Jiyeon Ryu, Tingling Lai, Susan Colaric
Joanne Cawley, Habibe Aldag
Educational Psychology 523

February 29, 2000

The role of imagery in human cognitive processing has sometimes been ignored in favor of an emphasis on verbal processing. But in experiments conducted during the last three decades, Allan Paivio has carefully developed an empirical research agenda that has led to a theory that places equal importance on both verbal and non-verbal processing. The Dual Coding Theory assumes there are two cognitive subsystems, one specialized for the representation and processing of nonverbal objects and the other specialized for dealing with language. The theory has been applied to many cognitive phenomena including mnemonics, problem-solving, concept learning, and language. This paper will explore the development of the theory, explain the major components of the theory with a specific focus on its use in problem solving, discuss neuropsychological evidence, present criticisms of the theory, examine the applications of the theory and end with a brief discussion of research needed in the future.

Development of the Theory

Paivio began his graduate studies at McGill University in 1954 working with Dr. Wallace Lambert in the area of bilingual processing. As graduate students often do, Paivio borrowed from his advisor's research interests to conduct an experiment as part of his coursework. In this initial study Lambert and Paivio (1956) examined the difference between the adjective-noun order and the noun-adjective order as indicators for recall. The basis for this study was a disagreement with the associative habit view of language behavior that stated that the sequences of nouns and modifying adjectives would be learned more easily when the adjectives are listed ahead of the nouns rather than after them. They believed the noun-adjective pairing would be more effective as demonstrated in image mnemonics techniques being used as a memory aid in public speaking. This was in fact true, leading to the development of the conceptual peg hypothesis of image-noun associative memory – the idea that nouns, since they are more concrete then adjectives, serve as memory "pegs" for associated items in memory.

This study laid the basis for Paivio's research agenda in the 1960s; "the initial purpose of my research program in the early 1960s was to identify the effective variables, concentrating first on the attributes of the words that served as conceptual pegs and next on the thought processes they arouse, which together might explain why they help us to remember new information" (Paivio, 1991a). A study conducted in 1963 (Paivio, 1963) confirmed noun-adjective pairs were learned more easily in the noun-adjective order than the reverse and that recall increased when the nouns were concrete rather than abstract. This was explored further in his 1965 study in which he found learning benefited more from noun concreteness when the concrete nouns served as stimuli rather than responses for their associated adjectives. It was at this time that he hypothesized that the imagery of the noun was the salient variable in mediating recall; "concrete nouns are superior to abstract nouns in their capacity to elicit sensory images, and that imagery can mediate the formation of an associative connection between members of a pair (p. 37)". Paivio and Yarmey (1966) sought to verify this hypothesis through the collection of data on participants' use of imagery, verbal and other strategies during the learning of the paired words. They found that self-reported imagery use was related to higher recall.

The next step in the research agenda was to eliminate other attributes which had the potential to be relevant in aiding recall (Paivio, 1968). Such other factors were identified as measures of imagery and concreteness, familiarity, distinctiveness, interest value, verbal associative meaningfulness and associative reaction time. Subjects were asked to scale 96 nouns on 30 variables and a factor analysis was performed to examine word attributes and verbal learning. Memory scores were correlated with different attributes of the nouns. Measures of concreteness and imagery (which were highly correlated with each other) were the strongest correlates of noun recall, especially with pair associates when the word attributes were varied on the stimulus side of pairs. Rated ease of imagery was "the best single predictor of recall scores for words, especially when the words served as stimulus members in paired associated learning" (Paivio, 1991b).

In a further effort to distinguish between imagery and verbal processes, Paivio and Yuille (1969) designed a series of studies to test the effects of imagery instructions, item attributes, and reported learning strategies. They concluded, "The common effective process was indeed imagery, which was generated to word pairs during learning, and reactivated by a concrete stimulus word during recall so that the response word could be retrieved from the image." (Paivio, 1991a, p. 5).

