Module 4

Question 1

most rapid growth

Answer 1

the most rapid growth happens prenatally, with infancy in second place, and then growth rate slows until middle childhood. If you think about it, embryos and fetuses are regularly doubling in size, whereas children are growing a few inches each year.

Question 2

proximodistal

Answer 2

which means from close in to far out. That means that “close in” structures like the head and trunk grow faster than the far out structures like the limbs. This is why babies have proportionally much larger heads and bodies than adults and children.

Question 3

cephalocaudal

Answer 3

meaning from head—cephalo—to tail— caudal, and refers to neuronal development.

This means that children will be able to perform gross motor movements—those that require larger and less precise muscle movements—before fine motor movements, like precise movement of the hands and fingers

Question 4

What do children need to grow?
Food

Answer 4

children need good nutrition and enough food in order to develop properly. Because they’re growing so rapidly, babies need to consume about 50 calories per half a kilogram of body weight, whereas adults only need about 15 to 20 calories for half a kilogram of body weight. Babies and kids need to get enough vitamins, nutrients, and macronutrients like carbohydrates, fat, and protein. Children need to enough grains, dairy and alternatives, meat and alternatives, and especially fruits and vegetables in order to develop optimally.

Question 5

What do children need to grow?
Sleep

Answer 5

Kids also need to get enough sleep, especially since 80% of human growth hormone is released during sleep. Three-year-olds need about 11 hours of sleep per night, whereas 7-year-olds need 10, and 12-year-olds need 9

Question 6

What do children need to grow?
Social/emotional care

Answer 6

Finally, kids need social and emotional care in order to grow. Extreme social or emotional neglect, stress, or abuse can cause a condition called psychosocial short stature, where children fail to grow appropriately due to the extreme stress that they’re under. Once they’re rescued, they typically catch up and grow quite rapidly in a small amount of time.

Question 7

Puberty

Answer 7

is another important growth milestone. During puberty, children usually go through their adolescent growth spurt and they reach sexual maturation. Both sexes experience bone, muscle, and fat growth, but males develop more muscle and greater heart and lung capacity, while females develop more fat, which they’ll need to support their developing fertility.

Question 8

Primary sex characteristics

Answer 8

Sexual maturation changes both primary and secondary sex characteristics. Primary sex characteristics mean changes to the reproductive organs, including the ovaries, uterus, and vagina in females and the scrotum, testes, and penis in males.

Question 9

Menarche

Answer 9

is when a female has her first period, although it’s possible that it’s not yet a true period—because ovulation might not start for up to 18 months. This is why girls often have very irregular periods at first. Either way, she has started to build up a uterine lining each month, and she will also begin to produce cervical and vaginal fluids.

Question 10

spermarche

Answer 10

occurs, which is when a male first ejaculates. Sometimes this occurs during sleep and is colloquially referred to as a ”wet dream.” Menarche and spermarche both tend to occur at an average age of 13.

Question 11

secondary sex characteristics

Answer 11

Adolescents also experience changes in secondary sex characteristics, which include non-reproductive organs.

For girls, this includes breast growth and a widening of the pelvis.

For boys, it includes the development of facial hair and a broadening of the shoulders.

For both sexes, it will include the development of body hair, including pubic hair, and changes in the voice and skin.

Question 12

Factors that affect the onset of puberty

Answer 12

The onset of puberty is affected by many of the same factors as general growth.

For example, just like genetics influence how tall you’ll be, genetics also influence the timing of puberty.

Adolescents are more likely to go through puberty at the same time as their parents, and identical twins tend to be more in sync with their pubertal timing than fraternal twins.

Question 13

Factors that affect the onset of puberty

menarche

Answer 13

Most influences have been studied more in girls, because menarche is a clearer marker of the onset of puberty than the changes that occur in boys.

Good nutrition usually leads to earlier menarche, whereas poor nutrition is associated with later menarche.

This is probably because females need adequate nutrition and fat stores to menstruate; otherwise, their bodies wouldn’t be able to support a pregnancy.

Question 14

Factors that affect the onset of puberty

stress, depression, and a harsh upbringing

Answer 14

actually lead to earlier menarche. Why might that be?

Researchers hypothesize that evolution has shaped women’s bodies to optimize their reproductive success given the available environment.

