Some questions:
* How do infants learn language so quickly?
* To what extent is language development dependent on nature or nurture?
* Do all children develop language in the same way?
* How do you evaluate language development in infants?
Prelinguistic communication
Do we learn anything in the womb?
DeCasper and Spence (1986)
* Newborns modify sucking rate to Dr. Suess books that were read to them in the womb.
* Newborns prefer mother's voice over strangers and fathers
Indicates that newborns have innate preparation to perceive speech at birth
Speaking to infantsMotherese, baby talk
Higher pitch, more variable, more exaggerated
Maintains attention better than adult speech
Do children prefer child or adult-directed speech?
Fernald and Kuhl (1987)
* 4 month old infants reinforced for turning head
* Infants tended to turn head towards voice speaking child-directed speech
Development of communicative intent
At 8 months, infants start to show communicative intent Goal directed behavior
Making sounds to elicit responses
Pointing to objects, Touching adults for attention
Moving something to make something else visible
Communicative acts (Bates, Camaioni and Volterra ,1975)
Assertions:Use an object as means of obtaining attention
* Blowing rasberries
* Gestures
* Rattles
* Holding toy out to adult
Requests: Use of an adult as a means to an object
* Pointing
* Taking things from adults
Prelinguistic infants use gestures to communicate and get attention
* Training for turn-taking
* Permits feedback from parents
The development of speech perception
Categorical perception in infants
/ba/ /pa/ differ in Voice Onset Time (VOT)
/ba/ <25 msecs
/pa/ >25 msecs
Do infants detect differences in voice onset times?
Eimas, Siqueland, Juscyzk and Vigorito (1970)
1-4 month old infants
Habituation procedure recording pacifier sucking rate
Infants respond with higher sucking rates to perceived changes in stimuli
Procedure:
Present pairs of stimuli:
perceived VOTs
Pair 1: /ba/ /pa/ 20 40 msecs
Pair 2: /ba/ /ba/ 0 20 msecs
Pair 3: /pa/ /pa/ 60 80 msecs
Habituate on one item of a pair, then switch to the other item of the pair
Infants' sucking rate changes with pair 1, but not with pairs 2 or 3
Infants are born with mechanisms attuned to speech categories
Do infants perceive phonemic distinctions that are not part of their language?
/r/ /l/ distinction in asian languages (freeze vs. please)
Zulu click consonants
Lasky, Syrdal-Lasky and Klein (1975)
4-6.5 month old infants from Spanish speaking households
Three VOT contrasts
1) 20 vs. 40 msec VOTs (voiced vs. voiceless) (found in Spanish, English)
2) -60 vs. -20 msec VOTs (prevoiced) (found in Thai, but not Spanish)
3) -20 vs. 20 msec VOTs (found in Spanish)
Infants detect the first two VOT contrasts but not the third.
Evidence for categorical perception of other languages
How does experience with your own language shape the perception of phonemic distinctions?
By 10 months you can listen to an infant's babble and identify what language they are speaking
Perception of Hindi 't's (Werker ,1989)
Distinction between 't's declines so that by 10-12 months it is almost equivalent to adult non-Hindi speakers
Overview of Language Development
Month (approx)
0+ Crying
2 Cooing
4 Babbling many speech sounds
10 Babbling home language
12 One-word stage
24 Two-word, telegraphic speech
24+ Rapid development of language to complete sentences
Prelinguistic vocalization: crying, cooing, babbling
First month: crying
Second month: Cooing "oooh" "aaah"
Cries and coos are innate, but modified by experience. talkiing positively to a baby, smiling etc. increases cooing
Babies coo back during conversations with adults.
5th to 6th month reduplicated babbling. "bababa"
* Babbling phonemes of multiple languages
* Combining consonents and vowels "ba", "ga", "da"
Babbling is inborn. All infants babble and coo similarly
9 to 11 months, variegated babbling "dabaguba"
* Phonemes of home language are repeated regularly, foreign phonemes begin to drop out.
