Engineering Psychology

1
Engineering Psychology Human Performance

• Outline of Lecture 3
• Review of lecture 2
• Human Information Processing
• Another example of human error
• The importance of conceptual models
• Communicating conceptual models through design

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A Model of Human Information Processing
3
Sensory Processing

• For human factors, the primary emphasis is on the
  visual, auditory, and proprioceptive senses of
  the body, although some olfactory displays do
  exist (e.g., additives to natural gas that allow
  us to detect leaks)
• what is proprioception?
• Perception of body states e.g., need to urinate,
  stomach ache
• also includes kinesthetic sense -- limb position
• can refer to knowledge of your bodys orientation
  in space the direction of gravity
• Characteristics of the senses apply important
  constraints on human performance

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A Model of Human Information Processing
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Short Term Sensory Store (STSS)

• Each sense has a mechanism for prolonging the
  representation of the physical stimulus for a
  short period
• Characteristics of the STSS
• pre-attentive information is stored whether you
  attend it or not
• veridical does not change or process the
  stimulus appreciably
• decays rapidly
• Examples
• vision iconic memory (duration 200-300 ms)
• audition echoic memory (duration 2-8 s)

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A Model of Human Information Processing
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Perceptual Encoding and Attention

• Incoming sensory information is interpreted in
  the context of previous experience (information
  in long-term memory)
• Top-down and bottom-up processing
• Top-down contribution of previous experience
• Bottom-up contribution of incoming data

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A Model of Human Information Processing
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Perceptual Encoding and Attention

• Perceptual encoding is limited by attention
• Attention
• selection of information for further processing
  attentional searchlight
• pool of resources - limitation to the number of
  stimuli or tasks one can attend
• attention limits also apply to decision making
  and response execution stages

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Perceptual Encoding

• Levels of Complexity
• simple detection (stimulus present or absent)
• recognition, identification
• categorization vs. analog judgments
• unidimensional vs. multidimensional judgments
• unidimensional absolute judgment
• multidimensional pattern recognition

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A Model of Human Information Processing
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Decision Making

• Once a stimulus is perceived, we must decide what
  response to make
• Automatic vs. controlled decisions
• automatic quick
• no attention needed
• learned reflexes
• long-term memory procedure executes automatically
  in response to the stimulus
• controlled slow
• attention required, typically conscious of
  thoughts
• interaction with working and long-term memory
  systems
• may involve rehearsal (to store new information)
• weighing of costs and benefits

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A Model of Human Information Processing
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Response Execution and Feedback

• Once the decision has been reached to execute a
  particular response the complex motor movements
  of the response must be executed
• Typically, we monitor the consequences of our
  actions, producing closed-loop feedback
• Model is circular rather than linear

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A Model of Human Information Processing
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An example of human error

• Casey (1993) Set Phasers on Stun and other true
  tales of Design, Technology, and Human Error, 2nd
  Ed.
• Chapter 1 Set Phasers on Stun
• What went wrong?

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The Importance of Accurate Conceptual Models of
Systems

• Conceptual model
• operators internal representation of how a
  system operates
• Mental model (from Cognitive Psychology)
• Operator can perform thought-simulations of the
  system, which allow
• prediction of system behaviors not previously
  experienced
• effective troubleshooting of malfunctioning
  systems

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Communicating conceptual models

• Well-designed systems communicate an accurate
  conceptual model to the user
• How?
• Affordances
• Constraints
• Visibility
• Mappings
• Feedback

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Communicating conceptual models

• Affordances fundamental properties of a thing
  that determine how it can be used
• Proper use of affordances in design provide
  strong clues to the operation of a device
• natural affordances
• e.g., a door handle affords pulling, while a
  plate affords pushing
• Unnatural affordances often result in
  mis-operation of a system

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Communicating conceptual models

• Constraints limitations in the manner in which a
  device can be used
• sometimes constraints are designed to be natural
• e.g., many hand tools can only be used one way
• sometimes constraints are added to a system
• e.g., transmission locks that require the brake
  to be engaged

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Communicating conceptual models

• Visibility part of conceptual model that is
  readily visible to the user (system image)
• aided by natural affordances and constraints
• trades off with complexity (clutter)
• functions of a system are most visible if each
  function has a dedicated control, e.g., a car
• devices with many functions can result in
  extremely complex and cluttered displays
• mode button or switch to toggle button mode
• each button operates multiple functions
• reduces clutter at the cost of visibility

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Communicating conceptual models

• Mappings relationship between controls,
  displays, and system states
• natural mappings appearance and movement of
  control provides an accurate conceptual model
• direction of control movement is same as physical
  movement of device
• shape of control conveys meaning to operator
• unnatural mappings arbitrary relationships

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Communicating conceptual models - Mappings

• Good Mappings Poor Mappings

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Communicating conceptual models

• Feedback information sent back to user to
  confirm the results of actions
• necessary for skilled performance of many tasks,
  even highly practiced ones, e.g., speaking,
  writing
• feedback even more important during learning
• immediate feedback is most effective
• delays in feedback can severely impair
  performance, e.g., adjusting the shower, computer
  operation

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Communicating conceptual models

• How would you redesign the Therac-25 to provide
  the operator with an accurate conceptual model?

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To Prepare for Next Class

• If you have not already done so
• Read N2, W2 pages 17-34
• If you desire, send me a five-digit arbitrary
  number so that I may anonymously post your grade