Highlighting A technique for bringing attention to an area of text or image. Highlighting is an effective technique for bringing attention to elements of a design. If applied improperly, however, highlighting can be ineffective, and actually reduce performance in these areas. The following guidelines address the benefits and liabilities of common highlighting techniques.1 General Highlight no more than 10 percent of the visible design; highlighting effects are diluted as the percentage increases. Use a small number of highlighting tech-niques applied consistently throughout the design. Bold, Italics, and Underlining Use bold, italics, and underlining for titles, labels, captions, and short word sequences when the elements need to be subtly differentiated. Bolding is generally preferred over other techniques as it adds minimal noise to the design and clearly highlights target elements. Italics add minimal noise to a design, but are less detectable and legible. Underlining adds considerable noise and compromises legibility, and should be used sparingly if at all.2 Typeface Uppercase text in short word sequences is easily scanned, and thus can be advantageous when applied to labels and keywords within a busy display. Avoid using different fonts as a highlighting technique. A detectable difference between fonts is difficult to achieve without also disrupting the aesthetics of the typography. Color Color is a potentially effective highlighting technique, but should be used sparingly and only in concert with other highlighting techniques. Highlight using a few desaturated colors that are clearly distinct from one another. Inversing Inversing elements works well with text, but may not work as well with icons or shapes. It is effective at attracting attention, but adds considerable noise to the design and therefore should be used sparingly. Blinking Blinking—flashing an element between two states—is a powerful technique for attracting attention. Blinking should be used only to indicate highly critical information that requires an immediate response, such as an emergency status light. It is important to be able to turn off the blinking once it is acknowledged, as it compromises legibility, and distracts from other tasks. See also Color, Legibility, and Readability. 126 Universal Principles of Design 1 See, for example, “A Review of Human Factors Guidelines and Techniques for the Design of Graphical Human-Computer Interfaces” by Martin Maguire, International Journal of ManMachine Studies, 1982, vol. 16(3), p. 237–261. 2 A concise summary of typographic principles of this kind is found in The Mac is Not a Typewriter by Robin Williams, Peachpit Press, 1990. Despite the title, the book is of value to non-Macintosh owners as well. General “You mean you can’t take less,” said the Hatter, “it’s very easy to take more than nothing.” “You mean you can’t take less,” said the Hatter, “it’s very easy to take more than nothing.” “Nobody asked your opinion,” said Alice. “Nobody asked your opinion,” said Alice. Bold, Italics, and Underlining Advice from a Caterpillar Advice from a Caterpillar Advice from a Caterpillar “I can’t explain myself, I’m afraid, sir” said Alice, “because I’m not myself, you see.” “I can’t explain myself, I’m afraid, sir” said Alice, “because I’m not myself, you see.” “I can’t explain myself, I’m afraid, sir” said Alice, “because I’m not myself, you see.” Typeface “What is a Caucus-race?” said Alice; not that she wanted much to know, but the Dodo had paused as if it thought that somebody ought to speak, and no one else seemed inclined to say anything. “What IS a Caucus-race?” said Alice; not that she wanted much to know, but the Dodo had paused as if it thought that SOMEBODY ought to speak, and no one else seemed inclined to say anything. Color Which brought them back again to the beginning of the conversation. Alice felt a little irritated at the Caterpillar’s making such very short remarks, and she drew herself up and said, very gravely, “I think, you ought to tell me who you are, first.” Which brought them back again to the beginning of the conversation. Alice felt a little irritated at the Caterpillar’s making such very short remarks, and she drew herself up and said, very gravely, “I think, you ought to tell me who you are, first.” Inversing Who stole the tarts? Who stole the tarts? Highlighting 127 Horror Vacui A tendency to favor filling blank spaces with objects and elements over leaving spaces blank or empty. Horror vacui—a Latin expression meaning “fear of emptiness”—regards the desire to fill empty spaces with information or objects. In style, it is the opposite of minimalism. Though the term has varied meanings across different disciplines dating back to Aristotle, today it is principally used to describe a style of art and design that leaves no empty space. Examples include the paintings of artists Jean Dubuffet and Adolf Wölfli, works of graphic designers David Carson and Vaughan Oliver, and the cartoons of S. Clay Wilson and Robert Crumb. The style is also commonly employed in various commercial media such as newspapers, comic books, and websites.1 Recent research into how horror vacui is perceived suggests a general inverse relationship between horror vacui and value perception—that is, as horror vacui increases, perceived value decreases. For example, in a survey of more than 100 clothing stores that display merchandise in shop windows, the degree to which the shop windows were filled with mannequins, clothes, price tags, and signage was inversely related to the average price of the clothing and brand prestige of the store. Bulk sales shops and chain stores tended to fill window displays to the maximum degree possible, using every inch of real estate