Editing Developmental psychology (section)

==Life stages of psychological development==
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{{See also|Child development stages}}

===Prenatal development===
{{Main|Prenatal development}}
{{See also|Fetal psychology}}
Prenatal development is of interest to psychologists investigating the context of early psychological development. The whole prenatal development involves three main stages: germinal stage, embryonic stage and fetal stage. Germinal stage begins at conception until 2 weeks; embryonic stage means the development from 2 weeks to 8 weeks; fetal stage represents 9 weeks until birth of the baby.<ref>{{cite book |last1=Berk |first1=Laura E. |title=Development Through the Lifespan |date=2018 |publisher=Pearson |isbn=978-0-13-441969-5 |oclc=946161390 |pages=76–81 }}</ref> The senses develop in the womb itself: a fetus can both see and hear by the second trimester (13 to 24 weeks of age). The sense of touch develops in the embryonic stage (5 to 8 weeks).{{sfn|Berk|2012|p=97}} Most of the brain's billions of neurons also are developed by the second trimester.{{sfn|Berk|2012|p=100}} Babies are hence born with some odor, taste and sound preferences, largely related to the mother's environment.{{sfn|Berk|2012|p=101}}

Some [[primitive reflexes]] too arise before birth and are still present in newborns. One hypothesis is that these reflexes are vestigial and have limited use in early human life. [[Piaget's theory of cognitive development]] suggested that some early reflexes are building blocks for infant sensorimotor development. For example, the [[tonic neck reflex]] may help development by bringing objects into the infant's field of view.<ref name="butterworth">{{Cite book | vauthors = Butterworth G, Harris M |title=Principles of Developmental Psychology |year=1994 |publisher=Lawrence Erlbaum Associates |isbn=978-0-86377-280-1 |url-access=registration |url=https://archive.org/details/principlesofdeve0000butt }}</ref>

Other reflexes, such as the [[walking reflex]], appear to be replaced by more sophisticated voluntary control later in infancy. This may be because the infant gains too much weight after birth to be strong enough to use the reflex, or because the reflex and subsequent development are functionally different.<ref name="bremner">{{Cite book | vauthors = Bremner JG |title=Infancy |year=1994 |publisher=Blackwell |edition=2 |isbn=978-0-631-18466-9 |url=https://archive.org/details/infancy0000brem_s1x4 }}</ref> It has also been suggested that some reflexes (for example the [[moro reflex|moro]] and [[walking reflex]]es) are predominantly adaptations to life in the womb with little connection to early infant development.<ref name="butterworth" /> Primitive reflexes reappear in adults under certain conditions, such as neurological conditions like [[dementia]] or traumatic lesions.

[[Ultrasound]]s have shown that infants are capable of a range of movements in the womb, many of which appear to be more than simple reflexes.<ref name="bremner" /> By the time they are born, infants can recognize and have a preference for their mother's voice suggesting some prenatal development of auditory perception.<ref name="bremner" /> Prenatal development and birth complications may also be connected to neurodevelopmental disorders, for example in [[schizophrenia]]. With the advent of [[cognitive neuroscience]], [[embryology]] and the neuroscience of prenatal development is of increasing interest to developmental psychology research.

Several environmental agents—[[teratogens]]—can cause damage during the prenatal period. These include prescription and nonprescription drugs, illegal drugs, tobacco, alcohol, environmental pollutants, infectious disease agents such as the [[rubella]] virus and the [[toxoplasmosis]] parasite, maternal malnutrition, maternal emotional stress, and Rh factor blood incompatibility between mother and child.{{sfn|Berk|2012|pp=102–115}} There are many statistics which prove the effects of the aforementioned substances. A leading example of this would be that at least 100,000 "cocaine babies" were born in the United States annually in the late 1980s. "Cocaine babies" are proven to have quite severe and lasting difficulties which persist throughout infancy and right throughout childhood. The drug also encourages behavioural problems in the affected children and defects of various vital organs.<ref>{{Cite news |id={{ProQuest|435860480}} |title=One of five expectant mothers use cocaine, U.S. study finds |agency = Associated Press |work=Toronto star |date=20 January 1989 |page=B5 }} Cited study: {{cite journal |last1=Frank |first1=D. A. |last2=Zuckerman |first2=B. S. |last3=Amaro |first3=H. |last4=Aboagye |first4=K. |last5=Bauchner |first5=H. |last6=Cabral |first6=H. |last7=Fried |first7=L. |last8=Hingson |first8=R. |last9=Kayne |first9=H. |last10=Levenson |first10=S. M. |title=Cocaine use during pregnancy: prevalence and correlates |journal=Pediatrics |date=December 1988 |volume=82 |issue=6 |pages=888–895 |doi=10.1542/peds.82.6.888 |pmid=3186380 }}</ref>

===Infancy===
{{Main|Infant and child psychology|Infant cognitive development}}
From birth until the first year, children are referred to as [[infant]]s. As they grow, children respond to their environment in unique ways.{{sfn|Berk|2012|p={{pn|date=January 2025}}}} Developmental psychologists vary widely in their assessment of infant psychology, and the influence the outside world has upon it.

