G theory

The title given to this article is incorrect due to technical limitations. The correct title is g theory, with a lowercase, and usually italicized, g.

g theory, which was named by Charles Spearman, stems from the observation that the scores of individuals on a variety of cognitive tests correlate positively. g can be derived from these test scores using the method of principle component analysis as the principle (or general) factor. Each cognitive test score can thus be broken down into general (g) and test-specific parts.

g is generally associated with a common conception of intelligence. g is important in almost every cognitive task studied, including regular daily activities, job performance, and even reaction time.

General cognitive ability, underlying IQ, is limited by the channel capacity of short-term memory. Mental power, that means the capacity C of short-term memory (measured in bits of information) is the product of the individual mental speed Ck of information processing (in bit/s), see below the external link to the paper by Lehrl and Fischer (1990), and the duration time D (in s) of information in short term working memory, that means the duration of memory span. Hence:

                     C (bit) = Ck(bit/s) x D (s)

The heritability of g is approximately 0.5. However, it should not be assumed that all of this heritability is genetic. g has been estimated to be between forty and eighty percent genetic. The heritability of most test performance is primarily a result of g. Race differences in cognitive test scores tend to be based primarily on g.

There are many biological and neurological factors that correlate with g such as brain size, nerve conduction velocity, sex hormones, and the brain's glucose metabolic rate during cognitive activity. g has been observed in mice as well as humans (Matzel et al 2003). The preponderance of the evidence suggests a biological basis for g.

The exact relationship between g and other factors of cognitive ability is a matter of debate. See the Carroll model (http://www.iapsych.com/carolmod.htm).

References

• Matzel LD, Han YR, Grossman H, Karnik MS, Patel D, Scott N, Specht SM, Gandhi CC. Individual differences in the expression of a "general" learning ability in mice. J Neurosci. 2003 Jul 23;23(16):6423-33.

External Links

• The Basic Period of Individual Mental Speed, Underlying IQ (http://www.volkmar-weiss.de/lehrl.html)