2. PSYCHOMETRIC THEORIES OF INTELLIGENCE.
Psychometric theories of intelligence entail the study of individual differences in performance on tests, which are observable and manifest and that are designed to measure intelligence, which is a latent and not directly observable trait. Consequently, the nature of intelligence (latent) is derived from the performance on tests (observable). These results are used to support or adapt theories about the structure or nature of intelligence (Tutorial Letter 101, PSY4988, 2011). There are various theories regarding the nature of intelligence and in this writing the prominent ones will be discussed. .
2.1 Early Theorists.
2.1.1 The Galton-Cattell Approach.
The first person to give the concept of intelligence scientific attention was Galton, who postulated that humans have a ˜general mental ability' that can be measured. His theory suggest that since all information reaches us through our senses (sight, touch, hearing), intelligence is hence the sum of all the simple sensory functions. Also, the more perceptive your senses are to differences, the larger the field on which your judgement and intellect can act, and subsequently the more intelligent you are. He worked closely with an American psychologist who studied in Germany and jointly they devised a variety of mental tests to measure sensory and motor abilities, such as reaction time, memory and the differentiation of size and colour. .
This approach was abandoned in the late 19th century due to testing difficulties, because no high correlations between these mental tests could be established and no correlation between accepted indicators of intelligence, such as common sense and teacher ratings. Further, the approach was costly and required a variety of specialised laboratory equipment to administer the tests repeatedly in order to establish reliability, this made it impractical (Walsh & Betz, 1995).