5 Steps to a 5 AP Psychology, 2010-2011 Edition (47 page)

Emotional development

Gender roles and sex differences

For thousands of years, philosophers and psychologists took sides in the
nature versus nurture controversy
, dealing with the extent to which heredity and the environment each influence behavior. Today, psychologists agree that both nature and nurture interact to determine behavior, but they disagree as to the extent of each. Many biological psychologists, neuroscientists, and evolutionary psychologists argue the nativist (nature) position that basic structures for our behavior are genetically determined, and their expression depends on interaction with the environment. In other words, development results mostly from genetically determined
maturation
—biological growth processes that bring about orderly changes in behavior, thought, or physical growth, relatively unaffected by experience. On the other side, behaviorists argue that physical structures are genetically inherited and intellectual structures are learned; the environment shapes us. Developmental psychologists conduct experimental and observational studies on identical twins, for example, to try to determine the relative contributions of nature and nurture. (See Behavioral Genetics in
Chapter 7
.)

A second controversy,
continuity versus discontinuity
, deals with the question of whether development is gradual, cumulative change from conception to death (continuity), or a sequence of distinct stages (discontinuity). Behaviorists who favor continuity focus on
quantitative
changes in number or amount, such as changes in height and weight. Vygotsky favored continuity. On the other hand, theorists such as Piaget, Kohlberg, Gilligan, and Erikson who favor distinct stages focus on
qualitative
changes in kind, structure, or organization. They theorize that the child and growing adult resolve conflicts or develop different abilities in stages through which everyone passes in the same order and that build upon one another; the growth pattern is discontinuous.

A third controversy,
stability versus change
, deals with the issue of whether or not personality traits present during infancy endure throughout the lifespan. Psychoanalysts, followers of Freud, believe that personality traits developed in the first 5 years predict adult personality. Change theorists argue that personalities are modified by interactions with family, experiences at school, and acculturation. Developmental psychologists research which characteristics are most likely to remain stable and consistent, and which are likely to be more flexible and subject to change. Some aspects of temperament, such as energy level and outgoingness, seem relatively stable, whereas social attitudes are more likely to change.

Developmental psychologists conduct experiments, naturalistic observations, correlational studies, and case studies that enable them to assess change over time. (See
Chapter 6
, Research Methods.) They use four basic research designs: longitudinal, cross-sectional, cohort-sequential, and retrospective studies.

A
longitudinal
study follows the same group of people over a period of time from months to many years in order to evaluate changes in those individuals. In 1921, Lewis Terman of Stanford University began studying a group of highly intelligent children who have been
studied throughout their lives, providing important information about changes in intellectual functioning across the lifespan. Longitudinal studies can be extremely costly to conduct, take a long time to produce results, and typically lose participants over time. If those who drop out differ from the other subjects in significant ways, results of the study may not be generalizable to the original population.

On the other hand, cross-sectional studies cost less, do not lose participants, and produce results quickly, but have other major weaknesses. In a
cross-sectional study
, researchers assess developmental changes with respect to a particular factor by evaluating different age groups of people at the same time. For example, to study lifespan changes in mathematical skills, psychologists could give the same math tests to groups of 15-, 25-, 35-, 45-, 55-, 65-, and 75-year-olds at the same time. Cross-sectional studies can be invalid if a
cohort
, group of people in one age group, is significantly different in their experiences from other age groups, resulting in the
cohort effect
, differences in the experiences of each age group as a result of growing up in different historical times. This difference is a confounding variable in the study. Obviously, most younger participants may have been exposed to calculators and computers their whole lives, whereas 65- and 75-year-olds have had fewer opportunities.

To minimize the major drawbacks of both longitudinal and cross-sectional research designs, some researchers conduct cohort-sequential studies. In
cohort-sequential
studies, cross-sectional groups are assessed at least two times over a span of months or years, rather than just once. Results from one cohort are compared with other cohorts at the same age to evaluate their similarity; differences indicate a cohort effect. In this way, researchers can separate age-related changes from cohort effects. These studies share disadvantages of longitudinal research, but to a lesser extent.

Biographical or retrospective studies are case studies that investigate development in one person at a time. Typically, a researcher interviews an individual at the older end of the age span of interest. The researcher reconstructs changes that have occurred in the subject’s life through the subject’s self-reports in interviews and examination of available data. Although these studies can be very detailed, they are not always correct because memory is not always accurate, and they may not be generalizable to a larger population.

