Dual coding theory is a general theory of cognition and mind. It originated in the 1960s to explain the powerful effects that mental imagery has on memory, and it has been extended since to account for increasingly more mental phenomena. Dual coding theory has inspired much research and debate in psychology, and it has played a major role in stimulating a modern resurgence of interest in mental imagery and its role in mind. It has been described as “one of the most influential theories of cognition this century” (Marks, 1997). It has been directly applied to education in several fields. The major volumes that detail the theory, its extensions, and its empirical base are Paivio (1971, 1986, 1991, 2007), Paivio and Begg (1981), and Sadoski and Paivio (2001).
Dual coding theory is sometimes referred to as a theory of mental imagery, particularly visual imagery. However, the theory is more than that. From an historical perspective, it is the first systematic, scientific attempt to bridge two traditions in philosophy and psychology: the imagery tradition and the verbal tradition. The imagery tradition can be traced to the emphasis on concrete experience and thought in Aristotle, the Renaissance educators' slogan of “things not words,” the pragmatism of George Herbert Mead and John Dewey, and aspects of the cognitive revolution in modern psychology. The verbal tradition emphasized the abstract and can be traced to the idealist philosophy of Plato, Peter Ramus's epitome of linear verbal organization, Immanuel Kant's transcendental idealism, and the exclusive emphasis on language in behav-iorist psychology. The historical tension between these traditions is recounted in Yates (1966), Carruthers (1993), Paivio (1971, 2007), and Sadoski and Paivio (2001). The implications of bridging these two traditions are far reaching but remain controversial in the early 2000s.
The core ideas of dual coding theory can be stated succinctly: The theory assumes that cognition involves the activity of two qualitatively different mental codes, a verbal code specialized for dealing with language in all its forms and a nonverbal code specialized for dealing with nonlinguistic objects and events in the form of mental images. These coding systems are separate but interconnected so that they can operate independently, in parallel, or through their interconnections. The linguistic, or verbal, code dominates in some tasks, the nonverbal code dominates in others, and both systems are frequently used together. The great diversity and flexibility of cognition all comes from activity within and between these codes. No deeper, abstract code is assumed.
Dual coding theory is based on the common assumption of a continuity between perception and memory. External experiences occur through the stimulation of people's senses and are encoded in memory traces that retain some of their original, concrete qualities as words and things. The theory is, therefore, multimodal because both verbal and nonverbal experiences can occur in different sense modalities, including vision, hearing, and touch (Braille) in the case of language, and all five senses in the case of mental images. Theories of working memory that propose different, modality-specific memory stores are generally consistent with dual coding theory. For example, the working memory theory of Baddeley and Hitch (1974) proposes a phonological loop for rehearsing inner speech and a visuospatial sketchpad for manipulating visual images. Dual coding theory assumes that long-term memory is modality specific as well.
Dual coding theory also assumes innate contributions to cognition and individual differences because all human nature is the product of the interaction of genes and the environment. More layers of complexity are built on these basic assumptions, including accounts of meaning, memory, knowledge organization, and learning. One direct implication of the theory is that pictures or concrete language (e.g., juicy hamburger) should be understood and recalled better than abstract language (e.g., basic assumption), a consistent research finding.
Perhaps the most productive application of dual coding theory has been to literacy. The theory offers empirically supported accounts of all aspects of literacy, including decoding, comprehension, and response in reading (Sado-ski & Paivio, 1994, 2001, 2004, 2007), written composition (Sadoski & Paivio, 2001), and spelling (Sadoski, Willson, Holcomb, & Boulware-Gooden, 2005). A large-scale instructional program to improve reading comprehension by teaching students to visualize while reading text was successfully applied in urban schools (Sadoski & Willson, 2006). Another application used kinesthetic imagery in teaching reading comprehension strategies such as how to locate the main idea (Block, Paris, & Whiteley, in press). An extensive review of applications to literacy is found in Sadoski and Paivio (2001, Chapter 8). A review of applications to other aspects of education is found in Clark and Paivio (1991).
The use of mental imagery and language in learning psychomotor skills also has been extensively studied. The procedure typically takes the form of guided relaxation followed by mentally imagining physical acts in detail from a verbally presented description. Two meta-analyses of experimental studies found substantial overall effects (Feltz & Landers, 1983; Driskell, Copper, & Moran, 1994). Studies employing heavily cognitive tasks (touching intersections on a grid) had larger effects than more purely motor tasks (tennis shot) or strength tasks (bench press). These techniques have been used to teach medical students to draw blood and perform basic surgery (Sado-ski & Sanders, in press).
The most ambitious extension of dual coding theory is its explanation of the evolution of mind (Paivio, 2007). In this view, hominid intelligence evolved from a primeval nonverbal base into a more recent period that incorporated language. Verbal and nonverbal thought have been synerg-istically bound since. Mental images from memory represented perceptually absent events whether past, present, future, possible, or impossible. In turn, language provided an increasingly sophisticated system of signs for efficient thought and communication between and within our human ancestors. This combination of imagination and language is seen as the evolutionary power source of all human progress (cf. Bronowski, 1978).
Dual coding theory can be contrasted with theories which assume that all cognition has a common, abstract code in the form of schemata or propositions (Sadoski, Paivio, & Goetz, 1991). This mentalese is assumed to be computational in nature, built into the brain like a computer's built-in machine code (Pylyshyn, 2003). Proponents believe that this conception is more elegant and parsimonious than dual coding theory, and some aspects of cognition have been modeled in computers to a degree (Seidenberg, 2005). However, Paivio (2007) responded that such theories lack elegance because of the complexity of their programming, and they cannot account for findings involving mental imagery, concreteness effects, and neuropsychological evidence. These debates remain unresolved and challenging.
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