Transcript No Slide Title

Bathtub control
• User’s goals:
– Warm bath
– Right amount of water
• Psychological variables
– Temperature & water depth
• Physical variables
– Cold water flow rate
– Warm water flow rate
Design exercise
Design the perfect bathtub control.
1. Assume you have unlimited budget
2. Bath control only… no shower.
3. Think about mapping controls to the
users goals (physical variables).
HCI Design Step 1
• Knowing the user
– Users are distinct individuals
– They have similar architectures
• Learning and memory for items is
similar
• Motor, visual and hearing performance
is similar
• HCI design is user-center Design
– Changing the system to fit the user.
– Not the other way around.
What do we need to know
about people?
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Perception
Memory
Vision
Information Processing
Mental Models
Learning
Skill
Individual Differences
Don’t make me think?
Same or Different?
A A
A A
A A
A a
A a
A B
Even simple decisions require
thought and depend on context
Things that make us think
Jobs
Employment Opportunities
Job-o-Rama
The Model of Human
Processor
• The Perceptual System
– Seeing, hearing, touching, (smelling,
tasting)
• The Motor System
– Movement
• The Cognitive System
– learning, reasoning, and problemsolving,
What we need to know about users
• They forget
• They make mistakes
• Behavior is guided by prior knowledge
They forget
• Short Term Memory
– limited duration (200ms - 30 sec)
– limited capacity (7 ± 2 chunks)
• Design implications
– Misinterpreted and overused (e.g. menu size)
– Use to watch for memory demands of the UI
– it is hard to remember much information
from one step in a process to another
(leave information on the screen)
– Task chunking leads to “closure”
Pay Attention ….
5476926264
What is the number?
5476926264
Pay Attention ….
505 646 6222
What is the number?
505 646 6222
• Information can be grouped
into chunked so that we can
increase our short-term
memory to 7 +/- 2 chunks
Another Example
T HEC ATR ANU PTH ETR EE
What is the String?
• THE CAT RAN UP THE TREE
• T HEC ATR ANU PTH ETR EE
• Patterns and meanings helps to
increase capacity of short-term
memory.
They forget
• Long Term Memory
– is organized and associative but imperfect
– recognition is easier than recall
• Design implications
– provide meaningful retrieval cues
– visibility is important (e.g. menus)
• but it has to make sense
– cues must be easily discriminated
• e.g. is it “options” or “properties”
• Half of you close your eyes.
• Now, the other half close your eyes.
How many saw
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Bagel
Coffee
Newspaper
--------------Freeway
Traffic
Jam
Memory
• Involves first encoding and then retrieving
knowledge
• We don’t remember everything - involves
filtering and processing what is attended to
• Context is important in affecting our memory
(i.e., where, when)
• Well known fact that we recognize things much
better than being able to recall things
– Better at remembering images than words
– Why interfaces are largely visual
Processing in memory
• Encoding is first stage of memory
– determines which information is attended to in the
environment and how it is interpreted
• The more attention paid to something,
• And the more it is processed in terms of thinking
about it and comparing it with other knowledge,
• The more likely it is to be remembered
– e.g., when learning about HCI, it is much better to
reflect upon it, carry out exercises, have discussions
with others about it, and write notes than just passively
read a book, listen to a lecture or watch a video about it
Context is important
• Context affects the extent to which
information can be subsequently retrieved
• Sometimes it can be difficult for people
to recall information that was encoded in a
different context
– e.g., You are on a train and someone comes up to you and
says hello. You don’t recognize him for a few moments
but then realize it is one of your neighbors. You are only
used to seeing your neighbor in the hallway of your
apartment block and seeing him out of context makes him
difficult to recognize initially
Activity
• Try to remember the dates of your
grandparents’ birthday
• Try to remember the cover of the last two
DVDs or you bought or rented
• Which was easiest? Why?
• People are very good at remembering visual
cues about things
– e.g., the color of items, the location of objects and marks
on an object
• They find it more difficult to learn and
remember arbitrary material
– e.g., birthdays and phone numbers
Recognition versus recall
• Command-based interfaces require users
to recall from memory a name from a
possible set of 100s
• GUIs provide visually-based options that
users need only browse through until they
recognize one
• Web browsers, MP3 players, etc., provide
lists of visited URLs, song titles etc., that
support recognition memory
The problem with the classic
‘72’
• George Miller’s theory of how much
information people can remember
• People’s immediate memory capacity is very
limited
• Many designers have been led to believe
that this is useful finding for interaction
design
What some designers get up to…
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Present only 7 options on a menu
Display only 7 icons on a tool bar
Have no more than 7 bullets in a list
Place only 7 items on a pull down menu
Place only 7 tabs on the top of a website page
– But this is wrong? Why?
