Psychology  is  derived  from  two  Greek  words meaning   'mind' and   `Study'   and   it is essentially the study  We  know that  psychology   as   an" independent  discipline  acquired separate   status very "recently. Formerly  it  was  studied  as  a  sub- branch of  philosophy,,     The  origin of   psychology can be  traced back   to  the  Golden-Age  of   Greece   and   then   it   was  mainly  a speculative   science relied much on astrology, religion, philo-sophy  and  mysticism for   interpretation  of  behaviour. For example,   the behaviour   of   an   individual was   said to have a relationship with the   time and date of birth of   the individual.
Psychology is a science concerned with the study of various types of behaviour. It studies how people think, respond, feel and learn, why they behave the way they do and what initiates and sustains their action. Theses processes are fundamental to our understanding of   the   way children learn and think. The aims of psychology  are  understand ,   predict  and control  behaviour  in  terms  of  modifying,   guiding  and changing  it. Psychology is a science and follows the scientific methods of empiricism, objectivity, verifiability, replicability and signification.
Modern psychology has been defined as empirical   science of behaviour based on careful observation and experimental investigation.       It focused on rational strategies for understanding, explaining,   controlling and improving behaviour.  It established law and principles   that could be used to predict the, likelihood of certain behaviour occurring under specified conditions.
There are many branches of psychology, each branch trying to study behaviour from its own standpoint. For instance,   developmental   psychology tries to study how the   various process we listed above develop in children.     Other areas of   specializations are clinical, counseling, educational,   social etc.

(a) MEANING OF DEVELOPMENTAL PSYCHOLOGY:- Developmental psychology  is  primarily concerned with origin and change of behaviour and related mental  and bodily events. It surveys the entire humand life span particularly from conception to adolescence. It studies and describes behavioural changes which accompany changes in age.     Since behaviours and abilities change most rapidly during the first few years of   life, child psychology is often used as a synonym for  much of  developmental  psychology. Behavioural changes with age  at  the end of life, old age are also much studies by this sub-field.
    Developmental psychology therefore understands the developmental processes from the moment of conception to adulthood. The development of learning, perception, social behaviour and motivation are of special interest to this sub-field.
    There are two aspects of developmental psychology and they are the research aspect the applied aspect. The research aspect uses scientific methods to provide answers to such issues as development of thinking in children. On the applied aspect, the developmental psychologist can apply what he used in studying disturbed children to the study of deviant behaviour found in adults.

    The concept of phases can be used to described periods of the life span. There is no one right way to divide up the life span. The ways in which period have been conceived in the past and in other cultures differ considerably. In addition, it is impossible to use a strict stage concept of development. Thus, we have chosen to use five chronological periods or phases that roughly correspond to our cultural usage and some other cultures in the world.
    The prenatal phase begins at conception an ends at birth. The second phase which is infancy begins at birth and continues until approximately age two. By the end of the second year, most children have begun to acquire language and symbolic thought in addition, most adults think of two year-olds as children rather than as infants, which corresponds to the developmental shift from non linguistic to linguistic communication. Of course, other important changes occur in social and emotional behaviour from infancy to child hood.
    The third phase, childhood, begins an early period around age two and continues through late childhood at around age twelve. Puberty is usually accepted as the end of childhood and the beginning of adolescence.
    Adolescence, the fourth phase, is a less definite period because its end is not defined as well as the end of other phases of development. Adolescents are generally accepted as adults when they acquire adult economic and social roles. Adulthood, the twenties and continues until death. This is clearly the longest phase, spanning early adulthood, the middle years, and the late adulthood until death. There are many social and biological changes in adulthood, although the rate of development is much slower than in the earlier years.
    These five phases are only one way to segment development, but such a division makes the discussion of concurrent behavioural changes more comprehensible. Although one should never forget that development is continuous across the life span. Although each person goes through periods of relatively rapid or slow development, his life shows a continuity from conception to death.