to display multiple mannequins, stacks of clothes, and advertising promotions, whereas high-end boutiques often used a single mannequin, no hanging or stacked clothes, no signage, and no price tags—if passersby need to know the price, they presumably could not afford it. This result is certainly consistent with common experience, but somewhat surprising as lavish decoration is historically considered an indication of affluence and luxury. It may be that the inverse relationship is actually between the affluence of a society and the perceived value associated with horror vacui—that is, for those accustomed to having more, less is more, and for those accustomed to having less, more is more. Others have speculated that the relationship is more a function of education than affluence. This area of research is immature and much follow-up is required to tease out the causal factors, but the preliminary findings are compelling.2 Consider horror vacui in the design of commercial displays and advertising. To promote associations of high value, favor minimalism for affluent and welleducated audiences and horror vacui for poorer and less-educated audiences, and vice versa. For information-rich media such as newspapers and websites, employ information-organizing principles such as alignment and chunking to retain the benefits of information-dense pages while mitigating horror vacui. See also Alignment, Chunking, Ockham’s Razor, Progressive Disclosure, and Signal-to-Noise Ratio. 128 Universal Principles of Design 1 Horror vacui is most notably associated with the Italian-born critic Mario Praz, who used the term to describe the cluttered interior design of the Victorian age. 2 “Visualizing Emptiness” by Dimitri Mortelmans, Visual Anthropology, 2005, vol. 18, p. 19–45. See also The Sense of Order: A Study in the Psychology of Decorative Art by Ernst Gombrich, Phaidon, 1970. Three shop windows with varying levels of merchandise on display. The perceived value of the merchandise and prestige of the store are generally inversely related to the visual complexity of the display. Horror Vacui 129 Hunter-Nurturer Fixations A tendency for male children to be interested in huntingrelated objects and activities, and female children to be interested in nurturing-related objects and activities. There are a number of innate cognitive-behavioral differences between males and females, one of which is early childhood play preferences. Male children tend to engage in play activities that emulate hunting-related behaviors, whereas female children tend to engage in play activities that emulate nurturing-related behaviors. Although such preferences were long thought to be primarily a function of social and environmental factors, research increasingly favors a more biologically based explanation. For example, that male children tend to prefer stereotypically male toys (e.g., cars) and females tend to prefer stereotypically female toys (e.g., dolls) has long been established. However, in studies where male and female vervet monkeys are presented with the same human toys, the male vervets prefer to play with the male toys and the female vervets prefer to play with the female toys. This suggests a deeply rooted, biologically based gender bias for certain play behaviors.1 Like play behaviors in other animals, these early childhood fixations likely had adaptive significance in preparing our hunter-gatherer ancestors for survival: male children for hunting and female children for child rearing. Though these fixations are essentially vestigial in modern society, they continue to influence our preferences and behaviors from early childhood through adolescence. Hunter fixation is characterized by activities involving: • • • • • Object movement and location Weapons and tools Hunting and fighting Predators Physical play Nurturer fixation is characterized by activities involving: • • • • • Form and colors Facial expressions and interpersonal skills Nurturing and caretaking Babies Verbal play Consider hunter-nurturer fixations in the design of objects and environments for children. When targeting male children, incorporate elements that involve object movement and tracking, angular forms, predators, and physical play. When targeting female children, incorporate elements that involve aesthetics and color, round forms, babies, and tasks requiring interpersonal interaction. See also Archetypes, Baby-Face Bias, Contour Bias, and Threat Detection. 130 Universal Principles of Design 1 See, for example, “Sex Differences in Infants’ Visual Interest in Toys” by Gerianne Alexander, Teresa Wilcox, and Rebecca Woods, Archives of Sexual Behavior, 2009, vol. 38, p. 427–433; “Sex Differences in Interest in Infants Across the Lifespan: A Biological Adaptation for Parenting?” by Dario Maestripieri and Suzanne Pelka, Human Nature, vol. 13(3), p. 327–344; and “Sex Differences in Human Neonatal Social Perception” by Jennifer Connellan, Simon Baron-Cohen, Sally Wheelwright, et al., Infant Behavior & Development, 2000, vol. 23, p. 113–118. When vervets are presented with human toys, female vervets prefer stereotypically female toys and male vervets prefer stereotypically male toys. This suggests a biological basis for gender-based play preferences in primates — including humans. The Pleo moves slowly and lacks the predatory or angular features that appeal to male children — better to have made it a velociraptor. Its baby face will appeal to female children, but its reptilian semblance, rubber skin, and rigid innards do not invite nurturing — better to have made it a soft, furry mammal. Despite its technical sophistication, Pleo lacked the basic elements necessary to trigger hunter or nurturer fixations in children, a likely factor in the