Laws of Interaction Design
Moore’s Law
Attributed to Gordon Moore,
co-founder of Intel, Moore's
Law is the empirical
observation made in 1965
that the number of
transistors on an integrated
circuit for minimum
component cost doubles
every 24 months
Essentially every two years,
computers will have more
power for less cost which is
currently still happening.
or designers, this means
that device designers will
have access to this ongoing
advances in technology
Design for this future!
Moore's Law Means More Performance.
Processing power, measured in millions of
instructions per second (MIPS), has steadily
risen because of increased transistor counts.
Source: http://www.intel.com/technology/mooreslaw/
Fitt’s Law
Implications for IxD
Fitts' law
• The time it takes to move from • Clickable objects like buttons
need to be reasonable sizes as
a starting position to a final
the size of the target matters
target is determined by two
factors:
– The distance to the target, and • The edges and corners of
screens are excellent places to
– The size of the target
position things like menu bars
and buttons
• The larger the targe, the faster
– they are huge targets because
it can be pointed to
they basically have infinite
• The closer the target, the
height or width
faster it can be pointed to
– The mouse will stop no matter
what
Resources
• Web Based Test of Fitts Law
• Pop up menus that appear next
to the object that a person is
– http://www.tele-actor.net/fitts/
working on – can usually be
• Tog’s Test
opened more quickly than can
– http://www.asktog.com/col
pull down menus at the top of
umns/022DesignedToGiveFi
the screen. These require
tts.html
travel to another part of the
screen
Hick’s Law
Hicks Law
• The time it takes for
users to make decisions
is determined by the
number of possible
choices they have
• Hicks law claims that a
user will more quickly
make choices from one
menu of 10 items than
from two menus of 5
items each, because of
the way items are
eliminated
• Hick’s law also states
that the time it takes to
make a decision is
affected by:
– Familiarity with the
choices, and
– Format of the choices
eg; sounds, words,
videos or buttons?
Design Implications
• It is better for products
to give users many
choices simultaneously
instead of organising the
choices into hierarchical
groups – eg drop down
menus
• (How controversial is
this?)
Magical Number 7
Miller’s Magical #7
• The human mind is
best able to
remember
information in
chunks of seven
items “plus or minus
two”
• We have difficulty
with our short term
memory when there
is an information
overload
Design Implications
• This does not mean
that there should
only be 7 items on
the screen at one
time
• Take care not to
overload a user’s
short term memory
capacity when
designing a product
• How does this relate
to Hick’s Law
Original Paper:
http://www.well.com/user/smalin/miller.html
Law of Conservation Complexity
Conservation of Complexity
• Some complexity is
inherent to every process.
• There is a point beyond
which you cant simplify a
process any further; you
can only move the
inherent complexity from
one page to another
• Eg: in an e-mail message
your email address and the
address of the person you
are sending the mail is
required. The email client
takes care of the user’s
address, the user is only
responsible for one
Design Implications
• All processes have elements
that cannot be made
simpler
• Look for reasonable places
to move the complexity in
the products you are
creating.
– The burden of complexity
needs to be shared as
much as possible by the
products interaction
designers make
Resources
• Laws of Interaction Design: an
interview with Larry Tessler
– http://www.designingforinteraction.
com/tesler.html
• The complexity Paradox
– http://www.asktog.com/columns/0
11complexity.html
Poka Yoka Principle
Poka Yoke Principle
• Originating with Japanese
industrial engineer Shigeo
Shingo at Toyota this principle
means "fool-proofing" a
design to ensure the user will
not make a mistake.
Examples
• a normal 3.5" floppy
disk: the top-right
corner is shaped so
that the disk cannot be
inserted upside-down.
• The new iPod Shuffle stops
playing music when the
earphone jack is unplugged.
When the earphones are
plugged back in, the music
resumes right where it left off.
Design Implications
• Ensure proper conditions
exist before a process
begins preventing
problems from occurring
the first place
• When preventions is not
possible, problems
should be stopped as
early as possible in the
process.
Resources
•
Poka Yoke: Mistake-Proofing Fool-Proofing - Failsafing
– http://www.saferpak.com/poka
_yoke.htm
Direct and Indirect Manipulation
• Direct manipulation
Schneiderman) refers to
the process in which , by
selecting a digital object
with a finger or with a
mouse of some other
input device, we can
then do something to the
object move it, turn it,
drag it , change its colour
etc
• Direct manipulations is
more easily learned as it
maps directly to our
physical experiences
• Good for manipulating
3D objects in digital
space
• Indirect manipulation, we
use a command or menu
that isn't directly a part
of the digital object to
alter that object
• Eg Ctrl A or Select all
Design Implications
• Need to decide how
digital objects in
products can be
manipulated: directly,
indirectly or both
Feedback and Feedforward
Feedback
• An indication that
something has happened
• Should occur early and
often
• Every action by a person
who engages with a product
or service should be
accompanied by some
acknowledgement of the
action
• If there is no immediate
feedback, users will repeat
the action they just did –
can cause serious errors
• Appropriate feedback is the
challenge for the designershow will the product/serice
respond; in what
manner?Simple or complex?
Feedforward
• The user knows what will
happen before the they
perform an action
• Can be a straightforward
message: eg pushing this
button will submit your
order
• Or simple hyper text cues
• Allows users to perform an
action with confidence
because it givesm them an
idea o f what will happen
next,
• Harder to design into
products and services than
feedback.