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Display design
When a computer operates in a manner that is not intended, humans often
demonstrate their
disgust by s
triking
the monitor. This monitor, or
visual
display, is simply the portal that allows
one to interact with the technology. The d
isplay
(
be it
visual, auditory, tactile, etc.) is an
artifact
designed to support the perception of relevant system variables and
to facilitate further
processing of that information. Before a display is designed, the task that
the display
is
intended to support m
ust be defined (e.g. navigating, controlling, decision making, learning,
entertaining, etc.). A user or operator must be able to process whatever
information that a
system
generates and displays; therefore, the information must be displayed
according to
pr
inciples in a manner
that will support perception, situation awareness, and understanding.
Engineering psychologist Christopher Wickens has placed these principles
into
four
categories
as depicted in the chart below.
.
Perceptual Principles
Princip
les Based on
Attention
Memory Principles
Mental Model
Principles
1.
Make displays
legible (or
audible)
6.
Minimizing
information
access cost
9.
Principle of
consistency
12.
Principle of
pictorial realism
2.
Avoid absolute
judgment limits
7.
Principle of
multiple
resources
10.
Principle of
predictive aiding
13.
Principle of the
moving part
3.
Similarity causes
confusion: Use
discriminable
elements
8.
Proximity
compatibility
principle
11.
Replace memory
with visual
information:
knowledge in the
world
4.
Top
down
processing
5.
Redundancy gain
THIRTEEN PRINCIPLES OF DISPLAY DESIGN
These principles of human perception and information processing can be
utilized to create an
effective
display design. A reduction in errors, a reduction in required training time,
an increase
in efficiency, and
an increase in user satisfaction are a few of the many potential benefits that
can be achieved through
the proper application
of these principles.
Certain principles may not be applicable to different displays or situations.
Some princi
ples may
seem to
be conflicting, and there is no simple solution to say that one principle is
more
important than another.
The principles may be tailored to a specific design or situation.
Achieving a functional
balance
among the
principles is critical fo
r an effective design.
Perceptual Principles
1.
Make displays legible (or audible)
If the characters
, objects
or
sounds
being displayed
are
not discernible, then the operator
cannot effectively make use of them.
From bad handwriting to small pitch font or even faint
buzzers and bells, if something cannot enter the consciousness from the
very beginning, then
the chances of it reaching the intended user or consumer for use is
extremely low. If a display is
difficul
t to use in perfect situations (good lighting and quiet), it probably won’t work
well at all
in a noisy high tempo environment that routinely make perception more
difficult.
Small pitch font and some none standard fonts are hard to read.
Light or faint
text is often difficult to read.
Can you hear me now? Cell phones often become problematic in loud
outdoors situations and
in poor
communication provider
coverage areas.
2.
Avoid absolute judgment limits
A
void making the operator
or user
judge the repre
sented variable level on the basis of a single
sensory dimension (color, size, pitch, etc.)
If a judgment is required, set the user up for success.
Limit the number of possible levels or differentiations required to no more
than 5 to 7.
------------------------There are 6 different dashed lines with six different saturation levels
on the left or beginning of this paragraph. Using the single variable of
saturation, a human
could probabl
y
only
reliably
differentiate
between the second one, the
third one and the sixth
one, and probably could only do this in ideal environmental conditions.
Use multiple parameters to code something (shape, size, tone, loudness,
etc) and be careful
with pushing the edges of human’s ability to differentiate simila
r qualities.
3.
Similarity causes confusion: Use discriminable elements
Similar appearing signals are likely to be confused.
The ratio of similar features to different
features is what causes signals to be noted as similar. For example,
JLM456 is more similar to
JLM457 than 56 is to 57. Unnecessary similar features should be removed
and dissimilar
features should be highlighted.
Looking at the switches below, the only differentiation is 1A and 7A, and
depending
on
where
you are standing and looking up to read, the differences might not be
noticeable at all.
4.
Top
down processing
Signals are routinely perceived and interpreted
based on
an
operator’s past experience.
Humans see and hear what they expect.
If the presentation of a signal is contrary to
expectations, or is the result of some unlikely or rare event, then more
physical evidence of
that signal must be presented to ens
ure that it is interpreted correctly.
Relay or line trips during a thunderstorm will usually immediately drive an
operator to perceive
things that are related to impacts associate
d
with that weather phenomena (such as lightening
strikes). Signals that can be associated with certain phenomena will drive
that type of decision
making even if the si
gnal
might not be associated with that impact. The context that the
operator is in always
matters
, as one’s expectations can drive perception
.
5.
Redundancy gain
P
resenting a signal in more than one way increases the likelihood it will be
interpreted
correctly
.
This can be done by presenting the signal in alternative physical forms (e.g.
color
and
shape, voice and print, etc.), as redundancy does not imply repetition. One
of the most
striking
example
s
of this is a traffic light,
as color and position are redundant. A person that is red and
green color blind can simply use the position of the lig
ht to discern the meaning of the signal
,
thus if one portion of the signal fails to effectively penetrate the signal, the
other may prevail.
When both signals are successfully received, the
confluence of the two signals, particularly if
the signals are fr
om different modalities (sight and sound), can actually produce a greater
impact at the human physiological level, resulting in greater chances of the
signal being
received. However, if the signals are not congruent, meaning the sound
says
one thing and t
he
visual signals
says
something else, perception and
comprehension will suffer both in latency (or
time) and accuracy (increased misperception).
An example of this
incongruent
pairing of
modalities
of sight and sound can be experienced in watching an old martial arts
movie where
the voice and lip movements are
not in synch.
Principles Based on Attention
6.
Minimize
information access cost
Frequently
accessed sources of info
rmation
should be readily available
. There is a cost of time
and effort when a user’s attention must be moved from display to display in
order to gather
information. Computer menus are sometimes deep and cumbersome as
the user tries to figure
out the appropriat
e steps or processes.
Visible menus, strategies to keep mode awareness and
efficient place keeping functions all help in this endeavor. An example of
this principle is the
right mouse button
on a computer will often bring
up
a
menu of common commands
.
Ce
rtain information is always important and should not require anything but
minimal effort to
access (e.g. speedometer on a car).
When the user’s attention is diverted from one location to
another to access necessary information, there is usually an associat
ed cost in time or effort. A
display design should minimize this cost by allowing for frequently
accessed sources to be
located at the nearest possible position. However, adequate legibility
should not be sacrificed
to reduce this cost.
7.
Principle of mult
iple resources
A user can more easily process information across different resources. For
example, visual and
auditory
information can be presented simultaneously rather than presenting all
visual or all
auditory information.
This principle supports infor
mation
or signals
that
are
not necessarily the
same
, as
was discussed in the concept of redundancy gain.
Certain signals are better for
directing attention, like a localized or directional auditory alarm, while other
signals are better