UNIT II                   
    The field of developmental psychology attempts to reliably describe, to understand, and to explain changes in human behaviour across the life span. Development psychologists construct theories, using information from psychology as well as from biology, sociology and anthropology, to help them understand, predict and explain human behaviour.
    Developmental psychologists are careful to use an appropriate level of explanation of behaviour by studying behaviour at environmental events that influence behaviour, and variations among individuals, as well as by conducting research on non human species and studying case histories of individuals. Replication studies are the best safeguard against accepting a chance finding as typical.
    Developmental psychology helps the teacher psychologist to understand and appreciate the needs of the children in his class, their capabilities and interests. This will definitely help him teach better and more meaningfully. He may decide to group the children depending on their interest, know what stories to tell, what examples to use and whether they should bring and use certain learning aids. Infact it helps the teacher to reach all the children in the class and have greater knowledge of them. Here, the teacher understands them better and appreciate the way they behave, feel and think, etc.
    Developmental psychology helps the teacher to detect development problems of the child and treat them accordingly. For instance, visual and hearing problems can be referred to specialists for proper diagnosis and early treatment. Maladjustment, problems can definitely be prevented if there is early detection. Problems of mal-nutrition can equally be handled if teacher talk to parents on it.
    It enhances the teacher's appreciation of the task involved in guiding children towards maximum self-realization. The teacher discovers the child and guides him towards the attainment of set educational objectives. The course also facilitates a deeper understanding of the various aspects and implications of the child's continuous growth and development. The teacher at any given stage relates the educational objective with the physical, social, emotional and intellectual development of the child. This will enable him involve an appropriate teaching methods and sustainable materials for a more effective result.
    Developmental psychologists question about the how and whys of development have led to much useful information about the regularity and lawfulness of humand development. Although, some questions about human development cannot yet be answered, what is known offers insight into an understanding of many facets of human development.

UNIT III                                 
    Though individuals differ in the rate of growth and development still the development follows an orderly sequence in all individuals and show high degree of similarity in the order in which various developments appear. Psychologists have reported several directional trends in the development. The following are the main trends:-
(a)    Cephalocadual: The first pattern is from head to toe. This means that in early childhood, growth is faster in the head and later spread downwards to other parts of the body. This trend which starts with the head and the brain, then down towards the body to the feet is known as cephalocaudal. A new born shows a remarkably developed head than the trunk and the feet and first lift his head, sit before standing.
(b)    Locomotion: Locomotion develops in a sequence in all infants of different cultures of the world. The sequence is creeping, crawling and walking though the timing may vary from one child to other.
2.    DEVELOPMENT IS A CONTINUOUS PROCESS: Development is a continuous process which begins from the time of conception till death. Development and growth is not always smooth and gradual. There are spurts in physical growth and psychological functioning as increases in height and growth during puberty stage, sharp rise in vocabulary during pre-school years and sudden improvement in problem-solving abilities during adolescence.
3.    DIFFERENT ASPECTS OF DEVELOPMENT ARE INTER-RELATED: - Different aspects of development are inter-related and inter-dependent. Child's early social behaviour is inter-related with his physical development. If the child is physically handicapped then his social behaviour will be retarded. The motor development of walking has positive effect on intellectual development of children. Thus we see that different types of developments are interdependent and help each other.
4.    DEVELOPMENT IS INDIVIDUALIZED PROCESS:-  There are individual differences in development. All individuals develop in their own way. Each child has his own rate of physical, entail, emotional and social development. If we observe six-year old children, we find great differences in their heights, weight, social, emotional and learning readiness. Even at different ages children have different rate of development. The rate of growth is very high in infancy and then slows down and continues through one's life.
5.    DEVELOPMENT BEHAVIOUR IS LARGELY CONTROLLED BY NEEDS:- A child who needs nutrients will concentrate on food and forget about other things. Similarly a child who needs to get into a peer group will strive to do so at the risk of other aspects of development.
