M. Terman (1877–1956) at Stanford University revised and refined the Binet-Simon test to increase its sensitivity at the higher end of the scale. The Stanford-Binet test, published in 1916, was the first test to use IQ scores. An IQ score (or intelligence quotient) is derived from a large sample of test results. Terman set the mean IQ score at 100 and the standard deviation at 10. By translating raw scores into IQ scores, the percentile rank of each score could be calculated. For example, an IQ score of 100 falls in the 50th percentile, of 80 in the 2.5th percentile, and one of 130 in the 99th percentile. The Stanford-Binet was the primary IQ test used for many decades and is currently in its fifth edition. In 1958, two years after Terman died, David Wechsler published the Wechsler Adult Intelligence Test (WAIS), which is now the more widely used IQ test.
What were the problems with the early IQ tests?
The problem with Galton’s approach was an utter lack of relationship between outside indications of intelligence, such as school performance, and the measures used. His tests had more to do with physical coordination and strength than intelligence and as such had no construct validity. Later tests also had problems with validity but these were more subtle. For the most part, they were extremely culturally biased, serving the anti-immigrant bias of the first several decades of the twentieth century. Here the biggest problem was generalizability, meaning the applicability of the test to a larger population. Some items only measured knowledge available to wealthy, English-speaking, and native-born Americans. Other items measured moral values more than strict intellectual skills. Later IQ tests addressed these problems by including non-verbal tests, considering cultural relevance when including items, and basing test norms on samples carefully constructed to match the demographics of the United States.
What does mental age mean?
Alfred Binet (1857–1911), a French psychologist, furthered the work of Galton and Cattell with his concept of mental age. While observing his own children develop new cognitive skills as they grew, Binet recognized that intelligence could be measured developmentally. By comparing the test performance of a child with the age at which such performance was expected, he could calculate a mental age for each child.
THE BRAIN: ANATOMY AND DEVELOPMENT
BASIC CONCEPTS IN NEUROSCIENCE
Why do we study the brain?
As early as 500 B.C.E., Alcmaeon of Croton identified the brain as the physical seat of the mind. Twenty-five hundred years later, modern science has proven this ancient Greek to be absolutely correct. There is no aspect of psychology that is independent of the brain. The very essence of our humanity—our thoughts, our feelings, our beliefs, and our values—all emerge from this three-pound lump of gray tissue. Moreover, with the remarkable advances of neuroscience in the last few decades, we now know more about the brain and its relationship to the mind than at any other time in human history.
What do neuroscientists assume about brain evolution and how does that influence our understanding of the brain?
In order to understand brain research, it is important to consider three basic assumptions that neuroscientists make about brain evolution. For one, the brain is believed to carry traces of its evolutionary origins deep within its tissues. Just as we carry traces of our earliest childhood within our adult personalities, the brain carries the history of our whole species within its very anatomy. Secondly, the brain has evolved up and out, so that the lowest and deepest parts of the brain are the oldest. The outermost, uppermost, and the furthest forward brain regions are the youngest on the evolutionary scale. Thirdly, our brains have increased in complexity across evolution. The older structures tend to be simpler and more primitive, both in their anatomy and in the behavioral functions they control. Likewise, the evolutionarily newer structures tend to be more complex.
What are the costs and benefits of brain complexity?
As brain structures have evolved toward greater complexity, we can ask what benefits complexity may offer. Are there any costs? In general, complexity allows for more flexibility. Complex systems have a broader repertoire of responses with which to adapt to complicated or changing circumstances. However, complexity is expensive. Complex systems take more energy and are more fragile than simpler systems. With more parts involved, it is easier for something to go wrong.
How costly is our brain?
Although our brain only weighs about three pounds (2 to 3 percent of the average person’s body weight), it uses up about 15 percent of the blood that our heart pumps out and about 20 percent of our body’s oxygen and glucose. In other words it uses up to ten times as much of the body’s resources as would be expected for its weight.
What terminology is important in brain anatomy?
Although we will try to stick to plain English in this book, it is useful to know the basic terminology used in the discussion of brain anatomy. As the brain is a three-dimensional structure, specific terms are used to distinguish up from down, back from front, and inside from outside. The terms anterior and posterior are used to refer to front and back, respectively, as are the Latin words rostral and caudal. Superior and inferior refer to top and bottom, respectively, as do the Latin words dorsal and ventral. Lateral refers to outside, while medial refers to the inside.
How do the Latin terms differ from the English ones?
The English terms are purely directional while the Latin ones are defined in reference to the body. Rostral and caudal are the Latin words for head and tail. Likewise, dorsal and ventral refer to the back and belly of a body (as in the dorsal fin of a shark). Medial means close to the body’s midline while lateral means away from it. Nonetheless, when we speak about the brain, rostral and caudal are generally understood to mean front and back, dorsal and ventral to mean top and bottom, and medial and lateral to mean inside and outside.
This illustration shows the lateral view of the brain.
What have we learned from animals?
Our understanding of the human brain is heavily indebted to the study of animal brains. Although the use of animals in biological research raises moral and ethical questions about animal rights, there is no question that much of our knowledge about the human brain derives from research on animal brains. Legally and ethically, we can perform much more invasive procedures on animal brains than we can on living human brains. Additionally, comparison of the brains of many different kinds of animals gives us critical insight into brain evolution.
What does the word phylogeny mean?
The word phylogeny means evolution. To say something is phylogenetically old means that it is old in evolutionary terms.
THE MAJOR STRUCTURES OF THE BRAIN
What are the major structures of the brain?
The brain is an intricate structure that looks like a boxing glove placed over a spiral of sea creatures. The outer layer of the brain is called the cortex, or the neocortex. It is a wrinkled surface that covers the top and sides of the brain. This is the part that looks like a boxing glove, albeit a wrinkled one. Underneath the cortex are the subcortical regions: the cerebellum and brain stem at the very base of the brain, the thalamus and related regions toward the middle of the brain, and the limbic system, which wraps around the thalamus. The basal ganglia are also in the middle