1. Tutorial 4: Case Study “Set Phasers on Stun” SY DE 142 – June 7, 2004
Introduction to Human Systems Engineering
Waterloo, Ontario, Canada

2. Outline Case Study: “Set Phasers On Stun”
Discussion on “Set Phasers on Stun”
Midterm Overview

3. Set Phasers on Stun Overview
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.

4. Set Phasers on Stun Interface 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?

5. 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

6. Set Phasers on Stun Feedback
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

7. Midteram Overview SY DE 142 Midterm: Room: DC 1350 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.

8. 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

9. Films Death on the Job Bhopal, a Lingering Tragedy Why Planes Crash
Broken Bus

10. Course Material Outline
Accident Analysis and Fault Trees
Mappings and Affordances
Gulfs of Execution and Evaluation
Human Action Cycle
Information Processing
Human Decision Making
Human Error - Mistakes
Human Error- slips
Human machine model
Displays
Control
Human-Computer Interaction
Usability Testing
Automation
More details on slides and in book.

11. Accident Analysis and Fault Trees
Linear interactions
Common mode interaction
Nonlinear interactions
Tight vs. Loose coupling
FMECA
Fault Tree Analysis
Chronological
Show causality
Events: action and time (time often implicit)
AND/OR gates
Last event at the top OR
AND

12. 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)”

13. Gulfs of Execution and Evaluation (and HAC)
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

14. HUMAN ACTION CYCLE GOAL Intention Evaluate Act Evaluate
Sequence of Actions (what should be done)
Gulf of evaluation!
Interpret
Gulf of execution!
Perception
How is state of the world perceived? Use senses
Act!
WORLD
Interpret

15. 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

16. 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)

17. 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

18. 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

19. 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)

20. Information Displays Human-Machine Model
Human machine system model :
Elements:
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

21. 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

22. Display forms Digital vs. Analog (precision vs. change)
Configural displays
Rankine cycle
Polar star display
Heads-up
Ecological displays

23. Control
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)

24. 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, ….)

25. 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)

26. Automation 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)

27. Automation Levels of automation Reliability Issues:
complacency (over trust),
mistrust,
dumb and dutiful effect.
Best form is Human Centered Automation

28. Good luck