If the environment is poor—the girl experiences a lot of stress and hardship—then it might be to her advantage to be able to reproduce as early as possible, in case a healthy, good-quality mate comes along.

This way, her offspring has a better chance of survival in a harsh environment, even though you should recall from a previous module that teen pregnancies are risky.

But when the environment is resource-rich and virtually stress- free, the strategy switches: in this case, it may be more advantageous for her to develop more fully and mature before having any children

Question 15

Factors that affect the onset of puberty
Absent father

The paternal investment theory.

Answer 15

girls experience menarche earlier when they have a poor quality or absent father, compared to if they have a loving and involved father. Research even suggests that if a father abandons his family when he has two daughters of different ages, the younger daughter will be more severely affected— causing her to menstruate earlier, on average, than her older sister—because she experienced the stress and poorer environment earlier in development, and will have spent more time without a father.

Question 16

minority WEIRD world,

Answer 16

One important thing to note as we begin our discussion of developmental milestones is that almost all research is conducted in a very small proportion of the world.

which stands for countries that are western, educated, industrialized, rich, and democratic, including Canada, the USA, western Europe, and Australia.

Question 17

majority world

Answer 17

Most people on earth live in the majority world though, where different developmental patterns and challenges are more typical.

For example, malnutrition is certainly a serious challenge to physical growth for some Canadian children, but the problem is much more widespread and severe in many other parts of the world.

Similarly, Canada’s universal healthcare program means that people have access to important vaccinations, medicine, and treatments, whereas untreated disease is an unfortunate human reality in much of the rest of the world.

Question 18

Infant nutrition

Answer 18

the recommendation is to breastfeed exclusively for the first 6 months, and continue to breastfeed until age two or longer while also introducing solid foods.

Question 19

extra benefits to breastfeeding

Answer 19

Because babies receive antibodies, white blood cells, and other immunity-boosting factors through breastmilk, they are less likely to get sick.

Since breastmilk is easy to digest, babies tend to have less diarrhea and constipation.

The transition to solid foods also tends to go more smoothly, because babies get exposure to the flavours of a mother’s diet through breastmilk, and so they get a chance to get used to these flavours.

Lastly, breastmilk can’t really be contaminated unless a mother is consuming certain drugs, whereas formula can be.

Question 20

Bottle-feeding

Answer 20

Bottle-feeding won’t harm a child though, and women should feel free to choose that option if they need to or wish to.

Mothers who bottle-feed can bond with their infants just as much as mothers who breastfeed, and bottle-feeding can also allow multiple people to feed the baby without the mother having to pump large quantities of breastmilk.

Women can feel a lot of pressure to be the perfect mothers, which may cause them stress if breastfeeding is proving to be too difficult.

This has led to a pushback on the old saying “breast is best”, and a switch to “fed is best.”

Question 21

Child nutrition

Answer 21

recommendations are similar to what experts recommend for adults, but just on a smaller scale.

For example, children should be offered mini versions of adult meals where about half the plate is made up of fruits and vegetables, a quarter of the plate is made up of high-protein foods like meat, beans, tofu, or dairy, and a quarter of the plate is made up of whole grains.

Water is recommended as the most common thing to drink, and snacks can be mini version of a plate with a choice of two of the three food groups.

Question 22

Child obesity

Answer 22

is a growing issue, but there are a few things that parents can do to promote healthy eating habits.

Parents shouldn’t require children to finish their entire plate of food, because this teaches the child to eat when they’re no longer hungry.

It’s also a good idea to avoid using food for comfort, like offering ice cream when a child is sad.

This teaches a child to use food rather than other healthier coping mechanisms when they’re upset.

Question 23

research-based strategies parents can use to get them to eat healthier.

Answer 23

A number of studies have shown that simply rewarding kids for tasting a vegetable increased their consumption of that vegetable, even three months later.

A non-food reward works best, like stickers if kids like those, but praise, can also be helpful, so parents can tell children “good job” when they try new foods.

Kids imitate what other people do too, so parents should model healthy eating behaviours by eating their own vegetables.

Kids may be particularly likely to imitate other kids that are their own age and same sex, so showing them photos or videos of other kids trying the foods can be helpful.

The best way to introduce new foods is to offer them one-at-a-time and in small amounts so that kids aren’t overwhelmed with unfamiliar foods.

They should be encouraged to try the food, but not forced to eat it.

