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SST102
Human Factors and
Systems Design
Study Guide (5CU)
Course Development Team
Head of Programme
:
Assoc Prof Chui Yoon Ping
Course Developer
:
Mr. Ravinder Singh
Production
:
Educational Technology & Production Team
© 2018 Singapore University of Social Sciences. All rights reserved.
No part of this material may be reproduced in any form or by any means without
permission in writing from the Educational Technology & Production, Singapore
University of Social Sciences.
Educational Technology & Production
Singapore University of Social Sciences
463 Clementi Road
Singapore 599494
Release V1.3
CONTENTS
SECTION 1: COURSE GUIDE
1.1 Introduction ……………………………………………………………………………………………1
1.2 Course Description and Aims …………………………………………………………………2
1.3 Learning Outcomes ………………………………………………………………………………..2
1.4 Overall Assessment ………………………………………………………………………………..3
1.5 Learning Materials ………………………………………………………………………………….3
SECTION 2: STUDY UNITS
STUDY UNIT 1
Learning Outcomes ……………………………………………………………………………. SU1-1
Overview ……………………………………………………………………………………………. SU1-1
Chapter 1: Introduction to Human Factors and Systems Approach ···· SU1-2
1.1
Introduction
1.2
Terms and Definitions
1.3
History
1.4
Goals and Objectives
1.5
Systems Design Approach
Chapter 2: Design and Evaluation Methods ……………………………………… SU1-7
2.1
Human Factors in Product Design Lifecycle
2.2
User-Centred Design
2.3
Cost/Benefit Analysis
2.4
Human Factors Methodologies
Self-Assessment Questions ……………………………………………………………… SU1-12
Answers to Self-Assessment Questions …………………………………………… SU1-13
STUDY UNIT 2
Learning Outcomes ……………………………………………………………………………. SU2-1
Overview ……………………………………………………………………………………………. SU2-2
Chapter 1: Visual Sensory Systems ………………………………………………….. SU2-3
1.1: Introduction
1.2: The Visual Receptor System
1.3: Bottom-Up vs Top-Down Processing
1.4: Depth Perception
1.5: Visual Search
1.6: Absolute Judgment
Chapter 2: Auditory, Tactile, and Vestibular System ……………………….. SU2-9
2.1: Introduction
2.2: Auditory Alarms
2.3: Sound Localisation and Speech Transmission
2.4: Noise Remediation
2.5: The Other Senses
Chapter 3: Cognition ……………………………………………………………………….. SU2-12
3.1: Introduction
3.2: Information Processing Model
3.3: Selective Attention
3.4: Perception
3.5: Working Memory
3.6: Long-Term Memory
3.7: Organisation of Information in LTM
3.8: LTM Implications for Design
3.9: Attention and Time-Sharing
Chapter 4: Decision Making ……………………………………………………………. SU2-17
4.1: Introduction
4.2: Decision Making Models
4.3: Heuristics and Biases
4.4: Skill, Rule, and Knowledge Based Behaviour
4.5: Improving Human Decision Making
Self-Assessment Questions ……………………………………………………………… SU2-22
Answers to Self-Assessment Questions …………………………………………… SU2-25
STUDY UNIT 3
Learning Outcomes ························································································ SU3-1
Overview ·········································································································· SU3-1
Chapter 1: Displays ······················································································· SU3-2
1.1: Introduction
1.2: Principles of Display Design
1.3: Alerting Displays
1.4: Labels
1.5: Monitoring Displays
1.6: Multiple Displays
1.7: Navigation Displays
1.8: Maps
1.9: Quantitative Information Displays
Chapter 2: Control ························································································· SU3-8
2.1: Introduction
2.2: Principles of Response Selection
2.3: Discrete Control Activation
2.4: Positioning Control Device
Self-Assessment Questions ········································································ SU3-11
Answers to Self-Assessment Questions ··················································· SU3-12
STUDY UNIT 4
Learning Outcomes ························································································ SU4-1
Overview ·········································································································· SU4-1
Chapter 1: Engineering Anthropometry and Workspace Design········· SU4-2
1.1: Introduction
1.2: Human Variability
1.3: Statistical Analysis
1.4: Use of Anthropometric Data in Design
1.5: General Principles for Workspace Design
1.6: Design of Standing and Seated Work Areas
Chapter 2: Biomechanics of Work ····························································· SU4-6
2.1: Introduction
2.2: Low-Back Problems
2.3: Seated Work and Chair Design
2.4: Upper-Extremity Cumulative Trauma Disorders (CTDs)
2.5: Hand-Tool Design
Self-Assessment Questions ········································································ SU4-10
Answers to Self-Assessment Questions ··················································· SU4-11
STUDY UNIT 5
Learning Outcomes ……………………………………………………………………………. SU5-1
Overview ……………………………………………………………………………………………. SU5-2
Chapter 1: Stress and Workload ………………………………………………………… SU5-3
1.1: Introduction
1.2: Environmental Stressors
1.3: Psychological Stressors
1.4: Level of Arousal
1.5: Workload Overload
1.6: Mental Workload Measurement
Chapter 2: Safety and Accident Prevention ……………………………………… SU5-9
2.1: Introduction
2.2: Factors that Cause or Contribute to Accidents
2.3: Human Error
2.4: Hazard Control
2.5: Risk-Taking
2.6: Warnings
Chapter 3: Selection and Training ………………………………………………….. SU5-13
3.1: Introduction
3.2: Learning and Expertise
3.3: Methods for Enhancing Training
3.4: Transfer of Training
Self-Assessment Questions ……………………………………………………………… SU5-16
Answers to Self-Assessment Questions …………………………………………… SU5-18
STUDY UNIT 6
Learning Outcomes ························································································ SU6-1
Overview ·········································································································· SU6-1
Chapter 1: Human-Computer Interaction ················································· SU6-2
1.1: Introduction
1.2: Software Design Cycle: Understand, Design, and Evaluate
1.3: Understand System and User Characteristics
1.4: Seven Stages of Actions
1.5: Conceptual Models and Metaphors
1.6: General Usability Guidelines
1.7: Dialog Styles
1.8: Usability Tests and Metrics
Self-Assessment Questions ·········································································· SU6-8
Answers to Self-Assessment Questions ····················································· SU6-9
SST102
Human Factors and
Systems Design
COURSE GUIDE
SST102 COURSE GUIDE
SECTION 1: COURSE GUIDE
1.1 Introduction
Welcome to your study of SST102 Human Factors and Systems Design, a 5 credit
unit (CU) course.
The Course Guide provides a structure for the entire course. As the phrase implies,
the Course Guide aims to guide you through the learning experience. In other
words, it may be seen as a roadmap through which you are introduced to the
different topics within the broader subject. This Guide has been prepared to help
you understand the aims and learning outcomes of the course. In addition, it
explains how the various materials and resources are organised and how they may
be used, how your learning will be assessed, and how to get help if you need it.
Course Schedule
To help monitor your study progress, you should pay special attention to your
Course Schedule. It contains study unit related activities including Assignment,
self-evaluations, and examinations. Please refer to the Course Timetable in the
Student Portal for the updated Course Schedule.
NOTE: You should always make it a point to check the Student Portal for any
announcements and latest updates.
You need to ensure you fully understand the contents of each Study Unit listed in
the Course Schedule. You are expected to complete the suggested activities either
independently and/or in groups. It is imperative that you read through your
Assignment questions and submission instructions before embarking on your
Assignment. It is also important you comprehend the Overall Assessment
Weighting of your course. This is listed in Section 1.4 of this Guide.
Manage your time well so you can meet given deadlines and do regular revisions
after completing each unit of study. They will help you retain the knowledge
garnered and prepare you for any required formal assessment. If your course
requires an end-of-semester examination, do look through the Specimen or Past
Year Exam Paper which is available on Learning Management System.
Although flexible learning – learning at your own pace, space and time – is a
hallmark at SUSS, you are encouraged to engage your instructor and fellow
students in online discussion forums. A sharing of ideas through meaningful
debates will help broaden your learning and crystallise your thinking.
1
SST102 COURSE GUIDE
1.2 Course Description and Aims
Human factors is about understanding human strengths and limitations and
designing systems that fit them. SST102 Human Factors and Systems Design
gives students an overview of the underlying philosophy, aims and approaches
of human centered systems design. Students are introduced to the human
sensory and physiological systems and cognitive processes. They are exposed to
basic principles of designing and evaluating workplaces and interfaces. Issues on
accidents, human error and designing for safety are also covered in this course.
1.3 Learning Outcomes
Knowledge & Understanding (Theory Component)
Students will be able to:
1
Define the human factors and systems approach
2
Discuss the principles underlying human factors and the implications for
design
3
Describe human capabilities and limitations and their relevance to
systems, workplace and environmental design
4
Explain human-machine system design principles
Key Skills (Practical Component)
Students will be able to:
5
Identify and make effective recommendations to correct human factors
deficiencies in existing human-machine-workplace-environment system
6
Illustrate how human factors principles are applied to deal with safety in
the workplace
7
Show how different human factors methods are appropriately applied for
evaluation, design and research.
2
SST102 COURSE GUIDE
1.4 Overall Assessment
The overall assessment weighting for this course is as follows:
Assessment
Description
Weight
Allocation
Assignment 1
Pre-Class Quizzes
6%
Assignment 2
Online Quiz
8%
Assignment 3
Examination
Group Based Assessment (GBA)
Closed book written examination. Answer
3 compulsory questions in 2 hours.
16%
70%
100%
TOTAL
SUSS’s assessment strategy consists of two components, Overall Continuous
Assessment (OCAS) and Overall Examinable Component (OES) (weighted 30:70
respectively) that make up the overall course assessment score.
(a)
OCAS: The three assignments indicated above constitute 100% of this
component.
(b)
OES: The Examination is 100% of this component.
To be sure of a pass result you need to achieve scores of 40% in each component.
Your overall rank score is the weighted average of both components.
1.5 Learning Materials
The following is a list of the required learning materials to complete this course.
Required Textbook(s)
Author(s)
Last name, First
name
Wickens, C. D., Lee,
J. D., Liu, Y., &
Sallie, G. B.
Title
An Introduction to Human
Factors Engineering (2nd
Edition)
3
Year
Publisher
2014
Pearson/Prentice
Hall
SST102
Human Factors and
Systems Design
STUDY UNIT 1
SST102 STUDY UNIT 1
LEARNING OUTCOMES
At the end of this unit, you are expected to:




Understand what is human factors or ergonomics.
Know the scope and goals of human factors.
Take a systems approach to human factors design.
Understand the stages of human factors involvement in the whole design
lifecycle.
 Centre the design process around the user.
 Perform analysis to show the value of implementing human factors efforts.
 Have an overview of methods such as prototyping, mock-ups, heuristic
evaluation, and usability testing.
OVERVIEW
This is the first unit for the course Human Factors and Systems Design. There are
altogether two chapters. Chapter 1 is an introduction to human factors and systems
approach, whilst Chapter 2 is on design and evaluation methods.
CHAPTER 1: Introduction to Human Factors and Systems Approach
This chapter introduces the field of human factors and the systems approach to
human factors design.
CHAPTER 2: Design and Evaluation Methods
This chapter shows the stages and importance of human factors and their
methodologies.
SU1-1
SST102 STUDY UNIT 1
Chapter 1: Introduction to Human Factors and Systems
Approach
1.1
Introduction
The intent in human factors arises from the fact that technological or product
developments have focused attention on the need to consider human beings or the
real human users in such developments. “Human factors” exists to guide the
applications of technology in the direction benefiting people and hence humanity.
Focus of Human Factors:
ï‚·
On human beings and their interaction with products, equipment, facilities,
procedures, and environments used in work and everyday living.
ï‚·
Emphasis is on human beings and how the design of things influences people.
ï‚·
Seeks to change the things people use and the environments in which they use
these things to better match the capabilities, limitations, and needs of people.
It involves the study of factors and development of tools that facilitate the
achievement of human factors goals (discussed below).
1.2
Terms and Definitions
ï‚·
Human Factors is the term used in the United States.
ï‚·
Historically, the study of ergonomics has focused on the aspect of human
factors related to physical work. Now, ergonomics is the preferred term in
Britain and Europe to describe all aspects of human factors.
ï‚·
Although the term engineering psychology has also been used, “human factors”
is more concerned with the application of the information from psychology to
the design of things.
ï‚·
Another discipline closely related to human factors, Cognitive Engineering,
focuses on the cognitive thinking and knowledge related aspects of system
performance.
SU1-2
SST102 STUDY UNIT 1
Some definitions:
ï‚·
Design for human use.
ï‚·
Human factors discovers and applies information about human behaviour,
abilities, limitations, and other characteristics to the design of tools, machines,
systems, tasks, jobs, and environments for productive, safe, comfortable, and
effective human use.
Sub-domains of study within human factors are displays, workload, biomechanics,
anthropometry, decision making, training, selection, job design, workplace layout,
etc. These areas will be covered in greater detail in the subsequent study units and
will make up the greater portion of this course.
1.3
ï‚·
History
Had its beginnings in the industrial revolution of the late 1800s and early 1900s.
It started with motion study and shop management and the study was of
skilled performance.
ï‚·
During WWII, the focus was on fitting the person to the job through the use of
tests for personnel selection.
ï‚·
Found during the war to be a problem in operating complex equipment so
focus was shifted to fitting equipment to the person.
ï‚·
Engineering psychology labs were established and the human factors
profession was born after the war.
ï‚·
From the 60s to 90s, more companies and industries recognised the importance
and contribution of human factors to the design of workplaces and their
manufactured products.
ï‚·
Today, greater human factors involvement also in computer equipment, user-
friendly software, office design, workplace safety, and legislation.
READ:
Pages 4–9 Chapter 1 of Human Factors in Engineering Design (Sanders,
M. & McCormick, E.), 7th ed. (1993).
SU1-3
SST102 STUDY UNIT 1
1.4
Goals and Objectives
The goal of human factors is making the human interaction with systems one that:
ï‚·
Enhances performance
ï‚·
Increases safety
ï‚·
Increases user satisfaction
These goals and objectives are accomplished through the human factors cycle in
which the human interacts with a system within an environment:
Performance
Identify
Problems
Human
System
Implement
Solutions
Equipment
Task
Environment
Training
Selection
ï‚·
The cycle begins with identifying problems and deficiencies in the humansystem interaction using knowledge of the user’s body (physical) and mind
(cognitive) and the system.
ï‚·
Implementing solutions through five different approaches:
1) Equipment design
Changes the nature of the physical system with which humans work.
2) Task design
Changes what humans do with the system.
SU1-4
SST102 STUDY UNIT 1
3) Environment design
Changes the aspects of the environment in which the work is carried out.
4) Training
Better equips the humans for the task with the necessary skills.
5) Selection
Recognises individual differences across humans that are relevant for good
system performance.
READ:
Pages 1–4 Chapter 1 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.5
Systems Design Approach
Human factors engineering should best be described in a systems context, and most
human factors problems are well addressed by a systems approach. A system is an
entity that exists to carry out some purpose and is composed of humans, machines,
and other things that interact to accomplish a goal.
Systems can be like cybernetic system that is a complex, multi-dimensional network
of information system, having communication processes, control mechanisms, and
feedback principles, or a simple human-machine system such as a person operating
a hand-held tool. “Human factors” typically considers human-machine systems,
where human beings and physical components interact to bring about, from given
inputs, some desired output. Various such systems exist such as manual systems,
mechanical systems, and automated systems.
Some characteristics of human-machine systems:
ï‚·
Systems have a purpose, goal, or objective.
ï‚·
Systems can be hierarchical and be composed of various subsystems.
ï‚·
Systems operate in an environment that can impose certain constraints.
ï‚·
System components serve various functions (sensing, information storage,
information processing and decision, and action) to achieve the system goals.
ï‚·
System components interact to achieve system goals.
ï‚·
Systems, subsystems, and components have inputs and outputs.
SU1-5
SST102 STUDY UNIT 1
System reliability is usually expressed as the probability of successful performance.
A system with various human and machine components will have a reliability
depending on how the components are combined. Components can be combined in
series, parallel, or both. As humans can be the weak link in some systems, humanmachine systems can be designed to provide parallel redundancy for some of the
human functions.
A systems design process effectively brings information on human capabilities,
limitations, and principles to bear on the design of systems. Human factors play a
vital role in this process, taking a systems approach to designing which involves the
following:
ï‚·
The purpose and objectives of the system are defined and system performance
specifications are listed.
ï‚·
The functions that the system has to perform to meet the objectives and
performance specifications are defined.
ï‚·
The basic design takes shape where functions are allocated, human
performance requirements are spelt out, and task analysis conducted.
ï‚·
Testing and evaluation is carried out.
Human factors methods and principles are applied primarily to the design of
products or systems to make them successful. These methods and principles are
applied in all product design phases: predesign analysis, technical design, and final test
and evaluation.
Although the design of the product or system interface may be the most visible
component or design element, human factors involvement generally goes beyond
just the interface design to also look at interaction level issues as focusing solely on
interface design may be ineffective.
READ:
Pages 13–20 Chapter 1 and 727–731 and 746–749 Chapter 22 of Human
Factors in Engineering Design (Sanders, M. & McCormick, E.), 7th ed.
(1993).
READ:
Pages 17–40 Chapter 2 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
SU1-6
SST102 STUDY UNIT 1
Human Factors and Systems Approach
(Access video via iStudyGuide)
Chapter 2: Design and Evaluation Methods
2.1
Human Factors in Product Design Lifecycle
In order to maximally benefit the final product, human factors must be involved as
early as possible in the product or systems design rather than performed as a final
evaluation after the design. The major stages of human factors in the product life
cycle include:
ï‚·
Front-end analysis
The purpose of front-end analysis is to understand the users, their needs, and
the demands of the work situation. Activities carried out during this stage
include a user analysis, environmental analysis, function and task analysis.
Much of the front-end analysis involves understanding and spelling out goals,
functions, and tasks. A goal is an end condition or reason for performing the
tasks, functions represent general transformations needed to achieve the goal,
and tasks represent the specific activities of the person needed to carry out the
function.
ï‚·
Iterative design and test
Once the front-end analysis has been performed and the required information
has been gathered, system specifications and conceptual design solutions can be
written. System specifications include performance requirements and features.
Usability requirements are also included and functional allocation is carried out
as well in this stage.
ï‚·
Implementation and evaluation
This process involves users and is concerned with any aspects of the system
that affect human performance, safety, or the performance of the entire humanmachine system. To properly evaluate a product or system, it should be tested
under conditions as close as possible to those under which it will ultimately be
used.
SU1-7
SST102 STUDY UNIT 1
READ:
Pages 14–15 and 17–40 Chapter 2 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.2
User-Centred Design
All human factors methods are ways to carry out the overriding methodological
principle in the field of human factors of centring the design process around the
user.
ï‚·
Done by studying the users’ task performance, determining their needs and by
getting constant feedback through involving the users at all stages of the design
process.
ï‚·
Does not mean that the user designs the product or controls the process.
ï‚·
Must adequately determine user needs.
ï‚·
General approach:

Early focus on the user and tasks

Empirical measurement

Iterative design using prototypes

Participatory design
There is a wide source of human factors information available that can be used
during the design process based on the context and detail required.
ï‚·
Databases on human capabilities can be found in data compendiums.
ï‚·
Precise recommendations that relate to specific areas can be found in design
standards such as MIL-STD-1472F and ANSI/HFES-100.
ï‚·
More abstract or general guides for the human factors specialist to follow can be
found in human factors principles and guidelines.
READ:
Pages 15–16 Chapter 2 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
SU1-8
SST102 STUDY UNIT 1
2.3
ï‚·
Cost/Benefit Analysis
Human factors analysis is an extra cost that must be justified to the
management.
ï‚·
A cost/benefit analysis shows the overall advantages of human factors efforts.
ï‚·
Cost of conducting a human factors analysis such as a usability study could be
calculated in terms of man-hours involvement of the human factors specialist in
designing and conducting tests.
ï‚·
The redesign benefits can then be quantified such as:

Increased sales

Decreased cost of providing training

Decreased customer support costs

Decreased development costs

Decreased maintenance costs

Increased user productivity

Decreased user errors

Improved quality of service

Decreased training time

Decreased user turnover

Increased employee satisfaction (lower turnover)

Decreased in sick leave

Decreased in number of accidents or injuries

Reduction in medical and rehabilitation expenses

Reduction in number of fines and lawsuits
READ:
Pages 12–14 Chapter 2 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.4
Human Factors Methodologies
To support human factors design activities, methods such as Heuristic Evaluation
and Usability Testing can be applied. Prototypes are built very early in the design
process to support these evaluation methods.
ï‚·
Prototypes

Product mock-ups that are crude approximations of the final product.

Have the look and feel and some functionality.
SU1-9
SST102 STUDY UNIT 1
ï‚·
Paper prototypes of software systems are screen designs sketched on paper.
Heuristic Evaluation

A systematic evaluation of the product or systems design to determine if it
complies with human factors criteria and guidelines.

Done by human factor or usability experts and does not include the users.

Multiple experts can uncover greater percentage of problems as opposed to
just one evaluator.

Evaluations can be performed using checklists by the human factors
evaluator or as walkthroughs with the users using the prototype system.
ï‚·
Usability Testing
Usability is the degree to which the system is easy to use or user-friendly. This
considers the following five variables:
1) Learnability
The system should be easy to learn.
2) Efficiency
The system should be efficient to use.
3) Memorability
The system should be easy to remember.
4)
Errors
The system should ensure users make few errors and allow easy recovery
from it.
5)
Satisfaction
The system should be pleasant to use.
The designs or systems are submitted to usability testing, which is the process of
having users interact with the system to identify human factor flaws overlooked by
designers.

Usability testing has evolved primarily in the field of human-computer
interaction

How many subjects are enough for usability testing?

What are the measures of usability testing?
SU1-10
SST102 STUDY UNIT 1
READ:
Pages 37–39 Chapter 2 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Design and Evaluation Methods
(Access video via iStudyGuide)
SU1-11
SST102 STUDY UNIT 1
Self-Assessment Questions
SAQ 1.1
What is one of the focuses of human factors or ergonomics?
SAQ 1.2
Name three main goals of human factors.
SAQ 1.3
What are the approaches to implementing solutions for deficiencies in humansystem interaction?
SAQ 1.4
What does a systems approach to the design process involve from a human factors
perspective?
SAQ 1.5
What are the major stages of human factors in the life cycle of products?
SAQ 1.6
What is the general approach in creating a user-centred design?
SAQ 1.7
How can human factors efforts or involvement in a project be justified to the
management?
SAQ 1.8
To support human factors design activities, what methods can be used?
SU1-12
SST102 STUDY UNIT 1
Answers to Self-Assessment Questions
Answer to SAQ 1.1
To seek to change the things people use and the environments in which they use
these things to better match the capabilities, limitations, and needs of people.
Answer to SAQ 1.2
To enhance performance, increase safety, and increase user satisfaction.
Answer to SAQ 1.3
The approaches are through equipment design, task design, environment design,
training, and selection.
Answer to SAQ 1.4
The purpose and objectives of the system are defined and system performance
specifications are first listed. Next, the functions that the system has to perform to
meet the objectives and performance specifications are defined. The basic design
then takes shape where functions are allocated, human performance requirements
are spelt out, and task analysis conducted. Finally, testing and evaluation is carried
out.
This human factored systems design process effectively brings information on
human capabilities, limitations, and principles to bear on the design of systems.
Answer to SAQ 1.5
These are the front-end analysis stage where users and their needs are understood,
the iterative design and test stage where system specifications and conceptual
design solutions are written, and the implementation and evaluation stage where
actual users test the system.
Answer to SAQ 1.6
It is to focus early on users and their tasks, taking empirical measurement, building
prototypes for iterative design, and having users participate at every stage of the
design process.
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Answer to SAQ 1.7
A cost/benefit analysis should be carried out, where the cost of the human factors
efforts could be calculated in terms of man-hours involvement of the human factors
specialist and the benefits of the redesign that results could be highlighted.
Answer to SAQ 1.8
Prototypes and mock-ups can be built and heuristic evaluations and usability
testing can also be carried out.
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Human Factors and
Systems Design
STUDY UNIT 2
SST102 STUDY UNIT 2
LEARNING OUTCOMES
At the end of this unit, you are expected to:
 Understand the properties of the human visual system.
 Know what influences top-down and bottom-up processing of visual
information.
 Understand how depth is perceived by the eye and know depth cues.
 Gain an overview of the serial search process.
 Know the limits of human capability to judge absolute values.
 Identify the criteria of designing effective alarms.
 Understand speech processing and the techniques to improve speech for better
processing.
 Have an overview of the other human senses such as tactile, haptic,
proprioceptive, kinaesthetic, and vestibular.
 Understand the various stages of the model of human information processing.
 List the perceptual processes and guidelines for supporting perception.
 Understand the difference between working memory and long-term memory.
 Discuss working memory limits and their implications.
 Discuss long-term memory information organisations and their implications.
 Know what divided attention is.
 Address time-sharing overload.
 Understand task demands and the resources available for them.
 Know the difference between normative and descriptive decision making
models.
 Recognise the rules-of-thumb and human biases present when making
decisions.
 Distinguish between skill, rule, and knowledge based behaviour adopted when
making decisions.
 Discuss some of the ways in which to improve human decision making.
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OVERVIEW
This is the second unit for the course Human Factors and Systems Design. There are
altogether four chapters. Chapter 1 is on visual sensory systems, Chapter 2 is on
auditory, tactile, and vestibular system, Chapter 3 is on cognition, whilst Chapter 4
is on decision making.
CHAPTER 1: Visual Sensory Systems
This chapter discusses important characteristics of human visual performance.
CHAPTER 2: Auditory, Tactile, and Vestibular System
This chapter addresses issues regarding the processing of auditory and other
sensory information.
CHAPTER 3: Cognition
This chapter addresses the basic mechanisms of how we perceive, think, and
remember, and the framework for processing information.
CHAPTER 4: Decision Making
This chapter shows the different decision processes that people adopt based on
situations.
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Chapter 1: Visual Sensory Systems
1.1
Introduction
The eyes view or perceive visual stimuli. There are several important characteristics
of human visual performance as it is affected by the interaction between
characteristics of visual stimulus and the human perceiver. The anatomy of the eyes
affects the characteristics of the light stimuli which may disrupt the ability to see in
certain working environments and is therefore of design concern in human factors.
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All visual stimuli that the human can perceive may be described as a wave of
electromagnetic energy (light).
– The wavelength determines the hue and the amplitude the brightness.
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The observer’s experience of visual intensity or brightness depends on the
properties of the light source, the distance from the light source, and the
reflective surface.
Luminous intensity (flux) comes from a light source (e.g., the sun or lamps).
Illuminance is the quality of light that falls on an object and depends on the
distance from the light source to the object.
Luminance is the quantity of light that is reflected back to the observer’s eye.
Reflectance is the ratio of luminance/illuminance.
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READ:
Pages 42–45 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.2
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The Visual Receptor System
There are visual receptor cells at the back of our retina that transform light
energy into neural energy to the brain.
There are two types of receptor cells, rods and cones. These have six different
properties which have implications for visual sensory processing:
1) Location
The middle region or fovea (around 2º of visual angle), inhabited only by cones.
2) Acuity
The amount of fine detail that can be resolved is greater when the image is on
the closely spaced cones.
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3) Sensitivity
The rods have greater sensitivity, characterising the minimum amount of light
that can be detected.
4) Colour sensitivity
Rods cannot discriminate different wavelengths of light, or colour.
5) Adaptation
Rods rapidly lose their sensitivity and take a longer time to adapt back to
darkness when stimulated by light.
6) Differential wavelength sensitivity
Cones are sensitive to all wavelengths, while rods are particularly insensitive to
long wavelengths (red light).

