Intellectual abilities

Intelligence is a crucial psychologic construct for understanding human behavioral differences. This construct is based on one of the most replicated findings in psychology (the positive manifold): individuals can be reliably ordered according to their cognitive performance. Those showing high levels in ability X are more likely to show high levels in the remaining abilities, while those showing low levels in ability X are more likely to show low levels in the remaining abilities. Intelligence is characterized as a general cognitive ability integrating more than 80 distinguishable but related abilities. The mainstream definition states that intelligence is a general mental ability for reasoning, planning, solving problems, think abstractly, comprehending complex ideas, and learning. Intellectual abilities are measured by standardized tests showing highly reliable and valid indices. Intelligence is a highly stable psychologic trait, but different abilities change following disparate trends across the life span. These average trends, however, (a) hide the wide range of individual differences in the rates of change and (b) are consistent with the fact that abilities show orchestrated changes, which is consistent with the positive manifold. This chapter presents examples of the conventional testing paradigm along with recent developments based on cognitive psychology and cognitive neuroscience.