9 Infancy (0 – 2 years)
Dr Jay Seitz
Any subject can be taught effectively in some intellectually honest form to any child at any stage of development.
- Jerome Bruner (1915-2016, Harvard Center for Cognitive Studies)
TABLE OF CONTENTS (TOC)
- Conceptual primitives
- Biological foundations
- Brain development
- The external and internal (i.e., proprioception) senses
- Means for exploring the world
- The embodied mind
- Perceptual, motor, and physical development
- Becoming self-aware: Theory of mind
- Language, thought, creativity, and freedom
- The emergence of language and thought
- Language development
- Development of gesture
- Numerical understanding and development
- The roots of consciousness
- Infant temperament
- Development of affect
- Sensorimotor development
- Using symbols: The symbolic stage
- Neurodevelopmental disorders
- Emerging sociality: Development of the attachment bond
- Prenatal, Perinatal, and Postnatal Development
Infancy (0 – 2 years)
Elizabeth Spelke’s research at Harvard comprises understanding the core cognitive capacities or “core knowledge” of human beings arising in infancy: Dr. Elizabeth Spelke.
She focuses on the origins and development of infant’s understanding of:
- Objects (“naive physics”)
- Actions (“agent-action relations”)
- People (“folk psychology”)
- Places (“incipient navigational abilities”)
- Number (“subitization” and counting)
- Geometry (“forms,” “intuitive geometry”)
These are also referred to as “conceptual primitives.” Essentially, she is asking what are the basic cognitive capacities that every human being the world over is born with, excepting severe pathology.
As Professor Spelke elucidates in her book (below), what do human infants know when they first encounter the world before learning begins? That is, what knowledge is innate in humans and how do they learn about this world of objects, actions, people, places, numbers, and geometry? The second volume of her book, How Children Learn, yet to be published, examines how and what children learn in the second year of life and beyond.
And importantly, are there the same core cognitive capacities that exist in all human cultures the world over that empower a newborn infant to acquire a native language and the unique values, skills, and concepts of the culture and society in which s/he was born?
Core Knowledge in Human Infants (2022)
What do infants know? How does the knowledge that they begin with prepare them for learning about the particular physical, cultural, and social world in which they live? Answers to this question shed light not only on infants but on children and adults in all cultures because the core knowledge possessed by infants never goes away. Instead, it underlies the unspoken, common sense knowledge of people of all ages, in all societies. By studying babies, researchers gain insights into infants themselves, into older children’s prodigious capacities for learning, and into some of the unconscious assumptions that guide our thoughts and actions as adults.
In this major new work, Elizabeth Spelke shares these insights by distilling the findings from research in developmental, comparative, and cognitive psychology, with excursions into studies of animal cognition in psychology and in systems and cognitive neuroscience, and studies in the computational cognitive sciences. Weaving across these disciplines, she paints a picture of what young infants know, and what they quickly come to learn, about objects, places, numbers, geometry, and people’s actions, social engagements, and mental states.
- Objects
Infants are able initially to organize arrays of objects into bounded, cohesive bodies even before they are able to reach for and manipulate objects. As they begin to develop, they are able to track objects even when briefly occluded–a teddy bear disappears momentarily behind a pillow–but not hidden objects of different shapes, colors or textures, although they have memory for those object properties. Indeed, very early in life human infants already know that the world is made up of objects that move in a coherent manner, do not vanish without reason, occupy space, and cannot be in two different places at the same time. And, more amazingly, we share some of these abilities with other species.
- Agents-Actions
Agents are beings that generate their own motion, prodding action. For instance, human infants understand cause, intention, action cost, and goal. That is, thy see the intention behind an object that is pushed, its cause (the person who pushed it), the action of actually pushing an object, and the goal of moving an object across a surface.
And they use this knowledge to guide their own incipient action on objects (e.g., pushing a toy train across the floor) as well as the object-directed action of others, such as a parent pushing a vacuum around the house. These early abilities support the causal reasoning and action planning of school-age children.
- People (“Social Beings”)
The “social system,” as it’s called, characterizes the people that inhabit the infant’s social world and share similar experiences and interpersonal engagement. In experimental situations, newborn human infants will spend more time looking at a still face that is looking at them than an identical face looking somewhere else. Indeed, infants learn from the words of others (“No, Johnny”) as well as their actions including gestures and what they are engaged in and attend to. This innate social system provides the basis for later moral and social reasoning. Nonetheless, young human infants lack a concept of people as social agents and whose behavior is both social and causal and guided by intentional mental states. That appears towards the end of the first year.
- Places
How do infants learn to navigate their world? Navigation depends on an incipient understanding of the abstract geometric properties of surfaces, the direction and distance those surfaces provide to the infant to travel on, and the navigable environment that a young infant faces: Where am I? Where are other things? And what path will take me from one place here to another place over there?
- Number
Early numerical understanding and use in human infants includes the ability to represent and use numerical magnitudes (known as the “approximate number system”). For instance, a young infant can see that this bowl has more cherries than that bowl, a numerical ability known as “subitization” or enumerating without counting. This core number system provides the underlying cognitive framework for understanding formal mathematics when the child attends school and begins to use words to count.
- Geometry (“Forms”)
The form system originates in an ancient core system for perceiving, tracking, categorizing, and reasoning about the forms and multivariate functions of natural objects. These natural objects include plants as well as the forms and functions of human artifacts (such as tools). It culminates in learning formal geometry in the school years.
And what about language?
The child who learns a language has in some sense constructed the grammar for himself on the basis of his observation of sentences and non-sentences (i.e., corrections by the verbal community). Study of the actual observed ability of a speaker to distinguish sentences from non-sentences, detect ambiguities, etc., apparently forces us to the conclusion that this grammar is of an extremely complex and abstract character, and that the young child has succeeded in carrying out what from the formal point of view, at least, seems to be a remarkable type of theory construction.
The fact that all normal children acquire essentially comparable grammars of great complexity with remarkable rapidity suggests that human beings are somehow specially designed to do this, with data-handling or “hypothesis formulating” ability of unknown character and complexity.
– Noam Chomsky (“A Review of B. F. Skinner’s Verbal Behavior” in Language, 35, No. 1, 1959, 26-58).