The majority of a newborn infant's time is spent sleeping.<ref>{{cite journal |last1=Hirshkowitz |first1=Max |last2=Whiton |first2=Kaitlyn |last3=Albert |first3=Steven M. |last4=Alessi |first4=Cathy |last5=Bruni |first5=Oliviero |last6=DonCarlos |first6=Lydia |last7=Hazen |first7=Nancy |last8=Herman |first8=John |last9=Katz |first9=Eliot S. |last10=Kheirandish-Gozal |first10=Leila |last11=Neubauer |first11=David N. |last12=O’Donnell |first12=Anne E. |last13=Ohayon |first13=Maurice |last14=Peever |first14=John |last15=Rawding |first15=Robert |last16=Sachdeva |first16=Ramesh C. |last17=Setters |first17=Belinda |last18=Vitiello |first18=Michael V. |last19=Ware |first19=J. Catesby |last20=Adams Hillard |first20=Paula J. |title=National Sleep Foundation's sleep time duration recommendations: methodology and results summary |journal=Sleep Health |date=March 2015 |volume=1 |issue=1 |pages=40–43 |doi=10.1016/j.sleh.2014.12.010 |pmid=29073412 }}</ref> At first, their sleep cycles are evenly spread throughout the day and night, but after a couple of months, infants generally become [[diurnal animal|diurnal]].<ref name=":2">{{cite book |last1=Patel |first1=Aakash K. |last2=Reddy |first2=Vamsi |last3=Shumway |first3=Karlie R. |last4=Araujo |first4=John F. |title=StatPearls |date=2025 |publisher=StatPearls Publishing |chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK526132/ |chapter=Physiology, Sleep Stages |pmid=30252388 }}</ref> In human or rodent infants, there is always the observation of a diurnal cortisol rhythm, which is sometimes entrained with a maternal substance.<ref name=":3">{{Cite journal |last1=Iwata |first1=Osuke |last2=Okamura |first2=Hisayoshi |last3=Saitsu |first3=Hiroki |last4=Saikusa |first4=Mamoru |last5=Kanda |first5=Hiroshi |last6=Eshima |first6=Nobuoki |last7=Iwata |first7=Sachiko |last8=Maeno |first8=Yasuki |last9=Matsuishi |first9=Toyojiro |date=Jan 2013 |title=Diurnal cortisol changes in newborn infants suggesting entrainment of peripheral circadian clock in utero and at birth |journal=The Journal of Clinical Endocrinology and Metabolism |volume=98 |issue=1 |pages=E25–32 |doi=10.1210/jc.2012-2750 |pmid=23150686 |doi-access=free }}</ref> Nevertheless, the circadian rhythm starts to take shape, and a 24-hour rhythm is observed in just some few months after birth.<ref name=":2" /><ref name=":3" />

Infants can be seen to have six states, grouped into pairs:
* quiet sleep and active sleep ([[dream]]ing, when [[REM sleep]] occurs). Generally, there are various reasons as to why infants dream. Some argue that it is just a psychotherapy, which usually occurs normally in the brain. Dreaming is a form of processing and consolidating information that has been obtained during the day. Freud argues that dreams are a way of representing unconscious desires.<ref>{{cite journal |last1=Zhang |first1=Wei |last2=Guo |first2=Benyu |title=Freud's Dream Interpretation: A Different Perspective Based on the Self-Organization Theory of Dreaming |journal=Frontiers in Psychology |date=2018 |volume=9 |page=1553 |doi=10.3389/fpsyg.2018.01553 |pmid=30190698 |pmc=6115518 |doi-access=free }}</ref>
* quiet waking, and active waking
* fussing and [[crying]]. In a normal set up, infants have different reasons as to why they cry. Mostly, infants cry due to physical discomfort, hunger, or to receive attention or stimulation from their caregiver.<ref>{{Cite web |date=2020-12-07 |title=Soothing a crying baby |url=https://www.nhs.uk/conditions/baby/caring-for-a-newborn/soothing-a-crying-baby/ |access-date=2023-12-28 |website=nhs.uk |language=en}}</ref>

====Infant perception====
Infant perception is what a newborn can see, hear, smell, taste, and touch. These five features are considered as the "five senses".<ref>{{cite book | vauthors = Bee D, Boyd H |title=The developing child |publisher=Pearson Education |location=Upper Saddle River, N.J. |isbn=978-0-205-25602-0 |page=36 |edition=13th|date=2011-12-12 }}</ref> Because of these different senses, infants respond to stimuli differently.<ref name="bremner" />

* [[Visual perception|Vision]] is significantly worse in infants than in older children. Infant sight tends to be blurry in early stages but improves over time. Color perception, similar to that seen in adults, has been demonstrated in infants as young as four months using habituation methods.<ref name="butterworth" /> Infants attain adult-like vision at about six months.{{sfn|Berk|2012|p=191}}
* [[Hearing (sense)|Hearing]] is well-developed prior to birth. Newborns prefer complex sounds to pure tones, human speech to other sounds, mother's voice to other voices, and the native language to other languages. Scientist believe these features are probably learned in the womb.{{sfn|Berk|2012|p=151}} Infants are fairly good at detecting the direction a sound comes from, and by 18 months their hearing ability is approximately equal to an adult's.
* [[Olfaction|Smell]] and [[taste]] are present, with infants showing different expressions of disgust or pleasure when presented with pleasant odors (honey, milk, etc.) or unpleasant odors (rotten egg) and tastes (e.g. sour taste). Newborns are born with odor and taste preferences acquired in the womb from the smell and taste of amniotic fluid, in turn influenced by what the mother eats. Both breast- and bottle-fed babies around three days old prefer the smell of human milk to that of formula, indicating an innate preference.{{sfn|Berk|2012|p=150}} Older infants also prefer the smell of their mother to that of others.<ref name="butterworth" />
* [[Haptic perception|Touch and feel]] is one of the better-developed senses at birth as it is one of the first senses to develop inside the womb.<ref>{{cite book | vauthors = Feldman RD, Papalia DE |title=A child's world: infancy through adolescence |year=2010 |publisher=McGraw-Hill |location=New York |isbn=978-0-07-353204-2 |page=57 |edition=12th}}</ref>  This is evidenced by the [[primitive reflexes]] described above, and the relatively advanced development of the [[somatosensory cortex]].<ref name="Slater">{{cite book |title=Introduction to Infant Development | vauthors = Slater A, Lewis M |isbn=978-0-19-928305-7 |publisher=OUP |location=Oxford |year=2006}}</ref>
* [[Pain]]: Infants feel pain similarly, if not more strongly than older children, but pain relief in infants has not received so much attention as an area of research.<ref name="MatthewMatthew">{{cite journal | vauthors = Mathew PJ, Mathew JL | title = Assessment and management of pain in infants | journal = Postgraduate Medical Journal | volume = 79 | issue = 934 | pages = 438–443 | date = August 2003 | pmid = 12954954 | pmc = 1742785 | doi = 10.1136/pmj.79.934.438 }}</ref> Glucose is known to relieve pain in newborns.<ref name="DilenElseviers">{{cite journal | vauthors = Dilen B, Elseviers M | title = Oral glucose solution as pain relief in newborns: results of a clinical trial | journal = Birth | volume = 37 | issue = 2 | pages = 98–105 | date = June 2010 | pmid = 20557532 | doi = 10.1111/j.1523-536X.2010.00389.x }}</ref>

