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Tutorial 4: Case Study. “Set Phasers on Stun” SY DE 142 – June 7, 2004 Introduction to Human Systems Engineering Waterloo, Ontario, Canada. Outline. Case Study: “Set Phasers On Stun” Discussion on “Set Phasers on Stun” Midterm Overview. Set Phasers on Stun Overview. Time: 1986

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tutorial 4 case study

Tutorial 4:Case Study

“Set Phasers on Stun”

SY DE 142 – June 7, 2004

Introduction to Human Systems Engineering

Waterloo, Ontario, Canada

  • Case Study: “Set Phasers On Stun”
  • Discussion on “Set Phasers on Stun”
  • Midterm Overview
set phasers on stun overview
Set Phasers on StunOverview
  • Time: 1986
  • Place: East Texas Cancer Center, Tyler
  • Synopsis:A computer glitch turns miracle machine into monster for one cancer patient. Mode error combine with lack of feedback deliver a blast of 25,000 rads down onto the patient.
set phasers on stun interface design
Set Phasers on StunInterface Design
  • Draw out the general Human machine system model and redraw it for this case.
  • What feedback was available to Mary Beth and what was missing?
set phasers on stun information displays
Set Phasers on Stun“Information Displays”

a: mary beth's command

b: control signal

c: rays

d: patient state

e: feedback on Therac state and actions

f: feedback on interface state and actions

(control signal sent)

g: interface information

Human = Mary Beth -

Interface = Therac Control Panel

Machine = Therac

World = Patient

set phasers on stun feedback
Set Phasers on StunFeedback
  • Mary Beth needed to know:
    • the control signal was sent
    • the Therac mode
    • that the Therac had sent out rays
    • patient state.
    • 14 marks: 5 for the draw, 5 for redraw and 4 for feedback
midteram overview
Midteram Overview

SY DE 142 Midterm:

  • Date: June 14, 2004
  • Time: 1:30 - 3:30pm
  • Room: DC 1350
  • Aids Allowed:
    • Text book: Wickens and Set Phasers on Stun
    • Calculator
  • Solutions must be written in pen, not in pencil.
case studies
Case Studies
  • Business in Bhopal
  • Silent Warning
  • In Search of the Lost Cord
  • An Act of God
  • The Wizards of Wall Street
  • Set Phasers on Stun
  • Death on the Job
  • Bhopal, a Lingering Tragedy
  • Why Planes Crash
  • Broken Bus
course material outline
Course Material Outline
  • Human Error- slips
  • Human machine model
  • Displays
  • Control
  • Human-Computer Interaction
  • Usability Testing
  • Automation
    • More details on slides and in book.
  • Accident Analysis and Fault Trees
  • Mappings and Affordances
  • Gulfs of Execution and Evaluation
  • Human Action Cycle
  • Information Processing
  • Human Decision Making
  • Human Error - Mistakes
accident analysis and fault trees
Linear interactions

Common mode interaction

Nonlinear interactions

Tight vs. Loose coupling


Fault Tree Analysis


Show causality

Events: action and time (time often implicit)

AND/OR gates

Last event at the top

Accident Analysis andFault Trees



mappings and affordances
Mappings and Affordances
  • Mapping : relation between action and its result in the world
      • Helps automatic processing when extremely strong between world and required action
      • Two kinds; natural (steering wheel), social/cultural (light switch)
  • Affordance:
      • perceived and actual properties of things that help to direct users’ actions, should be applied as a design principal

“Affordances become visible by establishing mappings, (what it does, how it works)”

gulfs of execution and evaluation and hac
Gulfs of Execution and Evaluation (and HAC)
  • Gulfs:
    • Execution: have an intention but can’t figure out action (difference in seq of action & action in the Human Action Cycle)
    • Evaluation: Can’t figure out whether the goal has been achieved
human action cycle






Sequence of Actions(what should be done)

Gulf of evaluation!


Gulf of execution!