Indeed, when Professor Chomsky wrote these words, an artificial intelligence laboratory had been formed just a few years before (1956) at MIT (Massachusetts Institute of Technology) where Chomsky and Morris Halle formed the first department of linguistics down the hall. At the time, research across both departments was concerned with, among other things, programming computers to understand and use natural language. This was the start of what became to be known as the “cognitive revolution.”
“Kismet” – A robot that can recognize and simulate emotion (MIT, 1998)
“Simon” – Georgia Tech, 2008
By the way, if you’re interested in chatting with a real computer, please check out ChatGPT on the web: ChatGPT. ChatGPT just came online on November 30, 2022, with billions of dollars in funding from Microsoft ($13 billion) and other companies. The company behind ChatGPT is OpenAI founded by Sam Altman, Elon Musk, and others and headquartered in San Francisco. It’s based on a large language model of computing. It’s the next wave of artificial intelligence. That’s why it’s interesting.
Is this the beginning of true artificial general intelligence (AGI) or is it all just a mirage?
Yet, at best, computers (software programs) only mimic superficial qualities of human thought.
Indeed, such programs are stuck in a prehuman or nonhuman phase of cognitive evolution. Their deepest flaw is the absence of the most critical capacity of any intelligence: to say not only what is the case, what was the case, and what will be the case — that’s description and prediction — but also what is not the case and what could and could not be the case. Those are the ingredients of explanation, the mark of true intelligence.
Whereas humans are limited in the kinds of explanations we can rationally conjecture, machine learning systems can learn both that the earth is flat and that the earth is round. They trade merely in probabilities that change over time.
True intelligence is demonstrated in the ability to think and express improbable but insightful things.
- Noam Chomsky (NYTimes, 03.08.2022, The False Promise of ChatGPT)
Early language acquisition
The language system
- Phonology is the sound system of language and the basic unit of sound is the phoneme.
Example: the ‘p’ and ‘b’ sounds in “pit” and “bit” are the basic units of sound. There are 44 phonemes in American English and over 800 worldwide.
- Syntax is word order. Transformational rules govern which words in what order can be combined with what as in “colorless green ideas sleep furiously.”
The syntax is correct but the sentence is unintelligible and lacks meaning.
- Semantics refers to meaning in language. The basic unit of meaning is the morpheme.
Example: The ‘-ing’ in “jumping” changes it from a physical state, ‘jump’, to an action, ‘jumping’.
- Pragmatics refers to the communicative effects of language.
- Vocal prosody or intonation is key here. How we intone words communicates the meaning behind the words.
- Social interaction: “Would you mind passing the salt?” We can communicate it as a question, command or declaration, which alters its communicative or informational effects.
How is language learned?
Nativists emphasize…
Language acquisition depends upon exposure during a certain critical or sensitive period (in humans we refer to them as “sensitive periods” because they have broader timelines than critical periods). This period is highlighted in the infamous case of “Genie,” who was locked in her room for the first 12 years of her life without any exposure to language. Indeed, we might agree with Professor Pufendorf about this infamous case.
More inhumanity has been done by man himself than any other of nature’s causes.
– Samuel von Pufendorf (1673, German philosopher, 1632-1694)
On the other hand, primates cannot learn human language, but only rudiments of American Sign Language (ASL) or a relatively small set of visual symbols because the underlying biological capacity for complex language is absent.
And then there is the phenomenon of idioglossia in identical twins or a “private language” that uniquely develops between them.
Environmentalists emphasize…
Language acquisition rests on imitation and reinforcement. Indeed, imitation may help some children learn language by reinforcing semantically correct utterances (i.e., factual errors) rather than grammatically correct ones.
Children only learn language in a rich social context. Indeed, a naturalistic experiment very nicely points this out:
A normal, hearing infant was born to deaf parents. The infant was exposed to TV in the home, but parents only communicated using American Sign Language (ASL). As a result, as the child grew older, s/he learned only ASL but not spoken English.
Parental speech styles to children appear to facilitate language acquisition. This is known as adult-to-child speech or “motherese.”
What is adult-to-child speech? Parents speak at a slower rate, use simpler syntax, rarely utter incomplete sentences, use expanded pitch contours, use short sentences and concrete nouns, and refer to objects in the child’s immediate vicinity.
Language acquisition in the first few years of life
First month: Infants are able to perceive human speech categorically, that is, they hear speech sounds in a specific range of phonological boundaries. This is called categorical perception.
3 – 4 months: Babbling
Occurs even in deaf children. Why? It’s an inborn ability and babbling sounds are not altered by the external environment.
Purpose:
- Mimics adult intonational patterns
- Reflects infant’s general state of excitement
- It suggests infant’s pleasure in playing with the sounds of language
- It exercises the vocal tract in preparation for language use
4 – 12 months: Prelinguistic communication
There are two (2) central communicative functions expressed by humans, either nonverbally or verbally.
- Pointing –> Declaring an object present
- Reaching –> Requesting an object
As their learning proceeds, infants come to discern how words and part-words combine in phrases, and how speakers use these combinations to share their experiences with others. Remarkably, infants detect and use the ordering of abstract categories of words both to learn individual word meanings and to discover the specific sound contrasts that distinguish one word from another in their native language.
Indeed, the most frequent, short, and unstressed function words and part-words in the world’s languages tend to convey meanings that map to core knowledge, because adult speakers and listeners access core concepts frequently, rapidly, and automatically.
– Prof. Elizabeth Spelke (“What Babies Know”).
12 – 18 months: First words are known as holophrases, that is, a word that stands for a whole sentence or larger meaning. Not surprisingly, they emerge at the same time as other symbolic activities.
- For example: Symbolic play, deferred imitation, and mental imagery.
- Early words are used in the service of the same two communicative functions in humans: Declaring and requesting.
Why are first words uttered in isolation at the one-word stage? Because the infant lacks syntax, the ability to string words together.
Indeed, there are striking differences to which children put their first words to use.
- Referential children: Use words to refer to objects and object properties. For example, “ball,” “red,” “allgone.”
- Expressive children: Use words to express feelings. For example, “Hi,” “more,” “goody-goody.”
- These differences have been correlated with socioeconomic class, educational level of parents, and sibling birth order.
18 – 24 months: Paired words or “duos.” These early paired words indicate that the sensorimotor relations acquired in early infancy are now mapped onto language.