demise of its manufacturer, Ugobe. Hunter-Nurturer Fixations 131 Iconic Representation The use of pictorial images to improve the recognition and recall of signs and controls. Iconic representation is the use of pictorial images to make actions, objects, and concepts in a display easier to find, recognize, learn, and remember. Iconic representations are used in signage, computer displays, and control panels. They can be used for identification (company logo), serve as a spaceefficient alternative to text (road signs), or to draw attention to an item within an informational display (error icons appearing next to items in a list). There are four types of iconic representation: similar, example, symbolic, and arbitrary.1 Similar icons use images that are visually analogous to an action, object, or concept. They are most effective at representing simple actions, objects, or concepts, and less effective when the complexity increases. For example, a sign indicating a sharp curve ahead can be represented by a similar icon (e.g., curved line). A sign to reduce speed, however, is an action not easily represented by similar icons. Example icons use images of things that exemplify or are commonly associated with an action, object, or concept. They are particularly effective at representing complex actions, objects, or concepts. For example, a sign indicating the location of an airport uses an image of an airplane, rather than an image representing an airport. Symbolic icons use images that represent an action, object, or concept at a higher level of abstraction. They are effective when actions, objects, or concepts involve well-established and easily recognizable objects. For example, a door lock control on a car door uses an image of a padlock to indicate its function, even though the padlock looks nothing like the actual control. Arbitrary icons use images that bear little or no relationship to the action, object, or concept—i.e., the relationship has to be learned. Generally, arbitrary icons should only be used when developing cross-cultural or industry standards that will be used for long periods of time. This gives people sufficient exposure to an icon to make it an effective communication device. For example, the icon for radiation must be learned, as nothing intrinsic to the image indicates radiation. Those who work with radiation, however, recognize the symbol all over the world. Iconic representation reduces performance load, conserves display and control area, and makes signs and controls more understandable across cultures. Consider similar icons when representations are simple and concrete. Use example icons when representations are complex. Consider symbolic icons when representations involve well-established and recognizable symbols. Consider arbitrary icons when representations are to be used as standards. Generally, icons should be labeled and share a common visual motif (style and color) for optimal performance. See also Chunking, Performance Load, and Picture Superiority Effect. 132 Universal Principles of Design 1 The seminal work in iconic representation is Symbol Sourcebook by Henry Dreyfuss, Van Nostrand Reinhold, 1984. The four kinds of iconic representation are derived from “Icons at the Interface: Their Usefulness” by Yvonne Rogers, Interacting With Computers, vol. 1, p. 105–118. Similar Right Turn Falling Rocks Sharp Stop Airport Cut Basketball Restaurant Electricity Water Unlock Fragile Collate Female Radioactive Resistor Example Symbolic Arbitrary Iconic Representation 133 Immersion A state of mental focus so intense that awareness of the “real” world is lost, generally resulting in a feeling of joy and satisfaction. When perceptual and cognitive systems are under-taxed, people become apathetic and bored. If they are over-taxed, people become stressed and frustrated. Immersion occurs when perceptual and cognitive systems are challenged at near capacity, without being exceeded. Under these conditions, the person loses a sense of the “real” world and typically experiences intense feelings of joy and satisfaction. Immersion can occur while working on a task, playing a game, reading a book, or painting a picture. Immersion is characterized by one or more of the following elements: 1 • • • • • • • • challenges that can be overcome contexts where a person can focus without significant distraction clearly defined goals immediate feedback with regards to actions and overall performance a loss of awareness of the worries and frustrations of everyday life a feeling of control over actions, activities, and the environment a loss of concern regarding matters of the self (e.g., awareness of hunger or thirst) a modified sense of time (e.g., hours can pass by in what seems like minutes). It is not clear which of these elements must be present in what combination to create a generally immersive experience. For example, theme park rides can provide rich sensory experiences with minimal cognitive engagement and still be immersive. Conversely, complex games like chess can provide rich cognitive engagement with minimal sensory experience and also be immersive. Given the wide range of human cognitive abilities and relatively narrow range of perceptual abilities, it is generally easier to design activities and environments that achieve immersion through perceptual stimulation than through cognitive engagement. However, perceptual immersion is more difficult to sustain for long periods of time and is, therefore, usable only for relatively brief experiences. Optimal immersive experiences involve both rich sensory experiences and rich cognitive engagement. Incorporate elements of immersion in activities and environments that seek to engage the attention of people over time—e.g., entertainment, instruction, games, and exhibits. Provide clearly defined goals and challenges that can be overcome. Design environments that minimize distractions, promote a feeling of control, and provide feedback. Emphasize stimuli that distract people from the real world, and suppress stimuli that remind them of the real world. Achieving the right balance of elements to achieve immersion is more art than science; therefore, leave ample time in the design process for experimentation and tuning. See also Chunking, Depth of Processing, Inattentional Blindness, Performance Load, and Storytelling. 134 1 The elements of immersion adapted from Flow: The Psychology of Optimal Experience by Mihaly Csikszentmihalyi, Harper Collins Publishers, 1991. See also Narrative as Virtual Reality by Marie-Laure Ryan, The Johns Hopkins University Press, 2000. Personalized audio guides, lavish contexts, and interactive elements make the R.M.S. Titanic exhibit more than just another museum exhibit—it is an immersive journey through time that allows visitors to personally experience the triumphs and tragedies of the R.M.S. Titanic. The exhibit, featuring such items as a boarding pass and a scale model of the ship, engages the sight, sound, smell, and touch of visitors in the experience, all the while leaving them in control of the pace of presentation and level of interaction. A sense of time is lost, and matters of the real world fade as the tragedy slowly unfolds. Immersion 135 Inattentional Blindness The failure to cognitively process a stimulus that is presented in clear view, leaving the observer without any awareness or memory of the stimulus.1 When focused on performing a task, observers are often blind to stimuli that are literally presented right before their eyes. For example, in 1972, an Eastern Airlines cockpit crew noticed that a landing gear indicator failed to light. They became so fixated on the cause that they failed to notice their loss in altitude or respond to ground alarms. The resulting crash killed more than 100 people. In 2001, a submarine commander looked through the periscope and saw no nearby ships. He ordered the submarine to rapidly surface and unwittingly crashed into another ship directly overhead. The ship overturned, killing nine people. These types of occurrences are common, and are not restricted to catastrophic incidents. It is inattentional blindness that enables many of the tricks and misdirections employed by magicians and illusionists. Inattentional blindness is one reason talking on a cell phone while driving is unsafe — the eyes may be on the road, but the mind is often elsewhere. In any situation where people fix their attention on a task, they will be blind to stimuli that are unexpected and unrelated to the task.2 How does one capture the attention of a person once he or she is focused on a task? It isn’t easy. Typically, being very different is a great way to capture attention. However, when people focus their attention on a certain kind of stimulus, being very different actually makes it less likely that a second stimulus will be noticed. For example, in 1996, Pennsylvania highway workers actually paved over a dead deer — they didn’t see it. It seems reasonable to think that a surprise such as seeing a deer in the road would have captured the workers’ attention, but again, counterintuitively, when people are task-focused, unexpected stimuli are actually worse at getting noticed than anticipated stimuli. When people are in this focused state, roughly 50 percent will be functionally blind to stimuli not related to the task. So, what does get noticed? Stimuli that are relevant to the goal (e.g., a shopper seeking a certain brand of soda will likely notice other soda bottles, but not dishwasher soap bottles), stimuli expressed through different modalities (e.g., auditory versus visual stimuli), faces — whether familiar or anonymous — seem effective at capturing attention, personally relevant stimuli (e.g., a person’s name), and threat stimuli (e.g., snakes).3 Consider inattentional blindness in all contexts where attention is key, including security, safety, product design, retail, and advertising. Given the robustness of the effect, the best strategy is to create or alter tasks to focus attention on desired stimuli (e.g., receiving a coupon book prior to visiting a store can predefine the shopping targets ahead of time). When trying to draw attention away from one stimulus to another, consider semantically similar stimuli, alternative modalities, faces, personal names, and threat stimuli. See also Immersion, Interference Effects, and Threat Detection. 136 Universal Principles of Design 1 Also known as perceptual blindness. 2 The seminal work on inattentional blindness is Inattentional Blindness by Arien Mack and Irvin Rock, The MIT Press, 1998. See also “Gorillas in Our Midst: Sustained Inattentional Blindness for Dynamic Events” by Daniel Simons and Christopher Chabris, Perception, 1999, vol. 28(9), p. 1059–1074; and “Selective Looking: Attending to Visually Specified Events” by Ulric Neisser and Robert Becklen, Cognitive Psychology, 1975, vol. 7, p. 480–494. 