Even if they reject it, parents should keep offering it on other days at other meals: food liking usually works on the mere exposure effect: the more you’re exposed to something, the more you like it.

when parents teach kids about nutrition and how the body needs different nutrients, kids tend to eat more vegetables.

Parents can also involve children in cooking meals, so that they have some ownership and pride in what they’ve made and so that they learn about foods and food preparation.

Question 24

Sleep requirements

Answer 24

A lack of sleep is associated with many difficulties, including problems focusing, aggression, obesity, difficulties with emotion regulation, and a higher likelihood of athletic injuries.

Infants need the most sleep, and sleep needs gradually decline throughout childhood, but even teenagers need an average of 9 hours of sleep.

To promote good sleep habits, a bedtime routine is a great idea.

This can include activities like toothbrushing, bedtime stories, reading books, or singing songs.

Electronic devices like TV, tablets, phones, and computers should be avoided though and not in the bedroom, since their light and excitement can interfere with sleep.

Bedrooms should also be dark, cool rather than too hot, and quiet.

Question 25

physical activity requirements

Answer 25

infants under 1 year should get at least 30 minutes a day, spread out throughout the day, of active time like tummy time, where they’re placed on their tummies, or activities like reaching, pushing or pulling things around, and crawling.

They also shouldn’t be restrained in a stroller or high chair for more than an hour at a time, and probably shouldn’t have screen time under the age of 2, with a few exceptions like maybe Facetiming with grandma and grandpa.

Toddlers and preschoolers from age 1 to 4 are an active bunch: they need at least 3 hours a day of physical activity, which probably consists mostly of play, especially energetic play.

It’s also recommended that they aren’t restrained for more than an hour at a time, and that they don’t spend more than an hour per day in sedentary screen time activities.

School-aged children and adolescents should get at least 1 hour of moderate to vigorous exercise each day like running or sports, in addition to several hours of lighter exercise like walking, and they shouldn’t spend more than 2 hours a day on screens.

Their exercise should include activities that get their heart pumping faster as well as activities that strengthen their bones and muscles.

Question 26

Promoting physical activity

Answer 26

more daily activity in schools so that kids have regular activity breaks every day.

Parents and schools can also promote more activities that people are likely to stick with when they grow up, especially activities that don’t require a whole group of people, like running, walking, racquet sports, and swimming.

Parents can limit screen time so that it doesn’t eat into physical activity time, and families can spend more time doing physical activities together,

Parents can also enroll their children in extracurricular physical activities like sports, martial arts, or dance, which can have several other important benefits aside from exercise.

some exercise is better than none, so gradually increasing exercise levels is better than getting discouraged about being too far away from the recommendations.

Question 27

The developing nervous system:

1st 2 weeks

Answer 27

in the third week of gestation, the ball of cells divides into three layers?

The ectoderm was the layer that eventually becomes the brain and spinal cord, and this is how that happens.

First, a section of the ectoderm called the neural plate begins to form a neural groove as it starts to fold in on itself.

Next, the groove will form into a neural tube and that fully closes by 4 weeks after conception.

These two weeks are when a lack of folic acid can prevent the full closure of the neural tube, leading to a condition like spina bifida.

Question 28

The developing nervous system:

The next 32 weeks

neurogenesis

Answer 28

Neurons are produced in one end of the neural tube starting at 10 weeks after conception, and not many more are produced after 28 weeks gestation.

This means that the 28-week-old fetus will probably have largest number of neurons it will ever have.

Unused or unnecessary neurons will die, and neurogenesis, the production of new neurons, only occurs modestly and in certain circumstances in adults.

Question 29

The developing nervous system:

The next 32 weeks

neural migration.

Answer 29

The brain is built in stages and layers, kind of like an onion.

The oldest and innermost layers form first, and the outer cortex forms last.

But because neurons are produced in the same place in the neural tube, they actually have to move to the outer layers by climbing on supporting cells.

This is called neural migration.

Question 30

The developing nervous system:

The next 32 weeks

Myelination

Answer 30

The six layers of the brain are all built by about 7 months after conception.

Myelination of axons also starts to occur by the fourth month, where fatty coatings are added to speed up neural transmission.

Sensory areas are myelinated first, and the cortex is the last to finish, which happens many years later in a person’s early 20s.

Question 31

The developing nervous system:

Childhood to young adulthood

Answer 31

brain maturation continues well into childhood, adolescence, and young adulthood.