For instance:
- Activity prolonged: Recurrence (e.g., “more milk”)
- People performing actions: Agent-action (e.g., “Johnny fall”)
2 – 5 years: Multiword sentences. By 2 ½ years the average child knows 400 words and new words are quickly learned in one or two exposures. However, speech is still “telegraphic” as in the utterance, “Baby eat cookie.”
Morphemes are also acquired during this period and are accumulated by dint of their increasing complexity. A morpheme is the smallest meaningful lexical item in a language. But a morpheme is not necessarily the same as a word. The main difference between a morpheme and a word is that a morpheme sometimes does not stand alone, but a word, by definition, always stands alone. The field of linguistic study dedicated to morphemes is called morphology.
Order of morpheme acquisition in development:
In, on (physical relations), -s (quantity), past irregular verb (time), possessive (self/other), infinitive (‘to be’, existence), articles (‘a’, ‘the’, universal/particular)
Followed by WH-questions: What, who, why, when, which?
By 5 years of age, the child has almost fully mastered adult syntax. So, in a few short years, children the world over acquire their native language in a few short years.
Indeed, the preschool child alone amasses up to nine (9) new words a day.
Language, Thought, Creativity, and Freedom
Well, there are basically two fundamental things that are species properties of humans, common to the species, no analog elsewhere. One of them is what we’re now using language. It’s essentially the core of our being. It sets us totally apart from the animal world. Another species property is simply thought. As far as we know, there’s no thinking in the world or maybe in the universe in anything comparable to what we have. And the two are closely linked — language is the instrument of thought and the means for formulating thought in our mind, sometimes externalizing it to others.
…These two capacities seem to have emerged together probably about the same time as Homo sapiens. They are common to all humans, apart from severe pathology. And there are no analogs in the animal world. In fact, there may not be anywhere far as we know….
…One of the striking things about language which greatly impressed the founders of the Scientific Revolution, Galileo and his contemporaries, is what is sometimes called the creative aspect of human thought. We are somehow capable of constructing in our minds an unbounded array of meaningful expressions…
…Well, this creative character through the centuries has been connected speculatively, but not absurdly, to a “fundamental instinct for freedom,” which is part of our essential nature. That is, resistance to domination and control by illegitimate authorities, maybe part of the same creative capacity, which shows up very strikingly in our normal use of language.
– Noam Chomsky (04.23.2021, New York Times; interview with Ezra Klein)
“Notes on Resistance,” Noam Chomsky, 09.27.2022: https://a.co/d/9Mxxe0S
Early Development of Gesture
How Does Gesture Develop?
- Deictic gestures: Indicative function (pointing): Early mode of referring to objects.
- 1st year: Exploring and orienting towards novel events.
- 2nd year: Looking in the direction of the mother’s pointing hand.
- Instrumental gestures: Regulate and change behavior of others (e.g., wanting to be picked up).
- Precursors to commands, demands, and requests.
- Expressive gestures: Movements of hands, face, and postures that express feelings and intentions (e.g., knitted brow).
- Understood through empathic understanding, kinesthesis, and the mirror neuron system.
- Enactive gestures: Movements that represent actions upon objects or actions performed with objects (e.g., pretending to comb one’s hair).
- Younger children need support of real objects whereas older children can perform actions with imaginary objects.
- Depictive gestures: Movements or configurations of movement that represent an action or a property of an object (e.g., using two fingers to represent a bird).
- 1;4 year old child: Slowly opens and closes mouth to represent analogous movement of a match box.
- Young children may not fully differentiate between a representation of an object (e.g., hammer) and a representation of the action of the object (e.g., hammering).
- 2-year-old: “A hole is to dig.” Child does not differentiate between what the object looks like and what you do with it.
Numerical Understanding and Development
“Animal arithmetic” is the ability to apprehend numerical quantities as well as memorize, compare, and add them approximately. We see this ability in rodents (rats), parrots, dolphins, and primates. That is, they all possess the ability to rapidly enumerate collections of visual and auditory objects, add them up, and compare their numerosities.
To be sure, subitization is the ability to enumerate without counting. In humans it depends on circuits in the visual system dedicated to localizing and tracking objects, that is, the ability to parse visual scenes into discrete objects. Human infants and animals: can easily subitize small quantities (1, 2, 3…4). Patients with damage to the brain that affects counting (“simultanagnosia”) can still subitize, however, because the brain mechanisms that underlie counting and subitization are independent systems, one numerical, the other visual.
Indeed, number itself is a property of sets of discrete physical objects and the ability to recognize and make use of properties of sets is shared across species. This “number sense,” as it is called, is present in animals and emerges spontaneously in children as they develop, including the capacity for numerical estimation, comparison of quantities, counting, simple addition and subtraction. Once young children learn to count, they have attained the ability to associate a repertoire of abstract levels (e.g., weekly allowance) to some kind of numerical representation (e.g., Arabic digits).
On the other hand, children’s failure on Piagetian tasks–such as object permanence at one year linked to reaching movements or inability to solve conservation tasks at 5 years–is linked to maturation of prefrontal cortex. That is because in infants and young children, these “problem-solving circuits” overseen by the prefrontal cortex are still emerging.
Cross-Cultural Comparisons
At 4 years of age, Chinese children typically can count to 40, whereas American children can only count on average to 15. Why?
The number system in China is easier to hold in short-term (working) memory and thus it speeds up calculation and makes acquisition of counting and the base 10 system easier.
For example, in Chinese:
4 is ‘si’, 7 is ‘qi’, and so on. That being said, the base 10 system used in elementary mathematics around the world is easy to work with because one can naturally use the 10 fingers in counting.
The Unfolding of Numerical Development
- 2 ½ year olds can differentiate number words from other adjectives.
- 3 ½ year olds begin to realize that the order of counting numbers is crucial but not actual objects themselves.
- 5 year olds appreciate the meaning of counting and understand the commutativity of addition, but only intuitively. That is, 3 + 2 = 2 + 3. But by 4 – 7 years, child intuitively understand what calculations mean and how best to select the right numerical procedure.
- By preschool, however, there is a sudden shift from intuition to rote learning of arithmetic. Although intuition is poorly understood, its textbook definition is reaching conclusions (the right answer) based on nonconscious processes of reasoning. Human memory at this age is still associative, not digital like a computer.
- By 3rd grade, 8 year-olds can memorize simple additions, but multiplication problem-solving time increases and the first “cognitive slips” begin to appear, such as 2 + 3 = 6.
