Intelligence, dual coding theory, and the brain

• First epoch: nonverbal-processing dominance. Beginning in ancient Greece (circa 500 BC) and expanding to 17th C.
• Second epoch: verbal processing dominance that began in the 16th C and lasted through the early days of Behaviorism
• Third epoch: nonverbal and verbal processing solitudes beginning as US army verbal and performance tests and expanding into hundreds of factor analytic
• IQ tests none of which include tests that connect verbal and performance abilities. This is a crucial missing link because it leaves unexplained how thinking and behavior can switch back and forth between processing of language and meaningfully-related nonverbal objects and events and it is also missing from recent brain models of intelligence.
• Bidirectional verbal–nonverbal links, called referential connections and processes, are a defining feature of Dual coding theory (DCT) that uniquely predict and explain behavioral and neuropsychological facts about memory and intelligence that elude the traditional factor analytic theoriew qned test batteries.

The distinction between verbal and nonverbal cognitive abilities has been a defining feature of psychometric theories of intelligence for the past century. Despite their popularity, however, these theories have not included functional connections between verbal and nonverbal systems that are necessary if they are to explain performance in intellectual tasks involving interactions between language and nonverbal knowledge. This functional gap limits the capacity of psychometric theories to explain and predict fundamental aspects of individual differences in cognitive abilities that have long been studied experimentally. This article summarizes the history, nature, and possible causes of the problem, and then concludes with a neuroscientifically-enhanced, multimodal dual coding approach to intelligence that focuses on the synergistic interactivity of verbal and nonverbal systems.