The gestural origins of language Michael Corballis University of Auckland
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
Jane Goodall on chimps “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.
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
LACK OF VOLUNTARY VOCAL CONTROL IN CHIMPS 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)
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
Two systems of vocal control LIMBIC SYSTEM NEOCORTICAL SYSTEM Anterior cingulate Motor strip Cerebral peduncle Pyramidal tract Peri-acqueductal grey Evolved in mammals, with increasingly differentiated control Nucleus ambiguous over hands, fingers, articulators, & vocal folds Ploog, D. (2002). In T. J. Crow (Ed.) The speciation of modern Homo Sapiens . OUP
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 observes 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 object … � …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 Flat hand Grip form Grip � 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
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 Parietal mirror neurons STS neurons respond to perception of biological motion, but not to action Frontal mirror neurons From Rizzolatti G, Sinigaglia C. (2010) Nature Reviews Neuroscience , 11 , 264-274
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”)
Signs are not mutually transparent between different sign languages Different signs for “tree” Bellugi, U., & Klima, E.S. (1976) Annals of NYAS, 280 ,, 14-538
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 RS+- RS++ RS-- -2 -1 0 1 2 3 R-L (in standard deviations) I I I I I I l
Problem � How to explain the higher incidence of left-cerebral language dominance than of right-handedness?
Annett’s “right shift” theory RS+ Dominant-recessive RS- influence in cerebral asymmetry Right Left Hemisphere dominant for language RS+- RS++ Additive influence RS-- in handedness Left-handed Right-handed
An alternative version RS+- RS++ RS-- Additive model for both cerebral asymmetry and Right Left handedness, with Hemisphere dominant for language reduced environ- mental influence RS+- for cerebral RS++ asymmetry RS-- Left-handed Right-handed
6. The gestural scaffold for speech development
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