Premed · Premed · Introductory Psychology
Lecture 17: Developmental Psychology: Infancy and Childhood
Introductory Psychology
Learning Objectives
By the end of this lecture, students will be able to:
- Describe the major research designs and issues in developmental psychology
- Outline prenatal development and the effects of teratogens
- Explain Piaget's stages of cognitive development and key critiques
- Describe attachment theory and Ainsworth's attachment styles
- Discuss moral development according to Kohlberg and its limitations
Lecture Content
I. Foundations of Developmental Psychology
Developmental psychology is the study of physical, cognitive, and social changes throughout the lifespan. Three central issues animate the field. The nature-versus-nurture debate concerns the relative contributions of genetics and environment to development. The continuity-versus-stages question asks whether development is a gradual, continuous process or one that unfolds in distinct qualitative stages. The stability-versus-change question examines whether traits remain consistent across the lifespan or undergo significant transformation.
Developmental psychologists rely on several research designs. Cross-sectional studies compare different age groups at a single point in time, offering efficiency but introducing the risk of cohort effects — generational differences that can be mistaken for developmental changes. Longitudinal studies follow the same individuals over time, capturing true developmental change but requiring substantial time and resources and being subject to participant attrition. Cross-sequential designs combine both approaches to disentangle the effects of age and cohort.
II. Prenatal Development
Prenatal development unfolds in three stages. The germinal stage (0-2 weeks) begins with a fertilized zygote that divides rapidly and implants in the uterine wall. During the embryonic stage (2-8 weeks), the major organs and body systems form, making this the period of greatest vulnerability to teratogens. The fetal stage (9 weeks to birth) is characterized by growth and maturation, with the fetus becoming viable at approximately 24 weeks.
Teratogens are agents that can cause birth defects. Alcohol is the leading preventable cause of intellectual disability, producing fetal alcohol spectrum disorders (FASD). Tobacco increases the risk of low birth weight, preterm birth, and sudden infant death syndrome. Drugs such as cocaine, opioids, and certain prescription medications also pose risks, as do infections (rubella, toxoplasmosis, Zika virus) and environmental chemicals (lead, mercury, radiation). The effects of teratogens are most severe during critical periods of organ formation.
III. Newborn Capacities
Newborns are far more capable than was once believed. They arrive equipped with reflexes — rooting, sucking, grasping, Moro (startle), Babinski, and stepping — that indicate neural development and, in some cases, disappear as the cortex matures. Sensory abilities are surprisingly well developed: newborns prefer faces and high-contrast patterns, though visual acuity is only about 20/400 at birth. Hearing is well developed; infants prefer their mother's voice and the sounds of their native language. Smell and taste are functional, with a preference for sweet tastes and the mother's scent. Researchers study infant cognition through habituation (the decrease in response to repeated stimuli) and preferential looking (the tendency to gaze longer at novel or surprising stimuli), both of which reveal the infant's capacity for discrimination and expectation.
IV. Physical and Motor Development
Brain development in infancy and early childhood is characterized by rapid synaptogenesis — the formation of enormous numbers of synaptic connections. This is followed by synaptic pruning, the elimination of unused connections according to a "use it or lose it" principle. Myelination continues well into the mid-20s, with the prefrontal cortex being the last region to mature. Critical periods represent windows of heightened sensitivity during which certain types of development — such as vision and language — proceed most readily.
Motor development follows a roughly universal sequence: lifting the head (around 2 months), rolling over (4-5 months), sitting (6 months), crawling (8-10 months), standing (10-12 months), and walking (12-15 months). While the sequence is consistent across cultures, the timing varies by individual and is influenced by both maturation and experience.
V. Piaget's Theory of Cognitive Development
Jean Piaget (1896-1980) argued that children are not miniature adults but rather think in qualitatively different ways at different ages. Central to his theory are several key concepts. A schema is a mental framework for organizing and interpreting information. Assimilation is the process of incorporating new experiences into existing schemas, while accommodation involves modifying schemas to fit new experiences. Equilibration is the drive to balance these two processes.
Piaget identified four stages of cognitive development. In the sensorimotor stage (birth to approximately age 2), infants know the world through sensory experiences and motor actions. The major achievement of this stage is object permanence — the understanding, developing around 8 months, that objects continue to exist when they are out of sight. The A-not-B error, in which infants search for a hidden object at its previous location, illustrates the gradual nature of this development. Stranger anxiety, appearing around 8 months, requires the cognitive ability to distinguish familiar from unfamiliar faces.
The preoperational stage (approximately ages 2-7) brings the capacity for symbolic thinking, including language use, pretend play, and drawing. However, thinking at this stage is limited by egocentrism (difficulty taking another person's perspective, as demonstrated by the three-mountain task), centration (focusing on one aspect of a situation while neglecting others), and a lack of conservation (the failure to understand that quantity remains the same despite changes in appearance, such as when water poured into a taller glass appears to be "more"). Children at this stage also exhibit animism (attributing life to inanimate objects) and irreversibility (difficulty mentally undoing an action).
During the concrete operational stage (approximately ages 7-11), children develop the ability to think logically about concrete, tangible events. They master conservation, classification, and seriation, and they understand reversibility. However, they still struggle with abstract and hypothetical reasoning. The formal operational stage (approximately age 12 through adulthood) brings the capacity for abstract, systematic, and hypothetical-deductive reasoning. Adolescents and adults at this stage can consider possibilities, test hypotheses, and engage in metacognition — thinking about thinking. Notably, not all adults consistently reach or use formal operations.
