Premed · Premed · Introductory Psychology
Lecture 18: Developmental Psychology: Adolescence and Adulthood
Introductory Psychology
Learning Objectives
By the end of this lecture, students will be able to:
- Describe the physical and cognitive changes that occur during adolescence
- Explain Erikson's stages of psychosocial development across the lifespan
- Discuss identity formation and social development during adolescence
- Identify the major physical, cognitive, and social changes of adulthood and aging
- Describe the psychological perspectives on death, dying, and bereavement
Lecture Content
I. Adolescence: Physical Development
Adolescence is the transitional period between childhood and adulthood, spanning roughly ages 10 to 20. Puberty, the period of sexual maturation when reproduction becomes possible, is triggered by hormonal changes — increased testosterone in males and estrogen in females. A rapid growth spurt produces increases in height and weight. Primary sexual characteristics involve the maturation of the reproductive organs, while secondary sexual characteristics include breast development, voice deepening, body hair growth, and changes in fat distribution. The average onset of puberty is approximately 10-11 years for girls and 11-12 years for boys, with significant individual variation. While the sequence of pubertal changes is predictable, the timing varies considerably.
The timing of puberty has psychological consequences. Early-maturing boys may initially be perceived as leaders and feel more confident, but they face higher risks for substance use and delinquency. Early-maturing girls face increased risk of depression, body dissatisfaction, social pressure, and eating disorders. These effects tend to diminish by adulthood.
II. Adolescence: Cognitive Development
Piaget's formal operational stage, which begins around age 12, brings the capacity for abstract reasoning, hypothetical thinking, and systematic problem-solving, though not all adolescents (or adults) consistently use these abilities. David Elkind described adolescent egocentrism, which manifests as the imaginary audience — the belief that others are constantly watching and evaluating one's behavior — and the personal fable — the conviction that one's experiences are unique and that one is invulnerable to harm. The personal fable contributes to risk-taking behavior, fueled by the sense that "it won't happen to me."
Brain development during adolescence explains much of the characteristic behavior of this period. The prefrontal cortex, which governs decision-making and impulse control, does not fully mature until the mid-20s, while the limbic system, which processes emotion and reward, matures earlier. This mismatch between emotional intensity and regulatory capacity accounts for the increased risk-taking, sensation-seeking, and emotional reactivity typical of adolescence. Myelination and synaptic pruning continue throughout this period, gradually increasing neural efficiency. Moral reasoning also advances, with increasing capacity for principled reasoning as described by Kohlberg's stages.
III. Adolescence: Social and Identity Development
Erik Erikson identified adolescence as the stage of identity versus role confusion, in which the central task is forming a coherent sense of self: "Who am I?" Adolescents explore different roles, values, beliefs, and goals. Successfully resolving this crisis leads to a strong, integrated sense of identity; failure leads to confusion and uncertainty about one's place in the world.
James Marcia extended Erikson's work by identifying four identity statuses based on the degree of exploration and commitment. Identity achievement describes individuals who have explored options and made commitments. Identity moratorium characterizes those who are actively exploring but have not yet committed. Identity foreclosure applies to individuals who have committed to an identity without exploring alternatives — often by adopting their parents' values without question. Identity diffusion describes those who have neither explored nor committed and appear apathetic about the process.
During adolescence, peer relationships become the primary social reference group. Conformity to peer norms peaks in early adolescence, and friendships become more intimate and emotionally supportive. Parent-adolescent conflict increases, though it typically centers on everyday issues rather than core values. Authoritative parenting — combining warmth with firm expectations — continues to be associated with the best developmental outcomes. Healthy development involves a gradual increase in autonomy and decision-making independence. Jeffrey Arnett has proposed that in industrialized societies, the period from roughly 18 to 25 constitutes a distinct developmental phase he calls emerging adulthood, characterized by identity exploration, instability, self-focus, a feeling of being "in between" adolescence and full adulthood, and a sense of open possibilities.
IV. Erikson's Psychosocial Stages (Full Lifespan Overview)
Erikson proposed eight psychosocial stages, each defined by a central crisis that must be negotiated. During infancy, the crisis is trust versus mistrust, resolved through reliable caregiving. In toddlerhood, the crisis is autonomy versus shame and doubt, as the child gains a sense of personal control. The preschool years present initiative versus guilt, as children develop purpose through directing play and activities. During the school years, industry versus inferiority emerges, with children mastering academic and social skills. Adolescence brings identity versus role confusion, as discussed above. Young adulthood centers on intimacy versus isolation — the formation of deep, committed relationships. Middle adulthood is defined by generativity versus stagnation, involving contributions to society and guidance of the next generation. Late adulthood presents the final crisis of integrity versus despair, in which individuals reflect on their lives with either satisfaction or regret.
Each stage builds on the resolution of previous ones, and unsuccessful resolution at one stage can affect later development. Critics have noted that the stages are somewhat vague, difficult to test empirically, and influenced by cultural context.
