INFANCY: INFANT,
FAMILY, AND SOCIETY
Chapter 4 – The Developing Brain and Nervous System: Health and Risk
Overview Chapter 4
• Measuring Brain Activity
• Basic Structures of the Nervous System
• Prenatal and Infant Brain Development: A Critical Period
• Optimal and Non-Optimal Brain Development During Infancy
Developmental Neuroscience
The study of the developing brain and nervous system as it relates
to psychological and behavioral functions, such as moving,
thinking, and feeling
Picture from pageresource.com
Measuring Brain Activity
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EEG (Electroencephalography)
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MEG (Magnetoencephalograpy)
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Uses magnetic fields to detect where blood is exchanging oxygen
Not good for use with infants (you have to lie still)
fNIRS (functional near infrared spectroscopy)
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Uses magnetic fields, rather than electricity
fMRI (functional Magnetic Resonance Imaging)
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Measures brain electrical activity
Uses infrared light that can pass through skin & tissues
PET (Position Emission Tomography)
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Uses radiation – not safe for infants
Video about recent imaging techniques used with babies
http://infantlab.psych.sc.edu/
BASIC STRUCTURES OF
THE NERVOUS SYSTEM
Basic Structures of The Nervous System
The Cells of the Nervous System
Neurons – the information storage and transfer cells of the
nervous system
Process electrical and chemical information & transmit this information
to other neurons
• About 140 billion neurons in the adult brain (140,000,000,000)!
• Each neuron can connect to up to 1,000 other neurons
•
Basic Structures of The Nervous System
The Cells of the Nervous System
• Action potentials
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electrochemical currents that travel
from the cell body along the axons to the
axon terminals, which connect to other
neurons
• Synapse
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connects the axon terminals of the
transmitting neuron to the dendrites
of the receiving neuron
Basic Structures of The Nervous System
The Cells of the Nervous System
• Neurochemicals
are exchanged between neurons
They ultimately change behavior
• Produce either inhibition or arousal of brain function
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• For example
Serotonin – alters mood by creating a state of quiet alertness and feelings
of well being (too little can lead to feelings of depression)
• Dopamine – helps with attention and thought, feelings of pleasure and
optimism, and regulation of movement (too much can lead to thought disturbances,
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such as in schizophrenia; too little to movement disorders, incl. Parkinson’s).
Basic Structures of The Nervous System
The Cells of the Nervous System
• Afferent neurons send signals to the brain
•
They transmit to the brain how things affect us
• Processor neurons – in the spinal cord and brain – analyze the
stream of information coming from receptor cells
• Efferent neurons are directly connected to muscles that alter or
effect internal and external behavior (e.g., in the muscles that regulate
movement)
Basic Structures of The Nervous System
The Cells of the Nervous System
• Glia Cells are support cells:
They support functions that are especially important during fetal and
infant brain development
• Some provide oxygen and nutrition & remove waste products
• Others create myelin, a coating that improves the integrity and speed of
conduction of neurochemical information along the axon
• Others (radial glia) provide a sort of scaffold for the neurons to grow &
migrate along
• One other type holds neurons in place (glia = glue)
•
Basic Structures of The Nervous System
Anatomical Structures of the Brain
The human brain has three basic regions:
Brain stem
2. Limbic system
3. Cortex
1.
Basic Structures of The Nervous System
Anatomical Structures of the Brain
• The brain stem contains the roots of the afferent and efferent
neurons of the Autonomic Nervous System (ANS), which is
responsible for regulation of basic body fucnctions
• The ANS has two branches
Sympathetic – prepares the body for action
• Parasympathetic – allows the body to relax
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• For healthy development, babies (and adults) need a balance
between arousal & rest
Basic Structures of The Nervous System
Anatomical Structures of the Brain
• The limbic system is located in the center 0f the head
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Related to processes such as memory, regulation (sleep-wake, breathing,
temperature regulation), emotion, responses to stress vs. relaxation
• Limbic structures that are important for infant development:
Hippocampus – (autobiographical) memory
• Amygdala – emotional memories (fear, safety)
• Hypothalamus – links the brain to the hormonal system of the body, via
the pituitary gland and the bloodstream, and is very important for the
early development of states of arousal, feeding, and self-regulation
•
Basic Structures of The Nervous System
Anatomical Structures of the Brain
When the amygdala senses
threat or stress, it sends
neurochemicals to the
hypothalamus to activate the
HPA Axis – hypothalamus,
pituitary, and adrenal glands
Basic Structures of The Nervous System
Anatomical Structures of the Brain
Hypothalamus: CRH
Pituitary gland: ACTH
Adrenal glands: Cortisol
Basic Structures of The Nervous System
Anatomical Structures of the Brain
• Cortisol – a blood sugar that prepares the body for action, in
response to stress
