Intelligence - In Pursuit of Rational Thought and Effective Action

Intelligence: What Is It?

Intelligence is the global ability of the individual to think clearly and to function effectively in the environment. This definition of intelligence is based on the thinking and writing of the clinical psychologist David Wechsler (1896–1981), author of the widely used Wechsler Intelligence Scales. (There will be more about the Wechsler Scales later.)

Intelligence is, to some extent, global. Second, intelligence is associated with the ability to think clearly. Third, intelligence implies the ability to function effectively in the environment

The research psychologist Howard Gardner has suggested that we speak of multiple intelligences in preference to global intelligence. Taking this approach, one kind of intelligence may be more or less independent of another kind of intelligence.

The Stanford-Binet Intelligence Scale: Intelligent Is as Intelligent Does

One of the first people to attempt to measure intelligence in an objective manner was the English scientist Sir Francis Galton (1822–1911). Working somewhat over one hundred years ago, he used the biometric method, meaning he tried to measure intelligence directly by evaluating such physiological measures as strength of grip and perceptual-motor speed. He found that there was little correlation between these measures and intelligence. Discouraged, he discontinued his research in this particular area of human behavior.

Only a few years after Galton abandoned the effort to measure intelligence, Alfred Binet, director of the psychological laboratory at the Sorbonne in Paris, was asked by France’s Minister of Public Instruction to devise a way to detect subnormal intelligence. The aim was to give extra instruction and assistance to children with cognitive problems.

The Wechsler Scales: Comparing Verbal Intelligence and Performance Intelligence

Working for a number of years as the chief psychologist for the Bellevue Psychiatric Hospital in New York City, David Wechsler conducted a substantial amount of research on intelligence. His work culminated in a set of highly regarded intelligence tests called collectively the Wechsler Scales. There are three individual tests, and in revised editions they are still used today. The three tests are: (1) the Wechsler Preschool and Primary Scale of Intelligence (WPPSI), (2) the Wechsler Intelligence Scale for Children (WISC), and (3) the Wechsler Adult Intelligence Scale (WAIS).

The Wechsler Scales recognize that there are different kinds of intelligence. Two in particular are emphasized: verbal intelligence and performance intelligence. Verbal intelligence includes such abilities as word fluency, abstract reasoning, and mathematical ability. Performance intelligence includes such abilities as visualization, the perception of the relationship of parts to a whole, and the capacity to relate well to other people. As a consequence, it is possible to obtain two separate IQ scores, a verbal IQ and a performance IQ. The two IQ scores can be combined for an overall IQ score.

The following description is based on the Wechsler Adult Intelligence Scale. Not only is the Scale divided into two large areas, it is also subdivided into a set of eleven subtests, six under the Verbal Scale and five under the Performance Scale. Keep in mind that the word scale is used because sets of questions proceed from easy to difficult. Evaluation is based on how high the subject can climb on the ladder of psychological difficulty. Here is the breakdown:

1. The Verbal Scale: Each of the following tests consists of a group of questions designed to assess a different area.
2. Information: level of general knowledge.
3. Comprehension: ability to understand questions and grasp concepts.
4. Arithmetic: capacity to grasp and employ mathematical concepts.
5. Similarities: ability to employ abstract thought.
6. Digit Span: tasks designed to measure attention span. Vocabulary: grasp of the meaning of words.
7. The Performance Scale: Each of the following tests is a set of tasks designed to assess a different area.
8. Digit Symbol: mental flexibility and ability to employ arbitrary symbols.
9. Picture Completion: ability to detect the missing parts of an organized whole (i.e., a Gestalt).
10. Block Design: ability to relate a printed pattern to a physical construction.
11. Picture Arrangement: ability to comprehend the “before and after” aspect of time. Also useful in evaluating the subject’s level of social intelligence.
12. Object Assembly: ability to place parts in a correct relationship to a whole.

The Concept of an Intelligence Quotient: Following the Bell-Shaped Curve

As already noted, the concept of mental age (MA) is of limited value because it is unstable. As one’s chronological age (CA) increases, so does one’s mental age. Consequently, a German psychologist named William Stern suggested that a ratio based on the comparison of mental age with chronological age would tend to be relatively stable. Stern proposed the following formula:

Validity and Reliability: Two Big Problems in Any Kind of Testing

Validity and reliability are important aspects of any kind of measurement and testing. Intelligence tests are—like gauges, clocks, and rulers—measuring instruments. Consequently, before they can be used to measure intelligence with any degree of confidence, their validity and reliability must be assessed.

A valid test is one that measures what it is supposed to measure. If an intelligence test really does in fact measure intelligence, then it is valid. But how can one ascertain that the test is valid? Just because the questions in a test seem valid does not mean they actually are. This kind of validity is called face validity, meaning that the questions have a surface appearance of validity.

The Interaction of Heredity and Environment: How They Exert Joint Effects

The topic under discussion in this section is sometimes called the naturenurture controversy, and it has a long history in philosophy, biology, and psychology. Nature refers to heredity; the primary characteristic of nature, or heredity, is the potential to reach a given level of intelligence. Nurture, on the other hand, refers to environment;the primary characteristic of nurture, or environment, is its capacity to bring forth, in the case of intelligence, the maximum cognitive potential that an individual has. Or, conversely, environment has the capacity to inhibit and restrict that potential.