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Human Abilities and Models
Sensory and cognitive abilities and models, models of human performance
Outline
Human capabilities and disabilities Senses Motor systems
Memory Cognitive Processes
Selective attention, learning, problem solving, language
Contextual models
Typical Person
Do we really have limited memory capacity?
Basic Human Capabilities
Do not change very rapidly Not like Moore’s law!
Have limits, which are important to understand Why do we care?
Better design! Want to improve user performance
Universal design – designing for all people, including those with disabilities
But… we’re all disabled sometimes Environment Fatigue Injury Aging Changing role of information technology
Usable Senses
The 5 senses (sight, sound, touch, taste and smell) are used by us every day each is important on its own together, they provide a fuller interaction with the natural world
Computers rarely offer such a rich interaction
Can we use all the available senses? ideally, yes practically – no
We can use • sight • sound • touch (sometimes)
We cannot (yet) use • taste • smell
Vision Fundamentals Retina has
6.5 M cones (color vision), mostly at fovea (1/3)˚
About 150,000 cones per square millimeter
Fewer blue sensing cones than red and green at fovea
100 M rods (night vision), spread over retina, none at fovea
Adaptation Switching between dark
and light causes fatigue
Vision implications (more to come in visual
design)
Color Distinguishable hues optical illusions
Acuity Determines smallest size we can see Less for blue and yellow than for red and
green
Color/Intensity Discrimination
The 9 hues most people can identify are:Color WavelengthRed 629Red-Orange 596Yellow-Orange 582Green-Yellow 571Yellow-Green 538Green 510Blue-Green 491
Blue 481
Violet-Blue 460
Color Surround Effect
Our perception of a color is affected by the surrounding color
Vision Difficulties
Color blindness About 9 % of males are red-green colorblind! See http://colorlab.wickline.org/colorblind/colorlab/
Low-vision The vast majority of visually disabled people have
some sight Blindness
Rely on other senses to receive information Specialized hardware and software
Screen readers Braille printers, etc.
Myopia and Hypermetropia
Myopia Hypermetropia (short-sighted) (far-sighted)
Macular degeneration
Diabetic retinopathy
Cataracts
Tunnel vision
Accommodating Partial Sight
Large monitor, high resolution, glare protection
Control of color and contrast Control of font size everywhere Keyboard orientation aids
Accommodating Blind Users
Screen Readers Full-featured Cursor-tracking, routing Dialogue focus View areas
Auditory or tactile output
http://www.freedomscientific.com/fs_products/software_jaws.asphttp://www.webaim.org/simulations/screenreader
Audition (Hearing)
Capabilities (best-case scenario) pitch - frequency (20 - 20,000 Hz) loudness - amplitude (30 - 100dB) location (5° source & stream separation) timbre - type of sound (lots of instruments)
Often take for granted how good it is(disk whirring)
Implications ?
Hearing uses
Redundant output Email beep + icon, IM sound + popup
message, etc. Output when screen not available Multimedia systems
Hearing problems or deafness
An increasing problem? Population Phone interfaces
Various technologies used: Communication aids Automated software (speech to text, etc.)
Touch
Three main sensations handled by different types of receptors: Pressure (normal) Intense pressure (heat/pain) Temperature (hot/cold)
Where important? Mouse, Other I/O, VR, surgery
Motor System
Capabilities Range of movement, reach, speed,
strength, dexterity, accuracy Workstation design, device design
Often cause of errors Wrong button Double-click vs. single click
Principles Feedback is important Minimize eye movement
See Handbooks for data
Work Station Ergonomics – to Facilitate I/O
Large Range of Physical ImpairmentsComplete lack of function
absence of a limb paralysis – usually due to spinal injury, the
higher the damage the greater the degree of paralysis
Lack of strengthTremor/lack of accuracySlowness
Implications
Try to minimize movement and strain Alternative input devices
Keyboard hardware and software Speech input Other input switches for more severe needs
Eye gaze, sip and puff, etc. Acceleration techniques
Word completion, macros, etc.