Affects the neurons in the limbic system
• Here, it heightens the formation of memories related to the stressful
event
• Once the event has passed, the production of cortisol is slowed down
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• Oxytocin – another hormone secreted by the pituitary
Gives a feeling of warmth, comfort, and safety
• Usually secreted when we are in close contact
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Basic Structures of The Nervous System
Anatomical Structures of the Brain
• The cortex (“tree bark”) is the outer layer of the brain
Forms synaptic connections with the limbic system
• Divided into lobes (anatomical regions)
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Occipital lobe – processes visual information
Temporal lobes – auditory & speech processing
Parietal lobes – connected to the muscles and sense organs; integrate sensory &
motor information from different parts of the body into a body schema
Basic Structures of The Nervous System
Anatomical Structures of the Brain
• The insula – creates feelings of interoception, allowing us to feel
the inner condition of our bodies
• The frontal lobe – aka the prefrontal cortex
assists in reasoning, planning, organizing thoughts and behavior in
adaptive ways, regulating emotions and urges, carrying out problem
solving, and making judgments
• gives us the capacity to inhibit behaviors
•
Basic Structures of The Nervous System
Anatomical Structures of the Brain
The prefrontal cortex gives us the possibility of
voluntarily (rather than automatically)
regulating our body states and patterns of
behavior
The prefrontal cortex (PFC) has two parts:
Medial (mPFC)
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•
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Connects to emotional processing
areas (amygdala, hippocampus,
sensory regions of parietal lobes
As early as the first month of life,
the mPFC responds to infantdirected and emotional speech, &
pleasant smells
A few months later, it responds to
mutual gaze & familiar faces
Lateral (lPFC)
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Connects to areas related to
motor control
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Responds to speech that is not
directed to the infant & is not
emotional, and to non-human
objects
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Plays a role in holding objects in
working memory & in object
permanence
Basic Structures of The Nervous System
Anatomical Structures of the Brain
Right Hemisphere
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Controls movements on the left
side of the body
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More holistic & related to novelty
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Most social and emotional activity
is processed in the right limbic
sensory and prefrontal & face
recognition areas
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These parts change rapidly over
the first 2 years
Left Hemisphere
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Controls movements on the right
side of the body
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More analytical
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The left prefrontal, parietal, and
temporal cortices are important
for language & thinking
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They develop more rapidly after
the first 2 years of life
PRENATAL & INFANT
BRAIN DEVELOPMENT
Prenatal & Infant Brain Development:
A Critical Period
• The first weeks after conception to the age of 3 to 4 years is a
critical period for brain development
• The next section covers optimal vs.
non-optimal brain development &
the factors that enhance or hinder
brain growth
Prenatal & Infant Brain Development
Prenatal Development
• By the end of the 3rd week after conception, the embryonic disk
consists of three layers: endoderm, mesoderm, and ectoderm
• Stem cells in the ectoderm will become the skin, nails, teeth,
sweat glands, sense organs, and the nervous system
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Note that the skin, the largest and most sensitive organ, develops out of
the same layer of stem cells as the brain.
Prenatal & Infant Brain Development
Prenatal Development
• Neurogenesis – virtually all of one’s lifetime supply of neurons
are produced during the first 4 prenatal months
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Radial glial cells help the new neurons migrate to the right place
• After the 4th prenatal month, most of the brain’s development
occurs by making connections between cells and by “pruning,”
or selective death of unused neurons
Video clip of prenatal brain development
Prenatal & Infant Brain Development
Prenatal Development
• A neuron will die if
it is not connected to other cells during development,
• it does not get bathed in sufficient neurochemicals, or
• it does not receive the appropriate epigenetic signals from the fetal
environment to turn off the “suicide” genes that all neurons have
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• By the time a baby is born, about 50% of their prenatal neurons
have died
Prenatal & Infant Brain Development
Prenatal Development
During the 2nd half of the prenatal period, most brain
development occurs though synaptogenesis – the development
of connections between neurons
Prenatal & Infant Brain Development
Prenatal Development
• The initial “wiring up” of the brain to the body is usually completed by
the 7th prenatal month
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fetuses begin to feel pain & generate movements under the control of the brain
• In the 2nd half of pregnancy, axons are also becoming more efficient
by developing an insulation-like encasing of glial cells called myelin.
