Individual differences have been mostly ignored in cognitive/experimental psychology since the birth of the field, while the measurement of cognitive abilities has become a successful field of applied psychology. Because of its separation from mainstream research psychology, cognitive ability testing has focused on application, often without providing sound theoretical basis for the tests. More recently, the gap between cognitive/experimental psychology and differential/psychometric research has been closing. This stems from a rediscovery of variation in cognitive abilities in experimental psychology, owing largely to the concept of working memory. We present process overlap theory, a new theory of intelligence that is informed by cognitive psychology. The theory explains the positive correlations between diverse tests on the basis of overlapping cognitive processes and reinterprets the general factor of intelligence, g, as a formative construct. The consequences of this approach are discussed, including a focus on specific abilities rather than on global scores in cognitive test results.

There are many examples of human cognitive performance, from reading difficult texts to performing mathematical operations to solving complex problems. Success in these various activities is correlated: those who are better in one area are usually better in the rest, too. This is the most important finding in the field of human intelligence and it has led to the idea that, despite superficial dissimilarity, these cognitive activities all depend on the same general cognitive ability. However, in cognitive psychology and neuroscience there is ample evidence against this idea and for the fractionation of cognition into distinct faculties. But due to historical reasons the study of cognition mostly ignored individual differences, while the study of human intelligence was mostly uninformed by the general study of cognition and neuroscience. The question of general intelligence versus specific abilities is one of the oldest debates in psychology. In this paper we present process overlap theory (POT), which explains the...