ON TO THE APPLICATIONS

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.

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.

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.

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?

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.

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.

Analysis of and Existing Job - 3 Link Analysis

Analysis of sampling pattern of displays and controlsGoal: 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.

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.

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.

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 overloadsToo little to human bores and dehumanizes

○ Determine displays and controls

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.

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

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.

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 DataTextTables in books on reserve

○ McCormick and Sanders○ Kantowitz and Sorkin

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.

Examples of Anthropometric Data - 2

Dynamic MeasuresMeasures 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

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 DataChanges 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.

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

Requirements for Task Analysis Background Research

Determine GoalsInterview potential users to gain insight into their

needsLibrary Research on Design Issues

Structure of Task AnalysisDetermine flow of activityDetermine Possible Sources of Error/Frustration

PaperBackground and Task AnalysisGive Citations

Human Computer Interaction Issues to Cover

The WorkstationThe DialogueThe User Environment

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 DiscriminationVisual Fatigue (e.g., due to blurry letters)

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)

The Dialogue Mental representation of action of computer

from rules to modelsfrom specific steps to general expectations of

behavior User Interface

commands vs. menusrecall vs. recognitionMenus

○ Chunking and organization○ More organization vs. fewer substeps○ Flexability of use

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

The User Environment Lighting (internal and external)

Glare, and contrast and saturation reductionAdaptation related problems

Noise (from computer and others)Loss of concentration or disruption o f othersMasking of computer sounds

Support of useTraining and innovation

Unwilling usersAssuming the environment is dependent on

computer skill and use

Influence of the Web

Factors to considerSimilar to All programs

○ DistanceHow provide help?

○ Variation of environmentRoom and other conditions very

Unique to Web○ Variation of Setup, e.g. different browsers○ Limitations in Interface○ Loss of standardization