<image>A staircase or ladder diagram showing Erikson's eight psychosocial stages across the lifespan. Each step is labeled with the stage name, approximate age range, and the psychosocial crisis. Panel A: The first four stages (infancy through school age) shown as ascending steps in one color. Panel B: Stage 5 (adolescence) highlighted in a different color as the pivotal identity stage. Panel C: The final three stages (young adulthood through late adulthood) continuing the ascent. At each step, a small icon represents the key theme: a caregiver holding an infant (trust), a toddler exploring (autonomy), a child at school (industry), a teenager looking in a mirror (identity), a couple (intimacy), an adult mentoring (generativity), and an elderly person reflecting (integrity).</image>
V. Adulthood: Physical Changes
Early adulthood (the 20s and 30s) represents the peak of physical health and performance, including maximum muscle strength, sensory acuity, and reaction time. During middle adulthood (the 40s through 60s), physical abilities gradually decline. Menopause, typically occurring in the late 40s to early 50s, marks the cessation of menstruation and a decline in estrogen, accompanied by hot flashes, mood changes, and bone density loss. Men experience a gradual decline in testosterone but have no abrupt equivalent to menopause. Common sensory changes in middle adulthood include presbyopia (difficulty with near vision) and some high-frequency hearing loss.
In late adulthood (65 and beyond), sensory decline continues, immune function decreases, and vulnerability to chronic diseases increases. Brain changes include reduced volume and slower processing speed, though there is substantial individual variation. Physical exercise, social engagement, and cognitive activity can significantly slow age-related decline.
VI. Adulthood: Cognitive Changes
Crystallized intelligence — accumulated knowledge and verbal skills — remains stable or even increases throughout adulthood. Fluid intelligence — the ability to reason quickly and solve novel problems — peaks in young adulthood and gradually declines thereafter. Processing speed decreases with age. Among memory changes, recall declines more than recognition, working memory capacity decreases, and prospective memory (remembering to do things in the future) becomes less reliable. Semantic memory and procedural memory, however, are largely preserved. Wisdom — the ability to apply knowledge and experience to complex life situations — may increase with age.
Neurocognitive disorders represent pathological rather than normal cognitive decline. Alzheimer's disease is a progressive, irreversible dementia characterized by memory loss, confusion, and personality changes. Its neural hallmarks include amyloid plaques and neurofibrillary tangles. Risk factors include age, genetics (particularly the APOE4 allele), and family history, and acetylcholine deficits contribute to the symptoms. Vascular dementia results from reduced blood flow to the brain caused by strokes. It is crucial to recognize that normal aging is not dementia — most older adults maintain their cognitive function.
VII. Adulthood: Social Development
Sternberg's triangular theory of love identifies three components — intimacy, passion, and commitment — and proposes that different combinations produce different types of love: romantic love (intimacy plus passion), companionate love (intimacy plus commitment), infatuation (passion alone), and consummate love (all three). Relationship satisfaction depends on communication, equity, shared values, and emotional support.
Baumrind's parenting styles describe four patterns defined by the intersection of warmth and control. Authoritative parenting (high warmth, high control) is consistently associated with the best child outcomes. Authoritarian parenting (low warmth, high control), permissive parenting (high warmth, low control), and uninvolved parenting (low warmth, low control, the worst outcomes) round out the typology. Parenting is bidirectional: children's temperament influences parenting behavior just as parenting shapes child development.
Work serves as a source of identity, purpose, and social connection throughout adulthood. Middle adulthood is characterized by generativity — the drive to contribute to society and mentor the next generation. In late adulthood, socioemotional selectivity theory (proposed by Carstensen) explains that as people perceive their time horizon shrinking, they prioritize emotionally meaningful relationships over acquiring new information or expanding social networks. Activity theory holds that staying socially and physically active promotes well-being in old age. Disengagement theory, which suggested that withdrawal from society is natural and beneficial, has been largely discredited. Successful aging involves maintaining physical health, cognitive function, and social engagement.
VIII. Death, Dying, and Bereavement
Elisabeth Kubler-Ross's 1969 model described five stages of dying: denial, anger, bargaining, depression, and acceptance. These stages are not a rigid sequence — individuals may skip stages, revisit them, or experience several simultaneously — and the model has limited empirical support as a stage theory. The experience of dying is highly individual.
Grief is a normal response to loss, and its intensity and duration vary widely. Most people are resilient and recover without professional intervention. Complicated (prolonged) grief, in which debilitating grief persists for more than 12 months, may require clinical attention. The dual-process model of coping, proposed by Stroebe and Schut, describes healthy grieving as an oscillation between loss-oriented coping (processing the grief itself) and restoration-oriented coping (attending to the practical changes and new roles that loss demands).
<image>A lifespan development overview chart. The x-axis spans from birth to late adulthood (0 to 80+ years). Panel A: A line graph showing the trajectories of fluid intelligence (peaks in the 20s and gradually declines) and crystallized intelligence (rises steadily and plateaus in middle to late adulthood). Panel B: Below the graph, key developmental milestones and transitions are marked along the timeline: language acquisition, puberty, identity formation, career establishment, menopause, retirement. Panel C: A sidebar showing Sternberg's triangular theory of love with a triangle labeled with intimacy, passion, and commitment at each vertex, and different types of love (romantic, companionate, consummate) mapped to different combinations.</image>