3 See, for example, “What You See Is What You Set: Sustained Inattentional Blindness and the Capture of Awareness” by Steven Most, Brian Scholl, Erin Clifford, et al., Psychological Review, 2005, vol. 112(1), p. 217–242. In a now classic experiment on inattentional blindness, Daniel Simons and Christopher Chabris showed subjects a short video of two teams of students tossing a basketball and moving about quickly. Subjects were instructed to count the number of times the team in the white shirts passed the basketball, a challenging task given all of the movement. In the middle of the video, a student in a gorilla costume strolls to the center of the screen, beats her chest, and then strolls off the screen. Roughly half of the subjects in the experiment did not notice the gorilla. Inattentional Blindness 137 Interference Effects A phenomenon in which mental processing is made slower and less accurate by competing mental processes. Interference effects occur when two or more perceptual or cognitive processes are in conflict. Human perception and cognition involve many different mental systems that parse and process information independently of one another. The outputs of these systems are communicated to working memory, where they are interpreted. When the outputs are congruent, the process of interpretation occurs quickly and performance is optimal. When outputs are incongruent, interference occurs and additional processing is needed to resolve the conflict. The additional time required to resolve such conflicts has a negative impact on performance. A few examples of interference effects include: 1 Stroop Interference—an irrelevant aspect of a stimulus triggers a mental process that interferes with processes involving a relevant aspect of the stimulus. For example, the time it takes to name the color of words is greater when the meaning and color of the words conflict. Garner Interference—an irrelevant variation of a stimulus triggers a mental process that interferes with processes involving a relevant aspect of the stimulus. For example, the time it takes to name shapes is greater when they are presented next to shapes that change with each presentation. Proactive Interference—existing memories interfere with learning. For example, in learning a new language, errors are often made when people try to apply the grammar of their native language to the new language. Retroactive Interference—learning interferes with existing memories. For example, learning a new phone number can interfere with phone numbers already in memory. Prevent interference by avoiding designs that create conflicting mental processes. Interference effects of perception (i.e., Stroop and Garner) generally result from conflicting coding combinations (e.g., a red go button, or green stop button) or from an interaction between closely positioned elements that visually interact with one another (e.g., two icons group or blend because of their shape and proximity). Minimize interference effects of learning (i.e., proactive and retroactive) by mixing the presentation modes of instruction (e.g., lecture, video, computer, activities), employing advance organizers, and incorporating periods of rest every thirty to forty-five minutes. See also Advance Organizer, Performance Load, Errors, and Mapping. 138 Universal Principles of Design 1 The seminal works on interference effects include “Studies of Interference in Serial Verbal Reactions” by James R. Stroop, Journal of Experimental Psychology, 1935, vol. 28, p. 643–662; “Stimulus Configuration in Selective Attention Tasks” by James R. Pomerantz and Wendell R. Garner, Perception & Psychophysics, 1973, vol. 14, p. 565–569; and “Characteristics of Word Encoding” by Delos D. Wickens, in Coding Processes in Human Memory edited by A. W. Melton and E. Martin, V. H. Winston, 1972, p. 191–215. GO STOP Red Black White Pink Green Orange Yellow Purple Gray Reading the words aloud is easier than naming their colors. The mental process for reading is more practiced and automatic and, therefore, interferes with the mental process for naming the colors. In populations that have learned that green means go and red means stop, the incongruence between the color and the label-icon results in interference. In populations that have learned that a traffic arrow always means go, the introduction of a red arrow in new traffic lights creates potentially dangerous interference. Trial 1 Trial 2 Naming the column of shapes that stands alone is easier than naming either of the columns located together. The close proximity of the columns results in the activation of mental processes for naming proximal shapes, creating interference. Interference Effects 139 Inverted Pyramid A method of information presentation in which information is presented in descending order of importance. The inverted pyramid refers to a method of information presentation in which critical information is presented first, and then additional elaborative information is presented in descending order of importance. In the pyramid metaphor, the broad base of the pyramid represents the least important information, while the tip of the pyramid represents the most important information. For example, in traditional scientific writing, a historical foundation (tip of the pyramid) is presented first, followed by arguments and evidence, and then a conclusion (base of the pyramid). To invert the pyramid is to present the important information first, and the background information last. The inverted pyramid has been a standard in journalism for over one hundred years, and has found wide use in instructional design, technical writing, and Internet publishing.1 The inverted pyramid consists of a lead (critical information) and a body (elaborative information). The lead is a terse summary of the “what,” “where,” “when,” “who,” “why,” and “how” of the information. The body consists of subsequent paragraphs or chunks of information that elaborate facts and details in descending order of importance. It is increasingly common in Internet publishing to present only the lead, and make the body available upon request (e.g., with a “more…” link). The inverted pyramid offers a number of benefits over traditional methods of information presentation: it conveys the key aspects of the information quickly; it establishes a context