The results from this series of studies confirmed the conceptual peg hypothesis of paired associate memory tasks, generalized the hypothesis to other memory tasks and lead to the development of the Dual Coding Theory in which images and verbal representations exist in two separate systems that complement and supplement each other in developing memory.

Theory and Assumptions

Dual Coding Theory represents a set of assumptions, hypotheses and the implications about the origins and structural and functional properties of representational systems. It is based on the general view that cognition consists of representational systems called verbal and nonverbal systems. These are specialized for dealing with environmental information in such a way as to serve functional and adaptive behavioral goals.
 
 

Theoretical assumptions

Although the theory does not deny the human brain as a product of a biological evolution with species-specific functional properties, the main focus of the theory is based on specific experiences. The functionality of useful content of language and imagery can vary enormously, depending on specific experiences of each individual.

The representational systems constitute a person's perceptual, affective, and behavioral knowledge; in other words, internal/mental representations have their developmental origin in perceptual, motor and effective experience.

According to Paivio, "Human cognition is unique in that it has become specialized for dealing simultaneously with language and with nonverbal objects and events. Moreover, the language is peculiar in that it deals directly with linguistic input and output (in the form of speech and writing) while at the same time serving a symbolic function with respect to nonverbal objects, events and behaviors. Any representational theory must represent this dual functionality" (1986, p. 53).

Paivio refers to the nonverbal (symbolic) subsystem as the imagery system because its critical functions include the analysis of scenes and the generation of mental images (both functions encompassing other sensory modalities such as environmental sounds, feel of object in addition to visual). The verbal system deals with language specialized representations which includes auditory, visual words, end writing patterns of these words.

Symbolic and sensorimotor systems

Symbolic representations retain the properties of different sensory and response modalities. The verbal-nonverbal symbolic distinction is assumed to be orthogonal to the sensory modalities. For example, if the object is a word in auditory form or in a visual form, then it will be represented in verbal system. However, if it is in auditory but not related to language; then it will be represented in nonverbal/imagery representations.

The Representation-Processing (or Structure-Function) Distinction

The structural representations refer to relatively stable long-term information corresponding to perceptually identifiable objects and activities, both verbal and nonverbal. Processing refers to functional activities that include activation of either by appropriate stimuli (encoding), activation of one by the other (recoding), organization and the elaboration within each, as well as transformation, manipulation, and retrieval of information from either class.

Conceptual Structure of the Theory

Dual Coding Theory has a hierarchical conceptual structure. At the most general level, the theory is about symbolic systems, that is, cognitive systems that serve a symbolic or representational function. The general level divides into verbal, nonverbal symbolic subsystems, which in turn expand into sensorimotor (visual, auditory, haptic) subsystems at the next level. The lowest level consists of the hypothetical representational units of each system, called logogens and imagens.

Unit-Level Assumptions

The units of the representational systems, imagens and logogens, can be imagined as being similar to "chunks". They are unitary in the sense but can function as integrated informational structures. The main assumptions related to unitary structures are:

1. The representational units in each system are modality specific perceptual-motor analogues.
2. Units are hierarchically organized structures, vary in size.
3. Nonverbal units, imagens, is synchronously organized (permitting parallel/simultaneous processing up to some informational limit), for example a face, part of the face or a human body. Whereas, verbal components are sequentially organized from small to larger units, for example, from syllabus, words, poems, to stories (implying sequential constraints on intraunit processing).

The two systems are assumed to be structurally and functionally distinct. Structurally, they differ in the nature of representational units and the units organized into higher order structures. Functionally, they are independent in the sense that either system can be active without the other or both can be active in parallel. At the same time, they are functionally interconnected so that activity in one system can initiate activity in the other. The structural and functional distinctions combine to produce qualitative differences in the kinds of processing.

The main assumptions related to system level are:

1. The functional independence but interconnectedness of the two systems,
2. The probabilistic nature of interunit relations between and within systems
3. Processing mechanism and different levels of processing of (representational, referential, and associative) within and between system
4. Differential specialization for synchronous and sequential interunit processing within systems
5. Processing operations: The functional properties of the representational systems make it possible for representational information to be used in cognitive tasks and the guidance of behavior.