* Narrower speech spectogram with age
From babbling to speech (Lexical Development)
Cognitive maturation permits use of words
Initial words are often idiomorphs Invented words to describe object
Idiomorphs indicate:
* Children's language is creative
learning is not purely imitative, but involves invention
* Children learn that objects should be referred to in a consisten manner
First words (around 12 months)
Labels for features in their world (nominals)
* favorite toys (ball)
* family members (mama, dada, dog)
* events (bye-bye, bath)
Learning of the early words
Bias in learning words of objects that change or move in response to their actions ball vs. chair
Words that can not be manipulated are absent: diaper,
Frequent early words
* general nominals: ball, car
* specific nominals: mommy, daddy
* action words: up, go
* modifiers: dirty, pretty
* personal/social words: please, want
* function words what,
How do children learn words?
One process: referential learning
What word does an object in the world correspond to?
Errors in referential learning
Overextension: Identifes one attribibute of an object with a name and then applies that name to other objects with the same attribute
Errors can occur due to:
* functional: anything on a head is a hat
* contextual: a crib blanket is a nap
* affective: forbidden objects are hot
Underextensions: Use words in a more restrictive way than intended by adults
* Shoes only applies to mother's shoes
* lights only applies to headlamps on cars
This is a Cow, moooo
Cow! mooo
Problem for children: While mapping items in world to words, items can be from similar categories.
The role of adult speech in learning
Do you tell your child it's a rooster or a bird or an animal?
Caregivers tend to choose the basic level term
Basic level terms come from the center of the hierarchy in which broad similarities exist across exemplars of the category.
As these terms are learned, caregivers move up and down the hierarchy to fill out the semantic network.
95% of the time definitions given by adults refer to the entire object
Mothers are highly sensitive to children's pointing gestures and provide labels to objects more when children point
Adults appear to be sensitive to the learning process and provide appropriate terms, adjusting to the level of the child.
Cognitive constraints in lexical development
How does a child decide to what a word refers?
Children must have certain expectations about word learning in order to maximize their benefit.
Constraints on learning:
* Whole object bias: Children attach a new label to the entire object rather than part of an object
* Taxonomic bias: Children assume that the object label is a taxonomic category rather than a name for an individual of the category
* Mutual exclusivity bias: Objects only have one name. If a child know the name of an object, then the child will not apply a second name to the object
Markman and Wachtel (1988)
Children shown pairs of objects, one known, one unknown.
Puppet says "Show me the X" Children will pick the unknown object
However, if there is no other object present, then they will interpret the label as applying to part of the object. (Show me the claw when pointing to a hammer.)
Violations of mutual exclusivity: In order to learn hierarchical information, children must violate mutual exclusivity.
Ho Choy, Bernese Mountain dog, dog, animal
Children use biases until there is evidence to the contrary
When is a word more than a word? When it is a Holophrase
Holophrase: a single-word utterance used by a child to express more than the meaning typically attributed to that single word.
water, dog, bed, dada, down
What grammatical knowledge do children have when they make a holophrase?
Children do not have the same grammatical knowledge as adults, but are aware of different semantic relationships of the same words
Naming: Dada When looking at father
Possessor: Dada When looking at father's chair
Volition: Dada When looking at father and at bottle of milk
Agent: Dada When father enters room
Action: Down When child sits down
The development of grammar
The grammatical structure of two word utterances
Two word phase starts around 24 months
Basic child grammar Universal types of constructions in children across cultures
More than imitations or random combinations, child grammar follows a set of regular patterns
1) Combinations of content words without function words or morphemes
want bottle, push truck, more candy
Like telegraphic speech:
ship rescued, crew safe lost money, send cash
Shows understanding of information value of content words over function words
2) Regular patterns of word positions
allgone sock over sock allgone
more milk over mikl more
Shows understanding of grammatical word order
Do children at this stage understand word order?
17 months old shown two videos
Video 1: Big Bird tickling Cookie Monster
Video2 : Cookie Monster tickling Big Bird
Children heard Big Bird is tickling Cookie Monster vs. Cookie Monster is tickling Big Bird"
Children tend to look toward the appropriate video
Evidence for understanding of basic grammar
How do children learn what words fit into what grammatical categories?
Possible approach: Semantic Bootstrapping
Children use their knowledge of semantic relations to learn syntactic relations
Dog
A dog
A cat
A problem
(Agent, action, object acted upon)
John caught the ball
Mary hit the ball
Measuring syntactic growth
Mean length of utterances (MLU): number of morphemes per utterance
An index of childen's language growth
MLU level Morphemes
I 1-2 (putting words together)
II 2.25 (using grammatical morphemes)
III 2.75 (complex constructions such as:
IV 3.5 negatives/questions)
V 4.0
Index of Productive Syntax (IPSyn)
Counts of children's usage of noun phrases, verb phrases, questions, negatives and sentence structures
Why have a measurement of syntactic growth?
