Tactile Displays and Graphics
Guidelines for Designing Tactile Displays
There are a variety of situations which call for the information in graphic displays or tactile graphics to be maintained as is, or which suggest that the information be modified somewhat in order to make the tactile display usable by the blind reader.
In some cases, the size of the information must remain the same (e.g. if measuring is to be done), but the layout can be changed to facilitate locating and measuring lines or areas.
In some cases, the size or scale may be changed to facilitate the reader’s perception of important details and space/line differences (NOTE: at least 1/4 inch space between entities is necessary for the tactile reader to perceive them as separate; more space is needed if there is a difference in the height of the entities). If the need to enlarge results in having to split the diagram into more than one part, these splits should be made in such a way that it does not interfere with the concept being presented. Furthermore, the parts should be presented in a careful sequence, with special attention provided to help the student tie them together. A diagram containing the gestalt of the display (but with less detail) should be presented either as an introduction to the separate parts, or as a summary, whichever approach works best for the student. The student might also consider the use of a marking system to help keep track of the part he or she is working on with respect to its location on the “big picture” diagram.
The size of the symbols used must also be considered. The absolute size of the symbol is important because a) the blind reader cannot look closer to increase the size of the image on the retina, as the visual reader can, and b) the blind reader cannot use magnifiers to increase the symbol size, as the visual reader can. Furthermore, the relative size of the symbol makes a difference in the tactile reader’s ability to recognize it efficiently. It is more difficult and takes more time to recognize shapes if they are of a different size than the one originally presented. This suggests avoiding varying the size of symbols on displays or keys, unless the difference in size denotes different meaning. Many students may also benefit from working on size constancy.
The relative position of shapes or symbols is also an important consideration. The same shape, presented in different positions, is not readily recognized as being the same by most blind readers. Therefore, the position of symbols or pictures should not be changed if it is important that the student recognize these symbols as being the same. In addition, as with size constancy, teaching shape constancy may be helpful. Of course, sometimes the change in a symbol’s position denotes different information, and is therefore necessary. Careful orientation to any display and its descriptive information and key is always very important.
Sometimes the layout, size and even format of the display are changed. This is acceptable and, in some cases, necessary, in order to present the original concept or purpose of the display in a way discernible to the tactile reader. The blind child cannot perceive the whole layout at once, and has great difficulty skipping over unimportant details while searching for essential information when a cluttered format is presented. Therefore, tactile displays must be carefully analyzed before rendering, and presented in an orderly and uncluttered format so the reader can locate all the significant information, not be confused by unimportant information, carry out problem-solving tasks (e.g. measuring, comparing), and keep track of his or her progress while working.
Often visual displays contain patterned or shaded backgrounds; in many cases, these background patterns are not relevant to the purpose of the diagram. To the tactile reader, rendering these background patterns with various textures can be extremely distracting and confusing. Textured areas slow down the speed and decrease the accuracy of reading tactile diagrams, and make tracking lines through these areas very difficult. Therefore, avoid rendering such backgrounds unless they are an impor¬tant part of the information to be presented.
It is also often necessary to use simpler shapes to represent more complicated shapes or pictures for easier readability. This is appropriate as long as it is not necessary to maintain the same picture as is used in the original display. For example, The Boehm Tactile Analog presents the same concepts but simpler symbols are substituted for the pictures used in the original tasks. Many primary mathematics books use fairly complicated pictures (animals, birds, tractors, etc.) to indicate members of sets to be counted; the numbers of items in the sets are important for counting or comparison, but the exact duplication of complicated pictures is not important, and is often confusing.
Careful decisions should be made with regard to what elements of information to include and how to best present them through the use of tactile displays. When designing and producing tactile diagrams, the following additional suggestions may be useful:
- Focus on the purpose of the tactile graphic; this will help to identify what information is critical to include.
- Edit the printed display carefully before making it into a tactile display, deciding on important information to include, unnecessary elements which may be confusing, and ways for clearly rendering areas and symbols.
- Consider the individual student who will be using the tactile aid; his or her background, experience with graphic materials, cognitive and language level, etc. will help to insure that the particular aid is appropriate.
- Consider the life of the aid—will it need to survive for a long time, be used very frequently, under a variety of conditions? Choose materials accord¬ingly.
- Proofread the tactile diagram (both the master and the copy) with your fingers, not just your eyes.
- Identify critical features necessary to make the graphic aid accurate (e.g. intersections on graphs, extension of number lines to cover problems to be solved, exact areas and fractional parts if they are to be measured, etc.).
- When designing tactile graphics, keep non-essential information to a minimum--it can be confusing to the reader; avoid background textures unless they convey important information. It is especially difficult for blind readers to disregard unimportant details or background textures; therefore, grid lines could be left out if they are only background material and have no relationship to the diagram itself or to the student’s ability to solve the problem involved.
- Background lines such as grids or guidelines can be helpful, even neces¬sary, if precise location of points must be found in order to interpret the graph; in such cases, these gridlines or guidelines should be rendered with lower key types of lines than those used for more important information such as data point lines, etc.; similarly, axis lines should be clearly presented, but they should not override the purpose of the graph.
- Scale is very important if it is involved in the work to be carried out or the information to be obtained; it is not important if it does not play a role in the problem-solving at hand, or provide useful information, or if it causes the user to become confused by crowding or blurring important symbols or lines. It may be much more effective to enlarge details which are critical to the use of the diagram so that they can be perceived more accurately. If scale is modified, this should be described on the diagram or on a facing page with the key or other relevant information.
