Which Individuals Were Important in the Introduction of Testing for the Individual Differences in Psychology and What Were Their Contributions?

'The capacity for understanding' and 'the ability to comprehend' are two of many definitions that portray intelligence. Intelligence and personality are examples of psychological characteristics that can differ from person to person, and are known as individual differences. The main focus of this essay is intelligence and different discoveries made by a range of psychologists. Before entering in to detail about how psychologists have designed different methods to investigate intelligence further, it is important to consider the nature versus nurture debate and its influence on the discovery of intelligence as an individual difference. There is a conflict between heredity (Nature) and environment (Nurture) in modern day and until the 20th century; intelligence was thought to be inherited. This was a large negative because it meant that those of low intelligence could not be helped. However in the 17th century, psychologists thought that intelligence was nature based and malleable. In the 1950's, psychologists started to believe that experience largely contributed to intelligence. They thought that this experience was particularly important in early childhood and this then lead to the progression to compensatory education programmes. Many psychologists then designed intelligence testing (psychometrics) in order to further investigate intelligence and to see whether it is due to Nature or Nurture. Sir Francis Galton, Alfred Binet and Charles Spearman are the main contributors to this debate.

Sir Francis Galton (1822-1911), gained a reputation as the founder of individual psychology and as the originator of the mentalist movement. Through an expedition, led by Galton in 1850, to explore South West Africa, he became an enthusiastic observer and collector of natural facts. Galton's belief on the Nature Nurture topic was that the potential for high intelligence was inherited but it must be nurtured by a proper environment. Galton carried out a lot of work on intelligence and personality with the usage of questionnaires which emphasised his part in the contribution of the idea of intelligence. Galton explored the hereditary origins of success in humans and he began collecting data in 1869 for his first important book 'Hereditary Geniuses'. His thesis concluded that genius or talent is generally, rather than environmentally, determined.

Galton carried out experiments on subjects who were chosen as talented if they were publically reputable. According to Galton, 1 in 4000 had this title. Galton noticed that there seemed to be an increase in ability up to culmination in the most eminent member and a general decrease in those who follow. Galton was first before Mendel to discover the law where two parents contribute to half of an individual's total heredity and grandparents a quarter. This led him to introducing the idea of eugenics and he proposed that the general intelligence of the public could be improved if only the intelligent people mated (see An Introduction to the History of Psychology, 2001 p267). In 1884, Galton set up anthropometric laboratory to make a systematic study of human traits such as height and weight. A large scale of human were measured in every way possible and from this Galton was able to create the belief that sensory acuity is related to intelligence. From observations, Galton also made the conclusion of 'regression towards the mean'. This was through the results which he found when correlating children's heights with parents. Galton found regression amongst all inherited characteristics which diverges from earlier view that eminent people have eminent offspring, and this relationship was strengthened by visually displaying the data (see A History of psychology 2004 p448). Although he carried out various different experiments and discovered a range of information, he was not successful in devising tests for general ability, but did launch the idea of the test for intelligence.

Galton did however influence a French medical doctor, Alfred Binet greatly. Binet studied a wide range of experimental psychology and developed more effective and durable means of measuring intelligence. His early work was mainly concerned with hypothesis. He also studied high levels of cognitive skills such as chess and was asked to come up with a way to diagnose subnormal children, especially those on the borderline of normal functioning. He developed a practical test based on assembling scales of intellectual tasks that could be performed by normal children at specific ages. The tests Binet created enabled someone to measure the mental age of a child and then set as a ratio to the child's actual age (A history of psychology 2004 p448). From these tests it was then possible to compare performance of a subnormal child to performances of other children the same age (government commissioned work). The subnormal children would be the ones that could not solve problems others children their age could. Having detected these subnormal children, they were removed from class and given special education. These practical tests were useful than Galton's theoretically driven tests. Binet's test could determine