in which to interpret subsequent facts; initial chunks of information are more likely to be remembered than later chunks of information; it permits efficient searching and scanning of information; and information can be easily edited for length, knowing that the least important information will always be at the end. The efficiency of the inverted pyramid is also its limiting factor. While it provides a succinct, information-dense method of information presentation, the inverted pyramid does not allow the flexibility of building suspense or creating a surprise ending, so is often perceived as uninteresting and boring. Use the inverted pyramid when presentation efficiency is important. Develop leads that present a concise overview of the information, followed by short chunks of information of decreasing importance. If interestingness is important and has been compromised, include multiple media, interesting layouts, and interactivity to complement the information and actively engage audiences. When it is not possible to use the inverted pyramid method (e.g., in standard scientific writing), consider a compromise solution based on the principle by providing an executive summary at the beginning to present the key findings. See also Advance Organizer, Form Follows Function, Ockham’s Razor, Progressive Disclosure, and Serial Position Effects. 140 Universal Principles of Design 1 The development of the inverted pyramid is attributed to Edwin Stanton, Abraham Lincoln’s Secretary of War (1865). See, for example, Just the Facts: How “Objectivity” Came to Define American Journalism by David T. Z. Mindich, New York University Press, 2000. This report of President Lincoln’s assassination established the inverted pyramid style of writing. Its economy of style, a stark contrast to the lavish prose of the day, was developed for efficient communication by telegraph. Inverted Pyramid 141 Iteration A process of repeating a set of operations until a specific result is achieved. Ordered complexity does not occur without iteration. In nature, iteration allows complex structures to form by progressively building on simpler structures. In design, iteration allows complex structures to be created by progressively exploring, testing, and tuning the design. The emergence of ordered complexity results from an accumulation of knowledge and experience that is then applied to the design. For example, a quality software user interface is developed through a series of design iterations. Each version is reviewed and tested, and the design is then iterated based on the feedback. The interface typically progresses from low fidelity to high fidelity as more is learned about the interface and how it will be used. Iteration occurs in all development cycles in two basic forms: design iteration and development iteration.1 Design iteration is the expected iteration that occurs when exploring, testing, and refining design concepts. Each cycle in the design process narrows the wide range of possibilities until the design conforms to the design requirements. Prototypes of increasing fidelity are used throughout the process to test concepts and identify unknown variables. Members of the target audience should be actively involved in various stages of iterations to support testing and verify design requirements. Whether tests are deemed a success or failure is irrelevant in design iteration, since both success and failure provide important information about what does and does not work. In fact, there is often more value in failure, as valuable lessons are learned about the failure points of a design. The outcome of design iteration is a detailed and well-tested specification that can be developed into a final product.2 Development iteration is the unexpected iteration that occurs when building a product. Unlike design iteration, development iteration is rework—i.e., unnecessary waste in the development cycle. Development iteration is costly and undesirable, and generally the result of either inadequate or incorrect design specifications, or poor planning and management in the development process. The unknowns associated with a design should ideally be eliminated during the design stage. Plan for and employ design iteration. Establish clear criteria defining the degree to which design requirements must be satisfied for the design to be considered complete. One of the most effective methods of reducing development iteration is to ensure that all development members have a clear, high-level vision of the final product. This is often accomplished through well-written specifications accompanied by high-fidelity models and prototypes. See also Development Cycle, Fibonacci Sequence, Most Advanced Yet Acceptable, Prototyping, and Self-Similarity. 142 Universal Principles of Design 1 A seminal contemporary work on iteration in design is The Evolution of Useful Things by Henry Petroski, Vintage Books, 1994. See also Product Design and Development by Karl T. Ulrich and Steven D. Eppinger, McGraw-Hill Higher Education, 2nd ed., 1999. See also “Positive vs. Negative Iteration in Design” by Glenn Ballard, Proceedings of the Eighth Annual Conference of the International Group for Lean Construction, 2000. 