Syntactic learning in non-human primates and neuroimaging of evolutionary precursors to language

Matthew G. Collison

Laboratory for Comparative NeuropsychologyInstitute of Neuroscience

Newcastle University

Where are the evolutionary precursors to human language in the primate brain?

Old World Monkeys (Rhesus Macaque)

25 million years

Humans

8 million years

New World Monkeys (Cotton Top Tamarin)

Great Apes (Chimpanzee)

35 million years

From what did human language evolve?

Syntax: What is it and how do we study it in nonhuman animals?

Syntax is a key components of human language: “the ability to understand the sequence (grammar) of words in a sentence” Very difficult to study in nonhuman species.

However the core computations of syntactic processing can be studied in nonhuman animals using artificial grammars.

Artificial-language (syntactic) learning in monkeys

Grammatical

Ungrammatical Grammatical

Ungrammatical

Fitch & Hauser 2005, Science

Finite State Grammar

Phrase Structure Grammar

%Look

s

Another example: Infants and tamarins learning a different type of “grammar”Saffran et al., Cognition 2008

InfantsTamarins

Old World Monkeys (Rhesus Macaque)

25 million years

Humans

8 million years

New World Monkeys (Cotton Top Tamarin)

Great Apes (Chimpanzee)

35 million years

?

Subclass associations used in word languages

Subclass (Male) Words used Subclass (Female) Words used A1 Biff B1 hepA2 Cav B2 lumA3 Klor B3 pell A4 Dupp B4 lokeA5 Jux B5 pilk

Rhesus macaque experiment

Familiarisation Phase

Test Phase ABAB- A2A3B3B2 A1A2B2B1 A4B5A3B2 AABB- A1B1 A3B3 A2B2A3B3 A2A1B3B5

BBAA- B3B1A1A3 B3B2A2A3 B3B5A2A4

BABA- B2A2B3A3 B4A4B2 A2 B3B1A2A5

Prediction: Double Dissociation

Macaques exposed to FSG will consider PSG sequences as more interesting to look at, but if they were exposed to PSG the opposite effect is predicted.

% looks

Behavioural Results

A) Experiment 1 – Familiarisation to PSG B) Experiment 2 – Familiarisation to FSG

PSG

PSG

The human language regions respond to artificial grammars

Diffusion Tensor Imaging - Connectivity

Friederici 2006

Macaque fMRI: Potential ‘syntactic-learning’ network

PSG Familiarisation

Threshold = 0.01

FSG Familiarisation

Threshold = 0.01

X = 53Y = 85.5

Z = 22

X = 39Y = 84.5

Z = 20

Striatum (implicit learning system)

Dorso-lateral frontal cortex (possibly Broca’s area)

Conclusions

Rhesus Macaques are capable of learning a more elaborate grammar (both FSG and PSG) than tamarins.

fMRI responses to the grammatical sequences shows at least 2 sites as part of the potential ‘syntactic-learning’ network that may have evolved to support language in humans.

Precursor to Statistical learning

Precursors to Syntactic grmmar

Future work to be done

How much more can rhesus macaques learn.

Further fMRI to replicate/support or extend the observations here.

What are the neuronal mechanisms underlying syntactic processing?

InfantsA1A2A3B3B2B1

TamarinsABAB

Old World Monkeys (Rhesus Macaque)

25 million years

Humans

8 million years

New World Monkeys (Cotton Top Tamarin)

Great Apes (Chimpanzee)

35 million years

Evolutionary development of language

Rhesus MacaqueAABB