Introduction
Mental imagery doth occupy a position of considerable import within the purview of long-term memory studies (Matlin, 2009). The present disquisition shall address the manner in which information is represented through images, and also the individual variations observed in the faculty of employing such imagery.
Representation of Spatial Information
Mental imagery doth refer to mental representations of visual/spatial knowledge, including the physical properties of the objects or events represented. Visual stimuli that are attended to are held briefly in veridical (true) form in the sensory register, and thence are transferred to working memory (WM). The WM representation doth appear to preserve some of the physical attributes of the stimulus it represents (Gagné, Yekovich, & Yekovich, 1993). Images are analog representations that are similar, albeit not identical, to their referents (Shepard, 1978).
Imagery hath been valued as far back as the time of the ancient Greeks. Plato did opine that thoughts and perceptions are impressed upon the mind as a block of wax, and are remembered as long as the images last (Paivio, 1970). Simonides, a Greek poet, believed that images are associative mediators. He devised the method of loci as a memory aid. In this method, information to be remembered is paired with locations in a familiar setting.
Mental imagery hath also been influential in discoveries. Shepard (1978) described Einstein’s Gedanken experiment, which marked the commencement of the relativistic reformulation of electromagnetic theory. Einstein imagined himself travelling with a beam of light (186,000 miles per second), and what he perceived corresponded neither to light nor to aught described by Maxwell’s equations in classical electromagnetic theory. Einstein reported that he typically thought in terms of images, and only reproduced his thoughts in words and mathematical equations once he conceptualised the situation visually. The German chemist Kekulé supposedly had a dream in which he visualised the structure of benzene, and Watson and Crick apparently used mental rotation to break the genetic code.
In contrast to images, propositions are discrete representations of meaning, not resembling their referents in structure. The expression “New York City” no more resembles the actual city than virtually any three words picked at random from a dictionary. An image of New York City containing skyscrapers, stores, people, and traffic is more similar in structure to its referent. The same contrast is evident for events. Compare the sentence, “The black dog ran across the lawn,” with an image of this scene.
Mental imagery is a controversial topic (Matlin, 2009). A central issue is how closely mental images resemble actual pictures: Do they contain the same details as pictures, or are they fuzzy pictures portraying only highlights? The visual pattern of a stimulus is perceived when its features are linked to a long-term memory (LTM) representation. This implies that images can only be as clear as the LTM representations (Pylyshyn, 1973). To the extent that mental images are the products of people’s perceptions, images are likely to be incomplete representations of stimuli.
Support for the notion that people use imagery to represent spatial knowledge cometh from studies where participants were shown pairs of two-dimensional pictures, each of which portrayed a three-dimensional object (Cooper & Shepard, 1973; Shepard & Cooper, 1983). The task was to determine if the two pictures in each pair portrayed the same object. The solution strategy involved mentally rotating one object in each pair until it matched the other object, or until the individual decided that no amount of rotation would yield an identical object. Reaction times were a direct function of the number of mental rotations needed. Although these and other data suggest that people employ images to represent knowledge, they do not directly address the issue of how closely images correspond to actual objects.
To the extent that students use imagery to represent spatial and visual knowledge, imagery is germane to educational content involving concrete objects. When teaching a unit about different types of rock formations (mountains, plateaus, ridges), an instructor could show pictures of the various formations and ask students to imagine them. In geometry, imagery could be employed when dealing with mental rotations. Pictorial illustrations improve students’ learning from texts (Carney & Levin, 2002; see Application 'Using Imagery in the Classroom' for more examples).
Using Imagery in the Classroom
Imagery can be used to increase student learning. One application involves instructing students on three-dimensional figures (e.g., cubes, spheres, cones) to include calculating their volumes. Verbal descriptors and two-dimensional diagrams are also used, but actual models of the figures greatly enhance teaching effectiveness. Allowing students to hold the shapes fosters their understanding of the concept of volume.
Imagery can be applied in physical education. When students are learning an exercise routine accompanied by music, the teacher can model in turn each portion of the routine initially without music, after which students close their eyes and think about what they saw. The students then perform each part of the routine. Later the teacher can add music to the individual portions.
Imagery can be used in language arts. For a unit involving writing a paragraph that gives directions for performing a task or making something, Kathy Stone asks her third-grade students to think about the individual steps (e.g., of making a peanut butter and jelly sandwich). Once students finish imagining the task, they can visualise each step whilst writing it down.
Art teachers can use imagery to teach students to follow directions. The teacher might give the following directions orally and write them on the board: “Visualise on a piece of art paper a design including four circles, three triangles, and two squares, with some of the shapes overlapping one another.” The teacher might ask the following questions to ensure that students are using imagery: How many circles do you see? How many triangles? How many squares? Are any of the shapes touching? Which ones?
Dance teachers might have their students close their eyes whilst listening to the music to which they will be performing. Then they might ask the students to imagine themselves dancing, visualising every step and movement. The teacher also might ask students to visualise where they and their classmates are on the stage as they dance.
Jim Marshall took his American history classes to a Civil War battlefield and had them imagine what it must have been like to fight a battle at that site. Later in class he had students produce a map on the computer that duplicated the site and then create various scenarios for what could have happened as the Union and Confederate forces fought.