The operative cognitive mechanisms are assumed to be at the unit level. There is no top-down activating mechanism except in the sense that specific input may activate complex representational structures from which component information can be retrieved, or activate units that have a general control function on subsequent processing, e. g. the instruction to image words will activate the nonverbal system. Properties of processing are:

a) Activation of representations: The overall probability of the activation and use of verbal and nonverbal representations is a function of the combined effect of stimulus situation and relevant individual difference variables. The stimulus variables include attributes of target stimuli (such as items to be remembered, comprehended), and contextual stimuli (such as instructions to arouse a set of task) in a given task.

b) Different levels of processing within and between systems: Three types of processing are identified: (1) representational, the direct activation of verbal or nonverbal representations, (2) referential, the activation of the verbal system by the normal system or vice-versa, and (3) associative processing, the activation of representations within the same verbal or nonverbal systems. A given task may require any or all level of processing.

c) Organizational and transformational processing: Differential specialization for synchronous (nonverbal) and sequential (verbal) interunit processing within systems.

d) Automatic and conscious level processing in both systems: Researches on imageless thought and vividness of mental imagery supports the general hypothesis that nonverbal symbolic systems can function at the unconscious level as well as conscious level.

Basic Functional Categories Served by the Symbolic Systems

The functions and categories of symbolic systems implicates how all the structural and functional properties of symbolic systems are utilized in the case of complex task such as problem solving or remembering a set of properties. Two main functions are mnemonic and evaluative.

Dual Coding Theory suggests that the memory trace is a modality-specific encoded representation of verbal and nonverbal input information. Some portion of the total encoded perceptual-motor reaction pattern constitutes the episodic memory trace.

Representational encoding is automatic and sufficient for come level of accuracy in recognition and recall test of memory (Pavio, 1986). Given appropriate contextual cues and the instructions to image, referential encoding may occur with high probability. The associative encoding occurs in the same representational unit such as sentences to verbal items or imaginal context to pictures.

Retrieval context as a production of the recoding activity is never identical to the input context. The encoding-recoding differences are sharper and more explicit in associative recall task. This implies that recoding is subject to the same influences as memory for the target episode itself.

The independent functional structure of imaginal and verbal codes can have an additive affects on recall. However, imaginal and verbal codes are unequal in mnemonic value perhaps by a 2:1 ratio favoring image code (Pavio, 1986). The sequential structure of verbal representation makes it more difficult to generate a functionally integrated verbal trace in a single trial which may account for this unequal mnemonic value.

The term evaluation refers to the determination of quantitative values of object and events: a) Scanning mental images to determine the relative distances between locations on imaged maps, b) counting the corners of an imagined blocked letter, c) reading out the information in an imagined matrix, and symbolic comparisons on any perceptual dimensions such as size, color are the examples from the research studies which represents evaluative functions. These tasks utilize both symbolic systems most of the time. Verbal cues can initiate and guide evaluative processing. The evaluative functional processes are largely under conscious control of verbal mechanism.

The following section explains how the Dual Coding accounts for problem solving.

Problem Solving

Paivio (1986) relates Dual Coding Theory to the area of problem solving; "performance is mediated by the joint activity of verbal and nonverbal systems, with the relative contribution of each system depending on characteristics of the task and cognitive abilities and habits of the performer. The more concrete and nonverbal the task, the greater the contribution of the imagery system; the more abstract and verbal the task, the greater the contribution of the verbal system" (p. 201). In the same publication he noted that there are differences in imaginal and verbal contributions to problem solving. The imagery system is synchronously organized, meaning that portions of images are retrieved in no particular order because an image is perceptually available in its entirety (Paivio, 1991a). Therefore, retrieved information is simultaneously available, and there is flexibility in processing content. Paivio (1986) suggests that creative thinking may result from these imaginal attributes. On the other hand, information from the verbal system is sequentially retrieved. This suggests that the verbal system contributes logical order to problem solving.

