Human Abilities

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Human Abilities

• Understanding the user
• A first step in Human-Centered Design

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Outline

• Human capabilities
• Senses
• Motor systems
• Information processing
• Perceive, think, act
• Memory
• Cognitive Processes
• Selective attention, learning, problem solving,
  language

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Typical Person )
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Basic Human Capabilities

• Do not change very rapidly
• Not like Moores law!
• Have limits, which are important to understand
• Our understanding of human capabilities does
  change, ie
• Cognitive neuroscience
• Theories of color perception
• Effect of groups and situation on how we act and
  react

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Human Capabilities

• Why do we care? (better design!)
• Want to improve user performance
• Knowing the user informs the design
• Senses
• Information processing systems
• Physical responding

Time and effort expendedto complete tasks
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Overview
I. Senses A. Vision B. Hearing C. Touch
D. Smell
III. Motor system A. Hand movement B.
Workstation Layout
II. Information processing A. Perceptual B.
Cognitive 1. Memory a. Short
term b. Medium term c. Long
term 2. Processes a. Selective
attention b. Learning c.
Problem solving d. Language
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Senses

• Sight, hearing, touch important for current HCI
• Smell, taste ???
• Abilities and limitations affect design

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Key concepts for Senses

• Just noticeable difference (jnd)
• How much of a change in stimulus is needed before
  can be sensed
• Tends to be logarithmic - Webers Law
• Magnitude of physical stimulus versus perceived
  magnitude
• (Doubling number of photons does not double
  perceived intensity)

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Vision (Covered in greater detail in section on
visual design)

• Visual System
• Eye
• Retina
• Neural pathway
• 80 of brains operation

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Visual Abilities

• Sensitivity
• luminance 10-6107 mL
• 10-4 mL -gt white paper in starlight
• 109 mL -gt sun surface at noon
• Acuity
• detection, alignment, recognition (visual angle)
• retinal position fovea has best acuity
• Movement
• tracking, reading, saccades
• Note Vision decreases with age
• Implications (??)
• Font size location depends on task
• Much done by context grouping

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Color

• Sensory response to electromagneticradiation in
  the spectrum betweenwavelengths 0.4 - 0.7
  micrometers

0.5
10-1
10-6
105
108
visible
gamma
ultraviolet
microwave
tv
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Color Vision
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Color Vision

• Color the retina
• 380 (blue) 770nm (red)
• Problems with cones or ganglion cells causes
  problems with color perception
• (Not really color blindness)
• 8 males, 0.5 females
• Implications (??)
• Avoid saturated colors
• Color coding should be redundant when possible

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Color JND
JND, mm
Color, from 400 to 700 mm V I B G Y
O R
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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 (??)

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Auditory JND

• Pitch
• Loudness
• Location

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Touch

• Three main sensations handled by different types
  of receptors
• Pressure (normal)
• Intense pressure (heat/pain)
• Temperature (hot/cold)
• Sensitivity, Dexterity, Flexibility, Speed
• Where important?
• Mouse, Other I/O, VR, surgery

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Touch JND

• Spatial - relevant for reading braille
• Pressure
• Temperature

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Smell
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II. Information Processing

• Three major systems of human information
  processing
• Perceptual (read-scan)
• Cognitive (think)
• Motor system (respond)

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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

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• There are other ways of thinking
• Actors in context vs. users of tools
• The MHP influence can be seen in some underlying
  HCI principles today

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Block Diagram
LONG-TERM MEMORY
R Semantic D Infinite S Infinite
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGE STORE
VISUAL IMAGE STORE
R Acoustic or Visual D (one chunk) 73 73-226
s D (3 chunks) 7 5-34 s S 7 5-9 chunks
R Acoustic D 1.5 0.9-3.5 s S 5 4.4-6.2
letters
R Visual D 200 70-1000 ms S 17 7-17
letters
PERCEPTUAL PROCESSOR C 100 5-200 ms
COGNITIVE PROCESSOR C 70 27-170 ms
MOTOR PROCESSOR C 70 30-100 MS
R Representation D Decay Time S Size C
Cycle Time
Eye movement (Saccade) 230 70-700 ms
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Recognize-act cycle

• Contents of WM trigger actions held in LTM

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Perceptual

• Memory structures
• Image Stores - Holds fixed image of outside world
  long enough for some analysis(will come back to
  this)
• Processes - Info goes to brain for more
  processing
• e.g. Pattern recognition
• Uses context knowledge

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Cognitive

• Cognitive model
• How does it work?