How will all the above information be useful in design?
What is the difference between scotopic and photopic vision?
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Rods and cones visual receptor cells have differences that are responsible for a
wide range of visual phenomena.
Three important aspects of sensory processing to which these have human
factors implications:
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1) Contrast sensitivity
The minimum contrast between a lighter and darker spatial area that can just be
detected. Measured by a grating.
– Print should not be too fine in order to guarantee its readability.
– What makes readable print?
– When should upper case and lower case letters be used?
2) Colour vision
Employed in a well-illuminated environment and also limited by colour
deficiencies of user population.
– 7% of male population colour deficient.
– Design for monochrome first.
– Use colour only as a redundant backup to signal important information.
3) Night vision
Loss of contrast sensitivity can affect perception in poorly illuminated
environments.
– Another hazard of night driving includes glare.
– It temporarily destroys the rod’s sensitivity to low spatial frequencies.
READ:
Pages 47–54 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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1.3
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Bottom-Up vs Top-Down Processing
The factors of the human visual system that affect the quality of the sensory
information that is perceived may be represented as affecting processing from
the bottom upward.
High contrast sensitivity may be described as an enhancement of bottom-up
processing.
Another type of influence on processing operates from the top downward. This is
perception based on knowledge and expectancies of what should be present.
Instructional sentences can leverage on top-down processing based on the way
they are written even if they are read in poor conditions.
Top-Down
Experience
Knowledge
Perception
Senses
Stimulus
Bottom-Up
READ:
Pages 54–55 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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1.4
Depth Perception
Movement and manipulation in a 3-D world is normally done quite accurately and
automatically. There are a number of depth cues to provide information of how far
away things are and the distance between them.
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There are three cues that operate on bottom-up processing and are only
effective for judging objects close to the viewer:
1) Accommodation
The extent to which objects are perceived to be close or far, is via signals sent to
the brain based on how much the eyeball lens shape changes to accommodate
or focus the image on the retina.
2) Binocular convergence
The amount of inward rotation of the eyeball muscles to bring an image to rest
on the retina.
3) Binocular disparity (Stereopsis)
The closer an object is to the observer, the greater the amount of disparity there
is between the view of the object received by each eyeball. The brain uses this
disparity, computed at a location where the two visual signals combine, to
estimate the object’s distance.
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There are six cues that operate on top-down processing and are effective for
judging more distant objects:
1) Linear perspective
Converging of parallel lines towards distant points.
2) Relative size
Objects of the same size that appear smaller are further away.
3) Interposition
Nearer objects tend to obscure the contours of objects that are further away.
4) Light and shading
3-D objects tend to cast shadows and reveal reflections on themselves.
5) Textural gradients
Finer texture or higher spatial frequencies signal more distant regions.
6) Relative motion
More distant objects show relatively smaller movement across the visual field.
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READ:
Pages 55–58 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.5
Visual Search
The process of visual search is an important aspect of human performance.
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Eye movements can be divided into pursuit and saccadic movements.
Pursuit movements are of constant velocity that follows moving targets.
Saccadic movements are abrupt, discrete movements from one location to the
next.
Saccadic movements include a movement time and a dwell, which is
characterised by its dwell duration and a useful field of view.
When searching a visual field, many searches are serial in that each item is
inspected in turn to distinguish targets from non-targets.
In an organised visual search space, search is carried out from top to bottom
and left to right.
The predicted time to detect a target can be calculated by multiplying the
number of items to be searched by the time to search each item, and then
divided by two. This is a useful model for predicting search times with lists,
phone books, and computer menus.
Two circumstances can render serial searches inappropriate:
1) Conspicuity
The bottom-up influence of how conspicuous is the target (such as a flashing or
uniquely coloured target).
2) Expectancies
The top-down influence of where the searcher expects the target to be (such as
the familiarity with the alphabet when searching a phone book).
READ:
Pages 58–61 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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1.6
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Absolute Judgment
Refers to the limited human capability to judge the absolute value of a variable
signalled by a coded stimulus.
Estimating height of bar graph is absolute judgment task with 10 levels.
Judging colour of traffic signal is task with only 3 levels.
People are not good at absolute value judgments.
They can do so accurately only if fewer than around 5 levels of any sensory
continuum are used.
READ:
Page 69 Chapter 3 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Visual Sensory Systems
(Access video via iStudyGuide)
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Chapter 2: Auditory, Tactile, and Vestibular System
2.1
Introduction
Acoustic or sound information can be conveyed through tones used in alarms and
communications through speech. The processing of this acoustic information has
influences on performance of an individual. The presence of noise in the
environment is another source of acoustic information that we may not want to
process.
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The stimulus for hearing is sound or a vibration of air molecules.
The acoustic stimulus can be represented by a sound wave with a frequency
(perceived as pitch) and amplitude (perceived as loudness).
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Sound intensity or sound pressure level is measured in decibels (dB) with the
formula 20 log (P1/P2), where P1 is the sound pressure we want to express and
P2 is a standard reference level.
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For the listener, loudness is a psychological experience that correlates with
sound intensity (loudness doubles with each 10dB increase in sound intensity).
READ:
Pages 71–76 Chapter 4 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.2
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Auditory Alarms
Auditory alarms induce a greater level of compliance than do visual alarms
since the auditory system is omni-directional.
We cannot choose to ignore audio signals that are presented in our
environment.
What are the properties of a good alarm system?
1) The alarm must be heard above the ambient background noise.
2) The alarm should not be above the danger level for hearing.
3) The alarm should not be overly startling or abrupt.
4) The alarm should not disrupt the perceptual understanding of other signals.
5) The alarm should be informative.
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a) The alerting and distinctive features of the alarm sound can be combined with
the more informative features of synthetic voice to create redundancy gain.
b) Auditory icons that sound like the conditions they represent can also be
designed to address problems in comprehension.
READ:
Pages 78–82 Chapter 4 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.3
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Sound Localisation and Speech Transmission
Auditory system less suited for precise spatial localisation and processes
sounds better in azimuth than in elevation and front-back.
Used when the eyes are heavily involved with other tasks or where signals
could occur anywhere around the person.
Auditory communications can be affected by bottom-up or top-down
processing.
Intensity of speech signals is much greater in vowels than consonants.
Consonants are much more susceptible to masking than vowels.
Is a male or female voice more vulnerable to masking of noise?
READ:
Pages 83–88 Chapter 4 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.4
Noise Remediation
If noise problems relate to communications difficulties in situations when the noise
level is below 85 dB, signal enhancement procedures may be used.
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Face-to-face communication cues provided by the lips.
Use of phonetic alphabets.
Choice of restricted vocabulary and common words.
If noise problems relate to communications difficulties in situations when the noise
level is above the action levels, noise reduction procedures must be adopted.
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Careful choice of tools or sound producing equipment.
Alteration of the environment or path from the sound source to the human.
What is the final resort if noise still cannot be reduced?
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Modalities:
When is auditory preferable to visual?
When is visual preferable to auditory?
READ:
Pages 92–95 Chapter 4 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.5
The Other Senses
Though visual and auditory senses are of greatest implications for the design of
human-machine systems, three other categories of sensory experience have some
direct relevance to design.
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Tactile and haptic sense (touch and feel)
Sensory receptors under the skin convey pressure information of hands and
fingers.
Sense of finger position provides information of manipulated shapes.
Examples are mechanical keys on keyboards and control handles.
Proprioception and kinesthesis (limb position and motion)
Receptor systems within the muscles and joints convey information of limb
position in space.
Together with kinesthesis convey sense of motion of the limbs.
Examples are joysticks and steering wheels.
Vestibular sense (whole-body orientation and motion)
Receptor located within the inner ear conveys information regarding translation
and rotation of the body.
Important for human-machine interaction where the systems move directly or
simulators.
Examples are virtual environments and below a ship’s deck.
READ:
Pages 96–99 Chapter 4 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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Chapter 3: Cognition
3.1
Introduction
The model of information processing highlights those aspects that typically
influence cognition: perceiving, thinking about, and understanding the world. The
human information-processing system is represented by different stages at which
information gets transformed.
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3.2
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Perception of information about the environment
Central processing or transforming that information
Responding to that information
Information Processing Model
The senses gather information which is then perceived, providing a meaningful
interpretation of what is sensed.
We think about or manipulate perceived information in working memory.
Information from long-term memory is retrieved every time we perceive
familiar information.
The perception and information processing then leads to the selection and
execution of a response.
Our actions generate new information to be sensed and perceived through the
feedback loop.
The many stages of information processing depend upon mental or attention
resources that are allocated to processes as required.
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READ:
Pages 101–102 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
3.3
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Selective Attention

Acquiring information about the environment which at times requires effort.
Necessary to achieve perception.
The selection of channels to attend (and filtering of channels to ignore) is driven
by:
Salience
Effort
Expectancy
Value
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Salience is a bottom-up process, characterised by attentional capture.
Expectancy and value are top-down processes.
Selective attention may be inhibited if it requires a lot of effort.
READ:
Pages 102–104 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
3.4
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Perception
Involves the extraction of meaning from the information processed by our
senses.
Three concurrent processes:
1) Bottom-up feature analysis
Analysing the raw features of a stimulus or event.
2) Unitisation
Past experience causes some things to be perceived as a unit.
Rapid and automatic.
3) Top-down processing
The ability to correctly guess what a stimulus or event is, even in the absence of
clear physical features.
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High expectations are based on associations and context.
Human factors guidelines for supporting perception:
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Maximise bottom-up processing
Maximise automaticity and unitisation
Maximise top-down processing when bottom-up processing is poor
Avoid confusions
Use a smaller vocabulary
Create context
Exploit redundancy
READ:
Pages 104–108 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
3.5
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Working Memory
Sometimes called short-term memory, it is the temporary store that keeps
information active while we are using it or until we use it.
Visuospatial sketch pad and phonological loop ‘storage systems’.
We can maximise working memory by chunking information.
It can hold 7+/- 2 chunks (Miller’s magic number).
Working memory is limited in capacity and duration unless it is rehearsed.
Confusability and similarity.
Attention can be diverted and depends very much upon the limited supply of
attentional resources.
Human factors implications of working memory limits:
Minimise working memory load
Provide visual echoes
Provide placeholders for sequential tasks
Exploit chunking (physical chunk size and meaningful sequences)
Superiority of letters over numbers (1-800-GET HELP)
Keeping numbers separate from letters
Minimise confusability
Avoid unnecessary zeros (use 2385 instead of 002385)
Consider working memory limits in instructions (order of text and negation)
READ:
Pages 108–114 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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3.6
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Long-Term Memory
A mechanism for storing information and retrieving it at a later time.
Semantic memory (for facts and procedures) and event memory (for specific
events).
Transfer of information to long-term memory is through learning.
Two important features that determine the ease of later retrieval:
1) Strength
Determined by frequency and recency of its use.
2) Associations
An item may be linked or associated with other items.
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Rote memory (rapidly forgotten) is based solely on frequency and recency, by
rehearsing items through repetition.
Forgetting is a failure of memory retrieval due to weak strength and
associations.
Recognition vs recall
Recall (in which one must retrieve the required item from memory) is lost faster
than recognition (in which a perceptual cue is provided in the environment).
READ:
Pages 114–116 Chapter 5 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
3.7
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Organisation of Information in LTM
Schema is the entire knowledge structure about a particular topic (college
courses, vacations).
Scripts are typical sequence of activities (getting online or shutting down
equipment).
Mental models are schemas of dynamic systems. It is the understanding of how
something works, based on expectancies and population stereotypes (turning a
knob clockwise).
Cognitive maps are mental representation of spatial information (layout of a
city or workplace).
Did you ever have to mentally rotate a map?
READ:
Pages 116–117 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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3.8
LTM Implications for Design
How do we design so that people do not have problems due to poor retrieval from
long-term memory?
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Encourage regular use of information to increase frequency and recency.
Encourage active verbalisation or reproduction of information that is to be
recalled.
Standardise.
Use memory aids (knowledge in the world vs knowledge in the head).
Carefully design information to be remembered.
Meaningful and semantically associated with other information
Concrete rather than abstract words
Distinctive concepts and information
Well-organised sets of information
Able to be guessed based on other information
Little technical jargon
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Design to support development of correct mental models (concept of visibility).
READ:
Pages 117–119 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
3.9
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Attention and Time-Sharing
To divide attention between two or more tasks or mental activities.
Four major factors contribute to the success or failure of divided attention:
Mental effort and resource demand (concept of automaticity)
Similarity in processing structures of both tasks (dimensions of multiple
resources).
Confusion
Allocating resources accordingly (what time-sharing strategies do you use?)
Address time-sharing overload in complex multitask environments.
Task redesign (relook the task analysis, what tasks are imposing too many
demands?)
Interface redesign
Training
Automation (how can it help?)
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READ:
Pages 129–134 Chapter 5 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Cognition
(Access video via iStudyGuide)
Chapter 4: Decision Making
4.1
Introduction
We make hundreds of decisions everyday considering multiple pieces of
information and selecting a course of action. Different decision processes are
adopted depending on the situation.
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4.2
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Decision making is represented by three phases:
Acquiring and perceiving information or cues.
Generating and selecting hypotheses about what the cues mean.
Planning and selecting choices to take.
Decision Making Models
Normative decision models are based upon the concept of utility.
Specify what people ideally should do.
What is the overall value of a choice and how much is the outcome worth to
you?
Do you consider all factors, possible choices, and their outcomes?
Descriptive decision models show how humans actually make decisions.
Rely on simpler and less complex means of selecting among choices.
When amount of information is small and time is unconstrained, we should
carefully analyse choices and their outcomes.
READ:
Pages 137–142 Chapter 6 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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4.3
Heuristics and Biases
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Heuristics are simplified shortcuts or rules-of-thumb (concept of satisficing).
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Can be optimal most times but can also lead to poor decisions and biases.
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Information processing limits in decision making:

Cue reception and integration
Pieces of information must be selectively attended, interpreted, and integrated
with one another.

Hypothesis generation and selection
The cues are used to generate hypotheses by retrieving information from longterm memory.

Plan generation and action choice
Alternative actions are generated by retrieving possibilities from memory.
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Heuristics and biases in receiving and using cues:
Attention to a limited number of cues
We can use only a small number of cues due to working memory limits.

Cue primacy and anchoring
First few cues receive greater importance and people stick to hypotheses based
on them.

Inattention to later cues
Cues occurring later are frequently ignored.

Cue salience
Perceptually salient cues are more likely to be captured and given more weight.

Overweighting of unreliable cues
We should realise all cues are not equally reliable or weighted.
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Heuristics and biases in hypothesis generation, evaluation and selection:
Generation of a limited number of hypotheses
Due to working memory limitations, we generate only a small subset of
possible hypotheses.

Availability heuristic
We would go for hypotheses we considered recently or more frequently.
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Representativeness heuristic
People diagnose a situation because the pattern of cues looks representative of
some other typical situation.

Overconfidence
We are biased in our confidence with different hypotheses in our working
memory.

Cognitive tunneling
Once a hypothesis has been chosen, we underutilise subsequent cues.

Confirmation bias
When considering additional cues to evaluate working hypotheses, we seek out
only confirming information.
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Heuristics and biases in action selection:
Retrieve a small number of actions
We are limited in the number of action plans we can retrieve and keep in
working memory.

Availability heuristic for actions
People retrieve the most available courses of actions from long-term memory
based on recency, frequency, and associations.

Availability of possible outcomes
The retrieval of associated outcomes is also subject to availability effects.

Framing bias
Our judgment is influenced by the manner of presentation of a decision to be
made.
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Have you used the above heuristics, such as the confirmation bias, and in which
situations?
READ:
Pages 142–150 Chapter 6 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
4.4
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Skill, Rule, and Knowledge Based Behaviour
The skill, rule, and knowledge based behaviour (Rasmussen) of people
depending on their level of expertise and decision situation.
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Skill based
People who are extremely experienced.
React to perceptual elements automatically.
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Rule based
People who are familiar with task but no extensive experience.
Input is recognised and rules from past experience triggered.
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Knowledge based
When faced with a new situation having no rules from past experience.
Analytical processing using conceptual information.
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What is recognition-primed (RPD) decision making?
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In what situations and by whom is (RPD) decision making carried out?
READ:
Pages 151–153 Chapter 6 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
4.5
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Improving Human Decision Making
Decision makers adjust their response according to experience, task situation,
cognitive-processing ability, and available decision-making aids.
So how do we improve human decision making?
1) Task redesign
Poor decision making does not mean you have to do something to the person.
2) Decision-support systems
Decision trees, expert systems, displays, and alerts can be utilised.
3) Training
Overcoming heuristics and biases.
Improving analytical, normative utility methods for decision making.
READ:
Pages 157–163 Chapter 6 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Decision Making
(Access video via iStudyGuide)
SU2-20
SST102 STUDY UNIT 2
Self-Assessment Questions
SAQ 1.1
What are the different properties of our visual receptor cells (rods and cones) that
have implications for visual processing?
SAQ 1.2
What are the aspects of sensory processing that the linked to visual phenomena due
to the difference between rods and cones?
SAQ 1.3
What is the difference between bottom-up and top-down processing?
SAQ 1.4
What are the depth cues for judging close objects (based on bottom-up processing)
and those for judging farther objects (based on top-down processing)?
SAQ 1.5
Name the circumstances where a serial search process will be rendered
inappropriate.
SAQ 1.6
What is the limit of absolute judgment in humans?
SAQ 1.7
What are the properties of a good auditory alarm system?
SAQ 1.8
What procedures should be used to overcome communication difficulties when
noise level is below 85dB?
SAQ 1.9
What procedures should be used to overcome communication difficulties when
noise level is above 85dB?
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SST102 STUDY UNIT 2
SAQ 2.0
Besides visual and auditory sensing, what three other categories of sensory
experience can be relevant to design?
SAQ 2.1
What are the stages of human information processing?
SAQ 2.2
What are the factors that affect selective attention?
SAQ 2.3
What are the three processes that perception proceeds by?
SAQ 2.4
Name the human factors guidelines for supporting perception.
SAQ 2.5
What is the difference between working memory and long-term memory?
SAQ 2.6
What are human factors implications of working memory limits?
SAQ 2.7
What are two important features that determine the ease of information retrieval
from long-term memory?
SAQ 2.8
Name the ways in which information is organised in our long-term memory.
SAQ 2.9
What are the long-term memory limitations for design?
SAQ 3.0
What are the factors that contribute to the success or failure of divided attention?
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SST102 STUDY UNIT 2
SAQ 3.1
What are the ways to address the overload created in multi-task environments?
SAQ 3.2
What is the difference between normative and descriptive decision models?
SAQ 3.3
Where can information processing limits impose on decision making?
SAQ 3.4
What are the heuristics or rules-of-thumb and biases in decision making during cue
reception and integration?
SAQ 3.5
What are the heuristics or rules-of-thumb and biases in decision making during
hypothesis generation and selection?
SAQ 3.6
What are the heuristics or rules-of-thumb and biases in decision making during
generation of plans and action?
SAQ 3.7
What are the differences in the skill, rule, and knowledge based behaviours in
decision making?
SAQ 3.8
What are the ways to improve human decision making?
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SST102 STUDY UNIT 2
Answers to Self-Assessment Questions
Answer to SAQ 1.1
The properties are location, acuity, sensitivity, colour sensitivity, adaptation, and
differential wavelength sensitivity.
Answer to SAQ 1.2
They are contrast sensitivity, colour vision, and night vision.
Answer to SAQ 1.3
Lower levels of stimulus processing based on the quality of the sensory information
are considered bottom-up processing, while processing based on our prior
knowledge and desire of expected information is top-down processing.
Answer to SAQ 1.4
For close objects the depth cues are accommodation, binocular convergence, and
binocular disparity, while for farther objects these are linear perspective, relative
size, interposition, light and shading, textural gradients, and relative motion.
Answer to SAQ 1.5
These are the conspicuity of the target and the expectancy of where the target
would be.
Answer to SAQ 1.6
It is less than around 5 levels of any sensory continuum used.
Answer to SAQ 1.7
It must be heard above the background ambient noise, it should not be above the
danger level for hearing, it should not startle the operator, it should not disrupt the
understanding of other signals by the operator, and it should be informative.
Answer to SAQ 1.8
Signal enhancement procedures such as face-to-face communication cues provided
by the lips, use of phonetic alphabets, and choice of restricted vocabulary and
common words should be used.
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SST102 STUDY UNIT 2
Answer to SAQ 1.9
Noise reduction procedures such as careful choice of tools or sound producing
equipment, and alteration of the environment or path from the sound source to the
human should be used.
Answer to SAQ 2.0
The other senses are tactile and haptic (touch and feel), proprioception and
kinesthesis (limb position and motion), and vestibular (whole-body orientation and
motion).
Answer to SAQ 2.1
The perceptual encoding stage (short-term sensory store and perception), central
processing stage (working and long-term memory), and responding stage (response
selection and execution). Attention resources are allocated to these stages where
required.
Answer to SAQ 2.2
The factors are salience, effort, expectance, and value.
Answer to SAQ 2.3
The processes are the analysing of the raw features of a stimulus or event (bottomup feature analysis), perceiving as a unit based on past experience (unitisation), and
the ability to correctly guess what a stimulus or event is (top-down processing).
Answer to SAQ 2.4
Maximise bottom-up processing, maximise automaticity and unitisation, maximise
top-down processing when bottom-up processing is poor, avoid confusions, use a
smaller vocabulary, create context, and exploit redundancy.
Answer to SAQ 2.5
Working (or short-term) memory is a temporary store that keeps information active
while we are using it or until we use it, while long-term memory is a mechanism
for storing information and retrieving it at a later time.
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SST102 STUDY UNIT 2
Answer to SAQ 2.6
We should minimise working memory load, provide visual echoes, provide
placeholders for sequential tasks, exploit chunking, recognise the superiority of
letters over numbers, keep numbers separate from letters, minimise confusability,
avoid unnecessary zeros, and consider working memory limits in instructions.
Answer to SAQ 2.7
They are the strength (how frequent and recent was it used) of the material and its
associations with other items.
Answer to SAQ 2.8
It is organised by schemas or scripts (knowledge about a topic or sequence of
activities), mental models (schemas of dynamic systems), and cognitive maps
(mental representations of spatial information).
Answer to SAQ 2.9
We should encourage regular use of information and active verbalisation of
information to be recalled, should standardise, use memory aids, and design
information to be remembered that is meaningful and semantically associated with
other information, has concrete rather than abstract words, has distinctive concepts
and information, has well-organised sets of information able to be guessed based
on other information, contains little technical jargon, and is designed to support
development of correct mental models.
Answer to SAQ 3.0
The factors are the mental effort required and resources demanded of the tasks, the
similarity in processing structures of the tasks, the confusion created, and the
allocation of resources.
Answer to SAQ 3.1
Through task redesign, interface redesign, training, and automation.
Answer to SAQ 3.2
Normative decision models are based on utility or the value of a choice, while
descriptive decision models are based upon how humans actually make decisions
based on simpler means.
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SST102 STUDY UNIT 2
Answer to SAQ 3.3
They can be during cue reception and integration (where information must be
selectively attended, interpreted, and integrated with one another), during
hypothesis generation and selection (where the cues are used to generate
hypotheses by retrieving information from long-term memory), and during
generation of plans and action (where alternative actions are generated by
retrieving possibilities from memory)
Answer to SAQ 3.4
During cue reception and integration, the heuristics and biases are giving attention
to a limited number of cues, cue primacy and anchoring, inattention to cues that
appear later, cue salience, and overweighting of unreliable cues.
Answer to SAQ 3.5
During hypothesis generation and selection, the heuristics and biases are
generation of a limited number of hypotheses, availability heuristic,
representativeness heuristic, overconfidence, cognitive tunnelling, and
confirmation bias.
Answer to SAQ 3.6
During generation of plans and action, the heuristics and biases are retrieving a
small number of actions, availability heuristic, availability of possible outcomes,
and framing bias.
Answer to SAQ 3.7
Skill based is when one is experienced and reacts to perceptual elements
automatically, rule based is when one is familiar but without experience in the task
and uses rules from past experiences, while knowledge based is when one is faced
with a new situation, has no rules to guide and has to analyse the information.
Answer to SAQ 3.8
Through task redesign, decision-support systems, and training.
SU2-27
SST102
Human Factors and
Systems Design
STUDY UNIT 3
SST102 STUDY UNIT 3
LEARNING OUTCOMES
At the end of this unit, you are expected to:









List the 13 different principles of designing displays.
Design displays for alerting or monitoring by users.
Know how to signal the identity or function of an entity to be displayed.
Address issues in designing multiple displays and display overlays.
Understand how to provide design features for navigational support in display
design and maps.
Know how to best design displays presenting a range of numbers and values
such as tables and graphs.
Know the five variables influencing the speed and difficulty in selecting a
response or action.
Understand the design features that make activation of controls better.
Know how to position control entities for better activation, and control device
characteristics.
OVERVIEW
This is the third unit for the course Human Factors and Systems Design. There are
altogether two chapters. Chapter 1 is on displays, whilst Chapter 2 is on control.
CHAPTER 1: Displays
This chapter shows how to design human-made artifacts to support perception of
system variables.
CHAPTER 2: Control
This chapter addresses the control process that actions lead to.
SU3-1
SST102 STUDY UNIT 3
Chapter 1 : Displays
1.1
Introduction
A display is a human-made artifact designed to support the perception of relevant
system variables and to facilitate the further processing of that information. A car
speedometer, aircraft warning tone, and the print on instruction labels are all
examples of displays, in various modalities that convey various forms of
information in various tasks.
ï‚·
The display acts as a medium between some aspects of the actual information in
a system and the operator’s perception.
ï‚·

Displays are classified along three dimensions:
Physical implementation of the display.
The nature of the task that the display is intended to support.
Based on characteristics of the human user who must perform those tasks.
READ:
Pages 165–166 Chapter 7 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.2
Principles of Display Design
The 13 principles of display design are associated with four distinct categories:
ï‚·
Perceptual principles
These are principles of display design that directly reflect perceptual operations.
1) Make displays legible (or audible)
Necessary, although not sufficient, for usable displays.
2) Avoid absolute judgment limits
Do not expect people to judge the level of a variable on the basis of a single
sensory variable like colour or size.
3) Top-down processing
People perceive and interpret signals according to what they expect to perceive
based on past experience.
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SST102 STUDY UNIT 3
4) Redundancy gain
A message is more likely to be correctly interpreted when the same message is
expressed more than once (e.g., traffic light).
5) Discriminability
Use discriminable elements as similarity causes confusion.
ï‚·
Mental model principles
We interpret what a display looks like and how it moves in terms of our
expectations of the system being displayed.
6) Principle of pictorial realism
A display should look like the variable that it represents.
7) Principle of the moving part
The moving elements of displays should move in a spatial pattern and direction
compatible with the user’s mental model of how the represented element
actually moves in the physical system (e.g., airplane displays).
ï‚·
Principles based on attention
Complex displays require three components of attention (selective, focused, and
divided) to process information.
8) Minimising information access cost
How much time and effort to access one display and then another?
9) Proximity compatibility principle
Sometimes, sources of information related to the same task must be mentally
integrated to complete the task. Parts of information should be close but not too
close.
10) Principle of multiple resources
Presenting visual and auditory information concurrently.
ï‚·
Memory principles
Short-term memory is vulnerable through having a limited capacity, while longterm memory is vulnerable through forgetting.
11) Replace memory with visual information: knowledge in the world
Important to present information in the world of what to do.
12) Principle of predictive aiding
Help predict future conditions.
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13) Principle of consistency
Design displays in a manner consistent with other displays that the user may be
perceiving concurrently or recently.
READ:
Pages 166–171 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.3
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Alerting Displays
Classified into three levels of alerts according to criticality:
– Warnings
Most critical category, signalled by salient auditory alerts.

Cautions
Less critical, less salient auditory alerts.

Advisories
Need not be auditory, but can be purely visual.
Can exploit redundancy by using both auditory and visual modes.
When would you use visual and/or auditory signals to present warnings?
What are the typical colour codes for warnings, cautions, and advisories?
READ:
Page 173 Chapter 7 of An Introduction to Human Factors Engineering
(Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.4
Labels
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Also a form of displays which are static and unchanging.
Usually presented as print but can also be icons.
Four key design criteria for labels:
Visibility/legibility
Remember contrast sensitivity?

Discriminability
Should not be confusing.

Meaningfulness
Avoid labels based only on icons and abbreviations, but use them for
redundancy.
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SST102 STUDY UNIT 3

Location
Should be physically close to and unambiguously associated with the entity it
labels.
READ:
Pages 173–175 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.5
Monitoring Displays
Displays for monitoring that support the viewing of potentially changing quantities
such as channel frequency, speed, and temperature that need to be set or may just
need to be watched.
ï‚·

Four criteria used to optimise monitoring displays:
Legibility
Again related to issues of contrast sensitivity.

Analog vs digital
Analog displays show rate and direction of change and are more easily read in
a quick glance. Digital displays are more appropriate for precise readings.
Design for redundancy.

Analog form and direction
Remember the principle of pictorial realism? The orientation of the display scale
should be in a form and direction that is congruent with mental models.

Prediction and sluggishness
Predictive displays can aid human performance.
READ:
Pages 175–178 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
SU3-5
SST102 STUDY UNIT 3
1.6
Multiple Displays
An important issue in multiple displays is the layout of all those displays.
ï‚·
Six guidelines for display layout:
1) Frequency of use
Most frequently used displays should be adjacent to the human operator’s
primary visual area.
2) Display relatedness or sequence of use
Related or sequentially used displays should be close together.
3) Consistency
Displays should always consistently be laid out with the same item positioned
in the same spatial location.
4) Organisational grouping
All displays within a group should be functionally related.
5) Stimulus-response compatibility
Displays should be close to their associated controls.
6) Clutter avoidance
There should be a minimum visual angle between all pairs of displays.
READ:
Pages 178–181 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.7
ï‚·
ï‚·

Navigation Displays
A navigational display should serve four fundamentally different classes of
tasks:
Provide guidance about how to get to a destination.
Facilitate planning.
Help recovery if the person becomes lost.
Maintain situation awareness regarding the location of a broad range of objects.
Route lists and command displays
The simplest form of navigational display provides a series of commands or
instructions.
Can also use synthesised voice commands. When will command displays be a
problem?
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SST102 STUDY UNIT 3
READ:
Pages 188–189 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.8
ï‚·
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Maps
Must be legible and avoid clutter.
What are the negative consequences of clutter on a map?
What are the solutions?
Create maps with minimal information.
Effective colour coding.
With electronic maps, it is possible to highlight needed information selectively
while leaving others in the background.
Decluttering allows the user to simply turn off unwanted categories of
information.
A good map supports the viewer’s rapid and easy cross-checking between
features of the environment and the map. Examples are ‘you are here’ maps.
Have you ever had to mentally rotate a map?
Maps should be of appropriate scale.
3-D maps may be appropriate for some tasks.
READ:
Pages 189–193 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.9
Quantitative Information Displays
ï‚·
ï‚·
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Use a table if precision with which a value must be read is high.
Use a graph if precision is not required but perception of trend is important.
Some guidelines for graphic presentation:

Legibility and discriminability
Related to issues of contrast sensitivity.

Clutter
Maximise data-ink ratio.

Proximity
Things that need to be compared are close or linked by common visual code.
SU3-7
SST102 STUDY UNIT 3
READ:
Pages 193–197 Chapter 7 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Displays
(Access video via iStudyGuide)
Chapter 2: Control
2.1
Introduction
Displayed information eventually leads to action or an effort to control some aspect
of a system or to respond to a displayed event. Control primarily involves the
selection and execution of responses.
2.2
Principles of Response Selection
The difficulty and speed of selecting a response or an action is influenced by several
variables, of which five are particularly critical for system design:
ï‚·

Decision complexity
The speed with which an action can be selected is strongly influenced by the
number of possible alternative actions that could be selected.
Hick-Hyman law of reaction time (RT) shows an increase in RT as the number
of possible stimulus-response alternatives increase.
The most efficient way to deliver a given amount of information is by a smaller
number of complex decisions than a large number of simple decisions.
ï‚·

Response expectancy
We receive rapidly and accurately information that we expect.
Compare a car suddenly stopping in front versus traffic light turning amber.
ï‚·

Compatibility
Good stimulus-response compatibility aids in response selection.
Location compatibility and movement compatibility.
ï‚·

Speed-accuracy tradeoff
Factors that make the selection of a response longer will also make errors more
likely.
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SST102 STUDY UNIT 3

However, if we try to execute actions very rapidly, we are more likely to make
errors.
ï‚·

Feedback
Nearly instantaneous feedback is good.
Feedback delayed by 100msec can be harmful if rapid sequences of control
actions are required.
READ:
Pages 199–201 Chapter 8 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.3
Discrete Control Activation
In addition to making the controls easily visible, there are several design features
that make the activation of such controls less susceptible to errors and delays.
ï‚·

Physical feel
There should be some feedback to indicate changes in state (e.g., visual,
auditory, and tactile).
ï‚·

Size
Inadvertent activation issues.
ï‚·

Confusion and labelling
Control activation errors also occur if the identity of the control is not well
specified to novice users.
READ:
Pages 201–202 Chapter 8 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.4
Positioning Control Device
ï‚·
ï‚·

Movement of a controlled entity, or cursor, to a destination, or target.
Fitt’s law of movement time (MT)
Related to amplitude of movement and width of target.
ï‚·

Control device characteristics
Direct position controls (light pen and touch screen)
Indirect position controls (mouse and touch pad)
Indirect velocity controls (joystick and cursor keys)
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Voice control
Useful in time-sharing activities where visual and manual systems are
occupied. Constraints are cost, acoustic quality, noise, etc.
Factors such as task performance dependence and the work space environment can
influence the effectiveness of control devices.
ï‚·
ï‚·

Task performance dependence
Direct position devices (touch screen and light pen) are best employed in point
and drag tasks.
Problems in accuracy due to instability of hands and fingers and finger
imprecision.
Indirect position devices (mouse) have greater precision and may be adjusted
for gain.
Work space environment
Direct position devices suffer greatly in a vibrating environment.
Some workspaces have no room for a mouse pad.
Joysticks that may be less effective in desktops are more advantageous in
mobile environments.
Voice control is difficult in a noisy environment.
High gain devices are faster but are less precise.
READ:
Pages 202–207 Chapter 8 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
SU3-10
SST102 STUDY UNIT 3
Self-Assessment Questions
SAQ 1.1
Name the principles of display design.
SAQ 1.2
How do you classify the different levels of alerts?
SAQ 1.3
What are the key design criteria for labels?
SAQ 1.4
What are the criteria used to optimise monitoring displays?
SAQ 1.5
What are the guidelines for the layout of multiple displays?
SAQ 1.6
What functions should navigational displays serve?
SAQ 1.7
How should you design maps?
SAQ 1.8
What are the guidelines when designing quantitative information displays?
SAQ 1.9
What are the variables that affect the difficulty and speed of response selection?
SAQ 2.0
What are the design features that make the activation of controls less susceptible to
errors and delays?
SAQ 2.1
What are the factors that can influence the effectiveness of control devices?
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SST102 STUDY UNIT 3
Answers to Self-Assessment Questions
Answer to SAQ 1.1
First are those that are based on perception such as making displays legible,
avoiding absolute judgment limits, encouraging top-down processing, exploiting
redundancy gain, and using discriminable elements. Next are those based on
mental models such as having pictorial realism and the compatibility of the moving
elements. Then are those based on attention such as minimising time and effort,
proximity compatibility, and concurrent presentation of visual and auditory
information. Finally are those based on memory such as placing knowledge in the
world, predictive aiding, and consistency.
Answer to SAQ 1.2
According to warnings (using salient auditory alerts), cautions (using less salient
auditory alerts), and advisories (where visual alerts can be used).
Answer to SAQ 1.3
The criteria are visibility, discriminability, meaningfulness, and location.
Answer to SAQ 1.4
The criteria are legibility, choosing between analog or digital depending on
situation, considering the analog form and direction, and having predictive
displays.
Answer to SAQ 1.5
The guidelines are layout according to frequency of use, sequence of use,
consistency, functional grouping, compatibility between the stimulus and response,
and avoiding clutter.
Answer to SAQ 1.6
They should provide guidance to a destination, facilitate planning, help recovery
when lost, and help maintain situation awareness.
Answer to SAQ 1.7
Avoid clutter by using minimal information, effective colour coding, and
highlighting only necessary information. Use an appropriate scale, allow easy
cross-checking with the real world and prevent people from having to mentally
rotate the map.
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Answer to SAQ 1.8
A table should be used if precision is required and a graph when trend is required.
The displays should be legible and discriminable, should avoid clutter, and there
should be proximity among things to be compared.
Answer to SAQ 1.9
The variables are decision complexity based on the number of possible alternative
actions available, the expectancy of certain responses, compatibility in stimulusresponse, the tradeoff between speed and accuracy of a response, and the speed
with which the feedback to a response is provided.
Answer to SAQ 2.0
The physical feel or feedback provided, the size of the control, and labelling the
identity of the control to prevent confusion.
Answer to SAQ 2.1
The factors are task performance dependence or what tasks the control devices are
used for, and the work space environment where the control devices are used.
SU3-13
SST102
Human Factors and
Systems Design
STUDY UNIT 4
SST102 STUDY UNIT 4
LEARNING OUTCOMES
At the end of this unit, you are expected to:
 Know the importance of considering human variability in design.
 Understand the concept of percentiles.
 Be able to effectively use anthropometric data of various populations for design
purposes.
 Recognise clearance and reach requirements of largest and smallest users.
 Know the general principles for designing optimal workspaces or workplaces.
 Understand and apply guidelines such as NIOSH for analysing lifting tasks.
 Optimise the design of workplaces or devices that require material handling.
 Gain an overview of seating postures and lower back disorders.
 List various seat design parameters in chair design.
 Understand the causes of disorders of the hand or fingers due to repetitive
motion as well as prevention.
 Know how to apply guidelines to reduce the risk of CTDs through better design
of hand tools for work.
OVERVIEW
This is the fourth unit for the course Human Factors and Systems Design. There are
altogether two chapters. Chapter 1 is on engineering anthropometry and
workspace design, whilst Chapter 2 is on the biomechanics of work.
CHAPTER 1: Engineering Anthropometry and Workspace Design
This chapter introduces the physical measure of humans and its implications on
workspaces.
CHAPTER 2: Biomechanics of Work
This chapter addresses human strength, physical work, and potential injuries.
SU4-1
SST102 STUDY UNIT 4
Chapter 1:
Engineering
Workspace Design
1.1
Anthropometry
and
Introduction
Anthropometry is a scientific discipline which provides the fundamental basis and
quantitative data for matching the physical dimensions of workplaces and products
with the body dimensions of intended users.
ï‚·
ï‚·
ï‚·
1.2
The study and measurement of human body dimensions.
Data are used to develop design guidelines for heights, clearances, grips, and
reaches of workplaces and equipment.
Purpose is to accommodate the body dimensions of the potential work force.
Human Variability
Human variability comes from a number of sources:
ï‚·

Age variability
Stature increases to about age 20-25.
ï‚·

Sex variability
Adult males are on average taller and larger than females.
Adult female dimensions are about 92% of corresponding male values.
ï‚·

Racial and ethnic group variability
Body size and proportions vary greatly between different racial and ethnic
groups.
Japanese are shorter in stature than Americans but average sitting height did
not differ much (Air Force).

ï‚·

Occupational variability
Can result from physical activity involved in the job, and the special
requirements of certain occupations.
ï‚·

Generational or secular variability
1cm growth per decade in American population
Improved nutrition and living conditions are possible reasons for this growth.
READ:
Pages 225–226 Chapter 9 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
SU4-2
SST102 STUDY UNIT 4
1.3
Statistical Analysis
In order to deal with human variabilities in design, an anthropometric dimension is
analysed as a statistical distribution rather than a single value.
ï‚·
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ï‚·

ï‚·
Normal distribution is used for anthropometric data.
In design, anthropometric data is most often used in percentiles.
A percentile value of an anthropometric dimension represents the percentage of
the population with a body dimension of a certain size or smaller.
50th percentile value is the mean of the population.
Structural anthropometric data (e.g., stature, shoulder breadth) are
measurements taken with the body in static positions.
Functional (dynamic) anthropometric data are obtained when the body adopts
various working postures (e.g., forward reach).
If you are 70th percentile in stature, how many people are shorter than you?
Is it possible to find an ‘average’ person who is 50th percentile on all body
dimensions?
Sample anthropometric data of Singaporean males:
Stature
Seated Height
Seated Eye Height
Shoulder Breadth
Seated Hip Breadth
Buttock-Knee Length
Seated Knee Height
Weight
5th
1602
851
742
399
310
523
469
48.5
50th
1704
905
795
448
369
572
516
63.2
95th
1805
958
847
497
427
621
563
77.9
READ:
Pages 226–235 Chapter 9 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
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SST102 STUDY UNIT 4
1.4
Use of Anthropometric Data in Design
Anthropometric data in tables provides the information for designing workplaces
and products. A systematic approach is used for applying anthropometric data in
design:
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Determine the user population or intended users.
Determine the relevant body dimensions.
Determine the percentage of the population to be accommodated.
Design for the extremes (5th and 95th percentile)
Design for adjustable range (driver car seat)
Design for the average (supermarket checkout counters)
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Determine the percentile value of the selected anthropometric dimension (5th,
95th, or some other).
Which dimension and percentile would you consider when determining the
height of a door?

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Make necessary design modifications to the data (e.g., footwear, headwear,
slump)
Use mock-ups or simulators to test the design.
READ:
Pages 235 – 238 Chapter 9 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.5
General Principles for Workspace Design
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Clearance requirements
Consider the largest or 95th percentile users.
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Reach requirements
Consider the smallest or 5th percentile users.
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Adjustability requirements
Adjusting the workplace (location, orientation of workplace).
Adjusting the worker position relative to the workplace (change in seat height,
use of platforms).
Adjusting the work piece (lift tables).
Adjusting the tool (adjustable hand tool).

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SST102 STUDY UNIT 4
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Visibility and Normal Line of Sight (LOS)
Normal LOS is the preferred direction of gaze when the eyes are at a resting
condition (about 10°-15° below the horizontal plane).
Primary visual displays should be placed within +/-15° in radius around the
normal LOS.
Component arrangement
Similar principles as display layout.
What are these?
READ:
Pages 238–245 Chapter 9 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
1.6
Design of Standing and Seated Work Areas
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Prolonged standing is a strainful posture.
Workers should not be required to stand for a long time.
Provide breaks
Use floor mats and cushioned soles for greater comfort during standing work.
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Seated workplace should be used for long term duration.
However, prolonged sitting can be harmful to the lower back.
Allow workers to stand up and walk after a period of seated work.
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Have you seen sit-stand workplaces or seats?
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Work surface height
Determined by the nature of the tasks performed.
Standing working height at 5-10cm below elbow level and seated working
height at elbow level.
What about working heights for precision work and heavier work?
Allow for adjustability.
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Work surface depth
Normal and maximum work area defined by sweep area of the arms.
Items to be reached immediately or frequently should be located within normal
work area.
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Work surface inclination
Horizontal surfaces preferred for writing.
Slightly slanted surfaces (about 15°) preferred for reading.
SU4-5
SST102 STUDY UNIT 4
READ:
Pages 246–248 Chapter 9 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
Engineering Anthropometry and Workspace Design
(Access video via iStudyGuide)
Chapter 2: Biomechanics of Work
2.1
Introduction
Mechanical forces are exerted by a worker in performing a task such as lifting a
load or using a hand tool. Awkward postures and heavy exertion forces are major
causes of musculoskeletal problems.
Occupational biomechanics plays a major role in studying and analysing human
performance and musculoskeletal problems in manual material handling and
provides the fundamental scientific basis for ergonomic analysis of physical work.
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2.2
Two most prevalent musculoskeletal injuries are low-back pain and upperextremity (fingers, hands, wrists, arms, and shoulders) cumulative trauma
disorders.
Low-Back Problems
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One of the most costly and prevalent work-related musculoskeletal disorders in
industry.
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Manual material handling
Lower back is the most vulnerable link.
Involving lifting, bending, twisting of the torso.
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Sedentary work environments requiring a prolonged static sitting posture.
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NIOSH lifting guide used for practical ergonomics purposes.
Lifting equation used to determine the recommended weight limit (RWL)
associated with lower back risk.
RWL = LC x HM x VM x DM x AM x FM x CM (a total of 7 multipliers)
SU4-6
SST102 STUDY UNIT 4
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Load constant (LC) of 23kg is the maximum recommended weight limit for
lifting under optimal conditions.
What are these ‘optimal’ conditions?
Seven parameters in the NIOSH equation are for designers to optimise
workplaces and devices for material handling.
Horizontal and vertical multipliers suggest that loads should be kept close to
the body and located at waist height if possible.
The asymmetric multiplier suggests that torso twisting should be minimised.
What does the frequency multiplier suggest?
How would you lift a heavy object from the ground?
READ:
Pages 256–267 Chapter 10 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.3
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Seated Work and Chair Design
A sitting posture can be particularly vulnerable to low-back problems.
Lordosis vs kyphosis
In unsupported sitting postures, disc pressure is much lower in an erect sitting
posture than in slumped sitting.
A properly designed seat can support a person to adopt a less strainful posture
and reduce the loads on the spine.
There are several seat design parameters.
What backrest inclination angle would you recommend?
What is the purpose of a lumbar support?
READ:
Pages 267–269 Chapter 10 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.4
Upper-Extremity Cumulative Trauma Disorders (CTDs)
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Also called Repetitive Strain Injuries (RSI) and can be even more costly than
low-back problems.
The disorders are largely due to the cumulative effects of repetitive, prolonged
exposures to physical strain and stress.
CTDs of the fingers
Repeated and prolonged use of vibrating tools and pressed against sharp edges.
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CTDs of the hand and wrist
Carpal tunnel syndrome is the most common.
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SST102 STUDY UNIT 4
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Occupational causes such as repeated use of conventional computer keyboards.
CTDs at the elbow
Repeated forceful wrist activities such as frequent use of a hammer.
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CTDs at the shoulder
Working with fast or repetitive arm movements or with static elevated arms
where hands are raised above the shoulder height.
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Comprehensive approach to the prevention of CTD through administrative and
engineering methods.
Administrative methods.
Training, work-rest cycles, warm-up exercises, task rotation.


Engineering methods
Redesign workplace and tools, eliminate elevated elbows and raised arms
during work, do not locate visual displays too high or too low.
Use automated equipment and supporting devices.
READ:
Pages 269–273 Chapter 10 of An Introduction to Human Factors
Engineering (Wickens, C., Lee, J., Liu, Y., & Sallie, G.), 2nd ed. (2014).
2.5
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Hand-Tool Design
Poorly designed hand-tools not only affect task performance and productivity,
but are a major cause of CTDs.
Four guidelines for the design of hand-tools:
1) Do not bend the wrist
The wrist should remain straight rather that bent or twisted.
2) Shape tool handles to assist grip
Tool handles should be padded, be sufficiently long, and have a curvature to
distribute forces on either side of the palm and fingers.
3) Provide adequate grip span
Grip strength is a function of grip span, and is maximum when span is around
7-8cm.
4) Provide finger and gloves clearances
Ensure full grip of object and minimise risk of squeezing or crushing the
fingers. Glove clearance for cold places or when handling hazardous materials.
– What are some of the inherent problems with wearing gloves and holding tools
or…
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