Developmental psychology studies the changes and how such changes occur over a course of an individual’s life events. It seeks to understand the changes that are universal, the changes that occur regardless of the individual’s culture or experiences. Moreover, it also seeks to understand why and how individual differences occur – why some people respond one way in a particular situation while others respond quite differently. Further, developmental psychology is particularly concerned with the process by which behavior changes during an individual’s lifetime.
By studying biological and cognitive development, psychologists and humanity hope to better understand, predict, and modify an individual’s behavior. BIOLOGICAL DEVELOPMENT Biological development refers to the changes in the body and brain from the moment of conception to old age. This development greatly influences people’s behavior. Three of these biological-related events are prenatal, from childhood to adolescent, and adult to aging. In prenatal development, the individual grows from a single fertilized egg cell, known as the zygote to an infant with billions of specialized cells.
This period is divided into 3 stages: namely, the germinal, embryonic, and fetal changes. In the germinal stage, the zygote has become a small mass of cells; in the germinal stage, the fetus` brain and heart begin to develop, arms and legs appear, limbs and critical internal organs are rapidly developing; and in the fetal stage, the fetus` respiratory system has developed. So at the end of prenatal period, an individual have grown from a single cell into an amazingly complex individual who, on average, is about 20 inches long and weighs about 7.
5 pounds. The brain during the prenatal development begins to develop between the second and third week after fertilization, and by 3. 5 weeks a primitive nervous system is present. By the time of birth, virtually all of the approximately 100 billion neurons in the human brain are already present (Cowan, 1979). In the child development, an individual is like a virtual growing machine. By the age of 2, the average child is about 70 % taller than at birth and nearly 400 % heavier (Eichorn, 1989).
As a rule of thumb, girls grow tall to about half their adult height by 18 months of age while the boys by the age of 2. Between the ages of 2 and 5 years, physical growth slows dawn and then levels off at a relatively steady rate until adolescence. The beginning of adolescence is also the onset of sexual maturation or puberty. The usual sequence of changes that occur during sexual maturation for girls are the following: breasts and pubic hair begin to develop and the onset of menstruation. For the boys, the first signs of puberty are the growth of penis and testes and the appearance of pubic hair.
These early signs of sexual maturation take place during a rapid increase in height, muscle size and strength especially for the boys with growth peak at about the age of 14 years old. The girls on the other hand have their growth peak at 12 years old. However, boys grow taller than girls on average. But the growth of different parts o f the body is not uniform during the growing years. Physical growth ceases, on average, at about 18 years of age in girls and 20 years of age in boys. However, biological development does not stop until the end of life.
The brain also grows rapidly during this period. At birth, the brain is about 25 % of its adult weight and size. By the age of 2, it has grown to about 75 % of its adult weight. Although all of a person’s neurons are present at birth, the number and complexity of the connections among neurons increase substantially after birth (Parmelee and Sigman, 1983), and this increase is partly responsible for the growth in brain size. Further, the increased neural connections and the development of myelin make possible more and more complex behavior and thought as an individual grows.
In some areas of the brain, these developmental changes continue until adulthood (Parmelee and Sigman, 1983). The adult and aging life events are basically a declining stage. A variety of biological developments takes place as people age, including redistribution of body fat, decrease in bone mass, and decrease in muscle size and speed of contraction. Biological changes progress into old age. Many elderly people actually become shorter, partly because they slump and partly because of a decrease in bone mass. Muscle size and speed of contraction also decrease.
Aging also takes its toll on internal body organs. The heart muscles become weaker, blood flow decreases, and breathing capacity continues to decline. Physical performance also declines. According to Stones and Kozma (1985), “these bodily changes are paralleled by declines in physical performance with age”. Beginning at about age 30, a person’s physical speed, strength, and endurance decline at an average rate at about 1. 5 % a year. The brain also continues to change biologically with age (Creasey & Rapoport, 1985).
It decreases in size and weight, and some areas of the brain lose 50 percent or more of their neurons, specifically at the age of 50, with an average decrease of 2 % of brain volume every 10 years thereafter (Miller, Altson, and Corsellis, 1980). These age-related changes in the brain undoubtedly contribute to deteriorations of sensory, motor, and cognitive function. But just like biological changes in the body, these age-related changes in the brain are averages – the actual amount of change varies considerably from person to person. COGNITIVE DEVELOPMENT
Cognitive development refers to the changes in knowledge about the world or specifically, it refers to the development of sensation and perception, of the ability to learn, to reason, and to solve problems. Just like biological development, cognitive development continues from birth through old age. The three cognitive-related events that I would like to discuss are newborn infants, childhood and aging. In infants, cognitive development begins from the moment of birth as they begin interacting with and gathering information about the world.