The interplay between the imagery and verbal systems is illustrated Paivio’s explanation of creativity. Paivio (1971) notes that creative discoveries have often originated with the use of concrete imagery. For example, Kekulé’s invention of the benzene ring (an organic chemistry devise) emerged from his visualization of a long row of atoms as a row of snakes, one of which gripped its own tail. The later development of such theories likely relies on the more logical verbal system.

Paivio’s theory of problem solving (1986) is illustrated through several tasks: cognitive maps, syllogistic reasoning, and mental practice effects on motor skills.

Cognitive Maps

Cognitive map tasks involve spatial problem solving (Paivio, 1986). The cognitive map research started with Tolman, who hypothesized that rats used a cognitive map to navigate through mazes. This finding, and other research, suggests that the use of cognitive maps involves synchronous mental representations. The principle of equiavailability states that when individuals learn a route map through sequential processing, they access that information as a picture-like map in which locations and routes are simultaneously available. Mapping may also facilitate basic recall. For example, Amlund, Gaffney and Kulhavy (1985) found that when fifth and sixth graders study a mimetic map (map features are drawings, not just labels) while listening to a story related to the map content, they recall the text better than students who do not use such maps. This study also supports Dual Coding Theory’s contention that the interaction of spatial and verbal information facilitates learning by increasing the number of relevant cues.

Syllogistic Reasoning

Syllogistic reasoning also illustrates problem solving from a Dual Coding Theory perspective (Paivio, 1986). An example of a syllogistic reasoning task is the following: "Bob is older than Jim. Kevin is younger than Jim. Who is older?" Such tasks require deductive reasoning or forming a conclusion from given information. Johnson-Laird (1972) suggests that learners may alter strategies as they become more experienced with these tasks. For example, learners may initially use an imagery strategy then switch to a linguistic strategy. Also, individuals may use a linguistic or an imagery strategy to solve this depending on their preferred strategy to use to solve these problems.

Mental Practice Effects on Motor Skills

Research has show that mental practice affects motor skills. In a meta-analysis, Feltx and Landers (1983) found that mental practice influences performance more than no practice at all. In a specific context, Doheny (1993) found that nursing students who used a guided imagery strategy performed better at giving an intramuscular injection than students who did not use such a strategy. Paivio (1986) explains such findings in light of motivational and cognitive functions of imaginal and verbal processes. Motivational effects includes physiological arousal, positive affect and goal directedness. These motivational effects result in less tension, less negative verbalization and images of failure, and more images of success. Mental practice cognitively influences general behavioral strategies and specific motor responses. Successful use of mental practice hinges on accurate and precise images of successful performance (based on either previous experience or observation) and how well the learner remembers this information during performance.

Representational and Referential Processing in Problem Solving

Mayer’s work also provides evidence for the problem solving implications of Dual Coding Theory, in addition to support for the theory in general. Mayer and Anderson (1991) note that the presentation of both verbal and visual information promotes creative problem solving more than if verbal and visual information is given separately. Using a two experiment approach, Mayer and Anderson (1991) found that students who are given a verbal description at the same time as animation significantly outperform other students (animation without words, words without animation, and no training) on a measure of creative problem solving. However, students did not differ on recall of verbal information. Mayer and Sims (1994) found similar results in a study using scientific content. Mayer and Anderson explain such findings in light of Dual Coding’s principles of referential and representational connections. Students in the verbal and animation condition have more opportunities to build referential connections than the other students since they are concurrently presented with verbal and visual information. Referential connections facilitate problem solving. On the other hand, learners do not differ in the extent of representational connections because all students had an opportunity to form such connections.

Neuropsychological Evidence for Dual Coding Theory

Paivio’s early research, discussed earlier, is confirmed by a large number of recent studies that examine the independence hypothesis (Thompson & Paivio, 1994), referential processing (Paivio, Clark, Digdon, & Bons, 1989), and recall and problem solving (Mayer & Sims, 1994). Furthermore, there is neuropsychological evidence for Dual Coding Theory.

