The development of body, thought and language - a summary of chapter 11 of Psychology by Gray and Bjorklund (7th edition)

Psychology
Chapter 11
The development of body, thought and language

Physical development

Prenatal development

Zygotic, embryonic and fetal phases

The prenatal period is conventionally divided into three phases:

• The zygotic phase
  When sperms join egg, combining the genes, the zygote begins its journey to the uterus.
  During this time (2 weeks) the zygote divides many times, eventually implanting in the uterine wall. This ends the zygotic phase and beginning the embryonic phase. (40 percent of zygotes do not survive this earliest phase. And one third of those who do are lost in later phases by miscarriages).
• The embryonic phase
  From the third to about the eight week after conception. During this time, all major organ systems develop.
  The embryo receives nutrition from the mother’s bloodstream via the umbilical cord through the placenta (which develops inside the uterus during pregnancy). The placenta also exchanges oxygen, antibodies and wastes between the mother and embryo.
• The fetal phase
  The final phase of the prenatal period. It extends from about 9 weeks until birth.
  The most prominent feature is growth and refinement of organs and body structure.
  The fetus changes in proportion. The head of the fetus at 9 weeks is proportionally large relative to the rest of the body, and this decreases, with the body catching up by the time the baby is born.
  Cephalocaudal development: the change in proportions.

By the end of the 12^th week after conception, all the organs are formed, though not functioning well, and are in same proportion to each other as in a full-term newborn, just smaller.
The external genitalia begin to differentiate between males and females between the 9^th weeks but are not fully formed until about the 12^th week.
In the 8^th week, the embryo begins to move and activity increases by 12 weeks.

Fetuses ‘behave’ and are able to perceive some stimuli.
By 6 months fetuses respond to their mothers’ heartbeat and sounds from outside the womb, including language.

The effects of experience during the prenatal period

Although embryos and fetuses are sheltered from the outside world they are nonetheless subject to the effects of experience.

Teratogens: environmental agents that cause harm during prenatal development.
Most teratogens are in the form of substances that get into the embryo’s or fetus’s system from the mother through the umbilical cord.
A teratogen’s potential effect on prenatal development depends on how early or late in pregnancy the exposure occurs. If an organ has been developed, exposure to a potential teratogen will have little or no effect on future development.

It is not just teratogens that embryos and fetuses respond to, but other aspects of experience, such as nutrition and maternal stress.
The developing fetus can use this information as a ‘forecast’ of the environmental conditions it will eventually face after birth, and start adjusting its physiological and behavioral profile to match the requirements of the world it will probably encounter.

Infancy: roughly the first 18 to 24 months after birth. It is the time of most rapid developmental change, change that lays the foundation for further development.
If the prenatal period lasted much longer, a newborns brain would be too large to fit through the birth canal. This means that much of brain development occurs after birth in humans.

Physical development: puberty and adolescence

The head and brain grow rapidly over the first 5 or 6 years and approach adult levels by age 10.
The lymphoid system develops rapidly early in life, greatly exceeding adult dimensions by about age 12, and just as rapidly decreases over adolescence.
The reproductive system shows little until adolescence.

Puberty: the developmental stage leading up to adolescence when glands associated with the reproductive system begin to enlarge, bringing about changes in physical appearance and behavior.
Increases in hormones in both males and females contribute to changes in physical stature reproductive ability and emotions and behavior related to sexual attraction.

Puberty does not happen all at once, but is a series of related events, typically spanning over 4 to 5 years.
Other pubertal events continue to change over time.

How infants learn about the environment

The infant as explorer

Infants’ sensory systems all function at birth (although vision is still quite immature).
Within a short time after birth, they do not only respond to stimuli but do so selectively, in ways that seem well designed for learning.

Infants look selectively at novel objects

Babies gaze longer at new stimuli than at familiar ones.
Habituation and (with new stimuli) dishabituation.
This preference for novelty makes sense if we assume that infants are actively trying to learn about their world.

Infants’ bias for looking at novel stimuli is so reliable that developmental psychologist use it to assess infants’ abilities to perceive and remember.