* Age is not a good predictor since there are large individual differences
* Permits a comparison of children at the same level of language development
* Can be used to predict later reading disabilities
Which comes first: production or comprehension?
Comprehension tends to precede production
My child is faster than yours!
Individual differences in child language development
Children's learning strategies
Referential strategy:
Learn words (nouns, verbs, adjectives) by reference to environment
Dog, Car, Mommy.....
Develop sentences from words
Expressive strategy:
Learn words with emphasis on social interaction
Stop it. Time to go home. I want it.
Children tend to: have more diverse vocabularies
utter whole sentences
focus on sentence intonation
Effects of learning stratgies on later development
Referential children build up to sentences
while
Expressive children must break down sentences to words and then create new sentences
Referential children start off using high proportion of nouns, but then noun use decreases
while
Expressive children use mix of nouns and pronouns, and thennoun use increases
Over time, the two styles merge.
How do children start off as Expressive or Referential learners?
Caregivers of Referential children tend to use more descriptive terms and tend to label objects more.
Does it matter which strategy a child adopts?
American Sign Language
Learning of ASL by children in deaf households.
* Manual babbling
* One-word stage comes a few months earlier than speaking children
* Two word stage follows rules of word (sign) order
Course of language development is similar for signed and spoken languages
Later stages of language acquisition
Further development of grammar
The acquisition of grammatical morphemes
(Starts around 2.5 MLUs)
Grammatical morphemes: Unit of meaning added to sentences/words to make sentence grammatical
Past tense (ed)
plural inflections (s, es)
prepositions (in, on)
What is learned and in what order?
1 Present progressive I eating
2-3 Prepositions in, on
4 Plural dogs, gooses, mooses
5 Irregular past tense broke, fell ,threw, went, sat
6 Possessive Peter's hat
7 Uncontractible copulaThis is hot
8 Articles a, the
9 Regular past tense She walked, He watched
.....
What leads to this order of development?
Possible hypotheses:
1) Exposure to language
* Frequency with which children hear morphemes prior to acquisition (Moerk, 1980))
2) Linguistic complexity
* Measure semantic and syntactic complexity of language
* Degree of complexity corresponds to order of what is learned
Productivity in morphology (Berko, 1958)
This is a wug
Now there is another one.
There are two of them.
There are two ________
John likes to rick
Tomorrow he will rick
he also _______ yesterday
he ________ every day
This is a bik.
He is wearing a hat
It is the _______ hat.
Children are not just learning morphemes in rote fashion. They are acquiring morphological rules
Additional evidence for rules: Overregularizations
The acquisition of irregular verbs
He goed, Sara breaked the cup.
Learning irregulars verbs: 3 stages
1) Use the word correctly. I went to school
2) Overregularlizes I goed to school
3) Generalizes exception rules for irregular past tense
I went to school
Crosslinguistic differences in the development of grammar
Do all children learn grammar constructions around the same level of development?
Examples:
* Sesotho children learn passive voice earlier than english speakers
* Likely due to frequency of exposure
* Hebrew speaking child form questions when they are at 1.2 to 2.6 MLUs
* English speaking child form questions when they are at 3.5 MLUs
Hebrew questions: Declarative statement with rising intonation He is hungry?
English questions: Subject-Verb phrase inversions
Is he hungry?
Key factors in cross-linguistic differences:
* Frequency of exposure
* Grammatical simplicity
Processes of language development
What are the necessary and sufficient conditions for language development?
* Environmental conditions
* Cognitive conditions
* Innate conditions
Environmental conditions: The linguistic environment
How do you test if exposure to language helps language development? The Unthinkable experiment
Feral and Isolated Children
Victor, The Wild Boy of Aveyron
No speech, but uttered sounds
Trained by Itard using behavior modification and typical langauge training techniques
Extent of language development and learning:
* Named objects only when presented, but not when he requested them
* Gestural communication interfered with language learning
* Association of words with particular objects (little generalization)
Possible explanations:
* Victor mentally retarded
* Itard used bad training techniques
* Victor was past the critical period
Genie
Isolated from age 20 months to 13.5 years
Confined to a chair/bed all the time
Seldom spoken to
Extensive language training program once she was found
Extent of language development and learning:
* Good use of phonology
* Rapid semantic development
learning of complex concepts (colors and numbers)
* Very few grammatical morphemes
* No complex syntactic devices
* Good cognitive development (problem solving etc.)