The Mind
And now on to memory and cognition…
The “Model Human Processor”
A true classic - see Card, Moran and Newell, The Psychology of Human-Computer Interaction, Erlbaum, 1983 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) Neglects effect of other people
Memory
Perceptual “buffers” Brief impressions
Short-term (working) memory Conscious thought, calculations
Long-term memory Permanent, remember everything that ever
happened to us
LONG-TERM MEMORY
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGESTORE
VISUAL IMAGESTORE
R = SemanticD = InfiniteS = Infinite
R = AcousticD = 1.5 [0.9-3.5] sS = 5 [4.4-6.2] letters
R = VisualD = 200 [70-1000] msS = 17 [7-17] letters
R= Acoustic or VisualD (one chunk) = 73 [73-226] sD (3 chunks) = 7 [5-34] sS = 7 [5-9] chunks
R = RepresentationD = Decay TimeS = SizeC = Cycle Time
PERCEPTUALPROCESSOR
C = 100 [5-200] ms
COGNITIVEPROCESSOR
C = 70 [27-170] ms
MOTORPROCESSOR
C = 70 [30-100] MS
Eye movement (Saccade) = 230 [70-700] ms
Sensory Stores
Very brief, but accurate representation of what was perceived
Physically encoded Details decay quickly (70 - 1000 ms visual; 0.9 - 3.5 sec
auditory) Limited capacity
Iconic – visual 7 - 17 letters; 70 - 1000 ms decay
Echoic – auditory 4 - 6 auditory; 0.9 - 3.5 sec auditory
Haptic - touch Attention filters information into short term memory and
beyond for more processing
Short Term Memory
Symbolic, nonphysical acoustic or visual coding
Decay 5-226 sec, rehearsal prevents decay Another task prevents rehearsal –
interference Use “chunks”: 7 +- 2 units of information
About Chunks
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
User and task dependent
Long-Term Memory
Seemingly permanent & unlimited Access is harder, slower
-> Activity helps (we have a cache) Retrieval depends on network of associations How information is perceived, understood and
encoded determines likelihood of retrieval Effected by emotion, previous memory
File system full
LT Memory Structure
Episodic memory Events & experiences in serial form
Helps us recall what occurred
Semantic memory Structured record of facts, concepts & skills
Semantic network theory Or theory of frames & scripts (like record structs)
Memory Characteristics
Things move from STM to LTM by rehearsal & practice and by use in context 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 Similar gets in the way
Recognition over Recall
We recognize information easier than we can recall information
Examples? Implications?
Processes
Four main processes of cognitive system: Selective Attention Learning Problem Solving Language
Selective Attention
We can focus on one particular thing Cocktail party chit-chat
Salient visual cues can facilitate selective attention Examples?
Learning
Two types: Procedural – How to do something Declarative – Facts about something
Involves Understanding concepts & rules Memorization Acquiring motor skills Automatization
Tennis Driving to work
Even when don’t want to Swimming, Bike riding, Typing, Writing
Learning
Facilitated By structure & organization By similar knowledge, as in consistency in UI design By analogy If presented in incremental units Repetition
Hindered By previous knowledge
Try moving from Mac to Windows
=> Consider user’s previous knowledge in your interface design
Observations
Users focus on getting job done, not learning to effectively use system
Users apply analogy even when it doesn’t apply Or extend it too far - which is a design problem
Dragging floppy disk icon to Mac’s trash can does NOT erase the disk, it ejects disk!
Problem Solving
Storage in LTM, then application Reasoning
Deductive -
Inductive -
Abductive -
Goal in UI design - facilitate problem solving! How??