- Studies of mathematical reasoning in children have demonstrated that reading and arithmetic memory are highly interconnected procedures that make use of the same strategies of verbal encoding of numbers as in “3 x 6” is equivalent to “eighteen.”
- But there are no detectable differences or advantages between either gender in numerical understanding, at least before schooling starts. With schooling, however, males seen to be better as a group in mathematical problem-solving, whereas females are better at mathematical calculation.
- We do know that androgens (e.g., testosterone) in males shapes the developing brain particularly as it relates to the processing of space and spatial understanding, which may partially account for their problem-solving ability in this area.
- On the other hand, Japanese 10-year-olds by visualizing a “mental abacus” in their heads (something like stored tables of multiplication facts)—can outperform a calculator or even a Western child prodigy in math.
Consciousness
When does consciousness first arise in the human infant?
Consciousness has multiple qualities and one can distinguish, in both humans and other animals (a) primary consciousness (awareness of one’s environment) and (b) secondary consciousness or self-awareness. Presumably, self-awareness arises by the middle of the second year in human infants although not a full-fledged “theory of mind” (see below). Research has shown that infants in the middle of the second year of life will blush when an adult places a smudge of red lipstick on their nose and then places them before a mirror, demonstrating that they clearly recognize themselves and begin to display self-awareness.
Self-awareness or secondary consciousness may have evolved only in complex vertebrates including hominins (humans), canines; cetaceans such as dolphins, porpoises, and whales; hominids such as chimps and bonobos; elephants; and magpies and possibly other corvids (a genera of birds including crows and bluejays).
Indeed, there are specialized neurons (spindle or von Economo neurons) that may contribute to it and are found in various brain regions, but particularly in the frontal cortical areas. These areas are important for attributing intention and sundry mental states to others–known as theory of mind–that are presumed to be absent or severely compromised in autistic spectrum disorders, among others. They also aid the processing of negative and positive emotions including empathy towards others.
Interestingly, von Economo neurons are found in dolphins, elephants, macaques, raccoons, and whales and may have similar functions. When von Economo neurons are malfunctioning or destroyed they result in pathological states, which we see in various social-cognitive disorders and diseases such as frontotemporal dementia, schizophrenia, and autism.
A robust “theory of mind” doesn’t arise in children, however, until about the fourth year of life. Theory of mind is the ability to ascribe mental states to others (“I wonder what Sally is thinking?”) as well as understand that the beliefs of the other person may differ from the child’s own beliefs or intentions. By this stage, young children understand that what they know may be different from what some else knows, such as a parent, and a true lie can be contemplated.
The Embodied Mind
Many aspects of thought (i.e., cognition) not just in humans but in other animals, is shaped by critical features of the organism’s body. For instance, sensory and perceptual systems and physical aspects of the animal’s body (e.g, eyes in the front opposed to the sides, four legs or two, keen sense of smell or sight) shape how the organism interacts with and comprehends its world. Even mental constructs such as concepts and categories (e.g., prey vs. friend) and reasoning and judgment, for example, “Should I eat that nut now or save it for later?” as seen in a scrub-jay (below) are shaped by the body’s interaction with the world.
We will explore aspects of locomotion in human infants, their use of the five external senses as well as one internal one (the proprioceptive sense), the infant’s use of symbols (e.g., counting on the fingers), how early tool use transforms human thought (see quote below) and the beginnings of sociality and emotion in interacting with others and understanding their social world.
To paraphrase Vladimir Lenin, the early 20th century social activist and politician, the hand was the ﬁrst human tool. Or, if you prefer, private property was ultimately derived from labor and it was the labor of the hands that produced and validated private property as one’s own: “To mix one’s labor with one’s hands,” to quote the 17th century English philosopher, John Locke.
– Dr. Jay Seitz, Mind Embodied: The Evolutionary Origins of Complex Cognitive Abilities in Modern Humans (2019, p. 74).
But first, let’s look at the biological foundations of modern humans.
Biological Foundations: Neurodevelopmental Disorders
Disorders or diseases that affect the development of the brain as well as the central nervous system result in deficits or delays in cognition, emotion, sociality, learning, and self-control. These are known as neurodevelopmental disorders and briefly described below.
- Intellectual or developmental disability (ID/DD) is defined as having a psychometric intelligence (IQ) under 70 as well as two (2) deficits in adaptive behaviors. Adaptive behaviors reflect an individual’s social and practical competence in meeting the demands of everyday living. So, for instance, a blind child may need to learn braille or become adept in the use of technology to overcome their limitations.
- Learning disorders (LD) including dyslexia, dysgraphia, and dyscalculia and individuals are entitled to 504 accommodations under the American with Disabilities Act (1990; 42 U.S.C. 12101) that prohibits discrimination based on disability and requires covered employers to provide reasonable accommodations.
- Autism spectrum disorders (ASD) include autism, Rett’s syndrome, and childhood disintegrative disorder.
- Developmental motor disorders including congenital injuries resulting in movement disorders leading to forms of cerebral palsy and neuromuscular diseases such as variants of muscular dystrophy.
- Tic disorders including focal tics, Tourette syndrome, Sydenham’s chorea, and Huntington’s disease (juvenile). The Tourette Association of America (headquartered in NYC) is a major fundraising organization for research and treatment for Tourette’s and other tic disorders: https://tourette.org.
- Traumatic brain injury (TBI) including concussions.
- Speech and language disorders including, specific language impairments (SLI), developmental phonological disorder (DPD), and stuttering.
- Neurotoxicants that cause various disorders including fetal alcohol spectrum and conduct disorders, methylmercury poisoning, as well as exposure to organophosphate pesticides, lead, arsenic, toluene, polybrominated diphenyl ethers, phthalates, and polychlorinated biphenyls (PCBs).
- Genetic disorders such as Fragile-X syndrome, Down syndrome, Williams syndrome, attention deficit hyperactivity disorder (ADHD), schizophrenia-related disorders, and hypogonadotropic hypogonadal syndromes.
Brain Development
The neocortex is the most evolutionarily advanced part of the brain forming the frontal, temporal, parietal, and occipital lobes, that is, the major parts of the thinking and memory regions of the brain (see illustration below).
The archicortex includes the hippocampus (beneath the temporal lobe), which is involved in the initial processing of memories but not where they are stored, which occurs in the temporal lobes.
