “the timesince the onset of human population growth, some10,000 to 100,000 years ago. … This is compatiblewith a model in which the expansion of modernhumans was driven by the appearance of a more-proficient spoken language” (Enard, W. et al. (2002)Nature, 418, 871)
! Another molecular analysis suggests mutation was42,000 years ago (Coop, G., et al. (2008). Molecular Biology andEvolution, 25, 1257-1259.)
BUT
! Recent evidence that the FOXP2 mutation
was present in the DNA of a 45,000-year-
old Neanderthal*
! This implies that the mutation may go back
400,000-5000,000 years, to the common
ancestor of humans and Neanderthals!
*Krause, J., et al. (2007). Current Biology, 17, 1908-1912.
BUT
! Evidence now suggests some mating
(DNA exchange) between
Neanderthals and non-African
humans from 50,000 to 80,000 years
ago (Green et al. (2010) Science 328, 710-
722)
! The FOXP2 story is not yet over
The power of speech
! Responsible for the “evolutionary
explosion” and development of modernity?
! Also responsible for the dominance of
humans over other hominins, and eventual
extinction of them all?
! Are other “revolutions” also dependent on
changes in communications systems
(writing, internet, cellphones)?
And we still gesture as we speak
‘And do you, Stephanie, promise to love, honor, and “obey”?’