Dual Coding Theory is supported by neuropsychological evidence on the functions of the hemispheres of the brain. EEG studies (Ley, 1983) support the contention that the left hemisphere is primarily in control of verbal processing, while the right and left hemispheres both contribute to performance in nonverbal tasks. Paivio (1986) claims that such studies support the independence assumption of Dual Coding Theory.

The neuropsychological evidence also supports representational and referential processing. In Paivio and Ernest’s 1971 experiment, images were presented via tachistoscope to either the left or right visual fields. The researchers found that field had no effect on a recognition task. Their study suggests that both hemispheres have the representations and processing skills for generating images.

Referential processing evidence comes mainly from brain damage research (Paivio, 1991). People with damage to the left hemisphere have difficulty naming objects but do not have any problems recognizing objects. This suggests that referential processing has been impaired but verbal representational and associative processes are unharmed.

The sequential and synchronous processing distinction is also addressed in neuropsychological research (Paivio, 1986). The evidence implies that the anterior regions of the left hemisphere are dominant in tasks that call for sequential processing, such as speech. This evidence is consistent with Dual Coding Theory’s assumption that verbal processing is sequential. In contrast, synchronous processing seems to generate mostly from the posterior regions of both hemispheres. Individuals with posterior brain damage have difficulty with spatial organization, suggesting that the posterior region of the brain is associated with imaginal processing.

Criticism of Dual Coding Theory

Discussion and criticism of Dual Coding Theory has been addressed by Paivio as well as other researchers in the field. In 1982, Paivio reviewed the studies related to the Dual Coding Theory, and identified sixty positive findings that supported it. At the same time, he also categorized negative evidence into three types: pseudo-negative findings, failure to find significant differences, and differences that were inconsistent with Dual Coding Theory. Pseudo-negative findings were those that were based on misinterpreatations of the data, such as misunderstanding that Dual Coding Theory claims picture naming is automatic, but Paivio said that he has never claimed automaticity of picture naming (Paivio, 1982). Such studies would have shown consistency with Dual Coding Theory if they had been interpreted correctly. Failure to find significant differences were those such as the Marschark and Paivio’s (1977) study regarding cue recall of concrete and abstract sentences. The third type, such as asymmetrical transfer pattern between pictures and words (Paivio and Marschark, 1980), is what Paivio declared were inconsistent with the theoretical assumptions of Dual Coding Theory.

Based on the negative evidence that Paivio listed above, this section intends to update the current status of Dual Coding Theory, and furthermore, to present some criticism that was found in the literature.

Concrete and abstract verbal material fail to differ in tasks where difference was expected

Paivio and his colleagues (e.g., Marschark and Paivio, 1977) have repeatedly failed to interpret integration of processing of memory for concrete and abstract sentences, although overall memory scores were always better for the concrete sentences than abstract sentences. The superiority of concreteness is a common finding completely in accord with the Dual Coding Theory, but the equivalent integration of what is remembered from concrete and abstract sentences seems to require an additional coding system. Although their recent experiments (Paivio, Walsh & Bons, 1994) reported that paired concreteness and relatedness have independent and additive effects on free recall and cued recall and further supporting the integration of memory, the results still could not rule out the possible interaction on these variables. However, for Paivio, it was not necessary to modify Dual Coding Theory, even though he agreed that he should "continue to seek interpretations consistent the basic assumption of Dual Coding Theory." (Paivio, 1982, p. 325)

Picture–word studies that are inconsistent with Dual Coding Theory

The results of following studies showed inconsistency with Dual Coding Theory. These results were, at the same time, inconsistent with common coding models.

The first study found faster symbolic comparisons with pictures than with words and with concrete than with abstract words, even in the case of such abstract attributes as pleasances, monetary value and animal ferocity (Paivio, 1982). Paivio argued that the attributes represented things and were stored in the imagery system or at least in close association with the core representations of such things, although abstract concepts that are less consistently correlated with specific perceptual attribute than is the case for more concrete concepts. Further, it might be patterned after the prototypical shape or form of the perceptual object. Other associated attributes, such as pleasantness, might involve stored proprioceptive or interocepective information that can vary in a continuous fashion and constitute the representational base for comparisons.