====Language====
{{Main|Language development}}
Babies are born with the ability to discriminate virtually all sounds of all human languages.{{sfn|Berk|2012|p=189}} Infants of around six months can differentiate between [[phoneme]]s in their own language, but not between similar phonemes in another language. Notably, infants are able to differentiate between various durations and sound levels and can easily differentiate all the languages they have encountered, hence easy for infants to understand a certain language compared to an adult.<ref>{{cite book |doi=10.1111/b.9780631203124.1996.x |title=The Handbook of Child Language |date=1996 |isbn=978-0-631-20312-4 |editor-last1=Fletcher |editor-last2=MacWhinney |editor-first1=Paul |editor-first2=Brian }}{{pn|date=January 2025}}</ref>

At this stage infants also start to [[Babbling|babble]], whereby they start making vowel consonant sound as they try to understand the true meaning of language and copy whatever they are hearing in their surrounding producing their own phonemes.

In various cultures, a distinct form of speech called "babytalk" is used when communicating with newborns and young children. This register consists of simplified terms for common topics such as family members, food, hygiene, and familiar animals. It also exhibits specific phonological patterns, such as substituting alveolar sounds with initial velar sounds, especially in languages like English. Furthermore, babytalk often involves morphological simplifications, such as regularizing verb conjugations (for instance, saying "corned" instead of "cornered" or "goed" instead of "went"). This language is typically taught to children and is perceived as their natural way of communication. Interestingly, in mythology and popular culture, certain characters, such as the "Hausa trickster" or the Warner Bros cartoon character "Tweety Pie", are portrayed as speaking in a babytalk-like manner.<ref>{{cite book |doi=10.1111/b.9780631203124.1996.00014.x |chapter=Phonological Development |title=The Handbook of Child Language |date=1996 |last1=Menn |first1=Lise |last2=Stoel-Gammon |first2=Carol |pages=335–360 |isbn=978-0-631-20312-4 }}</ref>

===Infant cognition: the Piagetian era===
Piaget suggested that an infant's perception and understanding of the world depended on their motor development, which was required for the infant to link visual, tactile and motor representations of objects.<ref>{{cite journal |last1=Lefmann |first1=Tess |last2=Combs-Orme |first2=Terri |title=Early Brain Development for Social Work Practice: Integrating Neuroscience with Piaget's Theory of Cognitive Development |journal=Journal of Human Behavior in the Social Environment |date=July 2013 |volume=23 |issue=5 |pages=640–647 |doi=10.1080/10911359.2013.775936 }}</ref> The concept of object permanence refers to the knowledge that an object exists even when it is not directly perceived or visible; in other words, something is still there even if it is not visible. This is a crucial developmental milestone for infants, who learn that something is not necessarily lost forever just because it is hidden. When a child displays object permanence, they will look for a toy that is hidden, showing that they are aware that the item is still there even when it is covered by a blanket. Most babies start to exhibit symptoms of object permanence around the age of eight months. According to this theory, infants develop [[object permanence]] through touching and handling objects.<ref name="bremner" />

Piaget's sensorimotor stage comprised six sub-stages (see [[Theory of cognitive development#Sensorimotor stage|sensorimotor stages]] for more detail). In the early stages, development arises out of movements caused by [[primitive reflexes]].<ref name="Gruber">{{Cite book | vauthors = Piaget J |year=1977 |title=The essential Piaget \| veditors = Gruber HE, Voneche JJ |location=New York |publisher=Basic Books |isbn=978-0-7100-8778-2}}</ref> Discovery of new behaviors results from [[classical conditioning|classical]] and [[operant conditioning]], and the formation of [[habit (psychology)|habits]].<ref name="Gruber" /> From eight months the infant is able to uncover a hidden object but will persevere when the object is moved.

Piaget concluded that infants lacked object permanence before 18 months when infants' before this age failed to look for an object where it had last been seen. Instead, infants continued to look for an object where it was first seen, committing the "[[A-not-B error]]". Some researchers have suggested that before the age of 8–9 months, infants' inability to understand object permanence extends to people, which explains why infants at this age do not cry when their mothers are gone ("Out of sight, out of mind").

====Recent findings in infant cognition====
In the 1980s and 1990s, researchers developed new methods of assessing infants' understanding of the world with far more precision and subtlety than Piaget was able to do in his time. Since then, many studies based on these methods suggest that young infants understand far more about the world than first thought.

Based on recent findings, some researchers (such as [[Elizabeth Spelke]] and [[Renee Baillargeon]]) have proposed that an understanding of object permanence is not learned at all, but rather comprises part of the innate cognitive capacities of our species.