How is state of the world perceived? Use senses




information processing how we think
Information Processing“How we Think”
  • Memory
    • Short term, long term , how to improve, knowledge in head vs. knowledge in world
  • Perception
    • Feature analysis (bottom-up processing), unitization, top down processing ----design implications
  • Attention
    • Selective, divided ---- design implications
    • Resource model, Multiple resource model
more information processing how we think
More Information Processing“How we Think”
  • Situation awareness (SA): being aware of meanings of dynamic changes in the environment
    • 3 stages: Perceive, understand, predict
    • Measuring SA: by SA Global Assessment technique (SAGAT)
  • Decision making
    • Normative model (methods: multi-attribute utility theory, expected value theory, SEUT)
    • Descriptive model (methods: satisfaction not optimal, heuristics, and biases to create easier ways of thinking)
human decision making
Human Decision Making
  • Heuristics and Biases in Human decision making (look at updated lecture notes)
    • could happen in any of the following stages:

1. Getting information input (input or cue biases)

2. Generating hypotheses and selection ( 6 biases).

3. Plan generation and action choice (4 biases).

  • SRK Framework
    • Skill based decisions (automated)
    • Rule Based decisions (procedural)
    • Knowledge based decisions
human error mistake
Human Error -- mistake
  • Mistake: wrong goal and intention but right action
    • Why it happens?
    • Types of mistake
      • mistaken similarity,
      • misjudged probability,
      • rationalizing small events,
      • social pressures/cultural factors and $
  • Forcing Functions
human error slips
Human Error -- slips
  • Slip: right goal and intention but wrong action,
    • Mostly occurs with skilled behavior (WHY?)
    • Mode Error: right action in wrong mode (therefore the action becomes WRONG)
information displays human machine model
Human machine system model :


user Interface machine World

begins with Action :

Operator acts on the interface.

Interface sends a control signal to the machine.

Machine acts on the world.

Feedback: (4 feedbacks)

State of world to interface

Action of machine to interface

Indication of control signal (machine to interface)

Information from interface to operator

Any missing item may cause an accident

Information DisplaysHuman-Machine Model
display contents
Display contents
  • should permit evaluation and execution
  • Display principles:
    • Perceptual (legible, give reference, redundancy, design for distinctive features)
    • Mental model (pictorial, moving part, ecological)
    • Attention (multi-resource, proximity compatibility, information access cost)
    • Memory (predictive aids, knowledge in the world, consistency
display forms
Display forms
  • Digital vs. Analog (precision vs. change)
  • Configural displays
    • Rankine cycle
    • Polar star display
  • Heads-up
  • Ecological displays
  • Control vs. display : control is same as display till user interacts with system through display
  • Very important in design same guidelines as displays.
  • Laws and principals:
    • Hick-Hyman law for Reaction Time
    • Fitts law for Movement Time
  • Control Types : zero order (mouse), first order (steering wheel) and second order (thrust of shuttle)
human computer interaction
Human-Computer Interaction
  • What your focus is as a designer:
    • User group:
      • who is using your system (novice, infrequent, frequent expert) and what should you know about these users.
    • Interaction styles:
      • how will the user (based on expertise) interact with the system (eg. Menu, form, QA, command language, function keys, direct manipulation, natural language, ….)
usability and user testing
Usability and user testing
  • Usability Approaches (4)
      • Cognitive walkthrough
      • Heuristic evaluation (Neilson’s usability principals)
      • Performance measurement
      • Field study
    • Tasks
    • Usability measures (satisfaction, learnability, errors)
  • When and why use automation
  • Classes of automation
      • Information acquisition (warnings, filters)
      • Information integration (pattern recognition, expert systems)
      • Action selection (TCAS)
      • Action execution and control (autopilots, cruise control)
  • Levels of automation
  • Reliability Issues:
    • complacency (over trust),
    • mistrust,
    • dumb and dutiful effect.
  • Best form is Human Centered Automation