Introduction

Science learning materials rely heavily on visuals to communicate important information to students trying to understand complicated ideas and solve difficult problems. Thus it's important for teachers to select materials -- including but not limited to textbooks - that contain effective visuals and, in turn, to use them effectively.

Line drawings, diagrams and photographs can elaborate, clarify, and make memorable the text that they accompany (1,3,6,& 7). This visuals type is called iconic because the spatial relations depicted in these two-dimensional visuals represent many of the actual spatial realities of concrete three dimensional things, for example, a physical object's position, orientation, shape, and size. Typical examples appear in some middle school-earth science textbooks to show how glaciers formed. Such line drawings illustrate glaciation by showing V-shaped valleys that fill with ice and snow and form glaciers, which carve out land and produce today's U-shaped glaciated valleys.

Illustrations showing the glaciation process accenting important relevant visual characteristics capture for students the method by which glaciers produced some of today's mountainous landscapes. Adjacent to the illustration is a prose description of important abstract points -- including a discussion of how ice, water, and rock combine with gravity and friction to sculpt. This description includes definitions of terms and explains some of the implicit abstractions suggested in the visual. Thus, the two text media complement one another (2).

A second useful type of illustration found in textbooks and elsewhere is called schematic. Schematic visuals function as summarizers of information, whereby essential concepts are presented in a quickly read format (4). For example, diagrams can be a powerful tool for summarizing the relationships between photosynthesis and respiration. These two related concepts contain numerous difficult-to-learn biochemical cycles--information that students must disentangle, segregate, group and compare. Research and classroom experience suggest that students who learn such cycles from diagrams rather than from prose do better on some school tests (9).

Tables and charts, too, are powerful summarizers of important information (4&5). Consider, for instance, the periodic table which is used as a unifying theme in some chemistry textbooks. Tables and charts are also useful summarizers of information not central to author's purposes, freeing additional textbook space for adequate explanations of truly important concepts. A good example is the one-page table found in chapter one of the nation's best-selling school text, Modern Biology , which lists the names and accomplishments of 20 major "contributors to biological knowledge." In earlier versions, the authors ramble on, page after page, using up valuable space. This technique of boxing information can be used to convince recalcitrant buyers that their favorite material has been covered while providing greater text space to explain other information of central importance (8).

Some Characteristics and Uses of Effective Visuals

Because visuals are so important, their selection is also important. The following 18 characteristics and uses of effective visuals are presented for science textbook visuals including iconic (such as line drawings and photographs of objects), schematic (such as flow charts and circuit drawings), and additional summarizing visual types (such as tables and charts).

These 18 statements about visuals are presented with questions and are derived from often-cited research studies. Each is supported by three research references in order of apparent value. The page number(s) are given for easy reference. Each question contains an example found in some middle and senior high school science textbooks.