Why?
• Inappropriate application of the theory
• People can scan lists of bullets, tabs, menu items
till they see the one they want
• They don’t have to recall them from memory
having only briefly heard or seen them
• Sometimes a small number of items is good design
• But it depends on task and available screen estate
Personal information management
• Personal information management (PIM) is a
growing problem for most users
– Who have vast numbers of documents, images, music
files, video clips, emails, attachments, bookmarks, etc.,
– Major problem is deciding where and how to save them
all, then remembering what they were called and where
to find them again
– Naming most common means of encoding them
– Trying to remember a name of a file created some time
back can be very difficult, especially when have 1000s
and 1000s
– How might such a process be facilitated taking into
account people’s memory abilities?
Personal information
management
• Memory involves 2 processes
– recall-directed and recognition-based scanning
• File management systems should be
designed to optimize both kinds of memory
processes
– e.g., Search box and history list
• Help users encode files in richer ways
– Provide them with ways of saving files using colour,
flagging, image, flexible text, time stamping, etc
Design implications
• Don’t overload users’ memories with
complicated procedures for carrying out
tasks
• Design interfaces that promote recognition
rather than recall
• Provide users with a variety of ways of
encoding digital information to help them
remember where they have stored them
– e.g., categories, color, flagging, time stamping
What we need to know about users
• They forget
• They make mistakes
• Behavior is guided by prior knowledge
The Stoop Effect Tells Us
• People have a hard time overcoming
well practiced skills (like reading)
• We need to design applications that
match acquired skills and work habits
• User testing is a good way of
determining if our designs violate
over learned skills
Mental models
• Users develop an understanding of a system through
learning and using it
• Knowledge is often described as a mental model
– How to use the system (what to do next)
– What to do with unfamiliar systems or unexpected situations
(how the system works)
• People make inferences using mental models of how to
carry out tasks
Mental models
• Craik (1943) described mental models as
internal constructions of some aspect of
the external world enabling predictions to
be made
• Involves unconscious and conscious
processes, where images and analogies are
activated
• Deep versus shallow models (e.g. how to
drive a car and how it works)
Everyday reasoning and mental
models
(a) You arrive home on a cold winter’s night to a cold
house. How do you get the house to warm up as quickly
as possible? Set the thermostat to be at its highest
or to the desired temperature?
(b) You arrive home starving hungry. You look in the fridge
and find all that is left is an uncooked pizza. You have
an electric oven. Do you warm it up to 375 degrees
first and then put it in (as specified by the
instructions) or turn the oven up higher to try to warm
it up quicker?
Heating up a room or oven that is
thermostat-controlled
• Many people have erroneous mental models
(Kempton, 1996)
• Why?
– General valve theory, where ‘more is more’ principle is
generalised to different settings (e.g. gas pedal, gas
cooker, tap, radio volume)
– Thermostats based on model of on-off switch model
Heating up a room or oven that is
thermostat-controlled
• Same is often true for understanding how
interactive devices and computers work:
– Poor, often incomplete, easily confusable, based
on inappropriate analogies and superstition
(Norman, 1983)
– e.g. elevators and pedestrian crossings - lot of
people hit the button at least twice
– Why? Think it will make the lights change
faster or ensure the elevator arrives!
Exercise: ATMs
• Write down how an ATM works
– How much money are you allowed to take out?
– What denominations?
– If you went to another machine and tried the same what would
happen?
– What information is on the strip on your card? How is this used?
– What happens if you enter the wrong number?
– Why are there pauses between the steps of a transaction? What
happens if you try to type during them?
– Why does the card stay inside the machine?
– Do you count the money? Why?
How did you fare?
• Your mental model
– How accurate?
– How similar?
– How shallow?
• Payne (1991) did a similar study and found that
people frequently resort to analogies to explain
how they work
• People’s accounts greatly varied and were often ad
hoc
Just enough Psychology
• People make mistakes because they
can easily get distracted by changes
in the task context.