Evidence doth show that people also use imagery to think about abstract dimensions. Kerst and Howard (1977) asked students to compare pairs of cars, countries, and animals on the concrete dimension of size and on an appropriate abstract dimension (e.g., cost, military power, ferocity). The abstract and concrete dimensions yielded similar results: As items became more similar, reaction times increased. For instance, in comparing size, comparing a bobcat and an elephant is easier than comparing a rhinoceros and a hippopotamus. How participants imagined abstract dimensions, or whether they even used imagery, is not clear. Perhaps they represented abstract dimensions in terms of propositions, such as by comparing the United States and Jamaica on military power using the proposition, “(The) United States (has) more military power (than) Jamaica.” Knowledge maps, which are pictorial representations of linked ideas, aid student learning (O’Donnell, Dansereau, & Hall, 2002).
Imagery in Long-Term Memory
Many a scholar doth concur that images are employed within Working Memory, yet they dispute whether such images are retained within Long-Term Memory (Kosslyn & Pomerantz, 1977; Pylyshyn, 1973). The Dual-Code Theory doth directly address this matter (Clark & Paivio, 1991; Paivio, 1971, 1978, 1986). Long-Term Memory possesses two manners of representing knowledge: A verbal system, incorporating knowledge expressed in language, and an imaginal system, storing visual and spatial information. These systems are interrelated—a verbal code may be converted into an imaginal code, and vice versa—yet material distinctions exist. The verbal system is suited for abstract information, whereas the imaginal system is used to represent concrete objects or events.
Shepard’s experiments lend support to the utility of imagery and offer indirect support for the Dual-Code Theory. Further corroborating evidence emanates from research demonstrating that when recalling lists of concrete and abstract words, individuals recall concrete words with greater facility than abstract ones (Terry, 2009). The Dual-Code Theory’s explication of this finding is that concrete words may be coded verbally and visually, whereas abstract words are typically coded only verbally. At recall, individuals draw upon both memory systems for the concrete words, but only the verbal system for the abstract words. Further research upon imaginal mnemonic mediators lends support to the Dual-Code Theory.
In contrast, Unitary Theory posits that all information is represented within Long-Term Memory in verbal codes (propositions). Images within Working Memory are reconstructed from verbal Long-Term Memory codes. Indirect support for this notion emanates from Mandler and Johnson (1976) and Mandler and Ritchey (1977). As with verbal material, individuals employ schemata whilst acquiring visual information. They remember scenes with greater facility when elements are in a typical pattern; memory is poorer when elements are disorganised. Meaningful organisation and elaboration of information into schemata improve memory for scenes, much as they do for verbal material. This finding doth suggest the operation of a common process, regardless of the form of information presented.
This debate notwithstanding, the employment of concrete materials and pictures enhances memory (Terry, 2009). Such instructional tools as manipulatives, audio-visual aids, and computer graphics facilitate learning. Albeit concrete devices are undoubtedly more pertinent for young children, given their want of cognitive capability to think in abstract terms, students of all ages benefit from information presented in multiple modes.
Individual Differences
The degree to which individuals employ imagery for mnemonic purposes doth vary according to cognitive development. As propounded by Kosslyn (1980), children are more inclined to avail themselves of imagery for the retention and recollection of information compared to adults, who evince a greater reliance upon propositional representation. Kosslyn presented children and adults with statements such as, “A cat has claws,” and “A rat has fur.” The task consisted of ascertaining the veracity of these statements. Kosslyn posited that adults could furnish responses with greater alacrity due to their facile access to propositional information from Long-Term Memory (LTM), whereas children would needs recall and scrutinise the image of the animal. To mitigate the confounding influence of adults’ generally superior information processing, certain adults were directed to examine an image of the animal, whilst others were at liberty to employ any strategy they deemed fit.
Adults exhibited a marked slowness in responding when subject to the imagery instructions as opposed to when permitted to choose their own strategy, yet no such distinction was observed amongst the children. These results intimate that children utilise imagery even when unconstrained, but they do not elucidate whether children are incapable of employing propositional information (owing to cognitive limitations) or whether they are capable but elect not to, deeming imagery to be more efficacious.
The employment of imagery is contingent upon the effectiveness of performing the constituent processes. Two distinct types appear to be involved. One assemblage of processes aids in activating stored memories of image components. Another assemblage serves to arrange said components into the requisite configuration. These processes may be localised in disparate regions of the encephalon. Individual disparities in imagery may arise due to variations in the efficacy of this dual processing (Kosslyn, 1988).
The utilisation of imagery by individuals of any age hinges upon the nature of the object to be imagined. Concrete objects lend themselves more readily to imagination than abstractions. A further factor influencing the employment of imagery is one’s aptitude in wielding it. Eidetic imagery, or photographic memory (Leask, Haber, & Haber, 1969), is in verity dissimilar to a photograph; the latter is perceived in its entirety, whereas eidetic imagery manifests in fragments. Individuals report that an image emerges and dissipates in segments rather than instantaneously.
Eidetic imagery is more prevalent amongst children than adults (Gray & Gummerman, 1975), yet even amongst children it remains uncommon (approximately 5%). Eidetic imagery may be forsaken during development, perhaps as propositional representation supplants imaginal thinking. It is also conceivable that adults retain the capacity to conjure vivid images but do not routinely do so, given that their propositional systems can represent a greater quantum of information. Just as memory may be enhanced, the capacity to form images may be cultivated, yet the majority of adults do not actively endeavour to hone their imagery.