Infants seek to control their environments

Within a few weeks after birth, infants begin to show a special interest in aspects of the environment that they can control.
The desire to control our environments seems to be a facet of human nature that exists in every phase of development. We survive by controlling our environment.

Infants explore increasingly with hands and eyes together

During their first 3 or 4 months of life, babies put practically anything that they can reach into their mouths.
They mouth objects in ways that seem designed to test the objects’ properties. With time, the explore increasingly in the more uniquely human way, with hands and eyes together, rather than with mouths.

By 5 to 6 months, babies regularly manipulate and explore objects in the sophisticated manner that is labeled examining.
They hold an object in front of their eyes, turn it from side to side, pass it from one hand to the other rub it, squeeze it, and in various other ways act as if they are deliberately testing its properties.
Such actions decline dramatically as the infant becomes familiar with a given object but return in full force when a new object is substituted for the old one.

Infants vary their examining in ways consistent with an object’s properties.

• They look at colorfully patterned objects
• Feel objects that have varied textures
• Shake objects that make a sound when shaken
• Squeeze objects that are pliable
• Pound objects that are hard.

Infants do learn about object’s properties through such examination. Examination is universal and doesn’t need to be taught.

Infants use cues to guide their behavior

Infants often use cues from adults to guide exploration.
Beginning in their first year of life, babies regularly exhibit gaze following.
Gaze following: follow the eyes. This ensures that infants will attend to those objects and events that are of greatest interest to their elders, which may be the most important things to attend to and learn about for survival within their culture. It also helps to promote language development.

Another achievement during the latter part of the first year is the infants’ ability to view other people as intentional agents. Individuals who cause things to happen and whose behavior is designed to achieve some goal.
This is clearly seen around 9 months of age when infants engage in shared attention with another person. It involves a three-way interaction between the infant, another person and an object.
By 12 months of age infants will point to alert others to objects they are not attending to.
Between 12 and 18 months of age they will point to direct and adult’s attention to an object the adult is searching for.

Humans may be the only species to be able to share a perceptual experience.

By the time that infants can craw or walk on their own infants engage in social referencing.
They look at their caregivers’ emotional expressions for clues about the possible danger of their own actions.

Infants’ knowledge of core physical principles

Infants possess core knowledge about the physical world, needing relatively little experience with their physical environment to arrive at these insights.
Infants are born with a small set of skeletal competencies specialized to make sense of the physical world.
So infants are prepared by evolution to make sense of the physical world so that some things are more easily learned than others.

Infants reveal core knowledge in selective-looking experiments

Babies look longer at unexpected events than at expected ones.
Experiments have demonstrated infants’ knowledge of core principles.
Core principles may be present early on, but nuances related to them are acquired with age and experience.

Infants reveal less knowledge in search tasks than in selective-looking tasks

Infants under about 5 months of age lack even the most basic understanding of object permanence (the principle that objects continue to exist when out of view).
In order to retrieve a hidden object, the baby not only must know where the object is, bus also must be able to use that knowledge to guide his or her reaching movements. Babies under five months have no difficulty reaching for objects that are in full view, but may be unable to use mental images of hidden objects to guide their reaching.

Dramatic improvements in infants’ search abilities occurs shortly after they learn to crawl or other ways to move about on their own.
For infants to move about on their own, they need to coordinate their vision with their muscular movements in new ways to avoid bumping into objects. As they move, they also see objects from new and varied perspectives. Such experiences may well help them learn to plan all sorts of effective movements, including those involved in retrieving hidden objects.

Three theories of children’s mental development

Piaget’s theory: role of the child’s own actions in mental growth

Mental development derives from the child’s own actions in the physical environment.
Children are constantly striving to figure out what they can do with the various objects that exist in their world.
By acting on objects, children develop mental representations (called schemes) with are mental blueprints for actions.
Schemes are a mental representation of a bodily movement or of something that a person can do with an object or category of objects.
The earliest schemes are closely tied to specific object and are called forth by an object’s immediate presence. As children grow older, they develop new, more sophisticated, more abstract schemes that are less closely tied to the immediate environment or to actual physical actions. They become schemes for mental actions.

Schemes develop through assimilation and accommodation

The growth of schemes involves two complementary processes

• Assimilation
  The process by which new experiences are incorporated into existing schemes. Few new stimuli fits perfectly in an existing scheme.
• Accommodation
  Existing schemes expand or change somewhat to accommodate the new object or event.

Children behave like little scientists

Infants and children behave like scientists.
Their exploration play can be thought of as experimentation. They are most strongly motivated to explore those objects and situations that they partly bot do not fully understand. These experiences can be assimilated into existing schemes, but not too easily, so that accommodation is required. This natural tendency leads children to direct their playful activities in ways that maximize their mental growth.
Children’s play is oriented toward discovery, not toward repetition of already known effects.

Reversible actions (operations) promote development

As children grow beyond infancy, the types of actions most conductive to their mental development are those called operations. Those actions whose effects can be undone by other actions.
Operational schemes: mental blueprints that allow them to think about the reversibility of their actions.
Understanding reversibility of actions provides a foundation for understanding basic physical principles.
Conservation of substance.

Four types of schemes: Four stages of development

1. The sensorimotor stage
   Sensorimotor schemes. This scheme provides a foundation for acting on objects that are present, but not for thinking about objects that are absent. Thought and physical action are one and the same.
   The major task is to develop classes of schemes specific for different categories of objects.
   Eventually the schemes develop in such a way that the child can use them as mental symbols to represent particular objects and classes of objects in their absence.
   Intelligence is limited to the infant’s own actions on the environment. Cognition processes from the exercise of reflexes to the beginning of symbolic functioning.
2. The preoperational stage
   Preoperational schemes emerge from sensorimotor schemes and enable the child to think beyond the here and now.
   Children have a well-developed ability to symbolize objects and events that are absent, and in their play they delight in exercising that ability
   Intelligence is symbolic, expressed via language, imagery and other modes, permitting children to mentally represent and compare objects out Om immediate perception.
   Thought is intuitive rather than logical and is egocentric. Children have a difficult time taken the perspective of anther.
3. The concrete-operational stage
   Intelligence is symbolic and logical. Thought is less egocentric. Thinking is limited to concrete phenomena and their own past experiences (it is not abstract).
4. The formal-operation stage
   Children are able to make and test hypotheses. Possibility dominates reality. Children are able to introspect about their own thought processes and can think abstractly.

Criticism of Piaget’s theory of stages

Piaget underestimated the mental abilities of infants and young children and overestimated those of adolescents and adults.

Vygotsky’s theory: role of the sociocultural environment in mental growth

Children develop in a sociocultural milieu in which they interact constantly with other people and with products of their cultural history.
Cognitive development is largely a matter of internalizing the symbols, knowledge, ideas and modes of reasoning that have evolved over the course of history and constitute the culture into which the child is born.

Tools of intellectual adaptation

Children learn to think as a function of the tools of intellectual adaptation that their culture provides. (Like number words, alphabets and books or pencils)
Children may discover concepts through their active manipulation of objects, but they do so with the tools that their culture provides them, and usually with the implicit assistance of significant others in their local environment.

The role of collaboration and dialogue in mental development

Development occurs first at the social level and then at the individual level.
People learn to converse with words before they learn to think with words.
People also learn how to solve problems in collaboration with more competent others before they can solve the same kinds of problems alone.
Zone of proximal development: the realm of activities that a child can do in collaboration with more competent others but cannot yet do alone.
Children’s development is promoted most efficiently through their behavior within their zones of proximal development.

Critical thinking derives largely from the social, collaboration activity of dialogue.

The child as apprentice

Children are attracted to activities and seek practice.
The goal of development is to function effectively as an adult in one’s society.

An information-processing perspective on mental development

Information-processing perspective attempt to explain children’s mental development in terms of operational changes in basic components of their mental machinery.
As children grow, their brains continue to mature in various ways, resulting in changes in their abilities to attend to, remember and use information gleaned through their senses.

Development of long-term memory systems: episodic memory comes last

The reason of infantile amnesia is that children before age 3 or 4 do not have well-developed explicit or declarative memory. (Which requires a degree of self-awareness and abstract encoding that develop gradually over childhood.
Implicit memories are available even to young infants. Young infants develop the ability to encode their experiences into words before they can form episodic memories of those experiences.

At about age 3 children begin, with some reliability to talk about their experiences as they experience them. Such talk seems to help them make sense of what they are doing, and may be essential to the formation of episodic memories.
At first such talk depends on the existence of an older conversation partner who can help the child organize the experience in a coherent way and find the appropriate words for it.

The ability to form detailed, long-lasting memories increases gradually throughout the years of childhood and reaches a plateau in late adolescence or young adulthood.
This improvement is accompanied by continued maturation of the brain, particularly the prefrontal lobes.

The development of basic-level processes: Executive function

Executive functions are mental processes involved in the regulation of thought and behavior.

• Working memory
  The amount of either verbal of visual information that a person can hold in working memory at any given time increases steadily throughout childhood and reaches adult levels at about age 15.
  These increases are accompanied by improved performance on standard tests of fluid intelligence.
• Inhibition
  Improved over childhood. Like children often have a difficult time inhibiting their speech.
• Switching
  Young children have difficulty shifting form one task or set of rules to another.

Each of these is related to the speed with which we can process information.
These basic-level cognitive abilities play a critical role in most higher-level cognitive abilities.

Changes in executive functions also occur at the other end of the life-span continuum.

Closely correlated with each of these measures of executive function is speed of processing. (The speed at which elementary information-processing tasks can be carried out.
Faster processing may result at least partly form the physical maturation of the brain that occurs throughout childhood, independent of specific experiences.
The prefrontal cortex plays a major role in executive functions and is one of the last brain areas to fully develop.

Children’s understanding of minds

To develop as fully functional humans, we must learn not just about the physical world but also about the social world around us.

Theory of mind: a person’s concept of mental activity; the ability to understand one’s thought, feelings and behaviors and those of others.
This implies having some causal-explanatory framework to attribute intention to and predict the behavior of others.

Even very young children explain behavior in mental terms

By the time children have learned language sufficiently to offer verbal explanations, they already explain people’s behavior in terms of mental constructs, especially in terms of perceptions, emotions, and desires.
They expect others to respond to objects that they (the others) can see but not to objects that they cannot see.
2 year olds have an understanding that another person’s desires can be different from their own. (14 month olds not).
Even one year olds can display a remarkable understanding of what is in another person’s mind.

Delay in understanding beliefs, especially false beliefs

Three-year-olds rarely offer explanations in terms of beliefs. They do not clearly understand that beliefs can differ from reality.
Three-year-olds denials of false belief apply even to their own false beliefs.

Perhaps the concept of false belief is particularly difficult to grasp because of its inherent contradiction. They are both false and true at the same time. They are false in reality but true in the minds of the believers. In this way they differ from the products of make-believe.

Make-believe as a precursor to the belief-reality distinction

Three-year-olds may have difficulty understanding false beliefs, but they have no difficulty understanding pretense.
Children’s understanding of false beliefs emerges from their earlier understanding of pretense.

Children everywhere engage in pretend play, whether or not they are encouraged to do so.
The brain mechanisms that enable and motivate pretend play may came about in evolution because such play provides a foundation for understanding nonliteral mental states, including false beliefs.

By pretending children develop a capacity to generate and reason with novel suppositions and imaginary scenarios, and in so doing may get to practice the creative process that underpins innovation in adulthood.

Play promotes false-belief understanding and pretending correlates close.
Children who have engaged in lots of pretend role-play with other children pass false-belief tests at a higher rate than do children who have engaged in less. The same for children who have older siblings. 
In social role-play children get used to the idea that other people can hold concepts in their heads that do not reflect reality.

Autism: a disorder in understanding minds

Autism, autism spectrum disorder is a disorder which is characterized by serve deficits in social interaction, serve deficits in acquiring language, a tendency toward repetitive actions, and a narrow focus of interest.
Among the earliest signs of autism in infants are failure to engage in prolonged eye contact, failure to synchronize emotional expressions with those of another person, and failure to follow another person’s gaze.
The deficit in language seems to be secondary to the lack of interest in communication. Children with autism rarely use gestures as an alternative form of communication, when they do, it is almost always for instrumental purposes. Those who learn language learn it late, almost invariably with the help of deliberate teaching, and their language always contains peculiarities that seem to reflect a lack of sensitivity to other people’s minds and perspectives.

People with autism perform poorly on false-belief tests and on test of ability to either deceive or detect deception.
The primary deficit is mindblindness (the inability to read minds)

The human capacity to understand mental representations (beliefs) is distinct from the capacity to understand physical representations (pictures).

Children with autisms lack of pretending play.
Children with Down syndrome do, and they develop a better understanding or false beliefs and deception than do children with autism.

Do Chimpanzees have a theory of mind?

Chimpanzees aren’t able to pass false-beliefs tasks.
In some circumstances, they seem to realize that if another chimpanzee or person is looking at something, that individual is aware of the objects. In other situations they don’t.
Chimpanzees seem to have the rudiments of theory of mind, but not much more.

Mindreading is unique to humans.

The nature of language and children’s early linguistic abilities

Language learning requires innate mechanisms that predispose children to it, coupled with an environment that provides adequate models and opportunity to practice.

Universal characteristics of human language

All languages use symbols (morphemes) that are arbitrary and discrete

Every language has a vocabulary consisting of a set of symbols, entities that represent other entities.
Morphemes: the symbols in language. This are the smallest meaningful units of a language.
In all languages (except sign) morphemes take the form of pronounceable sounds.
Most morphemes are words, but others are prefixes or suffixes used in consistent ways to modify words.  (Like dog is a morpheme, s is a morpheme and dogs is a word consisting of two morphemes).

Morphemes in any language are both arbitrary and discrete

• Arbitrary
  No similarity need exists between it physical structure and that of the object of concept for which it stands.
  When morphemes are arbitrary, new ones can be invented whenever needed to stand for newly discovered objects or ideas, or to newly important shades of meaning. This gives language a great flexibility.
  Like dog.
• Discrete
  It cannot be changed in a graded way to express gradations in meaning.
  (You cannot say something is bigger than another by changing the morpheme big. Rather, you must add a new morpheme to it or replace it with a different morpheme like huge).

All languages are hierarchically structured in a similar way

All languages share a particular hierarchical structure of units.

• The top level is the sentence.
• This can be broken into phrases.
• Which can be broken into words of morphemes.
• Which can be broken in phonemes (elementary vowel and consonant sounds)

The power of this four-level organization is that the relatively few phonemes can be arranged in different ways to produce an enormous number of possible words, which themselves can be arranged in different ways to produce a limitless number of possible phrases and sentences.

Every language has a grammar.
This specifies permissible ways to arrange units at one level to produce the next higher level in the hierarchy.
It includes rules of:

• Phonology: how phonemes can be arranged to produce morphemes
• Morphology: how morphemes can be combined to form words
• Syntax: how words can be arranged to produce phrases and sentences.

Grammatical rules are usually learned implicitly, not explicitly

Grammar is learned implicitly, without conscious effort, long before formal schooling.
People’s implicit knowledge of grammar is demonstrated in their ability to distinguish acceptation from unacceptable sentences. This is not based simply on meaning.

The course of language development

Early perception of speech sounds

Infants seem to treat speech as something special as soon as they are born, and maybe even before.
Very young infants hear the differences among speech phonemes. Babies younger than 6 months old hear the difference between any two sounds that are classed as different phonemes in any of the worlds’ languages.
At about 6 months of age, two kinds of changes begin to occur in their ability to discriminate between similar speech sounds:

• They become better at discriminating between sounds that represent different phonemes in their native language
• They become worse at discriminating between sounds that are classed as the same phoneme in their native language.

Cooing and babbling

Beginning at birth, infants can cry and produce various other vocal signs of distress.
At about 2 months they begin to produce a new, more speech like category of sounds. Cooing. (Consist of repeated drawn-out vowels)
At about 6 months cooing changes gradually to babbling. (Consist of consonant-and-vowel sounds)

Cooing and babbling occur most often when the infant is happy.
They seem to be forms of vocal play that have evolved to help the infant exercise an refine the complex muscle movements needed to produce coherent speech.
Coos and the earliest babbles do not depend on the infant’s hearing spoken sounds. (Deaf infants coo and begin to babble at about the same age. And early babbles are as likely to contain foreign-language sounds as native-language sounds).

At 8 months of age, hearing infants begin to babble in ways that mimic the rhythm and pitch patterns of the language they hear around them.
At about 10 months of age, hearing infants begin to produce babbled sounds that increasingly resemble syllables and words of their native language. At this age, deaf babies who are exposed to a sign language begin to babble with their hands.
Eventually, recognizable words appear in the hearing infant’s vocal babbling and the deaf infant’s manual babbling.

Word comprehension precedes word production

During the babbling phase of life, before the first production of recognizable words, infants begin to show evidence that they understand some words and phrases that they hear regularly.
9 month olds can respond to a number of common words by looking at the appropriate object when it is named and can follow simple verbal commands. By the time that they say their first word, infants may already know the meaning of dozens of words.

Naming and rapid vocabulary development

Babies’ first words are most often produced in a playful spirit.
New words come slowly at first, but then, typically at about 15 to 20 months of age, the rate begins to accelerate.
Relatively few words are explicitly taught, most often, the child must infer the meaning of a new word from the context in which others use it.

Most of the words learned, are nouns that refer to categories of objects in the child’s environment.
Children’s tendency to look at whatever an older person is looking at helps the identify objects that the older person is referring to when speaking. Infants are especially likely to follow an adult’s gaze when the adult is labeling an object in the environment.
Young children seem to have a number of cognitive biases, or built-in assumptions, that help them narrow down the likely referent to a new word they hear.

• A strong tendency to link new words with objects for which they do not already know a name.
  Toddlers begin to manifest this bias at about the same time at which their rate of vocabulary learning begins to increase rapidly.

By the time they can understand multiword sentences, young children are able to use their tacit knowledge of grammar to help them infer the meaning of new words, including verbs and other parts of speech as well as nouns.

Extending words to fit appropriate categories

In addition to linking a new word to its immediate referent, children must learn to extend it to new referents.
Young children (including one year olds) behave as though they assume that a newly heard label applies not just to the specific object that has been labeled, but also to other objects that are perceptually like the original one.

• Infants are biased toward assuming that labels are common nouns, not proper nouns.

By the time they are 2 years old, children can use the grammatical context of a sentence to discern whether a name for an object is a proper noun or a common noun.
Children sometimes overextend common nouns, using the more broadly than adult usage would allow.  - Is results when a child implicit defines a new word in terms of just one of a few of the prominent features of the original referent object.

• It also can derive from children’s attempts to communicate about objects that they have not yet learned to name.

Using grammatical rules

All children go through a relatively prolonged period during which each of their utterances is only one word long.
At about 18 to 24 months of age, they begin to put words together. At first they use content words almost exclusively, especially nouns and verbs, and usually arrange them in the grammatically correct sequence for simple, active sentences.
When children acquire a new grammatical rule, they almost invariably overgeneralize it at first. This is over regularization.
Over regularization confirms that children really know the rule. Otherwise it would be simple imitation. Children also use the rule with made-up words.

Through their own devices, children actively (and mostly unconsciously) infer grammatical rules from examples of rule-based language spoken around them and to them.

Internal and external supports for language developmental

Humans enter the world equipped in many ways for language.
We are born with

• Anatomical structures in the throat (the larynx and pharynx)
• Brain areas specialized for language
• A preference for listening to speech and an ability to distinguish among the basic speech sounds of any language
• Mechanisms that cause us to exercise our vocal capacities through a period of cooing and babbling

We are also born into a social world that provides rich opportunities for learning language.

The idea of special inborn mechanisms for language learning

Chomsky’s concept of an innate language-learning device

Grammatical rules are fundamental properties of the human mind.
A person must have some meaningful representation of the whole sentence in mind before uttering it and they must apply grammatical rules to that representation in order to fill out the lower levels of the hierarchy to produce utterance.
Grammatical rules are aspects of the human mind that link spoken sentences ultimately to the mind’s system for representing meanings.
All grammatical rules are based on fundamental principles (universal grammar) that are innate properties of the human mind.