The Model of Human
Processor
• The Perceptual System
– Seeing, hearing, touching, (smelling,
tasting)
• The Motor System
– Movement
• The Cognitive System
– learning, reasoning, and problemsolving,
Perceptual Processor
• Human Visual Performance
Arguments
– important items stand out by varying
properties of items, e.g., color, shape
– user search guided by organization
of screen elements, e.g., user’s eye
navigates from left to right and top
to bottom
Perceptual Processor
• Anything that is seen by our eyes
has to be processed
• The processing difficulty depends
the complexity of the visual scene
and on our previous memory of the
scene
Visual Processing Speed
• Images that we already are familiar
with simply match to images stored in
our memory
– the processing time is fast
– the processing effort is low
Pay Attention!
I am going to show the next
slide as fast as I can
M
Take out a pencil and draw
the character you just saw
Pay Attention!
I am going to show the next
slide as fast as I can
Take out a pencil and draw
the character you just saw
Visual Processing Speed
• For native English
readers, the
character on top right
is processed faster
• For native Chinese
readers, the
character on the
bottom right is
processed faster
A
Visual Processing Speed
• English character has same complexity
as Chinese character.
• Because the English character simply
needs to be mapped to a similar
character in our memory, the visual
understanding speed is much shorter
• Chinese students will, of course, be
faster with the Chinese characters
Design implication
• Provide external representations at the
interface that reduce memory load and
facilitate computational offloading
e.g. Information
visualizations have
been designed to
allow people to make
sense and rapid
decisions about
masses of data
Galitz: Graphical Design
Principles
• Principles come from the way the
human visual system works
• Principles relate to;
– HOW HARD IT IS TO PROCESS
VISUAL SCENE
– HOW MUCH OF SCENE CAN BE
MATCHED TO MEMORY
Organization of Screen
Elements
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Balance
Symmetry
Regularity
Predictability
Sequentiality
Economy
Unity
Proportion
Simplicity
Groupings
The Model of Human
Processor
• The Perceptual System
– Seeing, hearing, touching, (smelling,
tasting)
• The Motor System
– Movement
• The Cognitive System
– learning, reasoning, and problemsolving,
Motor Processor
• Human Motor Performance
Arguments
– items that are co-selected should be
close
– small items are hard to select
– selection while holding the mouse
button down is a harder motor task
Geometry and Movement
• Small targets are harder (and slower)
to hit with a mouse than big target
• long mouse movements are slower
than short ones
• icons pack differently from text
strings
• more keystrokes take longer to type
• switching between mouse and
keyboard is slow
Fitt’s Law
MT = a + b log2(2A/W)
where
MT = movement time
a,b = regression coefficients
A = distance of movement from start to target center
W = width of the target
Cognitive Processor
• Problem-Solving Arguments
– problems can be hard to solve if
represented poorly
– if the user has to map their problem
representation into a different one on
the screen, the problem will be harder
to do
• Learning Arguments
– Automatic learning
Problem-Solving
• it should be possible to select
operations relevant to goals
• it should be possible to know what an
operation has actually done
The dog is facing west.
Make him face east by changing the positions of just two matches.
His tail must remain up!
Solution!
Assumptions can make easy things hard.
We don’t always know what our user’s assumptions are.
And/Or questions
Student
Bill
???
Frank
Henry
???
???
???
Homestate
Arizona
Texas
Colorado
Arizona
New Mexico
Texas
New Mexico
Enter your question: Which students are from Texas and New Mexico
Who is from New Mexico and Texas?
Who is from New Mexico or Texas?
Texas
New Mexico
And/Or Method
• Thirty-six participants from a
temporary agency
– Word processing but no database
experience
– Were asked to test a new database
program which used English.
• Forty problems
– Equal numbers of And (Intersection) and
Or (Union) divided between one or two
database attributes
And/Or Results
Correct use
Actual use
OR
AND
And
.30
.99
Or
.60
.01
Neither
.10
.00
Attention
• big changes are more noticeable
• information presented close to where
the user is looking is more likely to be
read
• auditory signals cannot be ignored as
easily as visual signals
What we need to know about users
• They forget
• They make mistakes
• Behavior is guided by prior knowledge