Good Textbook Visuals

1. Portray Accurate Spatial Relations . Do the visuals portray accurate and realistic spatial relations (e.g. the earth and sun's relative sizes and separating distances) among illustrated objects and their parts? (8, p. 75; 2, p. 641; 7 p. 725; 6 p. 61).
2. Don't Distract Students' Attention. Do visuals (e.g., colorful photographs not directly related to the science of the textbook) distract students who are unclear about what should be learned? (8, p. 108, p. 118, p. 172; p. 129; 6, p. 107).
3. Are Appealing to Students. Do visuals (e.g., photos of erupting volcanos) add to a textbook's appeal without adding unreasonable publication costs? (1, p. 127; 8, p. 24, p. 130).
4. Spark Interest Curiosity and Inquiry Attitudes. Are selected visuals (e.g., photographs of inquisitive and enthusiastic chemists working in their laboratory) designed to spark interest, curiosity and inquiry attitudes without interfering with learning tasks central to the teacher's goals? (8, p. 26, p. 119, p. 122; 2, p. 660).
5. Relate to the Science. Are the visuals (e.g., large photos of amusement park rides with no apparent connection to the science described in the textbook) necessary and relevant to higher-order learning, or are they merely flashy devices used to sell science textbooks? (8, p. 73, p. 74, p. 124; 6, p. 107).
6. Illustrate Difficult-to-Image Information. Do the visuals illustrate some information (e.g., drawings representing stages of glaciation) that is very difficult to describe using just sentences? (2, p. 650; 8, p. 119; p. 160;2, p. 651, p. 657).
7. Highlight, Reintegrate, Reinforce and Rehearse. Are the visuals (e.g., schematic drawings of nitrogen and oxygen biological cycles) highlighting, reiterating, reinforcing and helping student rehearse important information for easier learning? (8, p. 126, p. 129; 2, p. 657;6, p. 122).
8. Focus Students' Attention. Are questions and other adjunct learning aids (e.g., arrows illustrating the flow of fluids around airplane wings) used to selectively focus students' attention on important information (e.g., temperature and heat of water changing energy states)? (4, p. 523; 5; 8, p. 135).
9. Summarize and Contrast Information. Do selected visuals used to help student summarize information (names and historical contributions made by scientists), segregate and compare contrasting points of view (e.g., Lamarck and Darwin's conceptions of how evolution works) and discriminate between highly similar yet different concepts (e.g., differing kings of vertebrate hearts)? (8, p. 185; 2, p. 666; 7, p. 715).
10. Customize Visuals . Are the visuals (e.g., contrasting vascular and non vascular plants) designed according to the goals of the authors--for example, using drawings to highlight structures, photographs to provide a sense of realism, and charts to compare two sets of variables? (6, p. 13;8, p. 173; 7, p. 715; 9, p. 384).
11. Reference Visuals in Text. Are the visuals (e.g., charts describing properties of mixtures) reasonably juxtaposed to relevant text and referenced in the science textbook for easy location? (2, p. 650, p. 651; 6, p. 107).
12. Help Students Remember. Are important objects (e.g., the human ear--see 6, p. 72-75) and their parts used to illustrate and increase the chances of students remembering the concrete concepts and subsequently solving problems in their working or short-term memories? (8, p. 88, p. 176; 2, p 653).
13. Help Students Remember. Are important objects (e.g., the human ear--see 6, p. 72-75) and their parts used to illustrate and increase the chances of students remembering the concrete concepts and subsequently solving problems in their working or short-term memories? (8. p. 88, p. 176; 2, p 653).
14. Help Low-ability Students . Do selected visuals (e.g., drawing of mechanical systems, drawing of concrete objects adjacent to their verbal labels) help students with low-spatial or verbal abilities by providing compensating illustrated information? (8, p. 135, j p. 169;2, p. 658, p. 665).
15. Help High-ability Students. Do selected visuals (e.g., drawings of growth hormones differentially placed on vascular plant stems) help students with high-spatial or verbal abilities by providing them with opportunities to capitalize on their exceptional perceptual and learning abilities? (i, p. 137, p. 181; 2, p. 658).
16. Understand Graphic Conventions. Do the visuals contain reasonable graphic conventions (e.g., shadings illustrating motions, left-to-right and top-to-bottom orientation patterns used in circuit diagrams) that are familiar to the students? (i, p. 74, p. 142, p. 161; 2, p. 653).
17. Place Visuals in Textbook. Do visuals (e.g., pulley systems) and their placement specifically facilitate readers' eye movements alternating between reading the text and inspecting the accompanying visual, resulting in increased chances of comprehension? (2, p. 652; 8, p. 130; 3, p. 13).
18. Orchestrate Textbook Visuals. Are selected visuals (e.g., drawings, photographs and texts describing the movement of blood through the heart) orchestrated in combination and used to present selected important concepts increasing students' chances of higher-order learning? (8, p. 118, p. 140; 2, p. 648, p. 652;7, p. 725).

More To Learn?

Readers interested in learning additional technical information about visual learning research are encouraged to read the reviews and original works cited in the references.   Remember, there are no magic formulas or panaceas concerning the selection and use of instructional visuals.  William G. Holliday is a Professor of Curriculum and Instruction at the University of Maryland at College Park.

by William G. Holliday, University of Maryland, Center for Science Education, College Park, MD

References

Chall, J. S., & Squire, J. R. (1991). The publishing industry and textbooks. In R. Barr, M. Karnil, P. Mosenthal and P. D. Pearson (Eds.), Handbook of reading research (vol. 1). New York: Longman, Inc.

Hegarty, M., Carpenter, P.A., & Just, M.A. (1991) Diagrams in the comprehension of scientific texts. In R. Barr, M.L. Kamil, P.B. Mosenthal & P.S. Pearson (Eds) Handbook of reading research (vol. 2). New York: Longman.

Holliday, W. G. (1988). The perils of illustrations. Basic Education, 32(10) pp 13-15.

Holliday, W. G. & Benson, G. (1991). Enhancing learning using questions adjunct to science charts. Journal of Research in Science Teaching, 28, 523-535.

Holliday, W. G. & McGuire, B. (in press). How can comprehension focus students' attention and enhance concept learning of a computer-animated science lesson? Journal of Research in Science Teaching.

Houghton, H. A., & Willows, D. M. (1987). The psychology of illustrations: Instructional issues (vol. 2) New York: Springer-Verlag. (This research-based review is an extension of the Willow & Houghton book).

Mayer, R. E., & Gallini, J. K. (1990). When is an illustration worth ten thousand words? Journal of Educational Psychology , 82, 715-726.

Willows, D. M. & Houghton, H. A. (1987). The psychology of illustrations: Basic research (vol. 1). New York: Springer-Verla. (Five chapters consulting this book and its companion, edited by Houghton and Willows were written by different authors with varying research-based perspectives.)

Winn, W. D. (1988). Recall of the pattern, sequence, and names of concepts presented in instructional diagrams. Journal of Research in Science Teaching, 25, 375-386.