According to Jean Piaget's developmental psychology, object permanence, or the awareness that objects exist even when they are no longer visible, was thought to emerge gradually between the ages of 8 and 12 months. However, experts such as Elizabeth Spelke and Renee Baillargeon have questioned this notion. They studied infants' comprehension of object permanence at a young age using novel experimental approaches such as violation-of-expectation paradigms. These findings imply that children as young as 3 to 4 months old may have an innate awareness of object permanence. Baillargeon's "drawbridge" experiment, for example, showed that infants were surprised when they saw occurrences that contradicted object permanence expectations. This proposition has important consequences for our understanding of infant cognition, implying that infants may be born with core cognitive abilities rather than developing them via experience and learning.<ref>{{cite book |doi=10.1093/acprof:oso/9780199692972.003.0002 |chapter=Learning about the mind from evidence |title=Understanding Other Minds |date=2013 |last1=Meltzoff |first1=Andrew N. |last2=Gopnik |first2=Alison |pages=19–34 |isbn=978-0-19-969297-2 }}</ref>

Other research has suggested that young infants in their first six months of life may possess an understanding of numerous aspects of the world around them, including:
* an early [[numerical cognition]], that is, an ability to represent number and even compute the outcomes of addition and subtraction operations;<ref>{{cite journal | vauthors = Wynn K | title = Addition and subtraction by human infants | journal = Nature | volume = 358 | issue = 6389 | pages = 749–750 | date = August 1992 | pmid = 1508269 | doi = 10.1038/358749a0 | bibcode = 1992Natur.358..749W | author-link1 = Karen Wynn }}</ref>
* an ability to infer the goals of people in their environment;<ref>{{cite journal | vauthors = Woodward AL | title = Infants selectively encode the goal object of an actor's reach | journal = Cognition | volume = 69 | issue = 1 | pages = 1–34 | date = November 1998 | pmid = 9871370 | doi = 10.1016/S0010-0277(98)00058-4 }}</ref>
* an ability to engage in simple causal reasoning.<ref>{{cite journal | vauthors = Leslie AM, Keeble S | title = Do six-month-old infants perceive causality? | journal = Cognition | volume = 25 | issue = 3 | pages = 265–288 | date = April 1987 | pmid = 3581732 | doi = 10.1016/S0010-0277(87)80006-9 }}</ref>

===Critical periods of development===
There are [[critical period]]s in infancy and childhood during which development of certain perceptual, sensorimotor, social and language systems depends crucially on environmental stimulation.<ref name="Siegler">{{Cite book | vauthors = Siegler R |year=2006 |title=How Children Develop, Exploring Child Development Student Media Tool Kit & Scientific American Reader to Accompany How Children Develop |location=New York |publisher=Worth Publishers |isbn=978-0-7167-6113-6}}</ref> [[Feral child]]ren such as [[Genie (feral child)|Genie]], deprived of adequate stimulation, fail to acquire important skills and are unable to learn in later childhood. In this case, Genie is used to represent the case of a feral child because she was socially neglected and abused while she was just a young girl. She underwent abnormal child psychology which involved problems with her linguistics. This happened because she was neglected while she was very young with no one to care about her and had less human contact. The concept of critical periods is also well-established in [[neurophysiology]], from the work of [[David H. Hubel|Hubel]] and [[Torsten Wiesel|Wiesel]] among others. Neurophysiology in infants generally provides correlating details that exists between neurophysiological details and clinical features and also focuses on vital information on rare and common neurological disorders that affect infants'''''.'''''

====Developmental delays====
Studies have been done to look at the differences in children who have developmental delays versus typical development. Normally when being compared to one another, mental age (MA) is not taken into consideration. There still may be differences in developmentally delayed (DD) children vs. typical development (TD) behavioral, emotional and other mental disorders. When compared to MA children there is a bigger difference between normal developmental behaviors overall. DDs can cause lower MA, so comparing DDs with TDs may not be as accurate. Pairing DDs specifically with TD children at similar MA can be more accurate. There are levels of behavioral differences that are considered as normal at certain ages. When evaluating DDs and MA in children, consider whether those with DDs have a larger amount of behavior that is not typical for their MA group. Developmental delays tend to contribute to other disorders or difficulties than their TD counterparts.<ref>{{cite journal | vauthors = Caplan B, Neece CL, Baker BL | title = Developmental level and psychopathology: comparing children with developmental delays to chronological and mental age matched controls | journal = Research in Developmental Disabilities | volume = 37 | pages = 143–151 | date = February 2015 | pmid = 25498740 | pmc = 4314378 | doi = 10.1016/j.ridd.2014.10.045 }}</ref>

===Toddlerhood===
{{Main|Toddler}}
Infants shift between ages of one and two to a developmental stage known as toddlerhood. In this stage, an infant's transition into toddlerhood is highlighted through self-awareness, developing maturity in language use, and presence of memory and imagination.

During toddlerhood, babies begin learning how to walk, talk, and make decisions for themselves. An important characteristic of this age period is the [[Language development|development of language]], where children are learning how to communicate and express their emotions and desires through the use of vocal sounds, babbling, and eventually words.<ref name=Upton>{{cite book| vauthors = Upton P |title=Developmental Psychology: Critical Thinking in Psychology|year=2011|publisher=Learning Matters|location=Exeter|isbn=978-0-85725-276-0|page=62}}</ref> Self-control also begins to develop. At this age, children take initiative to explore, experiment and learn from making mistakes. Caretakers who encourage toddlers to try new things and test their limits, help the child become autonomous, self-reliant, and confident.<ref name=ToddlerPlay>{{cite book| vauthors = Massi WS |title=Toddler Play|year=2001|publisher=Creative Pub. international|isbn=978-0-86573-435-7|url=https://archive.org/details/toddlerplaygymbo00wend}}</ref> If the caretaker is overprotective or disapproving of independent actions, the toddler may begin to doubt their abilities and feel ashamed of the desire for independence. The child's autonomic development is inhibited, leaving them less prepared to deal with the world in the future. Toddlers also begin to identify themselves in [[gender role]]s, acting according to their perception of what a man or woman should do.<ref name=UPton>{{cite book| vauthors = Upton P |title=Developmental Psychology: Critical Thinking in Psychology|year=2011|publisher=Learning Matters|location=Exeter|isbn=978-0-85725-276-0|page=84}}</ref>

Socially, the period of toddler-hood is commonly called the "terrible twos".<ref name=Newman>{{cite book| vauthors = Newman BM, Newman PR |title=Development Through Life : A Psychosocial Approach|year=2011|publisher=Wadsworth Cengage Learning|location=Belmont, CA|isbn=978-1-111-34468-9|pages=215–217 }}</ref> Toddlers often use their new-found language abilities to voice their desires, but are often misunderstood by parents due to their language skills just beginning to develop. A person at this stage testing their independence is another reason behind the stage's infamous label. Tantrums in a fit of frustration are also common.

