Intelligence and the "personal equation"

Over two centuries ago astronomers, studying star transit time, noted indiv idual differences in reaction times. This observation came to be known as t he "personal equation." Despite early efforts to establish a connection bet ween RT and general intelligence, it is only fairly recently that speed of information processing has again become a major focus as a critical element of intelligence. Much of the systematic work on this association has been conducted by Jensen. In addition to firmly establishing the relationship be tween RT and intelligence, Jensen has explored the role of intraindividual variability. Several generalizations can now be made: 1) average RT and sta ndard deviation of RT are correlated, but each has a unique connection with intelligence; 2) RT and standard deviation of RT reflect the operation of different processes; 3) the more complex the RT task, the greater the influ ence of intraindividual variability, 4) the contribution of intraindividual variability increases as IQ decreases; and 5) there are strong neurologica l and genetic influences on intraindividual variability. Jensen proposed a "neural oscillation" model to explain various features of intraindividual v ariability. His theory blends facts uncovered through behavioral research o n RT with neurological events.