One front has been the investigation of types of intellectual performance as related to the regions of the brain from which they originate. A researcher in this area, the American psychologist Jerre Levy, investigated the functioning of the two hemispheres of the brain. Levy and others found that the left hemisphere is superior in analytical functioning, of which the use of language, for instance, is a prime example. The right hemisphere, on the other hand, is superior in many forms of visual and spatial performance and tends to be more synthetic and holistic in its functioning than the left. Such patterns of hemispheric specialization are complex and cannot easily be generalized.
The specialization of the two hemispheres of the brain is exemplified in an early study by Levy and another American psychologist, Roger W. Sperry, who worked with split-brain patients, individuals who have had their corpus callosum severed. Because the corpus callosum, in the normal brain, links the two hemispheres, in these patients the hemispheres function independently of each other. But, as in normal persons, the right side of the body connects with the left hemisphere of the brain, and the left side connects with the right hemisphere.
Levy and Sperry asked split-brain patients to match small wooden blocks held in either their left or their right hand (but not looked at) with corresponding two-dimensional pictures. They found that the left hand did better than the right at this task, but, of more interest, they found that the two hands appeared to use different strategies in solving the problem. Their analysis demonstrated that the right hand found it relatively easier to deal with patterns that are readily described in words but difficult to discriminate visually. In contrast, the left hand found it easier to deal with patterns requiring visual discrimination.
A second front of research has involved the use of brain-wave recordings to study the relation between these waves and either performance on ability tests or in various kinds of cognitive tasks. Researchers in some of these studies found a relationship between certain aspects of electroencephalogram (EEG) waves and scores on a standard psychometric test of intelligence.
A third and relatively new front of research has involved the measurement of blood flow in the brain, which is a fairly direct indicator of functional activity in brain tissue. In such studies the amount and location of blood flow in the brain is monitored while subjects perform cognitive tasks. John Horn, a prominent researcher in this area, found that older adults show decreased blood flow to the brain, that such decreases are greater in some areas of the brain than in others, and that the decreases are particularly notable in those areas responsible for close concentration, spontaneous alertness, and the encoding of new information. These findings highlight the importance not only of understanding intelligence in general but also of understanding it as a faculty that develops over time.
Contents of this article:
Cognitive-contextual theories and biologic theories
Development of intelligence
Post-Piaget theories and the environmental viewpoint
The distribution of IQ scores and the malleability of intelligence