1. On to the Applications

2. Mental Workload
DEFINITION: The feeling of mental effort or the level of use of the human operators limited resources.
As task demand increases, resources left in reserve decreases.
When attentional resources are exceeded, further increases in task demand will reduce performance.
New airplanes and military systems are analyzed in terms of mental workload.

3. A Mental Workload Model
Model Developed at New Mexico State University

4. Measuring or Predicting Workload
Time-Line Analysis: Measure amount of time spent on task relative to amount of time available.
100% is all time available is being used.
Gives estimate of how time use changes during course of task, e.g. flying.
Dual Task Experiments
Primary Task measure: Change the nature of the main task and see how performance changes.
Secondary Task measure: Give a secondary task. Measure changes in its performance as the primary task is changed in difficulty.
Subjective Measures: self-report of users.
These measures do not always correlate well.
The secondary task is usually an intermittent task. This is like our proposed experiment. Does the secondary task of using a cell phone distract sufficiently to impair driving performance.

5. Beginning a Task Analysis
All designs begin with the goals and purposes of the overall system.
There are different levels of goals:
The function: an airplane moves things great distances in a relatively short time.
The job of the system: fighter vs. passenger jet.
The level of technology: mechanical vs. electronic instruments.
The cost of the finished system.
These types of questions provide and overview and set up constraints.
Remember:
Honor thy user!
There are always tradeoffs.
The technology question may be marketing - 777

6. Beginning a Task Analysis - 2
Relevant questions to keep in mind
Kantowitz and Sorkin, 1983
What inputs and outputs must be provided to satisfy system goals?
What operations are required to produced system outputs?
What functions should the person perform within the system?
What are the training and skill requirements for the operators?
Are the tasks compatible with human capabilities?
What equipment interfaces does the human need to perform the job?
Does the human help or hurt the machine, vice versa?

7. Analysis of an Existing Job
Process Analysis
Derived from the beginning of industrial engineering from the beginning of century.
Major goal: improve efficiency.
issues of safety and human need are not important here.
Specifics:
Each act, movement of the human, is identified as a therblig.
The therbligs necessary for the job are identified.
This technique allows for identification of wasted movements that can be combined or eliminated.

8. Analysis of an Existing Job - 2
Principles of Motion Economy
A list of principles for job and workspace design to increase movement efficiency.
Examples:
Use of Human Body:
Eye fixations should be as few as possible.
Layout of Workplace:
Tools, materials and controls should be located close to the point of use.
Materials and tools should be located for best sequence of movement.

9. Analysis of and Existing Job - 3
Link Analysis
Analysis of sampling pattern of displays and controls
Goal: to arrange elements to make moving from one display or control to another display or control more efficient and effective.
Collect Sampling Data:
List of which elements are used or viewed in which order
Frequency Data: how often each display is viewed.
Conditional Probabilities: given one display is viewed, what is the probability that another display will be viewed next.
Run through for both displays and controls.

10. Analysis of an Existing Job - 4
Link Analysis (continued)
The probabilities can assist layout.
If probability is high and element is important, the display or control should be centrally placed.
If a probability is high and importance is low (that is, the designer wishes to reduce the probability) the element should be moved to the periphery.
If two displays or controls are used in sequence, that is their conditional probabilities are high, they should be next to each other.

11. Analysis of an Existing Job - 5
Critical Incident Technique
Essentially errors or near errors are recorded
journals or interviews are used.
Since errors are often the result of design flaws, recording the errors can help analysis.
The record must be detailed or it will not be useful.
A large sample is necessary to see if errors are systematic, indicating a design flaw, or random, indicating human inattention.
This is perhaps the most used technique since driven by salience.

12. Analysis of Job in Design Stage
Hopkin’s Approach - a general plan
Analyze goals of job in terms of:
purpose
assumptions and constraints
Allocate functions
general refers to assigning tasks to humans and machines
not easy.
Too much to human overloads
Too little to human bores and dehumanizes
Determine displays and controls
I have a note to myself to note similarity to what started with. Problem - if task is in design there is nothing at the start.

13. Analysis of Job in Design Stage - 2
Timeline Analysis
same as for determining workload.
Failure Task Analysis
Analyze all anticipated failures to ensure that humans will be able to handle.
e.g. MD-11
In many cases, it is advisable to perform more than one of these analyses.

