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.
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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.
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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.
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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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