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Memory

• Four types
• Perceptual buffers
• Brief impressions
• Short-term (working) memory
• Conscious thought, calculations
• Intermediate (not in MHP)
• Storing intermediate results, future plans
• Long-term memory
• Permanent, remember everything ever happened to us

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Perceptual Image Stores

• Visual and auditory impressions
• visuospatial sketchpad, phonological loop
• Very brief, but accurate representation of what
  was perceived
• Details decay quickly (70 - 3500 msec)
• Limited capacity (4 - 17 letters)
• Rehearsal prevents decay
• Another task prevents rehearsal

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Short Term Memory

• Use chunks 5-9 units of information
• Display format (picture, text, sound) should
  match memory system used to perform task
• New info can interfere with old info

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About Chunks

• A chunk is a meaningful grouping of information
  allows assistance from LTM
• 4793619049 vs. 404 894 7328
• NSAFBICIANASA vs. NSA FBI CIA NASA
• My chunk may not be your chunk
• User and task dependent

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Long-Term Memory

• Seemingly permanent unlimited
• Access is harder, slower
• -gt Activity helps (we have a cache)
• Retrieval depends on network of associations

File system full
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LT Memory Structure

• Episodic memory
• Events experiences in serial form
• Helps us recall what occurred
• Semantic memory
• Structured record of facts, concepts skills
• One theory says its like a network
• Another uses frames scripts (like record
  structs)

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Memory Characteristics

• Things move from STM to LTM by rehearsal
  practice and by use in context
• We forget things due to decay and interference

Unclear if we ever really forget something -
just loose link to the info
Lack of use
Similar gets inway of old
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Processes

• Four main processes of cognitive system
• Selective Attention
• Learning
• Problem Solving
• Language

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Selective Attention

• We can focus on one particular thing
• Cocktail party chit-chat
• Salient visual cues can facilitate selective
  attention
• Examples?

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Learning

• Two types
• Procedural How to do something
• Declarative Facts about something
• Involves
• Understanding concepts rules
• Memorization
• Acquiring motor skills
• Automotization
• Tennis
• Driving to work
• Even when dont want to
• Swimming, Bike riding, Typing, Writing

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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
• gt Use users previous knowledge in interface

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Observations

• Users focus on getting job done, not learning to
  effectively use system
• Users apply analogy even when it doesnt apply
• Or extend it too far - which is a design problem
• Dragging floppy disk icon to Macs trash can does
  NOT erase the disk, it ejects disk!
• More on this in unit on structuring help

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Problem Solving

• Storage in LTM, then application
• Reasoning
• Deductive -
• Inductive -
• Abductive -

If A, then B
Generalizing from previouscases to learn about
new ones
Reasons from a fact to theaction or state that
caused it
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Observations

• People are more heuristic than algorithmic
• Try a few quick shots rather than plan
• Resources simply not available
• People often choose suboptimal strategies for low
  priority problems
• People learn better strategies with practice

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Implications

• Allow flexible shortcuts
• Forcing plans will bore user
• Have active rather than passive help
• Recognize waste

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Language

• Rule-based
• How do you make plurals?
• Productive
• We make up sentences
• Key-word and positional
• Patterns
• Should systems have natural language interfaces?

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III. 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

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Work station layout - Ergonomics

• Add scanned-image showing workstation

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Computer Capabilities

• Important for HCI too
• Intentional omission (time scope)
• (Take a CS course)

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Class DiscussionModel Human Processor

• What are the three major subsystems and their
  functions?
• What does it mean to say that certain
  subprocessors have variable rates?
• What is the recognize-act cycle? Is it like
  the fetch-decode-execute of a CPU?
• How do the authors define rationality?
• What are some of the other assumptions underlying
  the MHP model?
• Do you think this is a good model?

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Discussion PointsModel Human Processor

• Three subsystems
• Perceptual, cognitive, motor
• Each has own memories and processors
• Notion of a flow of symbolically coded sensory
  information
• Flow from perceptual to cognitive system
• Cognitive system applies LTM to decide on an
  action, actuates motor system

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Discussion PointsModel Human Processor

• Variable rates
• Cognitive cycle time decreases with increased
  task effort, practice, but increases with
  uncertainty
• Perceptual cycle time decreases with more intense
  stimuli
• Power law of practice (exponential decay of total
  task time with task rehearsal)
• Fitts law (hand tracking to targets in 1D)

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Discussion PointsModel Human Processor

• Procedural model fundamental basis is the
  recognize-act cycle
• WM initiates actions linked to LTM actions
  result in modified WM
• Predicts performance, not actions
• Assumes rationality
• Goals Task Operators Inputs Knowledge
  Process-Limits BEHAVIOR
• Human problem-solving finite state machine

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People

• Good

• Bad

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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

Computer is opposite! Allow one who does it best
to do it! (Function allocation)
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Recap
I. Senses A. Sight B. Sound C. Touch
D. Smell
II. Information processing A. Perceptual B.
Cognitive 1. Memory a. Short
term b. Medium term c. Long
term 2. Processes a. Selective
attention b. Learning c.
Problem solving d. Language
III. Motor system A. Hand movement B.
Workstation Layout