Language-acquisition device (or LAD) ware the entire set of innate mental mechanisms that enable a child to acquire language quickly and efficiently.
The LAD includes the inborn foundations for universal grammar plus the entire set of inborn mechanisms that guide children’s learning of the unique rules of their language.

Children’s invention of grammar

Young children invent grammar when it is lacking in the speech around them.
Pidgin language: a primitive, grammarless collection of words taken from various native languages.
Creole language: the pidgin develops in a true language, with full range of grammatical rules.

When the first Nicaraguan school for deaf was founded, the school did not teach sign language. But despite this, students began to communicate using hand signs. In a few years, signs became increasingly regularized and efficient, and a system of grammar emerged.  The youngest children contributed most to the grammatical structure of the language.

Children tacitly assume that language has grammar, so they unconsciously read grammar into language even where it doesn’t exist.

Critical period for learning the grammar of one’s first language

The LAD functions much more efficiently during the first 10 years of childhood than later in life.
Children who are deprived of the opportunity to hear and interact with a language during their first 10 years have great difficulty learning language later on and never master the grammar of the language they learn.

Learning within the critical period is much less important for second-language learning.

The language-acquisition support system

Normal language development requires not just the LAD but also the LASS.
Language-acquisition support system (LASS) is provided by the social words into which the baby is born.
In Western culture, and most others, adults regularly simplify their speech to infants and young children in ways that might help the children learn words and some aspects of grammar.
They enunciate more clearly,

• Use more musical tone of voice which greater pitch variation,
• Use short sentences that focus on the here and now
• Repeat and emphasize salient words
• Use gestures to help convey meaning

This is infant-directed speech.
It helps infants to distinguish individual words and to make connections between words and their referents.

Adults also frequently treat infants’ early vocalizations as if they were verbal statements.
Such responsiveness can lead to back-and-forth, conversation-like exchanges between infant and adult.

Parent’s speech to infants affects language acquisition

There is a positive correlation between the degree to which mothers speak to their infants, using appropriately simplified language, and the rate at which the infants develop language.
Problem: the correlation might derive more from genetic similarities than from language environments.

Adopted infants’ rates of language development correlates more strongly with their biological mother’s verbal abilities than with their adoptive mother’s verbal abilities. But the linguistic environments provided by the adoptive mothers also plays a significant role.

Parents’ verbal responsiveness to infants’ vocalizations plays a significant role in the rate of language acquisition.

Cross-cultural differences in the LASS

Children all over the world acquire language at roughly similar rates, despite wide variations in the degree and manner adults’ verbal interactions with infants.
Large variations can occur in the LASS without impairing infants’ abilities to learn language.

Bilingualism

The earlier children are exposed to a second language, the greater the chances they will become proficient in it.
The more similar two languages are to one another, the easier it is learn the second language.

Simultaneous and sequential bilinguals

Simultaneous bilinguals: people who are exposed from birth to two languages and are typically equally fluent in both languages.
Sequential bilinguals: learn a second language after mastering their first. Although they can gain proficiency in a second language, they rarely attain the level of linguistic mastery as in their first language.  (Like an accent).

People who master a second language relatively late in life do so in a different way, neurologically speaking, tan people who acquire two languages in childhood.
For early bilinguals, the same area of the brain becomes active when speaking sentences in both languages. This is not the case for late bilinguals.

Costs and benefits of bilingualism

Disadvantages:

• Children learning two languages at once typically show a delay in syntactic development and have smaller vocabularies in each language relative to monolingual children.
  But bilingual children’s total vocabularies are comparable to that of monolingual children.
• Bilinguals of all ages are slower at retrieving words from their long-term memories than monolinguals.

Advantages;

• Bilinguals are able to recognize a wider range of phonemes than monolinguals.
• Bilinguals are often more sensitive toward the cultural values of the speakers of both the languages they have mastered.
• Bilingual people show greater levels of task switching and inhibition than monolinguals.
• Bilingualism postpones the decline in executive functions in old age

Language learning by nonhuman apes

Apes are much better at acquiring vocabulary than grammar.