Written explanations in classrooms have the goal of teaching a new understanding to students. According to genre theory, writers build a set of characteristics into explanations that readers use to learn from their reading. Cognitive load theory and educational psychology specify how the set of characteristics in an explanation could be designed to teach new domain understandings to students who do not yet have expertise. A synthesis of these separate areas of scholarship suggests guidelines for providing explanations that effectively teach important content to particular students.
Genre theory specifies the characteristics of different genres and proposes a mechanism for how genres have developed. According to the theory, the identifiable patterns of structure and content that characterize any genre result from the work of communities of people completing recurring tasks and fulfilling shared purposes. A writer with a particular purpose in mind composes a text with content, structure, and style characteristics that a prospective audience also knows and can use to fulfill a purpose, which may or may not match the goal intended by the author. The author who would write an explanation chooses characteristics with the purpose of communicating a new understanding to potential readers. Well-designed explanations present information, examples, analogies, diagrams, pictures, and models as subexplanations. These subexplanations follow a logical order to form a bridge between readers' current understandings and the new understanding. The goal for the reader is to construct a new understanding by attending to the sub-explanations and following the text's logical order.
For example, the British physicist and astronomer, Sir James Jeans (1877–1946), wrote a short explanation titled “Why the Sky Is Blue” based on a series of radio talks for an audience with no formal knowledge of science. Jeans began by asking the reader to imagine standing on an ocean pier watching the waves roll in and strike the columns supporting the pier. This first subexplanation contrasted what happened to short and long ocean waves with the purpose of reminding the reader of an experience that the reader could readily imagine. The second subexplanation chronicled the movement of light waves through the atmosphere, a series of events that cannot be directly perceived. The third subexplanation mapped the model of water waves onto the model of light. The explanation ended with an explicit description of light waves moving through the atmosphere and ended with the two short sentences, “Consequently the blue waves of the sunlight enter our eyes from all directions. And that is why the sky looks blue.” This explanation presents four subexplanations logically ordered to juxtapose a readily perceivable and imaginable phenomenon that readers may have actually seen with a scientific model to bridge the knowledge of a novice and the understanding of an expert.
Explanations with these features appear in science textbooks in the United States, in science and social studies textbooks internationally, in science and social studies trade books, and in magazine articles and books written for the general public. They also appear in composition books prepared to teach important genres to novice writers (e.g. the anthology that includes Jeans's explanation). The educational community seems to have developed this genre to help learners gain new understanding.
Whereas rhetoricians have proposed a theory to explain the characteristics and development of genres, Cognitive load theory, developed by cognitive psychologists, explains how learning occurs and suggests constraints on the design of successful explanations. According to the theory, the mind is composed of a limited working memory through which information enters the mind and a limitless long-term memory, which stores information that has successfully been processed in working memory as organized schemas. The schemas are abstract structures that store large amounts of information. Working memory can hold only a small number of discrete “bits” of information, and thus can be something of a bottleneck. Learning cannot occur if incoming information overloads working memory capacity; if the cognitive load is too great. But a schema is processed as a single bit. Schemas effectively reduce cognitive load.
Cognitive load can be intrinsic, germane, or extraneous. Intrinsic cognitive load depends on the complexity of the information and whether the learner already has at least one relevant schema. If intrinsic load is not too great, the learner may have the capacity in working memory to engage in processes that are germane to learning, including constructing new schemas. Instruction is effective to the extent that it enhances germane cognitive load. In contrast, instruction may actually impede schema acquisition by enhancing extraneous cognitive load, such as requiring readers to search for or organize information within instructional materials rather than presenting information coherently.
Cognitive load theory provides a framework for understanding how well-designed explanations enhance learning. Psychologically, domain understandings, such as understandings about light developed by physicists, are stored in long-term memory as schemas. The purpose of classroom explanation is to reduce intrinsic and extrinsic cognitive load so that the reader has the working memory capacity to construct a new schema. The design of the subexplanations and how they are ordered must meet this goal in order for learning to occur.
Originally the theory specified that instruction could not modify intrinsic cognitive load. However, research by psychologists John Sweller and Richard Catrambone and others using explanations of chemistry models and written mathematics tasks suggests that presenting instruction as a series of simplified tasks can reduce intrinsic cognitive load. Young adolescent boys following instructions to build molecular models completed the tasks more quickly for 10 simple models with only two related elements each than for 2 complex models with several related elements. Other work using written mathematics tasks suggests that presenting instruction as a series of simplified versions of a complex task can reduce intrinsic cognitive load. Intrinsic cognitive load can be reduced by restricting the number of related elements that the learner must consider at a single point in time. Choosing incoming information that matches a known schema also reduces intrinsic cognitive load. The adoles-centswere faster for the complex models if the instructions were diagrammatic rather than text, matching the structure of a common graphic organizer used in school. Apparently, they had a schema that they could use to reduce the intrinsic cognitive load for even complex models. “Why the Sky Is Blue” offers an example of this process. It presents a sequence of subexplanations, each of which has a smaller number of related elements than is true for the explanation as a whole. It also begins with the ocean wave example, for which readers may well have a schema. Both of these features could reduce intrinsic load and thereby allow readers to understand the subexplanations about light waves.
In an explanation, any example, diagram, information, analogy and so on that does not relate directly to the schema to be acquired would increase extraneous cognitive load. Eliminating unnecessary input would reduce cognitive load and facilitate comprehension. For example, research by psychologist Richard Mayer and others has shown that learners reading a text with only a qualitative description of a model of ocean waves learned more than learners reading a text with quantitative data interspersed within the qualitative description. In the “Why the Sky Is Blue” example, this criterion is met, as each subexplanation relates to the light wave schema.
Texts that require the reader to expend working memory resources figuring out how to process the input also increase extraneous cognitive load. Designing a text to minimize processing unrelated to schema acquisition reduces this load. Research has shown that learners reading a text with captions that point out the relevant features in a diagram or highlighting that signals important relations in a text learn more than learners reading texts without these features. Reducing extraneous cognitive load is particularly important if intrinsic cognitive load is high. Reading diagrams that depicted the relations among chemical elements facilitated how quickly adolescents constructed complex models over reading prose explanations. Prose explanations would not directly represent the relations among elements in the model and might well require learners to create in working memory their own images, adding to the overall cognitive load.
Local coherence also reduces extraneous cognitive load. Readers reading texts with clear pronoun referents, paragraphs organized around a single idea, and paragraph topic sentences learn more than readers reading texts without local coherence, who must dedicate working memory capacity to creating the local coherence themselves. Topic sentences from “Why the Sky Is Blue” such as, “We have been watching a sort of working model of the way in which sunlight struggles through the earth's atmosphere”; (p. 703) and “The waves of the sea represent the sunlight” (p. 704), draw the reader's attention to important relations in the text and also could help readers connect the subexplanations, therefore decreasing extraneous cognitive load.
Eliminating redundancy can decrease cognitive load as well. If an explanation only has content that relates to the expert schema, provides enough support so that the learner does not have to figure out how to process the input, and is coherent, adding additional explanatory support is redundant. Processing this redundancy increases extraneous cognitive load. Learners who read more concise explanations without additional, less central explanatory content learned more than learners who read elaborated versions with additional explanatory content. Redundancy only exists when an explanation has been designed well enough to lead to schema acquisition without the additional content. “Why the Sky Is Blue” is short, and it is likely that this explanation would have redundant content only for readers who already have the light wave schema.
Germane cognitive load results from input that can stimulate the higher cognitive processes necessary for schema acquisition. The same features that decrease intrinsic and extrinsic cognitive load can also contribute to germane cognitive load if they enhance schema acquisition. For example, if all subexplanations are related to the schema, readers have the input to compare and contrast the sub-explanations, abstract general similarities, and construct a schema that incorporates the separate subexplanations. If the explanation signals the similarities explicitly through captions on diagrams, explicitly noting the relationships between analogs, or worked out mathematical examples, readers' attention will be further directed away from extraneous content and toward the similarities.
Research has suggested that providing subexplanations with different surface features can encourage learners to abstract the general similarities and construct a schema. The subexplanations in “Why the Sky Is Blue” present an analogy, the light wave model, a mapping of the analogy onto the model, and the sequence that results in the perception of the color blue. These multiple sub-explanations could be expected to enhance germane cognitive load and learning because they all exemplify the underlying relationships in the schema and are not so numerous as to become redundant. Learners would be thus more likely to focus cognitive effort on the relevant parts of the subexplanations.
The order in which an explanation presents subex-planations can also enhance germane cognitive load. Research on the development of expertise suggests that novices begin with simple schemas, and through practice, construct progressively more complex and useful schemas that ultimately are so well known that they are automatic and bypass working memory altogether. An explanation that begins with a simple, known schema followed by subexplanations that present progressively more complex schemas, could provide the input that a novice would be able to use to construct an expert schema. The subexpla-nations for “Why the Sky Is Blue” follow this simple to complex order.
The challenge in providing explanations to promote domain learning is that typically students either lack obvious schemas upon which to construct new understanding or the schemas that they do have are misleading and interfere with domain learning. First, learners may lack schemas for letter-sound correspondences and grammatical patterns in English. Consequently, they may require so much working memory capacity to process the symbols on the page that no capacity is left for schema construction. Second, students may not have a schema for the generic characteristics of explanation and therefore be unable to take advantage of the subexplanations and logical order in the text. Rather than processing the text as a single unit in working memory, they may instead be overwhelmed by the individual pieces of information in the explanation. Third, students may either have no schemas for the content in the text, or the schemas that they do have may be based on everyday experiences that interfere with their construction of counterintuitive domain-based understandings. Naïve understandings most obviously interfere with new understandings in science, but they can also occur for formalistic vocabulary in mathematics and stereotypes in social studies and English.