- The size of the diagram itself is important; generally, the area to be examined should be the size of one or two hands, depending on the concept and the student. If diagrams are too small, they may be too crowded and confusing; if they are too large, it may be difficult to experience different areas as being connected or related. Unless accurate scale is necessary, small diagrams with much detail might better be rendered using an enlarged version with an emphasis on critical features. Complicated diagrams could be split into several sections (an appropriate size for one- or two-handed reading) with a simplified overview diagram and descriptive note, as long as the use of the diagram would not require repeated flipping back and forth among parts in order to solve a problem.
- Material which may not fit efficiently on a vertical page might fit well on a horizontal page; some materials, such as graphs, might be more easily perceived if rendered on a horizontal axis. If a display is repositioned, caution should be taken to insure that the information itself remains accurate (e.g. curved lines curving downward in one position may end up curving upward in another position). If the display’s position is changed, this should be described in notes provided with the key and other relevant information.
- If information is presented in a random order in the visual display, this same information would be better presented in some organized fashion in the graphic display so as to avoid the potential for missing some of the entries.
- A wide enough margin should remain around the edges of the actual display so that the diagram can be thermoformed if necessary, or so that it can be bound or hole-punched for a notebook (if a diagram is to be bound or placed in a notebook, it should face away from the binding so that the binding will not be in the way of the reader’s hands).
- Spacing between lines and symbols is critical in order for the user to perceive symbols and lines as distinct features. For many students, even experienced users of tactile graphic aids, spacing of 1/4 inch between entities (symbols, lines) is necessary to distinguish separate symbols and lines.
- Spacing between braille characters and other lines or symbols is also critical and should also follow the 1/4 inch rule; additional space may be necessary if braille characters or symbols are placed next to information which is presented in especially high relief.
- Shapes can be rendered in higher relief, and lines at lower elevations to be more easily discriminated by the reader.
- Important lines should attract the reader’s attention immediately; this can be accomplished by using sharper or highly contrasted textured lines or by raising the elevation of these lines.
- Symbols and angles should be of sufficient size to be accurately perceived by the tactile reader.
- Lines which require measuring should be of sufficient relief that the reader can easily use a ruler or protractor; if the perimeter of an area is to be measured, place the labels of the line segments inside the shape so as not to interfere with the use of the ruler.
- When rendering bar graphs, keep bars close enough so the length relation¬ships can be easily read.
- When small differences must be detected on a display, use a combination of length or size with relative texture (e.g. longer bar has coarser texture); this may help increase reading accuracy.
- When making line graphs, use different types of lines to denote different information, rather than using the same type of line with different labeling.
- When rendering diagrams to coincide with classroom materials, symbols may need to resemble those in the print display for clarity of classroom discussion; however, this often results in using symbols which are tactually very confusing. Clear explanations and descriptive information along with simpler symbols may be more appropriate.
- All symbols should be defined and explained. Descriptions or keys to accompany a tactile diagram could be placed on the same page, but out of the way of the diagram itself, or on a separate facing page. Such placement can help to reduce clutter on the diagram. This is especially important if key information is in braille, since its size cannot be reduced to fit in smaller spaces within the chart or diagram, as is possible with print.
- While it is generally a good idea to use abbreviations when labeling diagrams in order to reduce clutter, it is better to use two-cell braille labels than one-cell braille labels since they enhance orientation and are less easily confused. Contracted braille should be used in labeling as long as the student is proficient with it.
- A braille label should not break the integrity of a shape; it should be placed either inside or outside the shape, depending on the task involved and the space available.
- Capitalization need not be followed in braille labeling, unless the capitaliza¬tion is a critical element of the information (e.g., a diagram involving line AB and line ab).
- It might be helpful to have a list of the Nemeth Code and other relevant symbols frequently used in mathematics available to the students for quick reference as they work with their diagrams.
- Tactile diagrams should be marked to indicate the top of the diagram for more efficient orientation.
- It is extremely difficult to effectively represent 3 dimensional objects in 2 dimensions, even with the use of raised line drawings using dotted lines as opposed to solid lines to denote those edges and angles which would be “unseen” if viewing the actual item visually. Raised line drawings often look very clear to the sighted individual because the concept has been experi¬enced or because perspective drawings are more easily understood visu¬ally. The assumption that these diagrams are equally effective for blind users is incorrect.
- A “collapsible cube” can be made to demonstrate both 3 dimensional and 2 dimensional frames: 2 rigid square planes are joined by 4 flexible vertical edges (“arises”). The cube can be used upright (3D), or the bottom frame can be held firmly on a flat surface with the top frame held directly above it, then the top frame is moved at a 45 degree angle (or any angle) to the side until it rests flatly on the desk surface. By moving the frame from a 3D to a 2D representation of the cube, the student may develop a better under¬standing of the derivation of a 2 dimensional representation of a 3 dimen¬sional cube.
- Numbers, letters and words written in braille on separate paper, cut out and glued to the diagram often result in distracting “boxes”, especially if thermo¬form copies are used; if possible, plan ahead and braille necessary sections first before producing the graphic elements of the diagram.
- Use lead lines only when absolutely necessary; when including them, however, use very low-key lead lines that will not interfere with the important lines of the diagram. Try to place the beginning and end of lead lines as close as possible to the features which they connect, without interfering with the connected labels or symbols.
- When possible, use consistent tactile symbols for frequently occurring visual symbols, pictures or concepts; exceptions occur when different symbols representing the same concept are actually part of the material to be taught.
- Since many texts use the same basic diagrams repeatedly, with only the labels on the diagrams changing, construct a sturdy set of basic braille diagrams (e.g., on foil sheets) and make a set of braille stick-on labels which can easily be added and removed as needed.