On to the Applications

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. 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.

4. 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.

5. 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?

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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

12. 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.

13. 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

14. 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.

15. 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

16. 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.

17. 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

18. 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.

19. 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

20. 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

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

22. 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)

23. 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)

24. 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

25. The Dialogue - 2 • Help and aiding interaction • 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

26. 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

27. 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