Human Abilities

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Human Abilities
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Cognitive Processes

• Attention
• Perception and recognition
• Memory
• Learning
• Reading, speaking and listening
• Problem-solving, planning, reasoning and
  decision-making

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Senses (Our Input System)

• Sight, hearing, touch important for the design of
  current Interfaces
• Smell, taste, other ???
• Abilities and limitations affect design

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Key concepts

• Absolute threshold
• Lowest detectable stimuli
• Signal detection theory
• Ability to tune in or tune out stimuli
• Just noticeable difference (jnd)
• How much change in stimulus is needed before we
  can sense difference?
• Sensory adaptation
• We react to change
• Absence of change leads us to loose sensitivity
  (psychological nystagmus)

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• Visual angle
• Total 200 degrees
• High-res 15 degrees
• Rods
• 120 million!
• B/W
• 1000x more sensitive than cones
• Cones
• 6-7 million
• 64 red
• 32 green
• 2 blue

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Visual phenomena

• Color perception
• 7-8 males cannot distinguish red from green
• 0.4 of women
• Peripheral vision
• Largely movement oriented
• Stereopsis
• Monocular (size, interposition, perspective,
  paralax)
• Binocular (retinal disparity, accommodation)

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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

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Motor System (Our Output 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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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)

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Model Human Processor
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Memory

• Perceptual buffers
• Brief impressions
• Short-term (working) memory
• Conscious thought, calculations
• Order of seconds
• Long-term memory
• Minutes, hours, days, years, decades
• Long term, large storage space

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Short Term (Working) Memory

• Working memory
• Visuospatial sketchpad, phonological loop,
  central control
• Characteristics
• Details decay quickly (70 - 1000 ms visual 0.9 -
  3.5 sec auditory)
• Limited capacity (7 - 17 letters visual 4 - 6
  auditory)
• Rehearsal prevents decay
• Chunking to remember more (7-2)
• Interference from LTM recent items

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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

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Different models/theories for decision-making/reas
oning

• Production systems
• If-then rules
• Connectionism (big idea in IS)
• Neural networks
• Hidden Markov models
• Bayesian networks
• Mediated action
• Actions must be interpreted in context
• Tools, setting, culture

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More useful stuff

• Case-based reasoning
• Learn from experience, reasoning same as memory
• Plans, schemes, and automation
• External/Embodied cognition
• Affordances

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Conceptual Mental Models
Conceptual Model
Mental Model
Mental model of mental model
User
Designer
Test hypotheses
Invokes existing knowledge and/or Affordances
guide action
Instantiated in
System
System model/image
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Everyday reasoning mental models

• 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?

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Mental models

• Users understanding (internal rep) of a system
• How to use the system (what to do next)
  (functional knowledge)
• What to do with unfamiliar systems or unexpected
  situations (how the system works) (Structural
  knowledge)
• People make inferences using mental models of how
  to carry out tasks
• Involves unconscious and conscious processes,
  where images and analogies are activated

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Cognitive Models

• Designers interpretation of how users should
  think/reason about the system
• Conceptual models based on activities
• Instructing the user instructs the system on
  what to do next
• Conversing the user and system are dialogue
  partners based on metaphor of human-human
  conversation
• Manipulating and navigating manipulate objects
  navigate through virtual spaces based on users
  knowledge of these activites in the real world
• Exploring and browsing based on peoples
  experiences with browsing other media, e.g.,
  magazines, radio, TV, libraries

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Cognitive Models (2)

• Conceptual models based on objects
• Books, tools, vehicles
• Usually implies a metaphor
• Metaphor uses an unconventional interpretation
  of the relationship between two entities
• Analogy is based on the accurate match between
  two entities the closer the match, the better
  the analogy
• In user interface design, we talk about
  metaphor, but we often mean analogy

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Building good Mental models

• Leverage existing knowledge and invoke correct
  associations/assumptions through good cognitive
  models
• Embed knowledge in the system
• Reduce memory load
• Computational offloading
• Remember Physics, devices environment shape
  mental models as well
• Allow for transparency to allow users to develop
  metter models

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Problems with metaphors?
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When to accommodate When to force new habits?