If A, then B
Generalizing from previouscases to learn about new ones
Reasons from a fact to theaction or state that caused it
Observations
We are more heuristic than algorithmic We try a few quick shots rather than plan
Resources simply not available
We often choose suboptimal strategies for low priority problems
We learn better strategies with practice
People
Good1. xxx
2. yyy
3. zzz
Bad1. aaa
2. bbb
3. ccc
Fill in the columns - what are people good at and what are people bad at?
People
Good Infinite capacity LTM LTM duration &
complexity High-learning capability Powerful attention
mechanism Powerful pattern
recognition
Bad Limited capacity STM Limited duration STM Unreliable access to
LTM Error-prone processing Slow processing
Models
Translating empirical evidence into theories and models that influence design.
Performance measures Quantitative Time prediction Working memory constraints
Competence measures Focus on certain details, others obscured
More on predictive models in March
Context and Cognition
Human information processor models all involve unaided individual
In reality, people work with other people and other artifacts
Other models of human cognition Situation action Activity theory Distributed cognition
How theories get used
Descriptive power – conceptual framework for describing the world
Rhetorical power – name important conceptual structures we can relate to the world
Inferential power – help make inferences (maybe about new change or design…)
Application – informing and guiding system design
Distributed Cognition (DCog)
HCI Proponent: Ed Hutchins Distributed collection of interacting people
and artifacts, and the communication and coordination between them
Distributed Cognition
Cognitive System – the people, artifacts and environments
Communicative pathways – the information channels
Describes information flow in terms of propagation across representational state Information is transformed through different
media (computers, displays, paper, heads)
What’s involved
The distributed problem-solving that takes place
The role of verbal and non-verbal behavior The various coordinating mechanisms that
are used (e.g., rules, procedures) The communication that takes place as the
collaborative activity progresses How knowledge is shared and accessed
Activity Theory
Long history from cognitive science HCI proponent: Bonnie Nardi
Explains human behavior in terms of our practical activity with the world
Provides a framework that focuses analysis around the concept of an ‘activity’ and helps to identify tensions between the different elements of the system
Two key models: one outlines what constitutes an ‘activity’; one models the mediating role of artifacts
Activity Theory
Unit of analysis is an activity Components:
subject, object, actions, operations
Noun Held by subject,motivates activity“object of game”
Goal-directedprocesses“tasks”
How actionis carried out
Individual model
A.T. Principles
Key idea: Notion of mediation by artifacts Our work is a computer-mediated activity
Starring role goes to activity In “regular” HCI, stars are person and machine
Context is not “out there”. It is generated by people in activities
Example: call center
DCog: Examine how information is transformed as it
goes from caller, to employee, into the system for information, back to employee and then caller…
Activity Theory Examine tensions between parts of the system
such as community, tools, rules, etc.
Situated Action
Noted proponent: Lucy Suchman
Much of the theory that underlies ethnography
Structuring of an activity grows out of immediacy of the situation
People engage in opportunistic, flexible ways to solve problems
Situated Action
Studies situated activity or practice Activity grows out of the particulars of a
situation Improvisation is important
Basic unit of analysis is “the activity of persons acting in a setting”
Example
Need 3/4 of 2/3 of cup of cottage cheese Just has a simple measuring cup available
Person solves problem by Measuring 2/3 cup Pouring out into a circle Divide into quadrants Take away one
One time solution to one time problem
Other comments on S.A.
Emergent property of moment-by-moment interactions
Improvisation Detailed temporal accounts De-emphasizes rigid plans and rational
problem solving
Comparing Models
The role of goals or intentions S.A.: “retrospective reconstructions” A.T. & D.C: central
Persistent structures S.A.: emphasize emergent/ contingent/ improvisatory
over routine/predictable A.T.: our activity assimilates experience of humanity D.C.: much focus on transformation of artifacts over
time
Comparing Models
People and things MHP: model each as a “machine”, study the
diad of H-C S.A.: qualitatively different, but mostly reactive A.T.: individual at center D.C.: both are agents, study multi-agent
system
Some Commentary
Take the reading with a grain of salt.
How does this influence design?