The second study regards picture word transfer effects in the comparison task. Paivio & Marschark (1980) obtained asymmetrical transfer effects with animal intelligence and pleasantness comparisons when subjects first completed a block of trials with one kind of material and then switched to comparisons of the same concept pairs with the other type of material. Switching from pictures to words appeared to have a negative effect whereas switching from words to pictures had a positive effect on subsequent reaction time. This result is inconsistent with the Dual Coding Theory.

Another critical result occurred in Linde’s study (1982) regarding the effect of picture–word manipulations in judgments of associative relatedness of pairs of items. The original Dual Coding position was that associative relations between concrete concepts are represented in both verbal and image system. This implies that associative decisions could be equally fast for picture pairs and word pairs, which is consistent with the assumption. However, Linde found that the decisions were just as fast with mixed picture-word pairs, which presumably would require the additional step of recoding one concept into the format of the other if associative relations are only represented within but not across systems.

Thinking about the storage capacity

Pylyshyn (1973) argued that visual imagery stored in picture form would exceed the storage capacity of the brain and also would require a perceiver in the brain to read the pictures. However, the visual encoding theorists maintain that the stored codes are not pictures but rather are analog representations or analog memories; that is the images are structurally related to the real objects in the same sense that keys and locks are related. Physically, keys and locks are quite different. However, only the matched key will open a particular lock. Similarly, only particular objects will activate the neural processes with which the object is represented. Then, the problem will shifted to whether analog representations are the same as those of verbal information or not. And if they are different from those of semantic memory, the size of these analog data should be determined into reasonable way.

Imagen (non verbal encoding system) encoding channel

Zimler and Keenan (1983) conducted three experiments compared congenitally blind and sighted adults and children on paired associate, free-recall, and imaging tasks presumed to involve visual imagery in memory, in all three, blind subjects’ performances were remarkably similar to the sighted. Hunt and Ellis (1999) mentioned some similar study reporting that blind subjects performed exactly as sighted subjects did on the memory test. Instructions to imagine objects as spatially contiguous produced better memory than did imagining objects as spatially separated for both blind and sighted subjects. These results suggest that imagery effects upon memory do not depend upon prior visual experience, nor does the remembered image seem to be the same thing as a visual perception. And it does not explain whether the "imagery storage" for blinds and sights are the same.

Conceptual critique: Do we need a Dual Coding Theory?

There are various models that describe human cognitive functions. Some researchers (e.g. Pylyshyn, 1973) proposed that the verbal mediation alternative to imagery was replaced by a computational analogue in which the language of mind become the logical proposition. The approach encompassed language as well, so that at the deep representational level, all perceptual and behavioral knowledge was reduced conceptually to a common form. The alternative was widely adopted in cognitive theories and explicitly contrasts with Dual Coding Theory (Paivio, 1991a). As Kieras states, "There is no fundamental difference in how perceptually based and verbal based information is represented in memory." (Kieras, 1978, pp. 533-534)

In addition to common code theories and Dual Coding Theory, there are still some other researchers who argue that more information should be encoded independently. For instance, a triple coding system may exist that includes imagery, language, and a prepositional interface. Another prospective is the new computational theories, connectionism. It seems to be prominent now in cognitive science and cognitive psychology.

The growth of Dual Coding Theory has reshaped the theory and has created more solid assumptions and reasonable interpretations to human cognitive functions. Although there are still many unresolved problems (e.g., the critiques we mentioned above), Paivio and his colleagues work continually to build a more powerful theoretical model. And along with their work done so far, the Dual Coding Theory has been applied to a variety of fields. The following will be some examples of the applications.