I like hear music ice cream truck
Think about Mom love Genie
Conclusion:
* Acquiring language after long periods of isolation is difficult
* Advanced cognitive development may not be enough for language to develop (necessary, but not sufficient)
Innate mechanisms in language acquisition
Do innate mechanisms constrain language development?
The language biogram hypothesis (Bickerton)
"Children have an innate grammar that is available biologically if our language input is insufficent ot acquire the langue of our community."
The development of Pidgins and Creoles
Pidgin: an auxiliary language that arises when speakers of several mutually unintelligible languages are in close contact
* Tends to be rudimentary
* No syntax rules
* No fixed word order
Creole: What develops when children grow up in a Pidgin speaking community
* Consistent word order
* Complex sentences
* Structure similar to other languages
Other evidence:
Deaf children develop gestural languages
Nicuraguan sign language
Evidence for an innate grammar that operates even without proper environmental input (a language bioprogram)
But what happens if a child receives appropriate language input?
The preemption principle: "If you hear people using a form of different from the one you are using, and do not hear anyone using your form, abandon yours anduse theirs"
Examples of the general innate mechanisms: Parameter setting (Chomsky)
Grammar can be defined as a set of parameters that vary from language to language
The Null-subject parameter
In Spanish you can drop the subject of a sentence
I go to school
Voy a la escuela
Children are born with a default value of dropping the subject, but English speakers learn that it is required and English speaking children soon learn to include it
The issue of negative evidence (The poverty of stimulus argument)
* Children receive very little negative evidence that a particular grammatical construction is incorrect.
* Parents tend to correct childen's semantic mistakes, but not their syntactic mistakes
So....
1) Positive evidence alone is consistent with too many competing grammars.
2) Negative evidence, which could constrain the problem space is not generaaly available.
3) Therefore, some constraints must be innate.
Summary
* The linguistic environment and when a child is exposed to language is important
* Cognitive processes alone are not enough to permit language development
* There are some innate mechanisms to language acquisition
Learning to read :The development of reading skills
Problem: Linking printed letters (graphemes) to phonemes
1) Young children often have an imperfect idea of what phonemes are
Phonemes are abstractions of sounds and do not represent natural physical sound segments
/d/ in bad, dim, dime, lid
2) Alphabets do not code each of their vowels with a unique symbol
/a/ in saw, say, sad
If phonological awareness plays a role in the development of reading skill, can we improve it through training?
Danish training program in phonological awareness over 8 months brought about improvements in reading
Prerequisites to reading
* Phonological Awareness
* Orientation skills
left vs. right, d vs. b
* Letter recognition
Knowledge of letter names in kindergarten is the best predictor of early reading acheivement
Early readers vs. late readers
Most children start reading in first grade, 1% some start earlier. Are there any differences in these children?
* Same range of IQ scores
* Come from varied socioeconomic and racial backgrounds
* Parents tend to read to them more and have more education
* However, not much difference between children after a few years of reading
But... reading to a child does generally improve overall reading skills
Methods of teaching reading Whole word vs. Phonics
Whole word:
* Teach whole words, since children don't recongize that letters represent sound units.
* Teaches word consciousness
* Teaches that many English words are irregular in spelling, must be learned in terms of their visual appearance
* As child learns, he/she will abstract out phonemes
Phonics:
* Analytic approach to words
* Exploits alphabetic principle
* Build from learning small set of letters to whole words
Which is better?
* Phonic approach uses a more consistent way of introducing new words.
* Slightly better learning in students
What really goes on in the classroom?
* A combination of both methods
* "Empirical research is generally irrelevant to the real-world decisions about how publishers design reading programs and which reading program is adopted by a school district "
Should you go out and buy "Hooked on phonics" for your child?
Top-down vs. Bottom up processing in learning to read
Using the context to help determining meaning
Do good readers use context or bottom up processing when reading?
Allington and Strange (1977)
Fourth-grade children categorized as good and poor readers
The frog hopped oven the snow
Poor readers said over Good readers said oven
Indicates that good readers rely more on bottom up processing.