Physical development focuses on maturation and critical periods. A
critical period
is a time interval during which specific stimuli have a major effect on development that the stimuli do not produce at other times.

Prenatal development
begins with fertilization, or conception, and ends with birth. The
zygote
is a fertilized ovum with the genetic instructions for a new individual normally contained in 46 chromosomes. (See Behavioral Genetics in
Chapter 7
.) During the first 2 weeks following conception, the zygote divides again and again forming first a hollow ball of cells that buries itself in the wall of the uterus, then a three-layered inner cell mass surrounded by outer cells attached to the uterine lining. Different genes function in cells
of the three different layers; the forming individual is now considered an
embryo
. During the embryonic period from the third through the eighth weeks following conception, organs start to develop as a result of differentiation and specialization of cells; and the placenta, umbilical cord, and other structures form from the outer cells. As organs develop, the embryo is particularly sensitive to environmental stimuli such as chemicals and viruses. Nutrients, oxygen, wastes, and other substances pass from the woman’s blood into and out of the developing organism through the placenta. By the end of the eighth week, the embryo has a head with partially formed eyes, limbs, and a skeleton composed of cartilage. At this point, all organs are present in rudimentary form, and the developing individual begins to resemble a human; it is a
fetus
, the developing human organism from about 9 weeks after conception to birth. During the fetal period, the organ systems begin to interact, bone replaces cartilage in the skeleton, and sex organs and sense organs become more refined.

Birth defects can result from a malfunctioning gene or an environmental stimulus. If the pregnant woman takes in poisonous chemicals or gets infected with a virus, developmental errors can result in birth defects that are not hereditary. Chemicals such as alcohol, drugs, tobacco ingredients, mercury, lead, cadmium, and other poisons; or infectious agents, such as viruses, that cause birth defects are called
teratogens
. The specific nature of a birth defect depends on which structures are developing at the time of exposure. Most birth defects develop during the embryonic period and are usually more severe than problems that develop later. The critical period for eyes, ears, arms, legs, and the heart is typically the first 3 months (first trimester) of pregnancy, while the critical period for damage to the reproductive system extends across the first and second trimesters of pregnancy. The critical period for the nervous system is all three trimesters. Because of the long critical period for brain development, many kinds of brain damage can result, the most severe during the embryonic and early fetal periods.

Fetal alcohol syndrome (FAS)
is a cluster of abnormalities that occurs in babies of mothers who drink alcoholic beverages during pregnancy. Low intelligence, a small head with flat face, misshapen eyes, a flat nose, and thin upper lip characterize children with FAS. Intellectual impairment ranges from minor learning disabilities to severe mental retardation. The more severe mental retardation results from exposure of the embryo/fetus during the early months of pregnancy. Currently, FAS is the leading cause of mental retardation in the United States. Cigarette smoking during pregnancy is associated with miscarriage, stillbirth, premature delivery, and low birth weight. Heroin- and cocaine-exposed fetuses that are born live may undergo withdrawal symptoms, and may be distractable and unable to concentrate. Researchers have difficulty pinpointing other prenatal effects of cocaine and heroin because affected babies are often exposed to additional substances and situations that can account for other symptoms.

Malnutrition and prescription and over-the-counter drugs can cause birth defects. Even certain nutrients ingested in large quantities can be teratogenic. For example, high doses of vitamin A can cause heart, nervous system, and facial defects. Viruses such as rubella can pass into the placenta and cause birth defects. During the first trimester of pregnancy, rubella can cause cataracts, deafness, and heart defects; during later weeks effects include learning disabilities, speech and hearing problems, and Type 1 diabetes.

At birth,
neonates
, or newborn babies, are equipped with basic reflexes that increase their chances of survival. A sequence of rooting, sucking, and swallowing reflexes enables the neonate to get food.
Rooting
is the neonate’s response of turning his or her head when touched
on the cheek and then trying to put the stimulus into his or her mouth. What touches the newborn’s cheek is frequently a nipple.
Sucking
is the automatic response of drawing in anything at the mouth.
Swallowing
is a contraction of throat muscles that enables food to pass into the esophagus without the neonate choking. The lack of some reflexes in a neonate can indicate possible brain damage to neuropsychologists. Among those they test are the
grasping reflex
, when the infant closes his/her fingers tightly around an object put in his/her hand, and the
Moro
or
startle reflex
, in which a loud noise or sudden drop causes the neonate to automatically arch his/her back, fling his/her limbs out, and quickly retract them. As the infant matures, developing voluntary control over behaviors, many of the reflexes disappear.