The paleocortex includes the oldest parts of the brain and one of the oldest sensory systems is the olfactory cortex (underneath in the base of the brain), where our sense of smell is housed.
The Major Lobes of the Human Brain
The diagram (below) shows the timing of both typical development of the fetus (green shading) and atypical development (purple shading).
Timing of Neurodevelopmental Disorders
Let’s look in a little more detail at how the brain develops.
The weight of the human brain at birth is approximately (~) 350 gms with a full complement of brain cells (there are ~ 69 billion neurons). At 15 years ~ 1200 gms. What is occurring in the brain that adds size and weight?
- New neuronal branches form creating more connections between nerve cells (neurons).
- Increase in the length of dendrites so that neurons have more distant connection with other neurons in the brain that are farther away.
- Formation of new synapses (spaces between the axons and dendrites of neurons that communicate by way of neurotransmitters)
- Increase in myelination (facilitated by brain lipids; e.g., cholesterol)
Myelination Promotes Faster Impulse Conduction From One Neuron to Another
- At birth, only a few areas and tracts of the brain are myelinated. For example, the brain stem centers that control the sucking reflex.
- Begins in the spinal cord by 3rd month of gestation enabling fetal reflexes (e.g., palmar grasp)
- Begins in the brain at 6 months and at 8 months the distinctive six layers of the cerebral cortex appear, which are characteristic of the “association areas” of the adult brain.
- Myelination strongly correlates together with the formation of new synapses, new neuronal branches, and increase in length of dendrites with progressive increase in weight of the brain from birth
- Myelination occurs throughout most of the lifespan
Myelination Timeline
1st month –> Primary motor area in the cortex becomes myelinated promoting early motor activity and behaviors. Myelination proceeds in a cephalocaudal (head-to-tail) direction.
- Motor and sensory areas: Upper trunk arm regions myelinate first promote reaching and pointing.
- Then, hips: Promote crawling.
- Then, bladder (lumbosacral plexus): Promotes toileting.
- Secondary/tertiary zones develop at a slower rate.
- But, the limbic system (emotions) develop rapidly at birth.
- Myelination is thus a form of canalization, the tendency of the nervous system to follow well-defined developmental paths.
2nd-6th month –> Primary sensory areas [front half of neocortex] become myelinated enabling infants to better record sense data of objects (e.g., color, sounds, lines, smells).
6th-12th month –> Secondary sensory areas [bottom half of neocortex] become myelinated enabling us to construe what an object is (e.g., a round, red object) as well as an object’s significance or meaning (e.g., apple).
2-4 years –> The cross-modal zones [that lie between the primary and secondary sensory areas] become myelinated and fully integrate the various sensory modalities (vision, audition, gustation, olfaction, and the haptic modality, “touch”). The cross-modal zones, for example, are able to integrate the sound (“ap’l”) with the sight of the fruit (round, red object).
So the cross-modal zones are important because they integrate connections and relations among objects (apples and bananas are “fruit”) resulting in an organized, wholistic sensory experience. This involves amalgamating the child’s sensory impressions into sequences of events such as recognizing that the refrigerator is a good place to obtain an apple.
Moreover, children’s use of symbols (language, number, pictures) depends on the maturation of the cross-modal zones as they begin to acquire the ability to attach sounds, words (the printed word ‘fur’), and their tactile sensation into an organized sensory impression.
Infra-human primates (bonobos, gorillas, chimpanzees), however, don’t display the same amount of growth of the cross-modal zones.
Why is that so?
The cross-modal zones arose late in evolution as well as mature late in the child’s life in the fifth year and are a reflection of the symbolic period in children’s development. Infra-human primates don’t undergo these extensive changes post-infancy to the same extent.
But, there is also neural plasticity in the development of the nervous system that ensures maximum flexibility early in life (e.g., laterality or the partitioning of key brain functions to different sides of the brain).
And there is the importance of critical or sensitive periods in development, where, for example, if a child is not exposed to language early in the life (the famous case of “Genie”), they fail to develop language as well as other cognitive abilities.
Moreover, exposure to the environment–computers, technology, and social media–modulates brain development in ways not fully understood. Likewise, early brain injury may stimulate anatomical reorganization of the neocortex. But, then, areas of the brain that develop later (e.g., the frontal lobes) are less committed and may take over compromised functions.
Importantly, the brain includes both cortical and subcortical structures.
Cortical (cortex)
- Cerebral cortex
Subcortical (subcortex; below the cortex)
- The spinal cord which relays information.
- The cerebellum which has many functions including the maintenance of equilibrium, muscle tone, the execution of motor and cognitive functions, as well as motor timing.
- The brain stem which is responsible for arousal, attention, and postural reflexes.
- The basal ganglia which is involved in the modulation and mediation of motor movements.
- The limbic system which is involved with emotion.
Lastly, in child development, spurts in brain growth occur during distinct developmental periods in ways not fully understood.
- 3-10 months
- 2-4 years
- 6-8 years
- 10-12 years
- 14-16 years
These spurts are studied by studying negative correlations between body and brain growth–indeed, 20% of metabolic energy is used in brain processes–through EEG studies, increase in development in cortical thickness, cerebral blood flow studies, as well as research on vision, hearing, and cognitive and language development in the developing child.
Early development
Three Major Systems
- The perceiving system: Detecting differences in the external world: Vision, sound, touch, taste, and smell.
- The making system: Actions upon the physical and social world.
- The feeling system: The experience of feelings, emotions, and ties to other persons.
Development of Affect
The Feeling System
Eight (8) emotions have been distinguished in infants in the first 9 months of life.
- Interest
- Joy
- Surprise
- Sadness
- Anger
- Disgust
- Contempt
- Fear
How are they distinguished in young infants? The key is that they closely resemble adult facial expressions.
Do emotions develop?
- Neonate: Undifferentiated excitement
- 2 – 3 weeks: Distress and delight
- 2 – 3 months: Distress gives way to –> fear, anger; whereas delight gives way to –> joy, affection
- By the 3rd year, jealousy, envy, ecstasy, and more complex emotions arise.
What is infant temperament?
Temperament in infants is an individual difference in behavior that is largely biologically based and relatively independent of learning and other factors.
It’s an aspect of personality that largely reflects the infant’s emotional style, attention span, activity level, distractibility, and adaptability.