Grey matter—which consists of cell bodies, dendrites, and unmyelinated axons—actually decreases over development.

This is mostly because we lose axons and dendrites that aren’t useful, and because axons that are useful become myelinated, which turns them into white matter.

Once again, the pattern is that basic processing areas like sensory, spatial, and motor areas mature earlier, and higher-level brain areas mature later, like the prefrontal cortex, which is responsible for complex processes like planning and inhibition, and some parts of the temporal lobe that link information from many other brain areas together.

Question 32

Synaptic pruning

Answer 32

happens when synapses disappear because they aren’t used very frequently.

Canadian psychologist Donald Hebb’s law, that “neurons that fire together wire together,” which is when synapses that are used a lot become strengthened.

The opposite is also true, and is sometimes called “use it or lose it.” If a connection in the brain isn’t necessary, then it makes the brain inefficient.

That usually means that it’s better to get rid of it.

synapses are rapidly being formed, reaching a peak just over 1 year of age: this is when you’ll have more synapses than you’ll ever have in your life.

After that, they start to be pruned away, contributing to the loss of grey matter that we see with age.

Question 33

synesthesia

Answer 33

One really interesting case where researchers believe synaptic pruning doesn’t happen normally is in a condition called synesthesia.

This is when stimulation of one sensory or cognitive aspect elicits perception or experience in a different area.

Researchers believe that synesthesia occurs when connections between different areas of the brain that would normally be pruned away are strengthened instead, which happen in around 4 or 5% of the population

Question 34

neonatal synesthesia hypothesis

Answer 34

the idea that we are all born synesthetic because newborns don’t seem to differentiate information from different senses.

In typical development, these connections are pruned away or inhibited, but in synesthesia, at least some remain.

If this is true, imagine how different the world of a newborn is from your own perceptions and experiences!

Some people may be predisposed to develop synesthesia, because it tends to run in families. Research also suggests that certain experiences may reinforce those predispositions.

Question 35

Plasticity

Answer 35

Plasticity refers to the brain’s ability to change in response to either the environment or to damage, like in a brain injury.

Question 36

Structural plasticity

Answer 36

structural plasticity, where certain brain structures change in size, density, or connectedness in response to environmental stimulation,

Question 37

functional plasticity

Answer 37

functional plasticity, where existing brain areas reorganize to take on some or all of the functions that were performed by a different area that has been damaged.

Question 38

Principles of specialization:

1.begins early

Answer 38

One of the reasons why plasticity may decline is because the brain becomes more specialized with age.

The first is that the process of specialization begins very early in development, even before birth.

As an example, by the time a baby is born, their left hemisphere already responds preferentially to their native language, the language that their mother spoke while pregnant.

This is not the case for foreign languages or for other auditory stimuli.

This means that areas in the left temporal lobe have already begun to specialize for language before the baby was even born.

Question 39

Principles of specialization:

2.Brain responses become more specific

Answer 39

The second principle is that the brain becomes more specific in two main ways.

First, the area that responds to a particular type of stimulation becomes more focused, kind of like a pinpoint laser rather than a large floodlight.

Second, that area starts to respond more specifically to a specific type of stimulus, and less to other types of stimuli.

As an example, here is the pattern of responses of the fusiform face area, the area of the brain that processes faces.

Early in development, it responds equally to face and non-face stimuli, but by adolescence and adulthood, it responds much more strongly to faces and less to nonfaces.

Question 40

Principles of specialization:

3. Brain areas specialize at diff rates

Answer 40

this is the idea that brain areas specialize and mature at different rates. For example, sensory areas specialize and mature earlier than areas of the brain that process complex, high-level information, like the prefrontal area of the frontal cortex.

Question 41

Principles of specialization:

4. Less specialization = greater plasticity

Answer 41

The fourth principle is that less specialization generally means more plasticity, so younger brains are more flexible at changing in response to the environment.

Question 42

Principles of specialization:

5. The brain needs experience to specialize

Answer 42

The last principle is that experience is required for the brain to specialize.

To illustrate this point, some children are born with dense cataracts in one or both eyes, that basically deprive them of any visual input until they have surgery.

Studies have found that when these children regain their sight, they have permanent deficits in certain aspects of face processing, and that their brains aren’t as specialized for face processing. Instead, face areas respond with less activation to faces, and they also respond to objects.