Myelination improves the speed of electrical conduction along the axon by a
factor of about 3
• Begins in the last few weeks before birth & continues throughout life
• Rapid development in first few postnatal months
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Prenatal & Infant Brain Development
Postnatal Development
Postnatal developments:
The networks between neurons become more complex
• More dendrites and axons grow
• More synapses and neurotransmitters develop
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Prenatal & Infant Brain Development
Postnatal Development
In the postnatal period, there is an overproduction of synapses,
which gradually becomes pruned back to the stronger
connections
At age 12 months, the baby’s brain has 150% of the synapses
that an adult has
• This number begins to decline in the 2nd year
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Prenatal & Infant Brain Development
Postnatal Development
• Different areas of the brain develop at different rates
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E.g., the visual cortex matures earlier than the prefrontal cortex
• Keep in mind that synapses connect and disconnect all the time,
over time scales of seconds, minutes, or hours
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It is not a steady growth and decline process
Prenatal & Infant Brain Development
Postnatal Development
• Experience-expectant functions
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The brain is expecting specific experiences, for which specific skills are
best adapted (e.g., pain produces crying)
• Experience-dependent functions
Most cells and synapses in the brain are open to any experiences
• “Use it or lose it”
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Prenatal & Infant Brain Development
Postnatal Development
There is a dynamic system of linkages between brain, experience,
and behavior. And during the first few months after birth, infants
experience stimuli of increasing intensity and complexity, and
connections favoring those types of stimuli will be strengthened.
Prenatal & Infant Brain Development
Development of Functional Neural Networks
There are four basic functional networks of the brain important to
infant development:
Arousal, attention, and emotion
2. Information processing and remembering
3. Regulation and executive function
4. Self-awareness
1.
Functional Neuronal Networks:
1. Arousal, attention, and emotion
• Regulates the sleep-wake cycle and cycles related to hunger,
thirst, physical arousal during exercise & stress, and sexualreproductive cycles in adolescents & adults
• Emotions – develop over the first year of life
E.g., fear develops at the end of the first year of life, as the amygdala
becomes myelinated and connected to other brain networks
• Around this time, emotional attachments form also
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Functional Neuronal Networks:
2. Information processing and remembering
• These brain networks for staying awake and paying attention
are also connected into a larger network that includes the
sensory organs, all the internal organs, and the muscles that
move the body
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What infants learn and remember involves their whole body – not just the
brain
Functional Neuronal Networks:
2. Information processing and remembering
Two basic kinds of memory:
Autobiographical memory (hippocampus plays important role – does not
become fully functional until about 3 years of age).
• Procedural memory (connections between cortex, limbic system, and
brain stem)
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Functional Neuronal Networks:
3. Regulation and executive function
• We need a mechanism for inhibition of the orienting reaction
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so that we can direct our attention to higher levels of processing that
encompass a sequence of actions and sensations
• We also need a means to have a ‘working’ or short-term memory
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to remember each of the steps in the sequence & to compare our actions
between different attempts at the same sequence, between one type and
another, and between ourselves and another person.
• Finally, we need to regulate our emotions
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so that we don’t give up on learning something new in the face of
complexity, distress, frustration, or fear
Functional Neuronal Networks:
3. Regulation and executive function
Most of the neural basis for executive function comes from
a network that includes all the prior networks along with
their connections in the prefrontal cortex (regulation) and
the insula (sense of self), which are the parts of the brain
that mature most slowly.
Functional Neuronal Networks:
3. Regulation and executive function
There is a peak in the development of the Prefrontal Cortex
around age 3 to 4 years
At this age, links between the PFC and the amygdala account for the
emergence of more independence and self-calming
• But even newborns have some prefrontal functions - helps with soothing,
but a lot of adult help is needed
• On the other hand, the PFC keeps developing until about the age of 25
• In some ways, adults serve as an ‘external PFC’
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Functional Neuronal Networks:
3. Regulation and executive function
Inhibitory control might be the most important executive function
Problems with this in preschool age are related to later cognitive,
emotional, and behavioral problems
• Prefrontal inhibition of the amygdala allows
for greater access to self-awareness and more
adaptive responses (so that we are not thrown
into “fight or flight” mode)
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Functional Neuronal Networks:
4. Self-awareness
• Recently, neuroscientists have discovered
that there are major networks devoted
almost entirely to sensing the inner
condition of the body and mind, including
Where our body is in relation to the environment
• How we move on different surfaces
• Body boundaries
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• Self-awareness goes through multiple developmental changes
during infancy
OPTIMAL AND NON-OPTIMAL
BRAIN DEVELOPMENT DURING
INFANCY
Optimal and Non-Optimal Brain Development
Stress is probably the single most important factor regulating
individual differences in brain development – beginning before
birth and continuing throughout life.
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Threat – the sense of being in danger from outside of ourselves
• Stress –
the body is unable to find a balance between
sympathetic & parasympathetic activity
From: http://developingchild.harvard.edu/index.php/key_concepts/toxic_stress_response
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Trauma – condition that results from prolonged sympathetic
activation and the resulting depletion of the body’s resources
and lack of time for recovery.
Shock trauma – the effect of a relatively brief and sudden event like an
injury or sudden loss
• Developmental trauma – when exposure to a threatening event occurs
over a longer period of time, such as neglect or abuse
•
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
Neuroception – non-conscious evaluation of safety or threat
Each baby in the first two years of life comes
to assess the social world as either a safe or
a threatening place
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
Three basic patterns of neuroception (Porges)
1.