2 A common problem with design iteration is the absence of a defined endpoint—i.e., each iteration refines the design, but also reveals additional opportunities for refinement, resulting in a design process that never ends. To avoid this, establish clear criteria defining the degree to which design requirements must be satisfied for the design to be considered complete. Quality design does not occur without iteration. For example, the design of the SnoWalkers snowshoes is the result of numerous design iterations over a two-year period. The design process made ample use of prototypes, which allowed designers to improve their understanding of design requirements and product performance, and continually refine the design with each iteration. Iteration 143 Law of Prägnanz A tendency to interpret ambiguous images as simple and complete, versus complex and incomplete.1 The Law of Prägnanz is one of several principles referred to as Gestalt principles of perception. It asserts that when people are presented with a set of ambiguous elements (elements that can be interpreted in different ways), they interpret the elements in the simplest way. Here, “simplest” refers to arrangements having fewer rather than more elements, having symmetrical rather than asymmetrical compositions, and generally observing the other Gestalt principles of perception.2 For example, a set of shapes that touches at their edges could be interpreted as either adjacent or overlapping. When the shapes are complex, the simplest interpretation is that they are adjacent like pieces in a puzzle. When the shapes are simple, the simplest interpretation is that they overlap one another. The law applies similarly to the way in which images are recalled from memory. For example, people recall the positions of countries on maps as more aligned and symmetrical than they actually are. The tendency to perceive and recall images as simply as possible indicates that cognitive resources are being applied to translate or encode images into simpler forms. This suggests that fewer cognitive resources may be needed if images are simpler at the outset. Research supports this idea and confirms that people are better able to visually process and remember simple figures than complex figures.3 Therefore, minimize the number of elements in a design. Note that symmetrical compositions are perceived as simpler and more stable than asymmetrical compositions, but symmetrical compositions are also perceived to be less interesting. Favor symmetrical compositions when efficiency of use is the priority, and asymmetrical compositions when interestingness is the priority. Consider all of the Gestalt principles of perception (closure, common fate, figure-ground relationship, good continuation, proximity, similarity, and uniform connectedness). See also Aesthetic-Usability Effect, Ockham’s Razor, Rule of Thirds, and Visuospacial Resonance. 144 Universal Principles of Design 1 Also known as the law of good configuration, law of simplicity, law of pregnance, law of precision, and law of good figure. 2 The seminal work on the Law of Prägnanz is Principles of Gestalt Psychology by Kurt Koffka, Harcourt Brace, 1935. 3 See, for example, “The Status of Minimum Principle in the Theoretical Analysis of Visual Perception” by Gary Hatfield and William Epstein, Psychological Bulletin, 1985, vol. 97, p. 155–186. Low resolution images (left) of a rock formation on Mars led many to conclude that intelligent life once existed there. Higher-resolution images (right) taken some years later suggest a more Earth-based explanation: Humans tend to add order and meaning to patterns and formations that do not exist outside their perception. These sets of characters are interpreted as single faces rather than multiple independent characters. Both sets of figures are interpreted as simple overlapping shapes, rather than a more complex interpretation— e.g., two inverted “L” shapes and a square, and two triangles and a fivesided polygon. Dazzle camouflage schemes used on war ships were designed to prevent simple interpretations of boat type and orientation, making it a difficult target for submarines. This is a rendering of the French cruiser Gloire. Law of Prägnanz 145 Layering The process of organizing information into related groupings in order to manage complexity and reinforce relationships in the information. Layering involves organizing information into related groupings and then presenting or making available only certain groupings at any one time. Layering is primarily used to manage complexity, but can also be used to reinforce relationships in information. There are two basic kinds of layering: two-dimensional and three-dimensional.1 Two-dimensional layering involves separating information into layers such that only one layer of information can be viewed at a time. Two-dimensional layers can be revealed in either a linear or nonlinear fashion. Linear layers are useful when information has a clear beginning, middle, and end (e.g., stories), and are revealed successively like pages in a book. Nonlinear layers are useful when reinforcing relationships between the layers. The types of nonlinear layer relationships can be hierarchical, parallel, or web. Hierarchical layers are useful when information has superordinate and subordinate relationships within itself (e.g., organizational chart), and are revealed top-down or bottom-up in rigid accordance with the hierarchical structure. Parallel layers are useful when information is based on the organization of other information (e.g., thesaurus), and are revealed through some correspondence with that organization. Web layers are useful when information has many different kinds of relationships within itself (e.g., hypertext), and are revealed through any number of associative linkages to other layers. Three-dimensional layering involves separating information into layers such that multiple layers of information can be viewed at a time. Three-dimensional layers are revealed as either opaque or transparent planes of information that sit atop one another (i.e., in a third dimension). Opaque layers are useful when additional information about a particular item is desired without switching contexts (e.g., software pop-up windows). Transparent layers are useful when overlays of information combine to illustrate concepts or highlight relationships (e.g., weather maps).2 Use two-dimensional layering to manage complexity and direct navigation through information. Consider linear layers when telling stories and presenting sequences of time-based events, and use nonlinear layers when emphasizing relationships within the information. Use three-dimensional layering to elaborate information and illustrate concepts without switching contexts. Consider opaque layers when presenting elaborative information, and transparent layers when illustrating concepts or highlighting relationships in information. See also Chunking, Five Hat Racks, Progressive Disclosure, and Propositional Density. 