6.    DIFFERENT ASPECTS OF GROWTH PROCEED AT VARYING RATES:- Hereditary and environmental factors help the different aspects of growth to proceed at varying rates. Thus a child may be tall for his age but average in language development. The typical child therefore has many "Ages". For example a child who is chronologically ten, might have a mental age of thirteen a social age of seven, a mental age of twelve.
7.    CRITICAL PERIOD IN DEVELOPMENT:- There are critical periods in the development of certain organs and functions of the body. If anything interferes with the organ at that particular time, it may result in permanent deficiency or mail-function. Example of such organs is the heart, kidney and the eyes. There is also a critical period for the development of language. At that time a child can learn almost any language.
8.    GROWTH GENERALLY PRECEDES FUNCTION:-  A muscle must grow fully before it can become functional for example, at age seven or from this age that child can engage in abstract thinking.
9.    DEVELOPMENT AS A PRODUCT OF INTERACTION:-  Development is a process resultant from a constant flux or inter-change of energy within an organism and his environment. Hereditary forces inherent in the genetic constitution of the individual and environmental forces influence the development of the organism. It is very difficult to distinguish the contribution either of the two forces. Individual is the by- product of the constant interaction of the individual with his environment.
10.    RATE OF DEVELOPMENT DIFFERS IN MALE AND FEMALE CHILD:- There is a difference in growth rate of boys and girls. Girls mature earlier in comparison to boys. Girls are falley and heavier than boys during pre-adolescence but by the end of adolescence boys surpass them.
HUMAN PRE-NATAL DEVELOPMENT                                                            
A.    Conception:- Foundation of Life  
    When a human organism is mature enough to reproduce his kind (ie around the age of 18 and so on) the mother sheds an egg every month and the father is capable of emitting millions of male gametes (spermatozoa).
    When shed, the female egg attempts to descend the fallopian tube and when mating takes place among married couples, an egg may thus be fertilized to form a zygote. The reproductive cell gametes contain the hereditary materials of life (genetic) materials, chromosomes or DNA molecules) which are capable of forming minor images of themselves. This is probably the basis of the children resembling their payments in appearance, in behaviour, motives, thinking and possibly in reactions.
    The hereditary materials also determine the sex of the child at the zygotic stage of contributing certain characteristics such as the sex of the child. Thus the zygotes are usually females and the zygotes are usually males. A simple illustration makes it clear.
    If Ada married Obi and they mate as in figure 3, DNA materials are arranged in the gamiest in such a way that following offspring from Ada and Obi.
    It is interesting that the hereditary materials that determine the male child comes from the man. When the zygote is formed, it may be divided into two or more complete portions when identical twins may be formed. Of course twins quite often result form different ova. These are the basic ways in which the various potentials for the often manifested abilities may be laid. Once these are laid, it is their exposure to the environmental forces that may determine the extent the limits set by heredity or nature will be met. Usually a process of growth, differentiation and specialization of parts precedes the arrival of integration and maturation which are the basic of learning and the development of all the attributes- biological, cognitive, social, emotional and so on.

PRE-NATAL DEVELOPMENT:- Once fertilization or conception has taken place a number of growth and development processes takes place in the growing child. The changes are very important in the realization of the genetic potential organized when the zygote is formed. While the whole process is actually continuous, it may be described under three main headings.
the zygotic stage of development
the embryonic stage of development
the foetal stage of development
The Zygotic Stage: The zygotic stage of pre-natural development is often described as setting in a day after fertilization has taken place. This is generally a period of rapid growth in terms of increase in the length and girth of the growing organism with the cells increasing in equational proportions. (This type of cell division is often described as mitotic) each cell replicates itself in all ways including the inherited genetic code.
    This phase may last for about two weeks. The zygote, which is hardly visible at a distance, finally descends the fallopian tube where fertilization took place and settles on the uterus within the tissue of the uterus all. This process is often described as implantation.
THE EMBRYONIC STAGE:-  This stage is marked by some laying down of some fundamental tissues. All the cells that have been formed at zygotic stage are reorganized and differentiated into functional categories. There are therefore tissue differentiation and a physiological division of labour. Three main tissues are laid down at this phase. They include:-
The outermost aggregation of cells (called the ectoderm tissues).   