===Childhood===
{{See also|Early childhood}}
[[Erik Erikson]] divides childhood into four stages, each with its distinct social crisis:<ref name="Bernardo J. Carducci 2009">{{cite book | vauthors = Carducci BJ | title = The Psychology of Personality: Viewpoints, Research, and Applications | publisher = John Wiley & Sons | date = 2009 | page = 189 }}</ref>
:* Stage 1: [[Infancy]] (0 to 1½) in which the psychosocial crisis is Trust vs. Mistrust
:* Stage 2: Early childhood (2½ to 3) in which the psychosocial crisis is Autonomy vs. Shame and doubt
:* Stage 3: Play age (3 to 5) in which the psychosocial crisis is Initiative vs. Guilt. (This stage is also called the "pre-school age", "exploratory age" and "toy age".)<ref>{{Cite web|url=http://www.vardhamaniqtoys.com/vision.aspx|archive-url=https://web.archive.org/web/20160304122300/http://www.vardhamaniqtoys.com/vision.aspx|url-status=dead|title=Vardhaman I.Q. Toys, "Vision"|archive-date=March 4, 2016}}</ref>
:* Stage 4: School age (5 to 12) in which the psychosocial crisis is Industry vs. Inferiority

====Infancy====
As stated, the psychosocial crisis for Erikson is Trust versus Mistrust. Needs are the foundation for gaining or losing trust in the infant. If the needs are met, trust in the guardian and the world forms. If the needs are not met, or the infant is neglected, mistrust forms alongside feelings of anxiety and fear.<ref name="Psychosocial Theory: Erikson">{{cite book |doi=10.31274/isudp.2022.122 |title=Individual and Family Development, Health, and Well-being |date=2022 |last1=Lang |first1=Diana }}{{pn|date=January 2025}}</ref> 

====Early Childhood====
Autonomy versus shame follows trust in infancy. The child begins to explore their world in this stage and discovers preferences in what they like. If autonomy is allowed, the child grows in independence and their abilities. If freedom of exploration is hindered, it leads to feelings of shame and low self-esteem.<ref name="Psychosocial Theory: Erikson"/>

====Play (or preschool) ages 3–5====
In the earliest years, children are "completely dependent on the care of others". Therefore, they develop a "social relationship" with their care givers and, later, with family members. During their preschool years (3–5), they "enlarge their social horizons" to include people outside the family.<ref>{{cite book |last1=Thornton |first1=Arland |title=The Well-being of Children and Families: Research and Data Needs |date=2001 |publisher=University of Michigan Press |isbn=978-0-472-09758-6 |pages=73–74 }}</ref>

[[Cognitive development#Preoperational stage|Preoperational]] and then [[Cognitive development#Concrete operational stage|operational]] thinking develops, which means actions are reversible, and egocentric thought diminishes.<ref>{{cite book | vauthors = Lightfoot C, Cole M, Cole SR | title = The Development of Children | publisher = Macmillan | date = 2008 | pages = 275–277 }}</ref>

The motor skills of preschoolers increase so they can do more things for themselves. They become more independent. No longer completely dependent on the care of others, the world of this age group expands. More people have a role in shaping their individual personalities. Preschoolers explore and question their world.<ref>{{cite web | publisher = Centers for Disease Control | title = Child Development: Preschoolers (3-5 years of age) | date = 11 February 2021 | url = https://www.cdc.gov/ncbddd/childdevelopment/positiveparenting/preschoolers.html }}</ref> For [[Jean Piaget]], the child is "''a little scientist'' exploring and reflecting on these explorations to increase competence" and this is done in "a very independent way".{{sfn|Halpenny|Pettersen|2013|pp=7,9}}

Play is a major activity for ages 3–5. For Piaget, through play "a child reaches higher levels of cognitive development."{{sfn|Halpenny|Pettersen|2013|p=14}}

In their expanded world, children in the 3–5 age group attempt to find their own way. If this is done in a socially acceptable way, the child develops the initiative. If not, the child develops guilt.<ref>{{cite book | vauthors = O'Connor B, Wells C, Applegate T | title = Health: You and Your World | volume =  1: Brief Edition | publisher = CreateSpace Independent Publishing Platform | date = 2015 | pages = 28 }}</ref> Children who develop "guilt" rather than "initiative" have failed Erikson's psychosocial crisis for the 3–5 age group.

====Middle and Late childhood ages 6–12====
For Erik Erikson, the psychosocial crisis during middle childhood is Industry vs. Inferiority which, if successfully met, instills a sense of Competency in the child.<ref name="Bernardo J. Carducci 2009" />

In all cultures, middle childhood is a time for developing "skills that will be needed in their society."<ref name="Barbara Engler 2013">{{cite book | vauthors = Engler B | title = Personality Theories | edition = 9th | publisher = Cengage Learning | date = 2013 | page = 142 }}</ref> School offers an arena in which children can gain a view of themselves as "industrious (and worthy)". They are "graded for their school work and often for their industry". They can also develop industry outside of school in sports, games, and doing volunteer work.<ref name="Marc H. Bornstein 2010">{{cite book | vauthors = Bornstein MH, Vandell DL, Rook KS | title = Lifespan Development: Infancy Through Adulthood | publisher = Cengage Learning | date = 2010 | page = 299 }}</ref> Children who achieve "success in school or games might develop a feeling of competence."