These findings show that early experience was necessary for the face areas to specialize properly. Interestingly, in people who were born blind, the face area responds to the feel of faces, as well as to voices.

This illustrates another point about specialization, which is that many brain areas are best designed to perform a particular function.

If it doesn’t receive the right input, it might be taken over by other functions, but sometimes these are similar to what it was originally supposed to do.

Question 43

Experience-expectant growth

Answer 43

is growth that happens in all members of a species at around the same time and that depends on experience.

It’s called expectant because the brain is thought to be set up to expect or receive a certain kind of input.

So the visual cortex is set up to receive visual information, and language areas of the brain are set up to receive language input.

If the area in question doesn’t receive the right input early in life, development can be very atypical, and may not ever recover fully.

This is essentially what critical or sensitive periods reflect: examples of experience- expectant growth that need to happen at a certain time.

Question 44

Innate growth

Answer 44

is used to describe the acquisition of traits and abilities that don’t require any experience with the environment.

This is probably a much narrower definition than you’re used to of the term “innate,” because the term gets thrown around a lot to mean a lot of different things.

Developmentalists mean that it really doesn’t require experience either in or outside of the womb, like the infant reflexes we went over in a previous module.

Question 45

When do babies start to taste?

Answer 45

in the womb.

Whatever the mother eats is infused into both amniotic fluid and breastmilk, and strong tastes are particularly detectable.

The reason for this is that fetuses swallow amniotic fluid, and they’ll tend to swallow more of it when the prefer the taste.

In one study, researchers injected either a sweet or a bitter taste into the amniotic fluid of 8-month-old fetuses to control the timing and concentration of the flavour.

Fetuses swallowed more of the sweet taste, suggesting that they prefer sweet flavours and dislike bitter flavours.

In response to sweet flavours, newborns make a lot of hedonic expressions: face and body movements that indicate pleasure or approach behaviour.

This includes smiling, sucking the fingers, smacking the mouth and lips, and slowly and repeatedly sticking out the tongue.

On the flip side, they make a lot of aversive expressions to sour and especially bitter tastes: these are expressions that indicate displeasure or withdrawal behaviour.

likely that these early preferences are adaptive, encouraging the infant to eat nutrient-dense food and dissuading them from eating rotten or poisonous food.

Question 46

Do infants recognize familiar orders?

Answer 46

Studies show that newborn infants will turn preferentially toward a gauze pad that is saturated with their own amniotic fluid rather than one that has been saturated with the amniotic fluid of a different baby, suggesting that they recognize and prefer the scent.

Within a couple days of the start of breastfeeding, newborns also turn toward the scent of their own mother’s breastmilk rather than the scent of a different mother’s breastmilk.

This shows just how incredible the baby’s sense of smell is.

It probably also has an important function, helping the baby to turn toward the breast in order to facilitate feeding.

Question 47

Touch perception in newborns

Answer 47

researchers habituated newborns to the feel of one of two shapes: a cylinder vs. a triangular prism.

They let the infant grasp one of the two objects for as long as they wanted to or could before becoming disinterested, and repeated this process on each trial until the infant became bored, shown by a drastic reduction in grasping time.

In the test phase, they either gave the infant the same shape again, or a different shape.

Infants dishabituated-–meaning they grasped longer—to the novel shape but not the familiar shape.

This means that they could tell the difference between the objects based on how they felt.

Importantly, the infants were tested so that they couldn’t see the object, so they were discriminating based on touch rather than on a different sense like vision.

Question 48

Kangaroo care

Answer 48

is the practice of holding an infant who is only wearing a diaper and maybe a hat on the bare chest, maximizing the amount of skin-to-skin contact.

It can be done for as little as an hour a day all the way up to around the clock, which obviously needs to be done in shifts.

It was developed in Columbia to help premature infants, who were at a very high risk of dying.

It’s been used especially in places that lack high-tech neonatal intensive care units, but it’s increasingly being used in minority-WEIRD countries as well who have access to many resources.

premature infants were much more likely to survive and even thrive when they were held in the kangaroo care position.

Question 49

Why kangaroo care works

Answer 49

First, skin-to-skin contact helps the baby maintain a constant temperature, which is difficult for them to do if they’re premature and haven’t developed enough fat.

This means that they have more energy leftover to grow instead of spending so much of it just trying to stay warm.

Second, skin-to-skin contact increases the release of oxytocin, which is sometimes referred to as the bonding hormone.

Oxytocin can help the baby and caregiver bond more closely, which can reduce stress in the baby.

If the mom is the kangaroo caregiver, oxytocin release also helps her breastfeed, further helping the baby grow and gain necessary fat.

Lastly, the kangaroo care position can be comforting to the infant because of the familiarity.

Question 50

Hearing

Answer 50

by about 5 to 6 months gestation.

Some studies have presented loud sounds to the fetus and monitored their movements using an ultrasound, making sure to give the mother noise-cancelling headphones so that didn’t influence the fetus’s responses.

Fetuses will give a little jolt with a startle response, suggesting that they probably heard the sound, although it’s also possible that they were responding to vibrations.

Other studies suggest babies can hear because they learn sound patterns while in utero.

Question 51

Auditory threshold

Answer 51

is one aspect of hearing that develops during infancy and childhood.

The threshold is the quietest sound that a person can still detect.

If we use adults’ threshold as the point of comparison, newborn’s auditory threshold is about 40-50 decibels higher, meaning that newborns need sounds to be a bit louder to perceive them.

This is a bit of a simplification though, because auditory thresholds depend on the pitch of the sound: how high or low the note is.

For low-pitched, bass sounds, newborns do okay: they still need the sounds to be louder than an adult, but they don’t need them to be extremely loud.

On the other hand, it takes a very long time for this to mature, which doesn’t happen until middle childhood.

High-pitched thresholds start off very poor: newborns need these sounds to be much louder than adults to perceive them.

But even though they start off very different from adults’, they mature very quickly, by about 6 months.

Question 52

There are a few reasons why babies aren’t good at hearing high-pitched sounds when they’re born

Answer 52

One is that they don’t have much experience with high-pitched sounds, since they’re encased in amniotic fluid when in utero, which acts as a low-pass filter, letting in low sounds but blocking out high sounds.

It would be similar to what you would hear while underwater in a swimming pool: you can probably hear the bass part of a song, but not the melody.

Newborns’ ears still contain a bit of fluid after they’re born which is another reason why high-pitched sounds are hard to hear.

Finally, their ear drum and basilar membrane, which is inside the cochlea, haven’t quite matured yet, which tends to affect high-pitched sounds more severely.

Question 53

Visual acuity

Answer 53

is an important aspect of vision, since it corresponds to the sharpness of our vision.

When you go to the eye doctor and read an eye chart, they are testing your visual acuity to see how much detail you perceive at a given distance.

For adults, a normal, healthy visual acuity is 20/20.

When infants are born, their acuity is very, very bad.

They’re not blind by any means, but their visual acuity is about 40 times worse than an adult’s.

This corresponds to a score of between 20/200 to approximately 20/400.

Even though it starts off poor, visual acuity matures rapidly in the first 6 months of life.

Even though 6-month-olds are almost adult-like in their visual acuity, it takes until they are about 4 to 6 years of age before it’s fully mature.

Question 54

Colour perception

Answer 54

is related to visual acuity because both aspects of vision are processed by the cone cells in the eye, rather than the rods.

To test colour perception in infants, researchers habituated infants to various shades of grey on each trial of a habituation phase.

Once the babies’ looking times had decreased sufficiently, indicating that they were bored of shades of grey, the researchers moved on to the test phase.

In that phase, babies were either presented with yet another new shade of grey, or a colour like red, yellow, green, or blue.

If babies looked longer to one of those colours, indicating dishabituation, then researchers could conclude that the babies perceived that colour.

Based on this method, we know that newborns can perceive red, but not other colours.

By only 3 months of age though, babies dishabituate to all of these colours and their colour perception is somewhat adult-like.

Question 55

Why colour perception and acuity are poor at birth

Answer 55

You may have noticed that both colour perception and acuity are poor at birth but mature rapidly.

This happens for a couple of reasons.

The first is that like high-pitched sounds, babies don’t receive visual experience while in utero, so their brains haven’t strengthened the necessary synapses yet.

The second reason is that their cones are immature: those cones will become longer, skinnier, and more densely packed as infants mature, allowing more precise vision.

Question 56

facial scanning patterns

Answer 56

Infants are attracted to faces right from birth, which probably helps them develop social and language skills.

