The gestural origins of language Michael Corballis University of - - PowerPoint PPT Presentation

Michael Corballis University of Auckland

The gestural origins of language

Or, how language went from hand 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 language evolved 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 manual

gestures have the desired 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 the world

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 gestures

are 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

• f 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 vocal gestures 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 vocal gestures 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

• ver 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 quite extensive 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 it

• bserves 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 neuron responds only if there’s an actual

• bject …

…even if it’s

hidden but the monkey knows it’s there

Object-related action is termed transitive

Transitive and intransitive action in humans

Mu rhythm

suppression indexes mirror neuron response

Suppression

greatest for grip (transitive)

Less for flat hand

and grip form (intransitive) but still significant

Muthukumaraswamy SD et al. (2004) Cognitive Brain Research, 19, 195-201 Flat hand Grip form Grip

Homologous areas in monkey and human brain

Primary motor

cortex

Premotor

cortex

Mirror neuron

• area. In

humans this is also Broca’s area

The extended mirror system in primates

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 action Frontal mirror neurons

Essential overlap between mirror system 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 to action-related sound, but not to primate calls

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 as

transitive actions. This allows the system to move beyond understanding of object-grasping to use of gesture in symbolic communication (e.g., mime, and eventually speech)

More complex programming to support

grammar? (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 of

spoken language

Arise spontaneously in deaf communities Emerge as pantomime but become

increasingly conventionalized and grammaticalized

Depend on same brain areas as spoken

languages (“sign language aphasia”)

Bellugi, U., & Klima, E.S. (1976) Annals of NYAS, 280,, 14-538

Signs are not mutually transparent between different sign languages

Different signs for “tree”

• 5. Handedness and

cerebral 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 gene influence 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

• f 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 gestural

scaffold 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.

Emergence of language

Emergence of intentional communication Manual components (gestures) Vocal components (words) Bimodal period Two-word stage 9 ……………………… 14 ……………..….. 24

Months Emergence of language

Emergence of intentional communication Manual components (gestures) Vocal components (words) Bimodal period Two-word stage 9 ……………………… 14 ……………..….. 24

Months

How did the switch

• ccur?

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 in primates

Gentilucci, M., et al. (2004). European Journal of Neuroscience, 19, 190-202.

Also in humans: Vocalization changes depending 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 person grasping 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, but

with 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, not an 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, so

that manual activities (e.g., making and using tools, cooking lessons, etc) can be demonstrated and verbally described at the same time.

Speech is much less demanding of energy

resources

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 switch

• ccur ?

Speech may have become dominant with 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 in evolution 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 Mirror System

Unaffected KE members show activation of

Broca’s area when generating verbs

Affected members show bilateral activation

excluding Broca’s area

Could FOXP2 have assimilated

• rofacial/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 after

the split from the apes

The more recent occurred not later than “the time

since the onset of human population growth, some 10,000 to 100,000 years ago. … This is compatible with a model in which the expansion of modern humans was driven by the appearance of a more- proficient spoken language” (Enard, W. et al. (2002)

Nature, 418, 871) Another molecular analysis suggests mutation was

42,000 years ago (Coop, G., et al. (2008). Molecular Biology and

Evolution, 25, 1257-1259.)

BUT

Recent evidence that the FOXP2 mutation

was present in the DNA of a 45,000-year-

• ld 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”?’