146 Universal Principles of Design 1 A similar concept is found in Designing Business: Multiple Media, Multiple Disciplines by Clement Mok, Adobe Press, 1996, p. 102–107 [Organizational Models]. 2 See, for example, Envisioning Information by Edward R. Tufte, Graphics Press, 1998, p. 53–65; 81–95 [Layering and Separation; Color and Information]. Two-Dimensional Layering Three-Dimensional Layering Linear Opaque Beginning Middle 1 Middle 2 End Olympia Salem Olympia Salem Sacramento Sacramento Phoenix is the capital of Arizona Phoenix Nonlinear Hierarchical President Vice President Services Word Synonym Word Synonym Word Synonym Web Related Information 62º Vice President Products Sales Manager Manager Parallel Transparent 87º Production Manager 65º 71º 90º Three-dimensional layering is useful for elaboration and highlighting. Relationships and patterns on one layer of information (left) are elaborated by layers of information that pop up or overlay (right). Related Information Related Information Home Page Related Information Related Information Related Information Two-dimensional layering is useful for presentation and navigation. Layers are revealed one at a time, like pages in a book. Layering UPOD p124-197_.indd 147 147 Legibility The visual clarity of text, generally based on the size, typeface, contrast, text block, and spacing of the characters used. Confusion regarding the research on legibility is as persistent as it is pervasive. The rapid growth and advancement of modern desktop publishing, Web-based publishing, and multimedia presentation continue to compound the confusion with increasing font and layout capabilities, display and print options, and the need to effectively integrate with other media. The following guidelines address common issues regarding text legibility.1 1 The seminal empirical works on legibility for print are Bases for Effective Reading, University of Minnesota Press, 1963; and Legibility of Print, Iowa State University Press, 1965, both by Miles A. Tinker. A comprehensive and elegant contemporary reference from a typographic perspective is The Elements of Typographic Style by Robert Bringhurst, Hartley & Marks (2nd ed.), 1997. 2 Legibility research on low-resolution computer displays continues to yield mixed results but generally supports Tinker’s original findings. However, be conservative to account for lowerresolution displays. 3 On lower-resolution displays and for type smaller than 12 point, use sans serif typefaces without antialiasing. Serifs and antialiasing blur the characters of smaller type and, therefore, compromise legibility. 4 Dark text on light backgrounds is preferred. High-contrast, inverse text can “visually bleed” to the background and dramatically reduce legibility. Factors other than legibility should be considered when selecting foreground/ background color combinations (e.g., color blindness and fatigue), so select carefully and test atypical combinations. 5 The speed with which text can be visually processed is greatest on long text lines (80 characters or more). However, readers prefer short text lines (35 to 55 characters). Unless visual processing speed is critical to the design task, shorter text lines are recommended. See, for example, “The Effects of Line Length and Method of Movement on Patterns of Reading from Screen,” by Mary C. Dyson and Gary J. Kipping, Visible Language, 1998, vol. 32(2), p. 150–181. Size For printed text, standard 9- to 12-point type is considered optimal. Smaller sizes are acceptable when limited to captions and notes. Use larger type for lowresolution displays and more senior audiences.2 Typeface There is no performance difference between serif and sans serif typefaces, so select based on aesthetic preference. Sentence case text should be used for text blocks. On low-resolution displays, antialiasing the text may marginally improve legibility, but primarily serves as an aesthetic enhancement of the typeface.3 Contrast Use dark text on a light background or vice versa. Performance is optimal when contrast levels between text and background exceed 70 percent. Foreground/ background color combinations generally do not affect legibility as long as you observe the minimum contrast level, so select based on aesthetic preference. Patterned or textured backgrounds can dramatically reduce legibility, and should be avoided.4 Text Blocks There is no performance difference between justified and unjustified text, so select based on aesthetic preference. For 9- to 12-point type, a line length of 3 to 5 inches (8 cm to 13 cm) is recommended, resulting in a maximum of about 10 to 12 words per line, or 35 to 55 characters per line.5 Spacing For 9- to 12-point type, set leading (spacing between text lines, measured from baseline to baseline) to the type size plus 1 to 4 points. Proportionally spaced typefaces are preferred over monospaced. See also Iconic Representation and Readability. 148 Universal Principles of Design
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