Critics of Piaget have argued that he underestimated the abilities of infants and young children (object permanence may appear earlier than he suggested), that stage transitions are more gradual and domain-specific than his discrete-stage model implies, and that he undervalued the role of social and cultural influences on cognitive development.
<image>A four-panel diagram of Piaget's stages of cognitive development. Panel A: Sensorimotor — an infant looking surprised when a toy is hidden under a blanket (object permanence), with a timeline showing development from birth to age 2. Panel B: Preoperational — a child looking at two glasses of liquid, one tall and thin, one short and wide, saying "This one has more!" (conservation failure), and a child behind a three-mountain display unable to describe what another person sees (egocentrism). Panel C: Concrete operational — a child correctly stating that the amount of liquid is the same in both glasses, demonstrating conservation. Panel D: Formal operational — a teenager solving an abstract logic problem with variables and hypotheses on a whiteboard. Key concepts are labeled at each stage.</image>
VI. Vygotsky's Sociocultural Theory
Lev Vygotsky (1896-1934) offered a complementary perspective, arguing that cognitive development is fundamentally shaped by social interaction and culture. His concept of the zone of proximal development (ZPD) describes the gap between what a child can accomplish independently and what they can achieve with guidance from a more knowledgeable person. Learning is most effective when it takes place within this zone. Scaffolding refers to the structured support provided by teachers, parents, or peers, which is gradually reduced as the child gains competence.
Vygotsky also emphasized the role of private speech — children talking to themselves to guide their thinking and regulate their behavior. He viewed this as a reflection of the internalization of social speech that eventually becomes inner speech. Piaget, by contrast, interpreted private speech as egocentric and less functional. Vygotsky further stressed that cultural tools — language, counting systems, literacy — profoundly shape cognitive development.
VII. Attachment
Attachment is the strong emotional bond between an infant and a primary caregiver. Harry Harlow's experiments in the 1950s and 1960s with rhesus monkeys demonstrated that contact comfort — the reassurance provided by a soft, warm surface — is more important for attachment than feeding. Infant monkeys preferred a cloth-covered surrogate mother over a wire surrogate that provided food. Monkeys raised in isolation showed severe and lasting social and emotional deficits.
John Bowlby developed attachment theory, proposing that attachment is an innate biological system that promotes survival. Infants develop an internal working model of relationships based on their caregiver's responsiveness, and a sensitive period for attachment exists during the first two to three years of life.
Mary Ainsworth's Strange Situation procedure, which observes infant behavior during separations from and reunions with the caregiver in a laboratory setting, identified four attachment styles. Securely attached infants (approximately 60%) are distressed at separation, happy at reunion, and use the caregiver as a secure base for exploration. Insecure-avoidant infants (approximately 20%) show little distress at separation and avoid the caregiver upon return. Insecure-ambivalent (resistant) infants (approximately 15%) are very distressed at separation and display mixed behavior at reunion — clinging yet also angry. Disorganized-disoriented infants (approximately 5%) show contradictory, confused behavior and are often associated with abusive or frightening caregiving.
Attachment style is predicted primarily by caregiver sensitivity and responsiveness, though infant temperament also plays a role. Secure attachment predicts better social relationships, emotional regulation, and overall adjustment, though these effects are significant rather than deterministic.
VIII. Moral Development
Lawrence Kohlberg proposed a stage model of moral reasoning based on responses to moral dilemmas such as the Heinz dilemma. At the preconventional level (typical of most children), moral reasoning is guided by self-interest: Stage 1 reflects an obedience and punishment orientation ("avoid punishment"), and Stage 2 reflects individualism and exchange ("what's in it for me?"). At the conventional level (typical of most adolescents and adults), reasoning is guided by social expectations: Stage 3 focuses on maintaining good interpersonal relationships ("be a good person"), and Stage 4 emphasizes maintaining social order ("follow the rules"). At the postconventional level (reached by some adults), reasoning is guided by abstract principles: Stage 5 focuses on the social contract and individual rights, and Stage 6 appeals to universal ethical principles of justice, human dignity, and equality, though this stage is rarely observed.
Kohlberg's theory has drawn several criticisms. Moral reasoning does not always predict moral behavior. The stages are culturally biased, emphasizing Western values of individual rights and justice. Carol Gilligan argued that Kohlberg's framework undervalues care-based morality, which is more characteristic of female moral reasoning. Jonathan Haidt's social intuitionist model proposes that moral judgments are typically intuitive and emotional, with reasoning constructed after the fact to justify gut-level reactions.
<image>A diagram of Ainsworth's Strange Situation paradigm and attachment styles. Panel A: A series of small scenes showing the procedure — caregiver and infant in a room, stranger enters, caregiver leaves, caregiver returns. Panel B: Four quadrants showing the four attachment styles. Secure: infant explores freely, is distressed at separation, and greets caregiver happily upon return. Avoidant: infant shows little distress and ignores caregiver upon return. Ambivalent: infant is very distressed and shows mixed approach-avoidance at reunion. Disorganized: infant shows contradictory behaviors such as approaching while looking away. Each quadrant includes the approximate percentage and the typical caregiver behavior that predicts it.</image>