Why?
* We have a limited number of resources when reading.
* Word recognition is an automatic process
* We can then allocate more processes to higher level comprehension
Establishing cohesion
Drawing inferences
Summarizing topics
The biological foundations of language
A shift of focus from looking at products of language to mechanisms of language
How do we know that it is the brain that produces/ processes language?
How do we know where in the brain langauge is produced/processed?
Aphasia: A language disorder produced by brain damage.
Broca's Aphasia
Paul Broca discovered halting, agrammatic speech after strokes and accidents
* Agrammatic speech
* Use only one word at a time
* Content words (nouns,verbs) preserved
* Function words (adjectives, articles) lost
* Comprehension appears to be ok.
Peter Horgan:
Describing dental Surgery:
Yes... ah... Monday... er... Dad and Peter Horgan..., and Dad... er. hospital... and ah... wednesday... wednesday, nine o'clock...and oh... Thursday ... ten o'clock, ah doctors... two...an'doctors...and er... teeth... yah...
Describing job in paper mill:
Lower Falls... Maine... Paper. Four hundred tons a day! And ah ... sulphe r machines, and ah... worrd... Two weeks and eight hours. Eight hours... no! Twelve hours, fifteen hours... working...workin... workin! Yes, and ah... sulphur. Sulpher and ... Ah wood. Ah ... handlin! and ah sick four years ago.
Is it just a failure of grammatical processing?
Wernicke's aphasia
Fluent, but little or no information value.
"What brings you to the hospital?"
"Boy, I'm sweating, I'm awful nervous, you know, once in a while I get caught up, I can't mention the tarripoi, a month ago, quite a little, I've done a lot well, I impose a lot, while, on the other hand, and you know what I mean, I have to run around, look it over, trebbin and all that sort of stuff."
"Thank you Mr. Gorgan. I want to ask you a few___"
"Oh sure, go ahead, any old think you want. If I could I would. Oh, I'm taking the word the wrong way to say, all of the barbers here whenever they stop you its going around and around, if you know what I mean, that is tying and tying for repucer, repuceration, well, we were trying the best that we could while another time it was with the beds over there the same thing..."
Comprehension difficulties:
"Touch your knee" results in touching ankle
Name objects:
table: "chair"
elbow: "knee"
clip: "plick"
butter: "tubber"
ceiling: "leasing"
comb: "close, saw it, cit it, cut the comb, the came"
paper: "piece of hankerchief, pauper, hand pepper, piece of hand paper"
Conduction aphasia: Loss of link between Broca's and Wernicke's areas arcuate fasciculus
* Broca's area is connected to Wernicke's area by a band of fibers.
* Able to understand and produce speech
* But unable to repeat what they have heard
If Broca's and Wernicke's areas are intact, but are cut off from the rest of the brain then No comprehension, but patients repeat everything they hear without understanding.
Syntax and semantics in Broca's and Wernicke's aphasia:
Is it a difference between production deficits and comprehension deficits?
Caramazza and Zurif (1976)
Comprehension capacities of Broca's Wernicke's and conduction aphasics
Listen to a sentence and point to picture that corresponds to the sentence
(1) The book that the girl is reading is yellow (non-reversible noun)
(2) The horse that the bear is kicking is brown. (reversible noun)
Wernicke's aphasics perform poorly on both sentences
Broca's and conduction aphasics perform well on nonreversible nouns, but perform at chance on reversible nouns
So, Broca's aphasia does have some comprehension deficits, although masked by semantic knowledge
The dog bit the man
Broca's patients judging grammaticality of sentences:
Can detect many violations in syntax
John was finally kissed Louise **Detected**
John was finally kissed by Louise
How many did you see birds in the park? **Detected**
The little boy fell down, didn't it? **Not Detected**
Broca's aphaisa summary:
* Many problems with syntact production
* Can construct some sytactic representations, although difficult
Wernicke's aphasics
* Problems of word retrieval
* Problems of semantic categorization
Caramazza and Berndt (1978)
Judge three words and say which two go together
Mother, husband, shark
Makes judgements based on affective characteristics
Mother, Father, Cook
Puts Mother and Cook together since patients mother was a good cook.
