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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: