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 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

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”

Human = Mary Beth -Interface = Therac Control PanelMachine = TheracWorld = Patient

a: mary beth's command b: control signal c: raysd: patient state e: feedback on Therac state and actionsf: feedback on interface state and actions (control signal sent)g: interface information

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

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 StunCalculator

Solutions must be written in pen, not in pencil.

Business in Bhopal

Silent Warning

In Search of the Lost Cord

An Act of God

The Wizards of Wall Street

Set Phasers on Stun

Case Studies

Death on the Job

Bhopal, a Lingering Tragedy

Why Planes Crash

Broken Bus

Films

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.

Accident Analysis andFault 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

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: 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

GOAL

WORLD

ActEvaluate

Intention

Act!

Evaluate

Gulf of execution!Gulf of evaluation!

Perception

How is state of the world perceived? Use senses

Interpret

Sequence of Actions (what should be done)

HUMAN ACTION CYCLE

Interpret

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”

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

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

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

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 DisplaysHuman-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

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

Digital vs. Analog (precision vs. change) Configural displays

Rankine cycle Polar star display

Heads-up Ecological displays

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)

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 Approaches (4) Cognitive walkthroughHeuristic evaluation (Neilson’s usability

principals)Performance measurementField study

TasksUsability measures (satisfaction, learnability,

errors)

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)

Automation

Levels of automation Reliability Issues:

complacency (over trust), mistrust, dumb and dutiful effect.

Best form is Human Centered Automation

Good luck