14. Analysis of Job in Design Stage - 3
Types of Design Relative to Errors
Exclusion
Design to make it impossible to commit errors
Doubt this is really possible
Prevention
Design to minimize the possibility of errors
Fail Safe
Design to minimize the effects of errors
You can combine the last two

15. Anthropometry
DEFINITION: measurement of the human body and its biomechanical characteristics (Adams, 1989).
Biomechanical refers to the mechanical (machine-like) capabilities of the human skeleto-muscular systems.
Thus, this field measures our sizes and how we move and move easily.

16. Anthropometry - 2 The Need for Anthropometry
We are not all the same size.
If systems were designed to fit only one person, the few if any would be able to use the system.
Poor design for mechanical abilities of the human body can lead to discomfort or injury, e.g., the height of keyboard for a computer.
Sources of Anthropometry Data
Text
Tables in books on reserve
McCormick and Sanders
Kantowitz and Sorkin
Harve and the tank story would be good here.

17. Examples of Anthropometric Data
Static Measures
Passive measures of the dimensions of the human body.
These measures are used to determine size and spacing requirements of work space.
Example Measures
height
weight
wing span
seat to elbow height.

18. Examples of Anthropometric Data - 2
Dynamic Measures
Measures of the dynamic properties of the human body, such as strength and endurance.
These measures are used to match the dynamic characteristics of controls to user.
Measures
range of motion for various joints
force of leg pushes
strength of fingers

19. How to Use Anthropometric Data
Know your population
If your measures are from a different group than your users are from problems could result.
Women are different from men.
Asians are different from Americans.
Use Recent Data
Changes in diet and habit lead to changes in size and fitness of population
Try on old suit of armor
Most size measures are done on nudes.
clothes change our sizes
think of seat belts in summer vs. winter.

20. How to Use Anthropometric Data - 2
Techniques of Design
Design for extremes
A standard is to design to fit 5th to 95th percentiles of the population
The chair is a common example.
Make the design adjustable
Ideally this is optimal, especially if adjustment only needs to be done once.
If the adjustment is hard or must be done frequently, the user may not do them.
Airline pilots are require to do this for cockpit.
The techniques can be combined
Always test the design

21. Requirements for Task Analysis
Background Research
Determine Goals
Interview potential users to gain insight into their needs
Library Research on Design Issues
Structure of Task Analysis
Determine flow of activity
Determine Possible Sources of Error/Frustration
Paper
Background and Task Analysis
Give Citations

22. Human Computer Interaction
Issues to Cover
The Workstation
The Dialogue
The User Environment

23. The Workstation Perceptual Issues (The Visual Display Unit or VDU)
Luminance (Foreground - 35 cd/m2)
Refresh Rate (Flicker)
Contrast (Minimum ratio of 3/1)
Legibility (Size, height/width ratio, and stroke width)
Polarity (Dark on Light is recognized easier, Bauer and Cavonius, 1980)
Chromatic Discrimination
Visual Fatigue (e.g., due to blurry letters)

24. The Workstation Antrhopometric issues Display level
We like to look down a little
If we don’t, we can get neck strain and back strain.
Keyboard layout, level, and shape
Stuck with QWERTY
Angle of hands can cause problems. It is worse if the keyboard is too high
Split can help. Angle each of the hands out.
Mouse (and other related pointing devices
Gain (movement of mouse relative to movement on screen)
Work area (e.g., place for papers books)

25. The Dialogue Mental representation of action of computer
from rules to models
from specific steps to general expectations of behavior
User Interface
commands vs. menus
recall vs. recognition
Menus
Chunking and organization
More organization vs. fewer substeps
Flexability of use

26. The Dialogue - 2 Help and aiding interaction Skill of User
Help vs. tutorials
During use vs. before
Online analysis of use with hints
Skill of User
Menus, help, etc. are slow and relatively inflexible but easy to learn
Menus vs Ribbons vs Breadcrumbs
Image (Icon) vs. Text
Commands (shortcut keys) are faster and more flexible but harder to learn
Thus skill level interacts with interface
Hypertext - Embedded Commands
Icons

27. The User Environment Lighting (internal and external)
Glare, and contrast and saturation reduction
Adaptation related problems
Noise (from computer and others)
Loss of concentration or disruption o f others
Masking of computer sounds
Support of use
Training and innovation
Unwilling users
Assuming the environment is dependent on computer skill and use

28. Influence of the Web Factors to consider Similar to All programs
Distance
How provide help?
Variation of environment
Room and other conditions very
Unique to Web
Variation of Setup, e.g. different browsers
Limitations in Interface
Loss of standardization