Application of the Theory

According to Dual Coding Theory we have more than one information process system, which implies that it will be better if more than one communication channel is used during learning. In particular, an increasing body of research evidence supports the contention that student learning is affected positively by presenting text and illustrations together (Bernard, 1990; Glenberg & Langston, 1992; Guri-Rozenblit, 1988; Mayer and Sims, 1994; Purnell & Solman, 1991; Reed & Beveridge, 1986; 1990; Waddill, McDaniel, & Einstein, 1988). Furthermore, computer-generated animation offers a potentially powerful medium for presenting visually based information to learners (Rieber, 1990b, 1991; White, 1984)

Fostering Imagery

In addition to the presentation of illustration with words, mental images can be intentionally and systematically induced to aid in recall. Pressley (1977) found that subjects (age seven and up) perform as well or better when given instructions to generate images as they do with pictorial representations of the interactive images; that is, self-generated images are sometimes more effective than experimenter-imposed images.

Mnemonic Techniques in Primary and Secondary Language Learning

Imagery also can be used as mnemonic techniques in second or foreign language learning (Paivio, 1980). Vocabulary learning had previously been shown to increase using a rhyming mnemonic scheme that consists of a series of ten or twenty peg words that rhyme with numerals which are then used as stimuli for the recall of new words by imagining the referents of the words in interaction with the rhyming pegs (Paivio, 1971). The same technique was applied to foreign language acquisition. Atkinson and his students (Atkinson, 1975; Atkinson and Raugh, 1975) developed an experimental version called "the keyword technique". The process involves establishing an acoustic and an imagery connection between an unfamiliar foreign word and its native language equivalent. The acoustic link reminds the learner of the relevant word whereas the imagery link provides a clue to the meaning of the word. The links are provided by a native-language word that sounds like the foreign word or part of it. Atkinson and his colleagues (1975) found that the keyword technique was more effective than standard translation practice and other non-imagery control conditions when used by American Anglophone students to learn Russian and Spanish vocabularies.

Text Comprehension

With respect to the meaning of larger verbal units, such as sentences and paragraphs, experimental research has also demonstrated a major role for imagery processes. Educational research has confirmed the importance of imagery and concreteness for the comprehension of sentences and larger textual units (Clark and Paivio, 1991). Image generation and supplementary pictures generally benefit text comprehension (Denis, 1984) and readability including speed (Glenberg et al., 1987, Flesch, 1950). Moreover, the same imagery manipulations that benefit memory for text should also benefit memory for orally presented information as in classroom lessons. Levin and Berry (1980), for example, asked fourth graders to recall information from tape-recorded newspaper stories. Children who listened to the stories while viewing relevant pictures recalled more than children who only heard the stories.

Mnemonic Techniques on Study Skills

Another kind of evidence for the important mnemonic role of imagery in educational learning comes from research on study skills. Clark and Paivio (1991) found a number of behaviors associated with quality study skills to be linked to imagery processes as did Kulhavy and Kardash (1988). Imagery processes are further emphasized in books and programs designed to improve learning and study skills. An early text by McMurry (1909) included a chapter on supplementing thought, which recommended the use of such imagery-related methods as imagination, elaboration, making illustrations, experiencing the material, and listing details. Contemporary study guides (e.g., Robinson, 1970) and study skills programs stress similar processes. Dansereau et al. (1979), for example, included imagery and network construction methods in their program. The network or cognitive mapping methods use spatial imagery to represent verbal associative structures. Imaginal elaboration is also a central component in the cognitive learning strategies program of Weinstein and her colleagues (1979) and in Wittrock’s model of generative learning (Wittrock and Alesandrini, 1990).

Dual Coding Theory as a Framework for Assessment

Besides providing a theory to promote more effective learning, Dual Coding Theory provides a useful framework for thinking about cognitive tests (Clark and Paivio, 1991). A large part of educational assessment involves tests of intelligence, achievement, and related cognitive processes; the distinct verbal and nonverbal cognitive systems of Dual Coding Theory corresponds to analogous distinctions in most test and theories of intelligence.These tests usually include subscales that measure nonverbal abilities, and factor analyses of general test batteries identify a perceptual-spatial ability factor that is distinct from verbal abilities (Anastasi, 1988). Nonverbal or imaginal processes contribute to the Performance scales of Weschler’s test (Weschler, 1974) and of Jackson’s (1984) Multidimensional Aptitude Battery, and to the simultaneous processing dimension (Das et al., 1975; Paivio, 1975) that underlies the Kaufman Assessment Battery for Children (Kaufman and Kaufman, 1983).

