= Adobe Reader Touch х 5.3.1 Problems with direct manipulation Spatial or visual representations are not necessarily an improvement over text, especially for blind or vision-impaired users who need special software. Graph- ical user interfaces were a setback for vision-impaired users, who appreciated the simplicity of linear command languages. However, screen readers for desk- top interfaces, page readers for Internet browsers, and audio designs for mobile devices enable vision-impaired users to understand some of the spatial relation- ships necessary to achieve their goals. A second problem is that direct-manipulation designs may consume valuable screen space and thus force valuable information offscreen, requiring scrolling or multiple actions. Studies of graphical plots versus tabular business data and of flowcharts versus program text demonstrate advantages for compact graphi- cal approaches when pattern-recognition tasks are relevant, but disadvantages when the graphics get too large and the tasks require detailed information. For experienced users, a tabular textual display of 50 document names may be more appropriate than only 10 graphic document icons with the names abbreviated to fit the icon size. A third problem is that users must learn the meanings of visual representa- tions. A graphic icon may be meaningful to the designer but, for users, may require as much learning time as a word, or more. Some airports that serve mul- tilingual communities use graphic icons extensively, but the meanings of these icons may not be obvious to people from different cultures. Similarly, some com- puter terminals designed for international use have icons in place of names, but 5.3 Discussion of Direct Manipulation 195 their meanings are not always clear. Titles that appear on icons when the cursor is over them offer only a partial solution. A fourth problem is that the visual representation may be misleading. Users may grasp the analogical representation rapidly, but then may draw incorrect conclusions about permissible actions, overestimating or underestimating the functions of the commuter based anala Amola testins must be carried out to Ask me anything 0 e H O 11:59 PM 31-Mar-17 = Adobe Reader Touch х 5.3 Discussion of Direct Manipulation 195 their meanings are not always clear. Titles that appear on icons when the cursor is over them offer only a partial solution. A fourth problem is that the visual representation may be misleading. Users may grasp the analogical representation rapidly, but then may draw incorrect conclusions about permissible actions, overestimating or underestimating the functions of the computer-based analogy. Ample testing must be carried out to refine the displayed objects and actions and to minimize negative side effects. A fifth problem is that, for experienced typists, taking a hand off the keyboard to move a mouse or point with a finger may take more time than typing the rel- evant command. This problem is especially likely to occur if the users are famil- iar with a compact notation, such as for arithmetic expressions, that is easy to enter from a keyboard but may be more difficult to select with a mouse. While direct manipulation is often defined as replacing typing of commands with pointing with devices, sometimes the keyboard is the most effective direct- manipulation device. Rapid keyboard interaction can be extremely attractive for expert users, but the visual feedback must be equally rapid and comprehensible. A sixth problem may occur on small mo devices with limited screen sizes. A finger pointing at a device may partially block the display, rendering a good portion of the device not visible. Also, if the icons are small because of the lim- ited screen size, they may be hard to select or, because of limited resolution and viewing capabilities (especially for older adults), not clearly distinguishable, resulting in their meanings becoming lost or confused. In addition to these problems, choosing the right objects and actions for a direct-manipulation interface may be difficult. Simple metaphors or analogies with a minimal set of concepts-for example, pencils and paintbrushes in a drawing tool-are a good starting point. Mixing metaphors from two sources may add complexity that contributes to confusion. Also, the emotional tone of the metaphor should be inviting rather than distasteful or inappropriate (Carroll and Thomas, 1982)-sewage-disposal systems are an inappropriate metaphor for electronic-message systems. Since the users are not guaranteed to share the designer's understanding of the metaphor, analogy, or conceptual model used, ample testing is required. Some direct-manipulation principles can be surprisingly difficult to realize in software. Rapid and incremental actions have two strong implications: a fast perception/action loop (less than 100 ms) and reversibility (the undo action). A standard database query may take a few seconds to perform, so implementing a direct-manipulation interface on top of a database may require special program- ming techniques. The undo action may be even harder to implement, as it requires that each user action be recorded and that reverse actions be defined. It changes the style of programming, because a nonreversible action is implemented by a simple function call, whereas a reversible action requires recording the inverse action. Web-based implementers of direct manipulation face further challenges, because the standard markup language (HTML) limits dynamic user interaction, 213 / 624 1 O Ask me anything 1 d 11:59 PM 31-Mar-17 = Adobe Reader Touch х 196 Chapter 5 Direct Manipulation and Virtual Environments even with the addition of JavaScriptTM The newer Dynamic HTML (DHTML) and XML offer greater flexibility (Golub and Shneiderman, 2003), but web-based direct manipulation is more easily accomplished in Java, Flash, or Ajax. As these tools become more widely accepted, web-based direct manipulation will spread, enabling users to move sliders, make selections, and perform drag-and-drop operations with the customized addition of user-generated content. 