Infant temperament is recognized early in life and remains quite stable over the first two years of life with three major categories of infant temperament that have been identified in the New York Longitudinal Study (1968): “Easy,” “Slow-to-Warm,-Up” and the “Difficult” infant.
Motor Development
The Making System
The infant makes or performs actions upon the world.
Cultures that promote early exercise promote precocious motor maturity. To be sure, early body and limb movements contribute to later making patterns (e.g., jumping).
- Neonate: Simple hand movements
- 2 month old: Swiping motions
- 4 month old: Edge slowly toward object with hand stretched open
- 5 ½ month old: Smooth and efficient reach
- 12 month old (1st year): Coordinate thumb and fingers in a precise pincer movement
- 18 month old (middle of 2nd year): Can catch moving objects
Adult acquisition of motor skills may be more difficult and operate under different principles than in early life, however.
Perceptual Development
The Perceiving System
First, a little background. There are, of course, five external senses including vision, audition, gustation, olfaction, and the haptic (touch) modality. While there are many chemical sensors both on the surface and within the body, a major internal sense is the proprioceptive sense.
Proprioception provides feedback to the brain from sensory receptors in the muscles, joints, tendons, and skin that makes available to the brain information about the position of the limbs in space and time and the weight and position of objects with which the infant body interacts. These connections undergo development from infancy.
From a brain perspective, the sensory cortices (i.e,, the sensory areas of the brain in the cerebral cortex) record the outside world of people, objects, and things; the sensorimotor cortices (i.e., motor areas of the brain) record the internal world of the infant’s body primarily through proprioception; and the infant’s subcortical structures create a link between these two worlds of outside and inside.
Signals from this sensory orchestra of external and internal senses are sent by afferent nerves to the motor and parietal as well as somatosensory cortices of the brain, which update the dynamic sensorimotor maps of the body.
FORM
By 8 weeks, infants prefer 3-dimensional to 2-dimensional forms. Why? They are beginning to develop conceptions of space and depth.
However, from birth, infants appreciate size and shape constancies. That is, size and shape remain constant even when objects recede in the distance or are turned on their axes.
COLOR
Similarly, young infants divide up the color spectrum just like adults suggesting that color perception is most likely innate in humans.
HUMAN FACES
Infants clearly perceive human faces by 6 weeks – 3 months
- That is, infant becomes capable of centering on complex geometric forms
- 3-month old infants can also discriminate smiling from frowning faces
PICTURES – Photographs and Line Drawings
By 4 months, human infants can decode information from pictures, that is, objects seen in real life from photographs or line drawings. But may need some experience with judging depth and distance from pictorial cues.
LANGUAGE SOUNDS
Infants also divide up the language spectrum just like adults suggesting it is innate. That is they perceive phonemes, the basic sounds of language, from birth. For instance, they hear the difference between the ‘p’ sound and the ‘b’ sound in “pit” and “bit.”
MUSIC and RHYTHM
Infants at 3 months can organize a series of taps into rhythmic configurations, by 5 months, recognize a pattern of pitches, and by 6 months, can sing back tones at their correct pitch.
SYNESTHESIA or CROSS-MODAL PERCEPTION
Infants are also sensitive to synesthesia or cross-modal perception discussed earlier. That is, the ability to relate discriminations from different sensory systems to one another.
- For example, ball seen, ball felt
- For example, voice heard, person seen
Six month old infants can associate a film seen with its proper sound.
- For example, infants watched two films, one of a bouncing toy kangaroo and the other of a bouncing monkey (sound heard from central speaker).
- Infants looked significantly longer at the film associated with its proper sound.
Indeed, synesthesia may help explain the development of figurative language–“the stop sign looked like a lollipop”–as well as the development of analogical reasoning.
How Do These Three Systems Interact?
Infants can imitate both facial and manual gestures in the first few weeks of life relying on the perceiving and making systems.
Infants can also transfer information across different sensory modalities (e.g., vision and proprioception).
Example of a complex interaction: The smile.
- Neonate: reflexive smile (making system). Infants will form a smile reflexively as part of their innate behavioral repertoire.
- Later infancy: Social smile (perceiving and feeling systems). Now, the infant produces a smile as part of a social interaction.
- How does the smile develop?
- In the second month, the smile can be elicited by almost any stimulus but particularly effective when the stimulus is moving.
- By the fourth month, a smile produced is linked to the recognition of anything familiar. Reinforces attachment to the primary caretaker.
- In late infancy the smile can be emitted in relation to pleasurable experiences, close family members, a familiar object (teddy bear), exploring, for instance, a parent’s face, as well as enjoyment in solving a problem.
Sensorimotor Development
According to Jean Piaget, the Swiss psychologist, the infant’s way of knowing the world is principally acquired through physical activity.
Piaget called these ways of knowing “sensorimotor schemes” or recurring behaviors toward objects. That is, the combination of the infant’s motor behavior (grasping, pointing, reaching, sucking, kicking, looking, hugging, and so on) with their sensory systems (kinesthesia, touch, gestation, olfaction, vision, and audition).
According to Piaget, the infant passes through 6 substages of the sensorimotor stage in the first two years of life. Three of these substages are characterized by the emergence of circular reactions or repetitions of physical acts.
- Primary circular reaction (3-5 months, substage 2): Body-centered.
- For example, the infant continually places her hand in the mouth.
- Secondary circular reaction (5-8 months, substage 3): Object-centered.
- For example, the infant continuously reaches for an object in the crib.
- Tertiary circular reaction (12-18 months, substage 5): Object-centered.
- The infant begins to use objects in unison to effect an action or, to put it another way, uses one object to obtain another. This is known as “means-ends relations” or “instrumental intelligence.”
- For example, the infant pulls on the sheets to get at a toy.
The substages represent increasing sophistication in the use of the infant’s sensorimotor skills.
According to Piaget, the infant also develops through a series of six substages in learning that the physical world of space and time is stable and unchanging. This is called the development of the object concept or the formation of object permanence.
- First 8 weeks: Substage 1: Objects for the neonate do not exist apart from his or her immediate physical interactions with them.
- 18-24 months: Substage 6: The infant has a complete object concept, that is, a sense of object permanence. Objects continue to exist in the infant’s mind even when no longer in view. This is true if an experimenter briefly places a teddy bear under a pillow but shows the infant when s/he removes it and puts it under a different pillow. This is known as a “visible displacement” and occurs in Substage 5.
- On the other hand, if the experimenter moves the teddy bear without showing the infant the actual teddy bear, this is known as a “invisible displacement” and only fully attained by human infants in the second half of the second year of life.
Early Social Development: Development of the Attachment Bond
According to Dr. John Bowlby (1907 – 1990), a British psychiatrist, an attachment bond is essential to children in order for them to develop a relationship with at least one primary caregiver. That is, a deep socioemotional affinity with another human being.
The infant needs a secure base to explore the world. In order to do this, the primary caretaker provides security by instilling a sense of trust according to the child psychologist, Erik Erikson (1902-1994). Interestingly, Erikson never obtained a degree after high school.
An essential aspect of the attachment bond is that it has survival value for the infant by initiating proximity-seeking behaviors (see below: Mother and Child in Mozambique).
The Developmental Unfolding of the Attachment Bond
Around 4-6 months an attachment bond is established with a primary caretaker. How evidenced.
- Clings to the caretaker.
- Signals fright and need for comfort and anxiety is reduced when held by primary caretaker.
- Follows the caretaker with eyes and limbs.
- Smiles at the caretaker.
6-7 months: Separation anxiety – Infant becomes anxious when separated from the primary caregiver.
7-8 months: Stranger anxiety – Infant becomes anxious when a stranger approaches, however, not all infants experience these separation qualms.
But consequences of long-term separation from the primary caretaker have long-term effects on the infant.
- Protest: Frenzied behavior
- Despair: “Hopelessness” Infant sits still with mournful face and will fly into rage if mother reappears.
- Forgetfulness: After many months.
- Long-term effects: Inability to sustain enduring relationships or intimacy with others.
- Developmental principle: Emotional concomitants of social behavior in adulthood arise from vestiges of infancy.
Quality of infant-caretaker bond is most important, not quantity.
- Eye-to-eye contact.
- Sensitivity to infant’s signals.
- Ability to respond immediately and appropriately.
- Consistency in response.
Attachment bond is universal and found in all cultures and even in other primates.
Types of Attachment
- 65% of human infants securely attached: Use their mothers as trusted bases from which to explore.
- 15% are insecurely attached (“resistant” or “ambivalent”): They are uncomfortable during normal play, excessively distressed by separation, and ambivalent when reunited with their mother.
- 20% suffer from a failure of attachment (“avoidant”): Rarely cry during separation and avoid their mother when reunited.
- Developmental implication: Mature adult is self-reliant and able to form stable relationships with others otherwise anxiety in adulthood and instability.
Attachment to Objects
It is called a “transitional object,” that is, a pacifier, security blanket, teddy bear, or other comforting object. The transitional object satisfies socioemotional needs and substitutes for the primary caregiver.
A Transitional Object
A Transitional Object
Transitional objects and transitional phenomena; a study of the first not-me possession – D. W. Winnicott (1953), https://pubmed.ncbi.nlm.nih.gov/13061115/. Donald Winnicott (1896 – 1971), a British pediatrician, was the first to formally describe the phenomenon of a transitional object, a concept he borrowed from his wife, Claire Winnicott, who was a British social worker.
Winnicott considered the “mother’s technique of holding, of bathing, of feeding, everything she did for the baby, added up to the child’s first idea of the mother” and created a secure “holding environment.” This same effect, according to Winnicott, was reproduced in the therapy session and has a positive therapeutic effect.
Nonetheless, peer interaction is extremely important for normal social and emotional development.
Harry Harlow’s experiments with Rhesus monkeys suggested that peers can be adequate substitutes, to some extent, for primary caregivers.
Moreover, the research has shown that fathers make adequate primary caretakers too.
- Fathers and mothers differ very little in how they react to their infants.
- However, fathers tend to pay special attention to their sons.
- But fathers and mothers tend to treat boys and girls differently and, as a result, get gender-typing of behavior.
Finally, multiple caretakers.
- Monomatric households (one-mother).
- Polymatric households (many-mothers).
- The research has shown that there is no significant difference in quality of attachment between monomatric and polymatric households.
- Research has also demonstrated that a high quality day care setting versus the infant/child remaining home with their mothers results in no discernible differences in measures of attachment to primary caregiver.
Prenatal, Perinatal, and Postnatal Development
Prenatal Development: Conception to Birth
- Germinal stage
- Embryonic stage
- Fetal stage
Influences on the maternal environment
- Diet and nutrition
- Alcohol, drugs, and smoking
- Mother’s age, emotional stress, and miscellaneous factors
Genetic programming in the human genome
- Background
- Genetic influences on the prenatal infant
Terminology
- Prenatal: Before birth
- Perinatal: 28th week prenatal to 28th day postnatal
- Postnatal: After birth
- Neonate: First 6 weeks after birth
The Biological Birth of the Human Infant
(1) Conception: Sperm + ovum = fertilized egg resulting in division and differentiation.
How do you study? (a) spontaneous abortion, (b) medical reasons for removing the fetus
from the womb.
(2) Germinal Stage (1st to 2nd week)
Implantation of fertilized egg in the uterus
(3) Embryonic Stage (2nd to 10th week)
- Cells organize into a hollow sphere (differentiation).
- 3 layers of cells form (articulation and hierarchic integration) – end of 2nd week
- Ectoderm – Outer layer: sensory organs, nervous system, skin, hair, nails, and teeth.
- Mesoderm – Middle layer: muscles, skeleton, excretory and circulatory systems including heart.
- Endoderm – Inner layer: Gastrointestinal tract, liver, lungs, and endrocrine glands.
