Transcript Human abilities - Personal Web Pages

Human Abilities
Sensory and cognitive capabilities
Typical Person
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Do we really have limited memory capacity?
Basic Human Capabilities
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Do not change very rapidly
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Not like Moore’s law!
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Have limits, which are important to understand
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Why do we care?
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Better design!
Want to improve user performance
Universal design – design for everyone, including
those with disabilities
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We’ll come back to this later in the semester…
Usable Senses
The 5 senses (sight, sound, touch, taste and smell) are used by
us every day
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each is important on its own
together, they provide a fuller interaction with the natural world
Computers rarely offer such a rich interaction
We can use
• sight • sound • touch (sometimes)
We cannot (yet) use
• taste • smell
Vision (more to come in visual design)
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Color
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About 9 % of males are red-green colorblind!
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See http://colorlab.wickline.org/colorblind/colorlab/
Color perception is weak in peripheral vision
Movement in our peripheral vision is distracting
Acuity (the smallest size we can see)
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Less for blue and yellow than for red and green
Color Surround Effect
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Our perception of a color is affected by the
surrounding color
Which is easiest to read and why?
What is the time?
What is the time?
What is the time?
What is the time?
What is the time?
From http://www.id-book.com
Audition (Hearing)
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Often take for granted how much we rely on it
(error beeps, disk whirring)
Sounds are transitory
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Good for alerts, redundant communication
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People become habituated to continuous sounds
Some sounds can also be distracting or annoying
We are very good at determining source of a sound
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Implications ?
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Attention
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Involves audio and/or visual senses
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Selecting things to concentrate on from the mass of
stimuli around us
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Focused and divided attention enables us to be
selective but limits our ability to keep track of all
events
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Structure information to capture users’ attention
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perceptual boundaries (windows), color, reverse video,
sound and flashing lights
From http://www.id-book.com
Activity: Find the price of a double room at the Holiday Inn in
Bradley
From http://www.id-book.com
Activity: Find the price for a double room at the Quality Inn in
Columbia
From http://www.id-book.com
Study
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Tullis (1987) found that the two screens produced
quite different results
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1st screen - took an average of 5.5 seconds to search
2nd screen - took 3.2 seconds to search
Why, since both displays have the same density of
information (31%)?
Spacing
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In the 1st screen the information is bunched up together, making it
hard to search
In the 2nd screen the characters are grouped into vertical
categories of information making it easier
From http://www.id-book.com
Design implications
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Representations of information need to be
perceptible and recognizable
Make information salient when it needs attending to
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Make things stand out with colour, ordering, spacing,
underlining, sequencing and animation
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Avoid cluttering the interface
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Sounds should be audible and distinguishable
Speech output should enable users to distinguish
between the set of spoken words
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From http://www.id-book.com
Motor System (Our Output
System)
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Capabilities
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Often cause of errors
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Wrong button
Double-click vs. single click
Principles
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Range of movement, reach, speed,
strength, dexterity, accuracy
Feedback is important
Minimize eye movement
See Handbooks for data
What goes on in the mind?
Core cognitive aspects
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Attention
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Perception and recognition
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Memory
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Reading, speaking and listening
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Problem-solving, planning, reasoning and decisionmaking, learning
The “Model Human Processor”
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A true classic - see Card, Moran and Newell, The
Psychology of Human-Computer Interaction,
Erlbaum, 1983
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Microprocessor-human analogue using results from
experimental psychology
Provides a view of the human that fits much experimental
data
But is a partial model
Focus is on a single user interacting with some entity
(computer, environment, tool)
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Neglects effect of other people
Memory
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Perceptual “buffers”
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Short-term (working) memory
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Brief impressions
Conscious thought, calculations
Long-term memory
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Permanent, remember everything that ever
happened to us
LONG-TERM MEMORY
R = Semantic
D = Infinite
S = Infinite
SHORT-TERM (WORKING) MEMORY
VISUAL IMAGE
STORE
R = Visual
D = 200 [70-1000] ms
S = 17 [7-17] letters
AUDITORY IMAGE
STORE
R = Acoustic
D = 1.5 [0.9-3.5] s
S = 5 [4.4-6.2] letters
R= Acoustic or Visual
D (one chunk) = 73 [73-226] s
D (3 chunks) = 7 [5-34] s
S = 7 [5-9] chunks
PERCEPTUAL
PROCESSOR
COGNITIVE
PROCESSOR
MOTOR
PROCESSOR
C = 100 [5-200] ms
C = 70 [27-170] ms
C = 70 [30-100] MS
R = Representation
D = Decay Time
S = Size
C = Cycle Time
Eye movement (Saccade) = 230 [70-700] ms
Sensory Stores
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Very brief, but accurate representation
Physically encoded
Limited capacity
– Iconic: 7-17 letters
– Echoic: 4-6
– Haptic: ??
Rapid Decay
– Iconic: 70-1000 ms
– Echoic: 0.9 – 3.5 sec
Short Term Memory
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Symbolic, nonphysical acoustic or visual
coding
Somewhat limited capacity
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7 +- 2 “chunks” of information
Slower decay
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5-226 sec
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rehearsal prevents decay
Another task prevents rehearsal -
interference
About Chunks
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A chunk is a meaningful grouping of
information – allows assistance from LTM
4793619049 vs. 704 687 8376
NSAFBICIANASA vs. NSA FBI CIA NASA
My chunk may not be your chunk
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User and task dependent
Long-Term Memory
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Semantic storage
Seemingly permanent & unlimited
Access is harder, slower
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-> Activity helps (we have a cache)
Retrieval depends on network of associations
How information is perceived, understood and
encoded determines likelihood of retrieval
File system full
LT Memory Structure
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Episodic memory
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Events & experiences in serial form
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Helps us recall what occurred
Semantic memory
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Structured record of facts, concepts & skills
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One theory says it’s like a network
Another uses frames & scripts (like record structs)
Memory Characteristics
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Things move from STM to LTM by rehearsal &
practice and by use in context
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Do we ever lose memory? Or just lose the link?
What are effects of lack of use?
We forget things due to decay and interference
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Similar gets in the way
Processing in memory
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Attention filters information into memory
and for more processing
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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
Context is important
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Difficult to remember things in another context
Activity
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Try to remember the dates of your grandparents’
birthday
Try to remember the cover of the last two DVDs or
games you bought or rented
Which was easiest? Why?
People are very good at remembering visual cues
about things
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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
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e.g., birthdays and phone numbers
From http://www.id-book.com
Implications?
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Which is an implication of 7 +- 2?
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Use about 7 items on a menu
Display 7 icons on a task bar
No more than 7 tabs on a window
7 bullets in a list
ALL WRONG!
Why?
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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
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But it depends on task and available screen, NOT memory
From http://www.id-book.com
Recognition over Recall
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We recognize information easier than we
can recall information
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Examples?
Implications?
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Externalizing to reduce memory
load
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Reminders, calendars, notes, shopping lists, to-do
lists - written to remind us of what to do
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Post-its, piles, marked emails - where placed
indicates priority of what to do
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External representations:
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Remind us that we need to do something (e.g. to buy
something for mother’s day)
Remind us of what to do (e.g. buy a card)
Remind us when to do something (e.g. send a card by a
certain date)
From http://www.id-book.com
Memory Summary
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Involves 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
Also better at remembering images than words
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Why interfaces are largely visual
From http://www.id-book.com
Design implications
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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
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e.g., categories, color, flagging, time stamping
From http://www.id-book.com
Other processes: Learning
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Facilitated
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By structure & organization
By similar knowledge, as in consistency in UI design
By analogy
If presented in incremental units
Repetition
Hindered
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By previous knowledge
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Try moving from Mac to Windows
Consider user’s previous knowledge in your interface
design
Encourage exploration
Other Processes: Problem Solving
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Users focus on getting job done, not learning to
effectively use system
We are more heuristic than algorithmic
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We try a few quick shots rather than plan
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Resources simply not available
We often choose suboptimal strategies for low
priority problems
We learn better strategies with practice
Users apply analogy even when it doesn’t apply
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Or extend it too far - which is a design problem
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Dragging floppy disk icon to Mac’s trash can does NOT erase
the disk, it ejects disk!
Implications
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Help users accomplish main tasks
Provide useful analogies
Allow flexible shortcuts and multiple ways to
accomplish a task
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Forcing plans will bore user
People
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Good
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xxx
yyy
zzz
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Bad
1.
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aaa
bbb
ccc
Fill in the columns what are people good at
and what are people
bad at?
People
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Good
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Infinite capacity LTM
LTM duration & complexity
High-learning capability
Powerful attention
mechanism
Powerful pattern recognition
Flexible problem solving
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Bad
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Limited capacity STM
Limited duration STM
Unreliable access to LTM
Error-prone processing
Slow processing
Example: Passwords
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What’s wrong with computer passwords?
How do people cope?
How to banks, sites, etc. cope?
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Suggested improvements:
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Have a tool remember them all
How about visual passwords?
Eliminate the need – use biometrics
Reminder: Assignment
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Task analysis due Monday
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And get started on your Project Part 1!