More modern approaches to examining aphasia
PET and MRI scans
Provides information on how brain is organized
Evidence for "category deficits"
Damage can produce people who can not recognize certain categories of objects
Fruits and Vegetables
Plants,
Animals
Body parts
Colors
Number
letter
nouns
verbs
facial expressions
Parts of brain may contain "indexes" to particular types of concepts
Indexes help activate information about concepts related to a particular concept
"Cat" activates: fur, four legs, ears, nose, eats mice etc.
Lateralization and Language
Different hemispheres perform different functions
* 97% of the time language in left hemisphere of right handers
* 68% of the time language in left hemisphere of left handers
other lefties have it in right or both hemispheres
Lefties more likely to withstand a stroke in one hemisphere without suffering from aphasia
Split brain research
Severing the corpus callosum to prevent spread of epliepsy
Left visual field goes to right hemisphere
Right visual field goes to left hemisphere
Present spoon to left visual field. What happens?
What did you see? "nothing"
Touch it with right hand: performance at chance
Touch it with left hand: performance is good
Does the right hemisphere do any language processing?
Present sentence pairs to the left visual field. Is there a difference?
The boy kisses the girl
The girl kisses the boy No difference
The girl is drinking
the girl will drink No difference
the dog jumps over the fence
the dogs jump over the fence No difference
the girl is sitting
the girl is not sitting **Difference**
Right hemisphere can respond to individual nouns: boy, girl
but not to verbal commands: tap, smile, frown
Right hemisphere has phonetic deficits:
Can not determine if ache and lake rhyme, although can comprehend them
Individuals with right hemisphere damage do not detect sarcasm, interpret statements literally
Priming: Both hemispheres show priming of semantic information, but right hemisphere can not supress inappropriate primes over time
John took a loan from the bank money, river
Evidence for very rudimentary syntactic mechanisms, but good semantic memory in right hemisphere
Lateralization in other species
Is the laterality of language special to humans?
Japanese Macaques
Peterson, Beecher, Zoloth, Moody & Stebbins (1978)
Macaque vocalizations presented to right or left ear.
Better performance of vocalizations to right ear
Evidence for left-hemisphere dominance for processing species specific sounds
Song birds (chaffinches, white-crowned sparros)
Developmental stages similar to human developmental stages
* Babbling stage
* Learning specific dialects based on exposure
Severing left side of chaffinch brain disrupts song
Severing right side of chaffinch brain has no effect on song
Languages in non-humans
Do other species possess language?
The language of Bees
Karl von Frisch
For food within 50 meters of the hive, bees perform Round dance
For food >50 meters from hive, bees perform tail-wagging dance
Direction of food: Orientation of dance
Distance to food: Amount of time waggling
200 meters 0.5 secs
4500 meters 4 secs
Testing the language of bees: The bee robot
Birds:
Alex: Grey parrot
Trained in name, numbers and features of objects:
green triangle, red square, blue circle
What shape?
How many?
What color
What's same?
What's different?
Performance around 85% correct
Primates
Early failures:
Training chimps to talk
Kellogg & Kellogg (1933), Hayes & Hayes (1951)
Raised young chimps in home like human babies
Chimps never learned to say many words:
Mama, cup, papa
But could it be a problem of production and not comprehension?
Training in ASL
Washoe
* 32 signs at 22 months old
* 132 at 5 years old
Generalization:
Open: applied to multiple contexts, doors, refrigerators, faucets
New words:
water-bird for swan
rock-berry for Brazil nuts
Learning from other apes:
Loulis learned 51 symbols from Washoe over 5 years
Syntax:
Roger tickle Washoe used interchangably with Washoe tickle Roger
but able to respond with answers from the correct grammatical category for Wh questions:
Who are you?
Where is the box?
When is dinner?
Knowledge of word classes
Please machine give apple
Generalization to:
Please Roger give apple
Please machine give candy
Criticisms and caveats of this approach to language
Signing as imitation
* Strong tendency to repeat signs their trainers had made
* Not much independent babbling with signs
Inadvertant cuing
* Clever Hans
* Performance often deteriorated when experimenter was not visible
Computer keyboard solved some of these problems
Video Questions
Is there a critical period of language learning for primates?
What methods are used to train/test primate language?
To what extent do Chimpanzees/Bonobos learn language?
Syntax
Semantics
Advanced concepts (numbers etc.)
How does Bonobo language development and comprehension compare to that of children?
Can child apes learn language from their parents?