The "peril during this period is that feelings of inadequacy and inferiority will develop.<ref name="Barbara Engler 2013" /> Parents and teachers can "undermine" a child's development by failing to recognize accomplishments or being overly critical of a child's efforts.<ref name="Marc H. Bornstein 2010" />
Children who are "encouraged and praised" develop a belief in their competence. Lack of encouragement or ability to excel lead to "feelings of inadequacy and inferiority".<ref>{{cite web | url = http://behavioralchild.com/milestones/ | vauthors = Broutian M | publisher = Milestones | title = Your child: early school years (7 to 11 years) stage of development | work = Your Child's Development | archive-url = https://web.archive.org/web/20151115170628/http://behavioralchild.com/milestones/ | archive-date= 15 November 2015 | access-date = 13 October 2015 }}</ref>

The [[Centers for Disease Control]] (CDC) divides Middle Childhood into two stages, 6–8 years and 9–11 years, and gives "developmental milestones for each stage".<ref name = "CDC_CD_6-8">{{cite web | work = Centers for Disease Control | title = Child Development: Middle Childhood (6-8 years of age) | date = 4 February 2021 | url = https://www.cdc.gov/ncbddd/childdevelopment/positiveparenting/middle.html }}</ref><ref name = "CDC_CD_9-11">{{cite web | work = Centers for Disease Control | title = Child Development: Middle Childhood (9-11 years of age) | url = https://www.cdc.gov/ncbddd/childdevelopment/positiveparenting/middle2.html | access-date = 15 October 2015 }}</ref>

====Middle Childhood (6–8)====
Entering elementary school, children in this age group begin to thinks about the future and their "place in the world". Working with other students and wanting their friendship and acceptance become more important. This leads to "more independence from parents and family". As students, they develop the mental and verbal skills "to describe experiences and talk about thoughts and feelings". They become less self-centered and show "more concern for others".<ref name = "CDC_CD_6-8" />

====Late Childhood (9–12)====
For children ages 9–11 "friendships and peer relationships" increase in strength, complexity, and importance. This results in greater "peer pressure". They grow even less dependent on their families and they are challenged academically. To meet this challenge, they increase their attention span and learn to see other points of view.<ref name = "CDC_CD_9-11" />

===Adolescence===
{{Main|Adolescent psychology}}
Adolescence is the period of life between the onset of puberty and the full commitment to an adult social role, such as worker, parent, and/or citizen. It is the period known for the formation of personal and social identity (see [[Erik Erikson]]) and the discovery of moral purpose (see [[William Damon]]). Intelligence is demonstrated through the logical use of symbols related to abstract concepts and formal reasoning. A return to [[egocentric]] thought often occurs early in the period. Only 35% develop the capacity to reason formally during adolescence or adulthood. (Huitt, W. and Hummel, J. January 1998)<ref>{{Cite web|url=https://pages.uoregon.edu/moursund/Math/developmental_theory.htm|title=Developmental Theory|website=pages.uoregon.edu|access-date=2021-05-07|archive-date=2021-05-16|archive-url=https://web.archive.org/web/20210516005242/https://pages.uoregon.edu/moursund/Math/developmental_theory.htm|url-status=dead}}</ref>

Erik Erikson labels this stage identity versus role confusion. Erikson emphasizes the importance of developing a sense of identity in adolescence because it affects the individual throughout their life. Identity is a lifelong process and is related with curiosity and active engagement. Role confusion is often considered the current state of identity of the individual. Identity exploration is the process of changing from role confusion to resolution.<ref>{{cite journal |last1=Syed |first1=Moin |title=Identity exploration, identity confusion, and openness as predictors of multicultural ideology |journal=International Journal of Intercultural Relations |date=July 2013 |volume=37 |issue=4 |pages=491–496 |doi=10.1016/j.ijintrel.2013.04.005 }}</ref>

During Erik Erikson's identity versus role uncertainty stage, which occurs in adolescence, people struggle to form a cohesive sense of self while exploring many social roles and prospective life routes. This time is characterized by deep introspection, self-examination, and the pursuit of self-understanding. Adolescents are confronted with questions regarding their identity, beliefs, and future goals. The major problem is building a strong sense of identity in the face of society standards, peer pressure, and personal preferences. Adolescents participate in identity exploration, commitment, and synthesis, actively seeking out new experiences, embracing ideals and aspirations, and merging their changing sense of self into a coherent identity. Successfully navigating this stage builds the groundwork for good psychological development in adulthood, allowing people to pursue meaningful relationships, make positive contributions to society, and handle life's adversities with perseverance and purpose.{{sfn|Erikson|Erikson|1998|p={{pn|date=January 2025}}}}

It is divided into three parts, namely:
# Early Adolescence: 9 to 13 years 
# Mid Adolescence: 13 to 15 years and
# Late Adolescence: 15 to 18 years

The adolescent unconsciously explores questions such as "Who am I? Who do I want to be?" Like toddlers, adolescents must explore, test limits, become [[autonomous]], and commit to an [[identity (social science)|identity]], or [[sense of self]]. Different roles, behaviors and [[ideologies]] must be tried out to select an identity. Role confusion and inability to choose vocation can result from a failure to achieve a sense of identity through, for example, friends.<ref>{{cite book |last1=Erikson |first1=Erik H. |title=Identity Youth and Crisis |date=1968 |publisher=W. W. Norton & Company |isbn=978-0-393-31144-0 }}{{pn|date=January 2025}}</ref>

