The modality-specific nature of DCT distinguishes it from more abstract,
common coding theories of cognition. Theories that emphasize the dominance of
language arose from religious and educational opposition to imagery during the
Renaissance. Such theories peaked in modern behaviorist interpretations of
thought as inner speech. Another class of common coding theories postulate
abstract mental entities and processes, usually called propositions or schemata.
More complex hybrid theories are essentially augmented forms of dual coding in
which verbal and nonverbal representations are connected to an abstract
conceptual system of some kind. Much research has been directed at testing DCT
against the alternatives.