Human Abilities Part 2 of 3

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Human Abilities - Part 2 of 3

• Understanding the user The Model Human
  Processor and Cognitive Abilities Information
  Processing

This material has been developed by Georgia Tech
HCI faculty, and continues to evolve.
Contributors include Gregory Abowd, Jim Foley,
Diane Gromala, Elizabeth Mynatt, Jeff Pierce,
Colin Potts, Chris Shaw, John Stasko, and Bruce
Walker. Comments directed to foley_at_cc.gatech.edu
are encouraged. Permission is granted to use with
acknowledgement for non-profit purposes. Last
revision November 2004.
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The Model Human Processor

• A true classic - see Card, Moran and Newell, The
  Psychology of Human-Computer Interaction,
  Erlbaum, 1983
• Microprocessorhuman analog using results from
  experimental psychology
• Provides a view of the human that fits much
  experimental data

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Block Diagram - Model Human Processor (MHP)
LONG-TERM MEMORY
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGE STORE
VISUAL IMAGE STORE
PERCEPTUAL PROCESSOR
COGNITIVE PROCESSOR
MOTOR PROCESSOR
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MHP is not Complete

• Only two senses
• Certainly the most important
• Focus is on a single user interacting with some
  entity (computer, environment, tool)
• Neglects effect of other people

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Three Processors

• Perceptual Processor
• Cognitive Processor
• Motor Processor
• Each has a cycle time (average and range),
  determined experimentally
• Represented by C

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Block Diagram - MHP Three Processors, Cycle
Times
LONG-TERM MEMORY
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGE STORE
VISUAL IMAGE STORE
PERCEPTUAL PROCESSOR C 100 5-200 ms
COGNITIVE PROCESSOR C 70 27-170 ms
MOTOR PROCESSOR C 70 30-100 MS
C Cycle Time Range
Eye movement (Saccade) 230 70-700 ms
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Three Memories

• Perceptual Store
• Short Term Memory
• Long Term Memory

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Block Diagram MHP Three Memories
LONG-TERM MEMORY
Memory 3 - permanent memory, hugh capacity
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGE STORE
VISUAL IMAGE STORE
Memory 2 - working memory, small capacity,
conscious thought, calculations
PERCEPTUAL PROCESSOR
COGNITIVE PROCESSOR
MOTOR PROCESSOR
Memory 1 - Perceptual Buffers to briefly store
impressions
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Memory 1 Perceptual Stores

• Memory structures
• Image Stores - Holds fixed image of outside world
  long enough for some analysis
• Processes - Info goes to brain for more
  processing
• e.g. Pattern recognition
• Uses context knowledge to make sense of what is
  seen/heard

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Perceptual Stores

• Visual and auditory impressions
• Visuospatial sketchpad, phonological loop
• Very brief, but accurate representation of what
  was perceived
• Details decay quickly (70 - 1000 ms visual 0.9 -
  3.5 sec auditory)
• Limited capacity (7 - 17 letters visual 4 - 6
  auditory)

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Memory 2 Short Term Memory

• Representation is either auditory or visual
• Rehearsal needed to prevent decay (try it)
• Without rehearsal, decays in minute or less
• Can store as long as are able to pay attention to
  rehearsal harder than you think (try it)
• Another task prevents rehearsal - interference
• New info can push out old info - interference
• Capacity is 5 to 9 chunks of information

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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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Memory 3 Long-Term Memory

• Seemingly permanent unlimited
• Access is harder, slower
• -gt Activity helps (we have a cache)
• Representations are semantic (declarative,
  procedural) and visual and auditory
• Facts, procedures, pictures, sounds
• Retrieval depends on network of semantic
  associations (linked lists)

File system full
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Block Diagram MHP Three Memories, Repn,
Decay Time, Size
LONG-TERM MEMORY
R Semantic Visual Auditory D Infinite S
Infinite
SHORT-TERM (WORKING) MEMORY
AUDITORY IMAGE STORE
VISUAL IMAGE STORE
R Acoustic or Visual D (1 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 Range
Eye movement (Saccade) 230 70-700 ms
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Another View of the Three Memories
Rehearsal
Perceptual Stores
Short Term Memory
Long Term Memory
Decay, Displacement
Decay? Interference?
Decay
Chunks
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Cognitive Processor Recognize-Act Cycle

• On each cycle contents of STM triggers actions
  in LTM associated with action in LTM
• This idea relates to the gulf of execution and
  gulf of interpretation concepts introduced in a
  different lecture

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Links from STM to LTM

• Conflicting links create problems!
• On the next slide - read the words

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Read the Words

• Black
• Green
• Red
• Blue
• Yellow

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LT Memory Structures

• 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

• Information moves from STM to LTM by rehearsal,
  practice, and 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 new info gets inway of old info
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Recognition vs. Recall

• Recognition
• You see or hear a stimuli which helps you
  retrieve info from LTM
• Recall
• You have to retrieve info from LTM without a
  specific stimuli
• Which is easier?
• Implications for UI design?

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Four Major Cognitive Processes

• Selective Attention
• Learning
• Problem Solving
• Language

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1 Selective Attention

• We can focus on one particular thing
• Cocktail party chit-chat - hearing key words can
  shift our attention
• Driving while talking - take customary route, may
  not be where are going
• Salient visual cues can facilitate selective
  attention
• Examples?

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2 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 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 Consider users previous knowledge in your
  interface design

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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 lecture on structuring help

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3 Problem Solving

• Storage in LTM, then application
• Reasoning
• Deductive -
• Inductive -
• Abductive -
• Goal in UI design - facilitate problem solving!
• How?? Take time to think about this right now!

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

• 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

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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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4 Language

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

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Recap - Human Abilities 1 and 2
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
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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?
• What are some of the other assumptions underlying
  the MHP model?
• How good is the model?

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People

• Good
• xxx
• yyy
• zzz

• Bad
• aaa
• bbb
• ccc

Fill in the columns - what are people good at and
what are people bad at?
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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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End Part 2