===Early adulthood===
{{Main|Young adult (psychology)}}
Early adulthood generally refers to the period between ages 18 to 39,<ref>{{cite journal | vauthors = Arnett JJ, Žukauskienė R, Sugimura K | title = The new life stage of emerging adulthood at ages 18-29 years: implications for mental health | journal = The Lancet. Psychiatry | volume = 1 | issue = 7 | pages = 569–576 | date = December 2014 | pmid = 26361316 | doi = 10.1016/s2215-0366(14)00080-7 }}</ref> and according to theorists such as Erik Erikson, is a stage where development is mainly focused on [[Interpersonal relationship|maintaining relationships]].<ref>{{cite book| vauthors = Kastenbaum R |title=Encyclopedia of Adult Development|year=1993|publisher=Oryx Press|isbn=978-0-89774-669-4|page=14}}</ref> Erikson shows the importance of relationships by labeling this stage ''intimacy'' vs ''isolation''. Intimacy suggests a process of becoming part of something larger than oneself by sacrificing in romantic relationships and working for both life and career goals.<ref name="Žukauskienė">{{Cite book |last=Žukauskienė |first=Rita |url=https://books.google.com/books?id=rYs0CwAAQBAJ&dq=%22early+adulthood%22+development&pg=PA17 |title=Emerging Adulthood in a European Context |date=2015-12-07 |publisher=Psychology Press |isbn=978-1-317-61271-1 |language=en}}</ref> Other examples include creating bonds of intimacy, sustaining friendships, and starting a family. Some theorists state that development of intimacy skills rely on the resolution of previous developmental stages. A sense of identity gained in the previous stages is also necessary for intimacy to develop. If this skill is not learned the alternative is alienation, isolation, a fear of commitment, and the inability to depend on others.

''Isolation,'' on the other hand, suggests something different than most might expect. Erikson defined it as a delay of commitment in order to maintain freedom. Yet, this decision does not come without consequences. Erikson explained that choosing isolation may affect one's chances of getting married, progressing in a career, and overall development.<ref name="Žukauskienė"/>

A related framework for studying this part of the lifespan is that of [[emerging adulthood]]. Scholars of emerging adulthood, such as Jeffrey Arnett, are not necessarily interested in relationship development. Instead, this concept suggests that people transition after their teenage years into a period, not characterized as relationship building and an overall sense of constancy with life, but with years of living with parents, phases of self-discovery, and experimentation.<ref name="Twenge">{{cite journal| vauthors = Twenge JM |title=Review of emerging adulthood: The winding road from the late teens through the twenties|journal=American Journal of Psychology|year=2008|volume=121|issue=4|pages=682–687|doi=10.2307/20445494|jstor=20445494}}</ref>

===Middle adulthood===
{{Main|Middle age}}
Middle adulthood generally refers to the period between ages 40 to 64. During this period, middle-aged adults experience a conflict between generativity and stagnation. Generativity is the sense of contributing to society, the next generation, or their immediate community. On the other hand, stagnation results in a lack of purpose.<ref>{{cite journal | vauthors = Helson R, Soto CJ | title = Up and down in middle age: monotonic and nonmonotonic changes in roles, status, and personality | journal = Journal of Personality and Social Psychology | volume = 89 | issue = 2 | pages = 194–204 | date = August 2005 | pmid = 16162053 | doi = 10.1037/0022-3514.89.2.194 }}</ref> The adult's identity continues to develop in middle-adulthood. Middle-aged adults often adopt opposite gender characeristics. The adult realizes they are half-way through their life and often reevaluate vocational and social roles. Life circumstances can also cause a reexamination of identity.<ref>{{cite journal |last1=Sokol |first1=Justin T. |title=Identity Development Throughout the Lifetime: An Examination of Eriksonian Theory |journal=Graduate Journal of Counseling Psychology |date=March 2009 |volume=1 |issue=2 |url=https://epublications.marquette.edu/gjcp/vol1/iss2/14/ }}</ref>  

Physically, the middle-aged experience a decline in muscular strength, reaction time, sensory keenness, and cardiac output. Also, women experience [[menopause]] at an average age of 48.8 and a sharp drop in the hormone [[estrogen]].<ref>{{cite journal | vauthors = Schoenaker DA, Jackson CA, Rowlands JV, Mishra GD | title = Socioeconomic position, lifestyle factors and age at natural menopause: a systematic review and meta-analyses of studies across six continents | journal = International Journal of Epidemiology | volume = 43 | issue = 5 | pages = 1542–1562 | date = October 2014 | pmid = 24771324 | pmc = 4190515 | doi = 10.1093/ije/dyu094 }}</ref> Men experience an equivalent endocrine system event to menopause. [[Andropause]] in males is a hormone fluctuation with physical and psychological effects that can be similar to those seen in menopausal females. As men age lowered testosterone levels can contribute to mood swings and a decline in [[spermatozoa|sperm]] count. Sexual responsiveness can also be affected, including delays in [[erection]] and longer periods of [[penile stimulation]] required to achieve [[ejaculation]].

The important influence of biological and social changes experienced by women and men in middle adulthood is reflected in the fact that depression is highest at age 48.5 around the world.<ref>{{cite journal | vauthors = Blanchflower DG, Oswald AJ | title = Is well-being U-shaped over the life cycle? | journal = Social Science & Medicine | volume = 66 | issue = 8 | pages = 1733–1749 | date = April 2008 | pmid = 18316146 | doi = 10.1016/j.socscimed.2008.01.030 | url = http://www.nber.org/papers/w12935.pdf }}</ref>

===Old age===
{{Main|Old age}}
The [[World Health Organization]] finds "no general agreement on the age at which a person becomes old." Most [[Developed country|"developed countries"]] set the age as 65 or 70. However, in [[Developing country|developing countries]] inability to make "active contribution" to society, not chronological age, marks the beginning of old age.<ref>{{cite web | title = Definition of an older or elderly person | work = World Health Organization | url = http://www.who.int/healthinfo/survey/ageingdefnolder/en/ | access-date = 11 October 2015 }}{{dead link|date=January 2025}}</ref><ref>{{cite journal |last1=Orimo |first1=Hajime |last2=Ito |first2=Hideki |last3=Suzuki |first3=Takao |last4=Araki |first4=Atsushi |last5=Hosoi |first5=Takayuki |last6=Sawabe |first6=Motoji |title=Reviewing the definition of 'elderly' |journal=Geriatrics & Gerontology International |date=September 2006 |volume=6 |issue=3 |pages=149–158 |doi=10.1111/j.1447-0594.2006.00341.x }}</ref> According to [[Erikson's stages of psychosocial development]], old age is the stage in which individuals assess the quality of their lives.<ref name="Miller2003">{{cite book |url=https://books.google.com/books?id=rPcwuEe9MBQC&pg=PA242 |title=Encyclopedia of Human Ecology: I-Z |vauthors=Miller JR |publisher=ABC-CLIO |year=2003 |isbn=978-1-57607-852-5 |pages=242– |access-date=4 December 2012}}</ref>