A second illustration of how Dual Coding Theory can model specific assessment tasks is provided by picture vocabulary tests, which are used widely to assess child language abilities and dysfunctions in early grades, in special education and clinical settings, and in many research studies (Denckla et al., 1981; Snowling et al., 1988; van der Wissel, 1988). Performance on production tests that require active naming, such as the Expressive One Word Picture Vocabulary Test (Gardner, 1979), varies with factors that are associated with a Dual Coding Theory model of picture naming. For example, pictures with a single label (e.g., apple, scissors) are easier to name than pictures with multiple labels (e.g., cat, purse). This effect of response uncertainty (i.e., number of different names) has been observed on the probability of errors (Johnson and Clark, 1988) and on reaction times in experimental research on naming (e.g., Lachman, 1973; Paivio et al., 1989).

Dual Coding Theory also provides analytical models for nonverbal tests and for educational correlates of imagery ability (Clark and Paivio, 1991). Nonverbal tasks involve the special properties of the imaginal system descried earlier, such as the capacity to integrate and redintegrate information. One property that has been particularly important in the individual difference domain is the capacity of images for spatial transformations. Many spatial tests, such as mental rotation tasks, involve dynamic transformations of spatial stimuli. Understanding how imaginal transformations are performed could therefore shed light on some controversial issues associated with individual differences in imagery ability and mathematics education, including controversial relations between gender, mathematics, and imagery ability (Clark and Paivio, 1991)

Future Direction

In this paper, the positive contributions of Dual Coding Theory as a general perspective on educational and psychological phenomena has been described, but many of the topics involve controversial empirical and theoretical issues that remain unresolved (Clark, and Paivio, 1991). For example, concrete sentences do not always demonstrate more integration than abstract sentences on memory tasks, and use of concrete examples in lectures does not always correlate with learning. Consideration of item attributes, individual differences, and instructions, and the joint contribution of imagery and verbal processes to psychological phenomena, need to be explored further (Clark, and Paivio, 1991).

Sadoski and Paivio (1994) claim more investigations are needed in several areas. First, the investigation of the measurement of imagery’s effect is needed. Traditional multiple-choice tests do not really measure the effect of imagery. Instead, Gambrell (1982) suggests open-ended prediction questions to study the imagery of students. Second, we need to consider and study the effect of individual differences in the spontaneous use of imagery or in employing imagery as a conscious strategy. For example, according to Pressley (1977), readers, particularly good readers, spontaneously and regularly use mental images in reading, and it is therefore difficult to determine to what extent experimental groups benefit from imagery instruction or training. Individual differences in this area can exert a confounding effect in studies, making mental imagery appear less valuable than it may actually be. Paivio (1988) cited the complex nature and predictive uncertainty of individual differences as one major problem facing imagery researchers. Third, a major problem facing researchers is the manner in which imagery serves to integrate information from text and to what extent such integration effects are contributed by the verbal system as well (Paivio, 1988). Verbal associative contexts, such as causal connections, logical sequences, cohesive ties, and strong verbal associations among words and phrases, may serve to integrate abstract texts to a degree as well. A central question is to what extent both imaginal and verbal integration processes operate independently or interactively (Sadoski and Paivio, 1994). Fourth, the role that Dual Coding Theory could play in explaining students’ response is another fruitful area for research. Few theories of reader response have linked themselves to established theories of psychology. Fifth, the application of Dual Coding Theory to text design needs to be studied. School textbooks are commonly criticized as being inadequate to promote learning or subject appreciation. The design needs to induce more comprehension, retention, and appreciation and Dual Coding Theory may play a role. Finally, further research involving the role of imagery in processing metaphor and figurative language and in composing text, and the objective physiological correlates of the occurrence of imagery is needed (Sadoski, 1992; Paivio, 1988).
 
 
 
 

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