- Heart connected to outlying organs via blood vessels – end of 1st month
- Embryo recognizably human – end of 2nd month (embryo: 1” long)
- Face begins being defined
- In the male embryo testes begin to produce androgens (e.g., testosterone)
- Nerve cells develop in the spine Early signs of behavior begin to show
- Motion in primitive limbs
- Response to tactile stimulation
(4) Fetal Stage (middle of 3rd month) (Fetus: 13 weeks: 3”; 16 weeks: 4 ½”)
- Electrical activity begins in the brain
- Some reflexes (i.e., automatic behavioral responses) develop including the palmar reflex (“palmar grasp”)
- Regular heart rate
- Differentiation of bodily functions; for example, arms and legs begin to move independently
- Face becomes well sculptured (4th month)
- External genitalia become distinctive (4th month)
- Blood begins to be produced in bone marrow (4th month)
- Head begins to move independently of rest of body: Tilting, retracting, and rotating (4th month)
- Limbs become moveable at all joints (4th month)
- By 5th month, stimulation of the brain will evoke appropriate bodily responses
- Face and eye responses accompany head and mouth movements anticipating newborn’s emotional expressions
- By 5th month, reflexes like sucking, swallowing, and hiccoughing develop
- By 5th month, full adult complement of nerve cells in CNS (Central Nervous System) are formed ~ 69 billion
- Premature infants born before the 5th month rarely live
- By 6th – 7th month: Further increase in size of fetus (Fetus: 28 weeks: 15” and 2 ¼ lbs: Infants who weigh less than 1 ½ lbs have a high risk of being permanently handicapped)
- By 6th – 7th month: Eye movements and opening and closing of lids intact
- By 6th – 7th month: Respiratory system strengthened and coordinated in preparation to leave the mother’s womb
- By 6th – 7th month: Endocrine system (glands) become active
- By 6th – 7th month: There is further development of the brain and one of the main reasons humans need a longer gestation period than other primates
(5) Psychological Birth of the Human Infant (8th – 9th month)
- Further differentiation and integration of CNS making possible more complex activities.
- Hearing mechanisms well-developed. However, the outer ear is closed and the middle ear is filled with liquid and therefore the fetus doesn’t hear sounds of normal intensity.
- Although the fetus exhibits various facial expressions, there is no way of knowing whether these correlate with felt bodily states. Development of the CNS at 28 weeks, however, seems sufficient to allow the detection of pain.
(6) Influences on the Maternal Environment
Background
- Within the womb, temperature, chemical balance, atmospheric pressure, and orientation with respect to gravity are carefully controlled.
- The placenta (fleshy disc rich in blood vessels that attaches the embryo to the uterine wall) transmits essential nutrients (oxygen, sugars, water) from the mother to the fetus by way of the umbilical cord and returns wastes for excretion. Fetus begins to manufacture complex amino acids (building blocks of protein) and carbohydrates.
Diet and Nutrition
- Immensely important to the development of the fetal nervous system An inadequate maternal diet can affect the interconnection of brain cells principally through myelination (speeding up of nerve impulses) during the last trimester of pregnancy and first two (2) years of life.
- Malnutrition can lead to growth retardation, malformation of the CNS, and vulnerability to disease.
- Excessive use or lack of certain vitamins can lead to congenital abnormalities.
Alcohol, Drugs, and Smoking
- Smoking during pregnancy may lead to infants with lower than average birth weights and birth defects (e.g., fetal growth retardation).
- Older children whose mothers smoked during pregnancy have more difficulties in school and are more likely to be hyperactive.
- Developmental principle: Prenatal influences may have effects not just on the newborn but in later childhood.
- Alcohol use during pregnancy can lead to fetal alcohol syndrome, mental retardation, and physical abnormalities.
- Psychoactive drugs may produce drug addiction in the newborn such as withdrawal symptoms including irritability, vomiting, and trembling.
- Radiation exposure during pregnancy can cause miscarriages.
- Viruses, such as the rubella virus (German measles) can pass from the mother through the placenta to the developing embryo causing mental retardation, heart defects, deafness, and eye cataracts.
- STDs (sexually transmittable diseases) can cause physical and mental abnormalities and spontaneous abortions.
- Mother’s age is also a critical factor.
- Women over 40 are at greater risk of bearing a child with genetic abnormalities such as Down’s syndrome resulting in mental retardation.
- Girls under 15 are at even greater risk and are in particular danger of stillbirth, miscarriage, and premature birth.
- Emotional stress in pregnant mothers may lead to increases in the hormone epinephrine, which may affect the fetus.
- For instance, pregnant mothers who are overly tense during the course of pregnancy tend to have more difficult labors and deliveries and their newborns tend to show more irritability, agitation, and crying.
- When the mother is under severe stress, fetus will kick more violently in the womb exhibiting up to ten times more activity than normal.
- RESEARCH: Infants who spent more time during their fetal periods near a noisy Osaka airport in Japan slept less soundly as newborns than normal children.
- RESEARCH: Heart rate changes when fetus is exposed to loud noises or classical music. How so?
- RESEARCH: When pregnant mothers enter rooms with bright lights or loud noises, six-month old fetuses show a startle reaction (reflex).
- RESEARCH: In contrast, soft lights and soft sounds attract fetuses and these responses in the fetus occur independently of the mother’s reactions.
Genetic Programming in the Human Genome
Genes are carried on chromosomes (46 pairs in humans: 44 autosomal, 2 sex chromosomes). Chromosomal abnormalities (0.5% incidence in general population) can cause congenital abnormalities in the newborn.
What causes chromosomal abnormalities?
- Internal influences such as Down’s syndrome (extra chromosome or “trisomy 21”).
- External influences such as viruses, chemicals, and radiation can cause mutations in genes.
Patterns of inheritance
Autosomal dominant inheritance involves a dominant gene that is non-sex-linked. For example, hereditary spherocytosis (a condition in which red blood cells assume a spheroid shape).
Bb x bb (found in at least one parent)
Bb Bb bb bb (expressed in at least half the sons and daughters)
Autosomal recessive inheritance involves a recessive gene that is non-sex-linked For example, sickle cell anemia (a condition in which red blood cells assume a sickle-like shape).
Bb x Bb (found in both parents)
BB Bb Bb bb (expressed in one quarter of offspring)
X-linked inheritance involves genes carried on the X chromosome. For example, glucose-6-phosphate dehydrogenase causes baldness.
Males (XY): Have only one X chromosome so the trait will always be expressed.
Females (XX): Depends on whether the gene is dominant or recessive.
Other forms of inheritance
- Down’s syndrome: Problems in independent assortment of chromosomes resulting in deletion or triplication of chromosome 21.
- Klinefelter’s syndrome (XXY): Extra X chromosome but phenotypically male resulting in mental retardation, small testes, and gynecomastia (breast-like development due to disorder of testicular failure).
- Turner’s syndrome (XO): Missing X chromosome and phenotypically female, that is, incomplete sexual development (amenorrhea, short stature, webbing of the neck, and deformities of the arm) as well as deficiencies in spatial visualization as a result of failure of ovaries to respond to pituitary hormone stimulation.In