But there are some pretty big changes in face perception during development.

newborns and 1-month- olds focus on very different parts of the face than 3-month-olds: they tend to fixate on the borders of the face, including the chin and hairline, whereas 3-month-olds focus almost entirely on the eyes and mouth.

because their acuity is poor, his leads them to look at the areas of the face with the highest contrast, which is usually the edges of the face.

Three- month-olds, on the other hand, can see well enough that they start focusing on the features that convey the most social information: they eyes and mouth.

Question 57

Vision: effects of deprivation

Answer 57

although it improves drastically even in the first hour after vision is restored, it never catches up to reach adult levels.

It’s also the case the longer children were deprived of visual input, the worse their face processing and visual acuity.

visual acuity and certain aspects of face processing must exhibit experience-expectant growth,

f a child experiences visual deprivation early in life, then these aspects of vision will be permanently affected.

This means that both visual acuity and certain aspects of face perception exhibit a critical or a sensitive period.

Adults who develop cataracts and later have them removed don’t experience the same permanent visual deficits, because their brain pathways have already developed and specialized based on the visual input or experience they received at the right time in development.

Question 58

Perceptual narrowing

Answer 58

is a pattern where infants become better at perceiving familiar stimuli, and worse at perceiving unfamiliar stimuli.

This usually happens during the first year of life.

Infants start out very flexible, able to adapt to various kinds of perceptual environments.

Their perception then becomes specialized by experience for the stimuli that they’ve been exposed to everyday, which happens by strengthening those synapses.

On the other hand, synaptic pruning happens for connections in the brain that aren’t reinforced because the infant doesn’t get any input that reinforces them.

Some of the major perceptual areas that exhibit perceptual narrowing are face perception, phoneme perception in language, and perception of musical metre.

Question 59

other-race effect or own race bias

Answer 59

both the youngest—3-month-olds—and oldest—9-month-olds could tell the difference between Caucasian faces, which isn’t surprising because this is the type of face that they were most frequently exposed to.

On the other hand, only 3-month-olds could tell the difference between other-race faces: by 9 months, infants had lost the ability to tell these apart and they looked equally long at both faces.

In face perception literature, and it might resonate with your own experiences.

People often find it difficult to tell apart members of another race, but this isn’t because one type of face is inherently more difficult to tell apart than another.

Rather, it’s because of experience and perceptual narrowing: we get better at discriminating faces that we’re exposed to, and worse at discriminating faces that we rarely or never see.

Question 60

The other species effect

Answer 60

Our specialized processing for faces even extends to other species!

In another study, 6-month-olds were equally able to tell apart human faces and monkey faces, but by 9 months, they had lost the ability to tell apart monkey faces.

Again, this is probably because infants see a lot of human faces, so their perceptual systems become attuned to those, but they don’t see many monkey faces.

Question 61

Musical metre perception

Answer 61

In music, perceptual narrowing happens in the metre, which is related to the beat of music.

North America and western Europe, metres are pretty simple.

There’s usually a two- or a four-beat pattern, but the beat of almost all music can be divided into twos or threes.

This means that the more important, sometimes louder beats occur at regular intervals.

the ones and the threes are evenly spaced apart. If you clapped to the beat, all of your claps would be evenly spaced.

In music with complex metres, like much of the music of Bulgaria and Macedonia, metres aren’t evenly divided by twos or threes.

This means that the important or louder beats don’t occur at regular intervals: one is longer than the other.

There is more time between a one and a four than there is between a four and the next one.

This means that if you clapped on one and four, you’d have one long and one short clap.

On the other hand, North American 6-month-old babies can detect changes to either kind of metre.

By 12 months, they have lost their ability to detect changes to complex metres unless they received at-home exposure,

Question 62

Phoneme perception

Answer 62

Phonemes are the speech sounds of language, like ”a,” “r”, “ch,” “ee,” or “b.” Different languages use different phonemes.

For example, “r” and “l” are two different phonemes in English, but this distinction doesn’t exist in Japanese.

Even though these two phonemes sound completely different to an English speaker, they can be very difficult for Japanese-speaking adults to tell apart.

Question 63

universal listeners or universal phoneme perceivers

Answer 63

Young infants are sometimes called universal listeners or universal phoneme perceivers because they can tell apart speech sounds from many different languages, not just their own native language.

By the first year of life though, infants lose the ability to tell apart many foreign phoneme contrasts that don’t exist in their own language.