Students who lack letter-sound and sentence grammar schemas struggle with almost all reading tasks. Because their struggles to decode and maintain fluency take up so much working memory capacity, it is of utmost importance that intrinsic load be minimal and other types of extrinsic load be eliminated. Intrinsic load can be minimized by providing explanations that rely heavily on pictures and familiar types of diagrams accompanied by a limited amount of text. Presenting the content in diagrams and pictures will eliminate the need for large amounts of decoding; accompanying these features with a limited amount of text will give the readers practice in decoding successfully and thereby constructing the decoding schemas that they are lacking. “Why the Sky Is Blue” has no features that would support readers who lack decoding schemas. It was written for adults who presumably have these schemas.
Firmly established content schemas can also minimize intrinsic cognitive load. Students who struggle to decode otherwise can at times read content about which they have well-established schemas quite fluently. The problem, of course, is that the purpose of explanations is to lead to new understanding. The optimal balance between known and new for readers who struggle to decode is an important area for future research.
Explanations can be designed to build on text schemas that students typically have and compensate for text schemas that they lack. The most firmly established text schema for most students is narrative. Educational psychologists Linda Kucan and Isabel Beck, for example, have demonstrated that fourth graders seem to be able to follow the logic in narratives and fail to follow the logic in expositions. Asked to recall after reading, children up through fifth grade and beyond tend to recall the gist of stories and unconnected bits and pieces of expository texts—what educational psychologist Bonnie Meyer has called the default list. Overall, explanation is exposition. It is structured as a series of subexplanations, not as a plot with characters. It might be expected that many students would lack a schema for explanation. However, subexplanations within explanations can be narrative. “Why the Sky Is Blue” starts with a narrative-like example with the reader as the main character, the waves and the pier as the setting, and what happens to the waves as the plot. It is possible that readers could use a narrative schema to process the remaining subexplanations even though the explanation as a whole is exposition.
Readers lacking a text schema can begin to construct one through signaling. Across a number of studies, research has demonstrated that introductions that synop-size the text structure; paragraph topic sentences and words such as “first,” “then,” and “however” that signal the structure of the text; and conclusions that summarize direct a reader's attention to the generic patterns in a text. Explanations with these features would prompt readers to process an explanation within working memory as a single unit rather than a succession of unrelated bits of information. “Why the Sky Is Blue” has no signals that would help readers process it as an explanation.
A challenge in most scholarly domains is to help students use expert models to explain everyday experience. In economics, models of supply and demand can explain fluctuations in price. In history, models of limited resources can explain why one country would invade another. In science, scholars have proposed and demonstrated causal models that can be used to explain and predict a wide range of phenomena. These models reduce phenomena to a set of core theoretical ideas that are often very different from the realm of everyday knowing. Indeed, a challenge in all domains, but particularly science, is to help students use expert models to explain everyday phenomena. Unfortunately, the schemas that students have, rather than guiding their understanding, can actually interfere with their construction of a new schema. Often texts for use in classrooms begin with the target model to be taught and do not address students' naïve models, typically failing to prompt students to construct a new schema. “Why the Sky Is Blue” fits this pattern, in that it does not directly address students' prior ideas about light.
A type of explanation called refutational text has proven to be an effective way to help readers adopt scientific models that may even be at odds with their naïve experience-based schemas. Refutational texts begin with a subexplanation that presents the naïve model based on everyday experiences, and follow with subexpla-nations that are logically ordered to demonstrate the limitations of the naïve model, present the scientific model, and point out how it addresses the limitations. Students who demonstrated naïve understandings before reading were more likely to demonstrate expert understanding after reading refutational texts than other students who conducted experiments, discussed in small groups, or read typical textbook material that did not “refute” their naïve understandings.
The most important implication for teachers is to choose and compose explanations carefully. The well-designed explanation begins with a schema that the teacher could expect students in the class to have. If the children's schema contrasts with the expert understanding, the explanation is designed as a refutational text. The effective explanation has no extraneous content and is locally coherent. Subexplanations are varied, including diagrams and pictures to highlight the relationships in the schema where appropriate, as well as narrative examples. The explanation is as explicit as possible, drawing connections among each successive subexplanation, highlighting important relationships and including informative diagram captions. Subexplanations follow a logical order, from part to whole, from simple to complex, from familiar to unfamiliar. Knowing the students well, the teacher chooses or develops an explanation with the optimal relationship between known and new to maximize germane cognitive load and student learning.
Most explanations will not match this set of characteristics perfectly. For example, “Why the Sky Is Blue” does not include diagrams and pictures, nor does it address possible naïve understandings. For less than perfect explanations, classroom instruction would need to provide what the explanation lacks. Students could draw missing diagrams or write captions for diagrams that are in the text, brainstorm before reading to access relevant schemas, and create graphic representations of the ideas in the explanation to highlight relevant content. Students could process more than one explanation, each of which could make up for lacks in the other. Even though research suggests that reading print may lead to learning more effectively than watching or listening to other types of media, students who lack decoding or relevant content schemas can learn better from a combination of print and other media than either by itself.
See also:Cognitive Load Theory
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