Erikson labels this stage as integrity versus despair. For integrated persons, there is a sense of fulfillment in life. They have become self-aware and optimistic due to life's commitments and connection to others. While reflecting on life, people in this stage develop feelings of contentment with their experiences. If a person falls into despair, they are often disappointed about failures or missed chances in life. They may feel that the time left in life is an insufficient amount to turn things around.<ref>{{cite journal |last1=Hearn |first1=Simon |last2=Saulnier |first2=Gary |last3=Strayer |first3=Janet |last4=Glenham |first4=Margarete |last5=Koopman |first5=Ray |last6=Marcia |first6=James E. |title=Between Integrity and Despair: Toward Construct Validation of Erikson's Eighth Stage |journal=Journal of Adult Development |date=March 2012 |volume=19 |issue=1 |pages=1–20 |doi=10.1007/s10804-011-9126-y }}</ref>

Physically, older people experience a decline in muscular strength, reaction time, stamina, hearing, distance perception, and the sense of smell.<ref name="Deary2011">{{cite journal | vauthors = Deary IJ, Johnson W, Gow AJ, Pattie A, Brett CE, Bates TC, Starr JM | title = Losing one's grip: a bivariate growth curve model of grip strength and nonverbal reasoning from age 79 to 87 years in the Lothian Birth Cohort 1921 | journal = The Journals of Gerontology. Series B, Psychological Sciences and Social Sciences | volume = 66 | issue = 6 | pages = 699–707 | date = November 2011 | pmid = 21743039 | doi = 10.1093/geronb/gbr059 | doi-access = free | hdl = 20.500.11820/a59dc7c1-af60-4f02-a8be-37987b26f9a4 | hdl-access = free }}</ref> They also are more susceptible to diseases such as cancer and pneumonia due to a weakened immune system.<ref>{{cite journal |last1=Larbi |first1=Anis |last2=Rymkiewicz |first2=Paulina |last3=Vasudev |first3=Anusha |last4=Low |first4=Ivy |last5=Shadan |first5=Nurhidaya Binte |last6=Mustafah |first6=Seri |last7=Ayyadhury |first7=Shamini |last8=Fulop |first8=Tamas |title=The Immune System in the Elderly: A Fair Fight Against Diseases? |journal=Aging Health |date=February 2013 |volume=9 |issue=1 |pages=35–47 |doi=10.2217/ahe.12.78 }}</ref> Programs aimed at balance, muscle strength, and mobility have been shown to reduce disability among mildly (but not more severely) disabled elderly.<ref name="Gill2002">{{cite journal | vauthors = Gill TM, Baker DI, Gottschalk M, Peduzzi PN, Allore H, Byers A | title = A program to prevent functional decline in physically frail, elderly persons who live at home | journal = The New England Journal of Medicine | volume = 347 | issue = 14 | pages = 1068–1074 | date = October 2002 | pmid = 12362007 | doi = 10.1056/NEJMoa020423 | doi-access = free }}</ref>

Sexual expression depends in large part upon the emotional and physical health of the individual. Many older adults continue to be sexually active and satisfied with their sexual activity.<ref>{{cite book| vauthors = Cavanaugh JC, Blanchard-Fields F | author-link2=Fredda Blanchard-Fields | name-list-style = vanc |title=Adult development and aging|year=2009|publisher=Wadsworth/Cengage Learning|location=Australia|isbn=978-0-495-60174-6|pages=89–90|edition=6th}}</ref>

Mental [[wikt:disintegration|disintegration]] may also occur, leading to [[dementia]] or ailments such as [[Alzheimer's disease]]. The average age of onset for dementia in males is 78.8 and 81.9 for women.<ref>{{cite journal | vauthors = Brinks R, Landwehr S, Waldeyer R | title = Age of onset in chronic diseases: new method and application to dementia in Germany | journal = Population Health Metrics | volume = 11 | issue = 1 | pages = 6 | year = 2013 | pmid = 23638981 | pmc = 3665482 | doi = 10.1186/1478-7954-11-6 | doi-access = free }}</ref> It is generally believed that [[crystallized intelligence]] increases up to old age, while [[fluid intelligence]] decreases with age.<ref>[https://web.archive.org/web/20000525173324/http://www.webster.edu/~woolflm/cognitions.html Woolf, Linda M. "Theoretical Perspectives Relevant to Developmental Psychology", Webster, 1998.]  Retrieved on 2012-03-16.</ref> Whether or not normal intelligence increases or decreases with age depends on the measure and study. [[Longitudinal study|Longitudinal studies]] show that perceptual speed, inductive reasoning, and spatial orientation decline.<ref name="What Can We Learn From Longitudinal">{{cite journal | vauthors = Schaie KW | title = What Can We Learn From Longitudinal Studies of Adult Development? | journal = Research in Human Development | volume = 2 | issue = 3 | pages = 133–158 | year = 2005 | pmid = 16467912 | pmc = 1350981 | doi = 10.1207/s15427617rhd0203_4 }}</ref> An article on adult cognitive development reports that [[Cross-sectional study|cross-sectional studies]] show that "some abilities remained stable into early old age".<ref name="What Can We Learn From Longitudinal"/>