They have all the rudimentary sensory abilities such as; they can see objects, can tell the different shapes and patterns but can’t change their focus very well. Their vision rapidly improves over the first six months to a year, although it may be several years until it is fully mature. Moreover, infants can also hear at birth but their threshold of hearing is higher and can’t discriminate well between sounds than adults. As with vision, an infant’s hearing improves rapidly over the first year, although it will be several years before it is fully mature.
Further, infants have a well-developed sense of taste (Cawart, 1981) as they can discriminate among different tastes; they can also smell and react to different odors; and their sense of touch is particularly well-developed. Infant’s motor behavior consists primarily of reflexes such as rooting, sucking, and grasping. These reflexes gradually give way to coordinated voluntary actions, such as sitting and walking. On the other hand, infant’s can learn from the moment of birth. They show habituation, a simple form of learning where they stop responding to a repeated stimulus.
They also learn through operant conditioning, which is making a particular response that brings about either reward or punishments. Although newborn infants can learn, they do not learn as readily as older children as their memory is not as good as that of adults. Children’s cognitive development theory is most influenced by Jean Piaget. He believed that people acquire knowledge by interacting with the world and that they construct knowledge through assimilation, which is incorporating new information and accommodation or modifying old information.
He further proposed a series of four stages of cognitive development, where he described children’s basic intellectual abilities sensorimotor, preoperational, concrete operational and formal operational. According to Piaget, these stages represent qualitatively different ways of thinking that occur relatively and abruptly and in the same sequence for all children. Though many psychologists challenged and modified Piaget`s theory, arguing that cognitive development is not really stagelike, its basic tenets remain widely accepted.
During Aging, changes in cognitive abilities seem to decline. This decline may be due to factors such as slow processing of information. Moreover, aging also show declines in memory performance, partly because they use fewer encoding strategies for remembering information and partly because they use fewer cues to retrieve information from memory. But long – term storage itself appears to be relatively unaffected by aging and, under favorable conditions, the elderly are nearly as good as young adults at remembering information.
Further, laboratory studies indicate that performance on a variety of problem-solving tasks declines with age. But these studies also show that training and practice can markedly improve older adults` problem-solving performance. What is more, when tasks are familiar and the subjects have experience with them, they show little or no decline in performance with age. Older people have accumulated a lifetime of experience, knowledge, and wisdom that they bring to everyday tasks, and this can offset cognitive deficits that may occur (Canestrari, 1986).
The picture of inevitable severe intellectual impairment that many people have of the elderly is therefore, a misconception. So, when we consider each of these life events though discussed separately, we will see that each of these two major threads in the development (biological and cognitive) of the individual are interwoven. Hence, we cannot separate one from the other and thus must be considered when studying about an individual’s development or life-span changes. References Canestrari, R. E. , Jr. (1986). Age changes in acquisition. In G. A. Talland (Ed.
) Human Aging and Behavior (pp. 169-188). New York: Academic Press. Cowan, W. M. (1997). The development of the brain. Scientific American, 241, 113-133. Cowart, B. J. (1981). Development of taste perception in humans: Sensitivity and preference throughout the life span. Psychological Bulletin, 90, 43-73. Creasy, H. & Rappport, S. I. (1985). The aging human brain. Annals of Neurology, 17,2-10. Eichorn, D. H. (1997). Biological Development: Current foci of research. In J. D. Osofsky (Ed. ), Handbook of infant development (pp. 253-282). New York: John Wiley & Sons.
Miller, A. K. H. , Altson, R. L. , & Corsellis, J. H. N. (1980). Variation with age in the volume of grey and white matter in the cerebral hemispheres of man. Neuropathology and Applied Neurobiology, 6, 119-132. Parmelee, A. H. , Jr. , & Sigman , M. D. (1983). Prenatal brain development and behavior. Handbook of child psychology, Vol II (95-1550. New York: John Wiley & Sons. Piaget, J. (1983). Piaget`s theory. In W. Kessen (Ed. ), Handbook of child psychology (4th ed. ). History , theory, and methods 9pp. 103-128). New York: John Wiley & Sons