Immobilization (freeze or faint)
2.
Mobilization (fight or flight)
3.
Social engagement
Pictures from: http://wallpapers55.com
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Mobilization: fight or flight
High level of arousal, activated by the
Sympathetic Nervous System (SNS)
• At the expense of body functions like
digestion and immune system
• Engagement with the environment (incl. people) requires a balance
between SNS and PNS (parasympathetic nervous system) so we can be
relaxed, yet alert
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Picture from: http://parentables.howstuffworks.com/family-matters/siblings-rivalry-and-brawling.html
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Immobilization: faint or freeze
If we are not able to respond to stress by fight
or flight, a more primitive and unmyelinated
part of the PNS is activated
• The body slows down to an extreme extent – the body also shuts down,
feigning death – frozen & unable to act
• Last-resort survival response of the nervous system
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Picture from http://appliedjung.com/practically/fear
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Vagal tone
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the availability of a myelinated vagal PNS that can help us relax in the face
of stress, measured by the ability of the heart to adjust its beat-to-beat
frequency in the face of stress
• Infants under the age of 6 months
Need more protection from others to buffer the effects of stress
• Are more likely to have lasting impairments of vagal tone leading to an
impairment of the ability to regulate basic body function and manage
stress, if this protection is not available
•
Picture from http://appliedjung.com/practically/fear
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Prolonged activation of the SNS and suppression of the PNS also
activates the HPA-axis, and leads to secretion of cortisol
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When there is persistent prenatal or postnatal stress, cortisol is
overproduced – and becomes toxic
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Cortisol can alter structures by changing epigenetic markers
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This process can also compromise the immune system
• Cortisol not only changes the neurotransmitters and receptors &
the connections between the limbic system & the rest of the brain
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It also changes the way early experiences are remembered
Video & website about toxic stress
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Too much stress
leads to a tendency to feel fear and stress in the future
• leads to PTSD – a decreasing ability of the individual to cope with the
stress in appropriate ways, creating a person who is more likely to freeze,
fight, or flee when they feel threatened
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• Early stress affects both mental and physical health
Because it impairs vagal-parasympathetic calming
• Because it dysregulates the HPA-axis, which changes key ares of the brain
related to self-regulation
• It also relates to epigenetic changes in DNA expression & cell development
•
Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
• Effects of early stressors in infancy:
Premature birth or LBW (after prenatal stress)
• Delays in motor & cognitive development & in attention & emotion regulation
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• In childhood & adulthood
Cognitive & memory impairments, learning disabilities, ADHD, depression,
anxiety, and poor school performance
• Higher risk for chronic diseases & immune disorders & early death
• Unhealthy lifestyles (e.g., substance abuse) & poor parenting of own children
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Optimal and Non-Optimal Brain Development
Effects of Prenatal & Infant Stress
Some short-term stress is good for infants,
children, and adults:
Dealing with everyday frustrations
• Adapting to new experiences
• Waiting to get our needs met
• Exploring uncertain environments
•
Picture from: https://medic-trans.com/acc-medlink/tips-on-medical-transport-of-a-child
Optimal and Non-Optimal Brain Development
How Can We Foster Healthy Brain & Bio-Behavioral Development?
• If prenatal and first-year stress is followed by early intervention
programs in preschool and day care during the 2nd year, there is ample
room for full or partial recovery
• For example
At 17 months old, infants exposed to higher prenatal cortisol had shorter
attention spans and fewer language skills & problem-solving skills – but only if
they had an insecure attachment to their mothers.
• Those with a secure attachment showed no effects of high prenatal cortisol
•
Optimal and Non-Optimal Brain Development
How Can We Foster Healthy Brain & Bio-Behavioral Development?
• In general, the effects of early experience have the potential to be
alleviated when certain types of resources are present in the
environment in later infancy and early childhood
• Support for parents is essential, so that they can provide adequate
support to their children
• Child factors important for recovery include the ability to talk about
their experiences & have a community of support
Optimal and Non-Optimal Brain Development
How Can We Foster Healthy Brain & Bio-Behavioral Development?
Three basic areas of intervention to relieve the effects of early stress
The infant’s family & social relationships
2. The safety of the built environment
3. Providing adequate nutrition & preventing disorders (e.g., type 2 diabetes)
1.
Optimal and Non-Optimal Brain Development
Conclusion
Infancy is a critical period for the development of the limbic system,
the insula, and the prefrontal parts of the brain – arousal, attention,,
and emotion; information-processing; regulation/executive function;
and basic bodily self-awareness – which is fundamentally and crucially
dependent upon the quality of sensitive caregiving, love, emotional
sharing, and social engagement received and perceived by the infant.