5.3.2 The three principles of direct manipulation The attraction of direct manipulation is apparent in the enthusiasm of the users. The designers of the examples in Section 5.2 had an innovative inspiration and an intuitive grasp of what users would want. Each example has problematic fea- tures, but they demonstrate the potent advantages of direct manipulation, which can be summarized by three principles: 1. Continuous representations of the objects and actions of interest with meaningful visual metaphors. 2. Physical actions or presses of labeled buttons, instead of complex syntax. 3. Rapid, incremental, reversible actions whose effects on the objects of interest are visible immediately. Using these three principles, it is possible to design systems that have these beneficial attributes: • Novices can learn basic functionality quickly, usually through a demonstra- tion by a more experienced user. • Experts can work rapidly to carry out a wide range of tasks, even defining new functions and features. • Knowledgeable intermittent users can retain operational concepts. • Error messages are rarely needed. • Users can immediately see whether their actions are furthering their goals, and, if the actions are counterproductive, they can simply change the direc- tion of their activity. • Users experience less anxiety because the interface is comprehensible and because actions can be reversed easily. Users gain a sense of confidence and mastery because they are the initiators of action, they feel in control, and they can predict the interface's responses. 214 /624 In contrast to textual descriptors, dealing with visual representations of objects may be more "natural" and in line with innate human capabilities: Action and visual skills emerged well before language in human evolution. 1 O Ask me anything 1 d 11:59 PM 31-Mar-17 = Adobe Reader Touch х 5.3 Discussion of Direct Manipulation 197 Psychologists have long known that people grasp spatial relationships and actions more quickly when they are given visual rather than linguistic represen- tations. Furthermore, intuition and discovery are often promoted by suitable visual representations of formal mathematical systems. The Swiss psychologist Jean Piaget described four stages of development: sensorimotor (from birth to approximately 2 years), preoperational (2 to 7 years), concrete operational (7 to 11 years), and formal operations (begins at approximately 11 years) (Copeland, 1979). According to this theory, physical actions on an object are comprehensible during the concrete operational stage, when children acquire the concept of conservation or invariance. At about age 11, children enter the formal-operations stage, in which they use symbol manipulation to represent actions on objects. Since mathematics and programming require abstract thinking, they are difficult for children, and designers must link symbolic representations to actual objects. Direct manipulation brings activity to the concrete-operational stage, thus making certain tasks easier for older children and adults. 5.3.3 Visual thinking and icons The concepts of a visual language and of visual thinking were promoted by Arn- heim (1972) and were embraced by commercial graphic designers (Mullet and Sano, 1995), semiotically oriented academics (semiotics is the study of signs and symbols) (de Souza, 2005), and data-visualization gurus. The computer provides a remarkable visual environment for revealing structure, showing relationships, and enabling interactivity that attracts users who have artistic, right-brained, holistic, intuitive personalities. The increasingly visual nature of computer inter- faces can sometimes challenge or even threaten the logical, linear, text-oriented, left-brained, compulsive, rational programmers who were the heart of the first generation of hackers. Although these stereotypes-or caricatures-will not stand up to scientific analysis, they do convey the dual paths that computing is following. Traditionalists sometimes scorn the new visual directions as WIMP (windows, icons, mouse, and pull-down menu) interfaces, while visual system proponents see the command-line devotees as stubborn and inflexible. In the computer world, icons are usually small (less than 1-inch-square or 64-by 64-pixel) representations of an object or action. Smaller icons are often used to save space or to be integrated within other objects, such as a window border or toolbar. It is not surprising that icons are often used in painting programs to rep- resent tools or actions (for example, lasso or scissors to cut out an image, brush for painting, pencil for drawing, eraser to wipe clean), whereas word processors usually have textual menus for their actions. This difference appears to reflect the differing cognitive styles of visually and textually oriented users, or at least dif- ferences in the tasks. Perhaps while users are working on visually oriented tasks it is helpful to "stay visual" by using icons, whereas while working on text docu- ments it is helpful to "stay textual” by using textual menus. 215 / 624 2 1 O Ask me anything A 11:59 PM 31-Mar-17
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