The cell organized around the middle of the growing embryo (often called mesoderm tissue) and
The cells organized around the interior of the embryo (called the endoderm tissue).
The process of tissue differentiation and physiological divisions of labour is often so orderly and marked that the outermost cells have been observed to develop into the outer structures in an individuals. Hence the ectoderm cells develop into outer structures such as the skin, skin hairs, ear, eyes, brain, limbs and other epidermal structures associated with the skin. Most of the structures are protective in function. The middle tissues often differentiate into muscles, bones while the internal tissues develop into internal organs such as kidneys, liver, lungs and so on.
There is no neural connection between the maternal and the embryonic nervous systems. Nevertheless, the emotional state of mother may indirectly influence the physiological state of the embryo. At about 18 days the embryo has already taken shape along longitudinal axis with its front, back, left and right sides, and a discernible head and tail. This is the development of the third week. By the fourth week there is the formation of a south region, liner intestine and more differentiation of cells into the head and brain regions.
Between the 8th and 9th weeks, the embryo is now about 1 inch long. The face mouth, eyes, ears, start to be well defined. There is also the appearance of the arms, legs. The internal organs like kidney, live lungs apart from taking one definite shapes, also start some functions e.g the liver starts to manufacture red blood cells.
The period of the embryo is thus a period of rapid development of the nervous system. The head at this stage is large in relation to the body. This shows the sensitive nature of the embryo, and any interference at this stage, whether chemical or mechanical, is more likely to cause a permanent nervous damage.

Foetal Stage                  
    At this stage the growing organism is called foetus. The major development talking place is the increase in size of the organs which have been in rudimentarily forms at the embryonic stage. There is also the change from the passive existence to active life as the foetus is capable of responding to tactice (touch) stimulation. At the end of the 12th week the about 3 inches long foetus begins to resemble the human being and the next four weeks marks a major development of the nervous system.
    At 16 weeks the mother feels the foetal movement, the human features become more apparent more especially as hairs begin to appear on the head. The hands become capable of gripping while the eye can blink.
    At 24 weeks the foetus is capable of `true inspiration and expiration", and can produce thin crying in case it is born prematurely.
    The 28th week marks the zone between viability (ability to live if born) and non viability. The major systems like the nervous, and circulatory systems have become well formed to function if the child is born, but of course special care in an incubator is needed and therefore the need for the special care units in the hospitals arises. The period form 28th weeks to birth 40 weeks is marked by further development of the body structures.

    Many factors influence the development of the unborn child. When everything goes well, the baby is healthy and normal. When there is negative influences, serious damage can occur. Some of the factors could affect the structures and result in permanent damage. But with good handling and natural processes the damage is temporary.

i.    Nutrition:- Good nutrition, provided by a balanced diet, helps the unborn baby to develop optimally. A balanced diet contains proteins, carbohydrates, fats and minerals. Nutrients help to provide the building materials and energy to support rapid cell growth and development throughout pregnancy. The faster the growth, the grater the demand for nutrients. Where the mother is malnourished (not eating balanced diet) the baby who relies on the mother for its nutrient requirements cannot grow properly. The organ which has most rapid growth i.e the brain, is usually he worst hit.
    Research results show that prolonged mal-nutrition has many effects. The brain does not have its full number of cells. Sometimes a condition known as MBD, (minimal brain dysfunction) occurs. The child appears normal in every respect except that there are slight defects or damage in the brain. Learning of certain types of materials can be affected in later years. Other effects associated with mal-nutrition are still births ( a baby dying before birth) miscarriage, difficult labour and low birth weight.

ii.    Health Maternal Disease:-  When the pregnant mother is healthy the unborn baby develops normally. But poor health of the of the mother can affect here ability to nourish and protect the unborn baby. There are certain infectious diseases which affect the growth of the baby. German measles or Rubella may result in defective eyesight and mental deficiency. Some forms of sexually transmitted diseases such as gonorrhea, syphilis and the much dreaded AIDS can be passed on to unborn child, and can cause abortion. Mumps could also have bad effect. Even continuous attacks of malaria can make the mother anemic and therefore unable to furnish the baby with normal oxygen supply and perhaps nutrients too. And so makes the baby small, premature of still birth or deaf.
iii    Drugs and Chemicals:- Drugs have to be used carefully during pregnancy because of their adverse consequences. Doctors have pointed out that material use of drugs and chemicals can have damaging effects on the fetus. Chemical substances from roots, herbs and barks of trees or other scientific chemical substances may cross the placental barrier through the circulatory system of the fetus and cause great damage especially in the first three months of pregnancy.
    Experts in medicine are of the opinion that pregnant mothers should avoid self medication for it is better to prevent fetal damage than to cause one and begin to cure it. E.g pregnant women take a German drug- thalidomide to help them in morning sickness but this results to physical defects. The drug affects the process of cell differentiation and growth since it was taken in the first trimester of pregnancy and so many babies were born without arms and legs.
    Other drugs that have been proved to have possible damage on the fetus include sleeping pills, quinine, and analgesics, antibiotics and contraceptives, chemical sprays used to destroy pest and plant.
    On the other hand, some drugs are medically prescribed to help mothers whose pregnancies were threatened. This help the children to grow well and they perform better in school work.
iv.    Alcohol Tobacco (Nicotine) and Smoke:-  For some years the WHO (world health Organization) has been warning people in developing countries about possible harmful effects of drinking, alcohol and tobacco smoking. These pregnant women who indulge in this  have babies with eye, ear or brain damage or mental retardation. The nicotine in the tobacco can affect the nutritional or oxygen supply to the fetus and make it not to have normal weigh  after birth. Small or under weight babies stand a higher risk of infections after birth than bigger babies. Alcohol, tobacco (chewed or smoked) and inhaled smoke from fire wood or cow dung may affect appetite and reduce nutrient intake by the pregnant mother. This in turn affects how much nutrition the fetus obtain from the mother.          

v.    Age of the Mother: - Another factor which can affect the well-being of an unborn baby is the age of the mother. Very young mothers and old mothers tend to have complications. Research has found that young adolescents before the age of 18 years (10-15 years) is at the risk of giving birth to a premature baby, or a still born and the first time mother after 35 years tends to have problems such as difficult labour, miscarriages, still birth, and abnormal babies. The triplets. Although some of them give birth to normal babies there is greater likelihood of their giving birth to "mongoloid" children. Mongolism is a condition where the children are mentally retarded and do not have normal facial features. Their eyes are small and narrow. The children have great difficulty looking after themselves and learning.
vi.    Accidents:- A light fall may not affect a pregnant woman and her unborn child adversely. But if she falls from a bicycle or is involved in an accident or a fight where she experience heavy impacts, the baby may be affected. The placenta may be partly detached or completely cut. This means that the baby may not have the usual nutrients. Bleeding may occur, also miscarriage or other complications. If the placenta becomes inefficient it affect development of the baby adversely so that brain damage, small size or premature birth may result.
vii.    Radiation (The use of X-Ray):- The use of X-ray and "burning effect of similar materials is to be discouraged. Only the medical doctor should order an x-ray to be taken when necessary. If for some reasons the x-ray is taken within the first trimester of pregnancy, some cells might be destroyed. Without replacements, the baby could be deformed. The eyes and the brain are usually the badly affected organs. The heart and respiratory system too can be affected.
viii.    Blood Incompatibility :-Sometimes certain blood factors of the father and mother of a baby do not agree. They are said to be incompatible, they cannot work together even for the sake of the baby. One such factor is known as Rh-factor (Rhesus factor) if there is such disagreement or incompatibility some complications result in such a way that miscarriage may occur or the baby may experience health problems.
xi.    Emotional Stress (Material Stress) :-Some pregnant women are often emotionally up set, nag unnecessarily and develop prolonged anxiety over minor issue. Sontag (1944) described the influence of maternal stress on the fetus in his studies on fetal behaviour and physiology as "Blood borne". During severe maternal stress hormones such as adrenalin, epinedire and ecetylcholine are released into the maternal blood streams. These hormones can cross the placental barrier and enter the blood stream of the baby fetus and interfere with growth and development. Emotional shock and stress may reduce her appetite and so the quality and quantity of nutrients also become reduced. Even when fed well, her body may refuse to utilize the food well. There is evidence to show that certain deformities may occur, the baby will be small. There could be mental retardation and some other nervous disorders such as epilepsy.
x.    Difficult Labour:- Because of the fact that medical facilities are not sufficient also with ignorance, and poverty many babies are born out side hospitals and medical clinics. It is only when labour becomes very prolonged and difficult that some pregnant women are rushed to the hospital. Sometimes the babies die before birth-still birth. Sometimes the supply of oxygen to the brain cells is poor so some brain cells die off. The child then suffers from MBD (minimal brain damage or even mental retardation which is more severe. The child may not learn certain subjects or have deformed limbs.                                         
RESEARCH METHODS IN CHILD PSYCHOLOGY:- Many research methods are used to study the child to acquire the knowledge about children's needs, characteristics and development. They help to find out whether any environmental factors have important effects on the children's development.
    Some basic approaches are used in the study of children. We will discuss four approaches to the study of children. They are as follows-:
longitudinal approach
Cross sectional approach
Correlational approach
Interventional approach
i.    longitudinal approach: - In the longitudinal study, the same group of children are studied repeatedly over an extended period of time, often a decade or longer. The period may be a school year, two terms or extend for several years. This approach is especially valuable for investigations in which there is an attempt to discover whether characteristics such as motor development, intelligence, dependence and behaviour problems are stable over long periods of time or subject to fluctuation. This approach must be used to study the latent or delayed influences of some early experiences on later development or behaviour. For example, current theory about personality development suggest that maternal rejection during childhood and adolescence is devastating. The only way to test the validity f this hypothesis is to select mothers who rejected their children during the early period and then to make a follow up studies of their children later on, assessing their subsequent social behaviour.
    Another illustration is with a teacher who wants to find out how well the children in the school are growing. As a school, the teacher may decide to take height measurements of the children in primary one B. perhaps two or three measurements are taken in 1989. in 1990 assuming that they are in primary two B, two or three measurements are taken again. The same process is repeated until they get to primary 6B. It will be possible to see how each of these children has grown in the 6 years. The teacher may also decide to study all the students in his class within one year. He takes periodic measurement of all the children probably 6 times in the year. This is a longitudinal study too.
    Obviously, the longitudinal method is expensive, time consuming and difficult to use.
Cross-Sectional Approach: - The second and more common method is the cross-sectional approach. Here the investigator selects a group of children at one age period or different groups of children at different ages and makes his observations at that time. For instance, the growth of reasoning ability can be studied with the cross-sectional method by selecting a group of six children with six ages and each has two years  gap from another-2,4,6,8,10 and 12 years, and comparing the average performances of the group in reasoning tests.
    Also, the above approach could entail taking different groups of children and studying them just once or twine per group within a short time. For instance, in the example we used, instead of study could be conclude in two weeks. All the children in primary one B, 2B, 3B and so on to primary 6B could be measured at about the same time. Different groups of children would be measured but then you would also know the average height of children in classes 1,2,3 to 6.
    The above approach takes a shorter time but you cannot say how a particular child say OKON grows over six years.
iii.    Correlational Approach: - In a correlational study, an investigator measures two variables for a group of people and determine whether people who score high on one measure also score high on the other. The illustration given for this correlational study is in the context of a particular research problem: "what is the effect of television violence on aggressive bahviour?.
    In relation to the above question for an example, information was obtained for a large sample of elementary school children about how much violent television they watched and how much aggressive behaviour they displayed at school (according to other children's reports).
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