Question 64

Motor milestones

Answer 64

are a huge part of the infant’s first year of life.

Newborns are mostly confined to the fetal position, but if given a few minutes for supervised tummy time a few times a day, by 1 month they should be able to lift their head, and by 2 months, their chest. Infants gradually learn to sit alone without support by 6 to 7 months, as well as grab things without toppling over.

Around 7 to 8 months, they might begin standing with help and crawling, although some infants might get creative at move around by scooting on their bums or creeping, which is when they use their hands to move forward but drag their torso and legs behind them.

Before they learn to walk at about a year of age, infants have learned to pull themselves up to a stand, stand independently without support, and they probably practiced cruising, which is where they walk while hanging on to things like furniture.

Question 65

Swaddling

Answer 65

is a common practice of wrapping an infant somewhat tightly in a blanket, kind of like a baby burrito.

It can be very calming for infants and it can help reduce crying and increase restful sleep, as long as the infant doesn’t get overheated.

But if infants are swaddled round the clock and even as they grow older, they might not get an opportunity to exercise their muscles, leading to some motor delay.

This also explains why in North America, infants who are born in the summer tend to have slightly delayed motor milestones compared to infants who are born in the winter.

By the time summer-born infants are old enough to start moving around, they might spend more time in bulky clothing that restricts their movements, like snow suits.

Question 66

stepping reflex study

Answer 66

In one study, researchers randomly assigned newborn infants to one of four groups.

In the active exercise group, parents elicited the stepping reflex by holding their babies upright on a flat surface for 3 minutes at a time, 4 times a day from the time they were 2 weeks old until they were 8 weeks old, when the stepping reflex usually disappears.

This was active because babies moved their own legs.

In the passive exercise group, parents laid the baby down and pumped the baby’s legs in the same stepping motion. It was passive because parents moved the babies’ legs rather than the babies themselves.

These two groups came into the lab for a baseline assessment of their stepping reflex before being assigned to one of the two exercise conditions, and each week after from weeks 2 to 8.

That means they also got a bit of active exercise when coming into the lab to get their assessment.

To test if this mattered, the researchers also had two control groups.

The no exercise control group didn’t do anything at home, but they still came in for the weekly stepping reflex assessments.

The 8-week control group came in only once, when they were 8 weeks old, meaning they had zero practice with the stepping reflex

Question 67

stepping reflex study results

Answer 67

Can see that the stepping reflex has completely disappeared as expected n the 8-week control group who had no experience, and is almost gone in the no exercise control group whose only experience was coming in each week to be assessed.

The most interesting comparison is between the passive and active groups.

The passive group did no better than the no exercise group by 8 weeks, so passive exercise didn’t seem to make any difference.

But not only did the active exercise group maintain the stepping reflex at 8 weeks, they also dramatically increased the number of steps they could make in a minute.

It’s clear that this group is the one who built enough muscle in their legs to be able to lift them even as they were getting chubbier.

When the researchers followed up with the infants many months later, it was also the case the infants in the active exercise condition started walking earlier than the other groups

Question 68

The visual cliff

Answer 68

new and experienced crawlers were placed on the shallow end of the visual cliff and beckoned to come over to the deep end by their mothers or someone holding an interesting-looking toy.

Researchers found that new crawlers, like this baby, crawled right on over to the deep side, suggesting that they hadn’t had enough locomotion experience to learn that this could be dangerous.

Experienced crawlers, like this other baby, were more likely to refuse to go over the cliff.

This suggests that they’ve learned that this is probably a risky decision.

One problem with the visual cliff is that once babies learn that the cliff is safe, you can’t test them anymore, because they’re in on the trick.

This also means that you can’t test several other research questions, like how big the cliff needs to be for them to avoid it.

Question 69

The gap
Relearning capabilities with each new position

Answer 69

Infants who are experienced with sitting and reaching know that once the gap gets too big, it is unsafe to reach for an attractive toy, so they refuse to do so.

But once the same infants start crawling, it’s like they forget everything they’ve learned once in the crawling position.

They’ll try to crawl across a gap that they would have avoided as a sitter, at least until they have amassed experience with crawling and learned what’s safe and what isn’t.

Even after that, they’ll make the same error when they start walking: trying to walk across an unsafe gap that they would have avoided as an experienced crawler, until they get enough walking experience.