The research problem was addressed by first examining theories of human function and performance along with existing sources of user ability data. I would also like to thank all my colleagues at the Cambridge Design Engineering Center and members of the Inclusive Design and Healthcare research groups, including James, Thomas, Suresh, Dawn, Carlos, Tim, Joy and Nick for their help and stimulating conversations.
Introduction
- Research Motivation
- Population Ageing and Disability
- Inclusive Product Design
- Research Aim
- Research Questions
- Scope
- Thesis Outline
This population aging is ubiquitous in the sense that it affects almost all countries of the world. An overview of the key elements of human sensory, cognitive, and motor capabilities is presented, based on existing literature and consultation with domain experts.
Background
Chapter Overview
Inclusive Design
- Inclusive Design Definition and Philosophy
- Historical Context
- The Inclusive Design Process
- Key Theoretical Concepts in Inclusive Design
- Challenges and Limitations to Inclusive Design
- Supporting Designers
- Section Summary
The Inclusive Design approach is a user-centred approach to design (Keates & Clarkson, 2003a; Poulson, Ashby, & Richardson, 1996), where the fundamental premise is that accessible and usable products and services can only be developed by the intended users first to know. (Keates & Clarkson, 2003a; Mayhew, 1999; Nielsen, 1993). Keates and Clarkson developed the Inclusive Design knowledge loop (Figure 2-3) as a framework for representing the iterative activities and information flow in the design process (Keates & Clarkson, 2003a).
Understanding Users with Disabilities
- Understanding Disability: The ICF Model
- Disability Data
- Section Summary
The World Health Organization (WHO) model of disability is shown in Figure 2-5 (World Health Organization, 2001). Fujiura provides an overview of disability measurement systems in the Handbook of Disability (Fujiura & Rutkowski-Kmitta, 2001).
Product Evaluation for Inclusive Design
- Product Evaluation Theory
- Empirical Versus Analytical Evaluation Methods
- Examining Analytical Evaluation Methods
- Predictive Methods for Inclusive Design Evaluation
- Advantages and Disadvantages of Current Methods
Predictive Evaluation: User Models User models are used to predict various interaction performance parameters. This is one of the few examples of inclusive design optimization in the anthropometric field.
The Capability Data Problem
- Accuracy of Predictions Using Capability Data
Even more fundamental to the lack of design-relevant performance data is the problem of the validity of predictions made from such data. In a third of the cases, the difficulty was overestimated, and in a tenth of the cases it was underestimated (Kanis, 1993).
Summary of Research Problem
User ability data should not only be representative of the population as a whole, but should also be design-relevant and multivariable, consisting of sensory, cognitive and motor skills data, all in the same database (multivariate data). Most current assessment methods are not based on the integration of sensory, cognitive and motor data at an appropriate level of detail.
Chapter Summary
Taking a holistic view, the interaction of users' skills will also be investigated, in order to achieve a better understanding of user-product interaction.
Research Approach
- Chapter Overview
- Methodological Approach
- Research Process Overview
- Phase 1: Reviews
- Review of theoretical foundations
- Review of user capabilities
- Review of product demands
- Review of Existing Capability Data Sources
- Phase 2: Exploring Inclusive Interaction
- Phase 3: Experiment
- Critique of the research methodology
- Chapter Summary
In the second stage of the research process, an observational study was conducted with seven participants using two toasters. First, the scope of the research was limited to measurable sensory, cognitive and motor skills.
Theoretical Considerations
- Chapter Overview
- Interaction: User Capability-Product Demand Theory
- Modelling: Human Functional Capability
- Modelling the Relationship Between Hierarchical Levels
- Linear Combination Models
- The Elemental Resource Model
- Comparing the IDC and the ERM
- Section Summary
- A Generic Analytical Evaluation Framework
- Chapter Summary
Two of the most popular models will be described: (1) linear combination models and (2) non-linear resource economic models. In the upper part of the diagram, a linear combination model assumes that different proportions or weights (b1, b2, b3 etc.) of low-level resource availability (RA) combine to give the level of performance on a high-level task. In the lower part of the diagram, a resource economic model assumes that the high-level tasks can be broken down into a set of resource demands (RD1, RD2, RD3) corresponding to a set of resource availability (RA1, .
The IDC is also focused on disability, with the origin of the axis representing some average level of sensory, cognitive, and motor performance of the population. The ERM discussed earlier is focused on performance with the axis baseline defined at zero performance levels.
Capabilities and Demands
Chapter Overview
Review of Human Capabilities
Guidelines for Designing Consumer Products for Greater Accessibility to the Handicapped - Working Draft 1.7 (Pirkl & Babic, 1988a).
Sensory Functions
- Vision
- Hearing
- Environmental Factors and Sensory Capabilities
Contrast Sensitivity: Contrast is a measure of the difference in brightness between an object and its background. Contrast sensitivity is a measure of the minimum contrast that can be perceived at different spatial frequencies. For design evaluation, the maximum size of the central field of view is the important benchmark.
However, sensorineural hearing loss is more prevalent in the population and results in variable threshold losses at different frequencies of the human frequency range (Moore, 1998). Visual and auditory signals can both be characterized by spatial frequency profiles, as in the audiogram's contrast sensitivity function (CSF) and sound frequency profiles, respectively.
Cognitive Functions
- Sensation and Perception
- Working Memory
- Long Term Memory
- Mental Models
- Response Selection and Execution
- Language and Communication
- Age Related Effects
The quality of information reaching the brain depends on the state of the sensory receptors. The central executive is responsible for attentional control and coordination of working memory subsystems. The overall capacity of the working memory system is estimated at approximately five to nine chunks of information (Baddeley, 2000).
Thus, two important performance measures of the working memory system are storage capacity in terms of the number of chunks that can be held, and speed and accuracy of processing. These models may reflect their understanding of the product's behavior and how it should be used (Norman, 1983; Van der Veer & Melguizo, 2003).
Motor Functions
- Hand and Arm Functions
- Gross Body Functions
- Speech Functions
- Common Conditions Causing Loss of Motor Function
Most products require hands and arms to operate controls and manipulate various product functions. Controls and handles can also be grasped and held between the fingers or within reach of the hand using grasping movements (Napier, 1956). Power grips use the palm of the hand in addition to the fingers to exert greater grip forces on the chassis and handles of the product (Napier, 1956).
Measuring the maximum linear, rotational, and grip forces that can be exerted with different grips is necessary to determine the maximum performance capabilities for each hand. Finger dexterity is the ability to make skillful, coordinated movements with the fingers of one or both hands to grasp, place, or move small objects (Crepeau et al., 2003).
Capabilities and Health: A UK Population Perspective
- Disability Prevalence
- Cluster Analysis
- Discussion
Based on MVA results, cases with missing values in 13 ability variables of interest and 15 health variables were removed. Each case in the data set was weighted to obtain estimates of the prevalence of disability in the population (Semmence et al., 1998). Thus, the graph shows the limitations of abilities related to mental functions, which are more widespread in the younger age groups (16-20 and 21-40 years) in contrast to the limitations of sensory and motor abilities, which are more widespread in the older age groups (61 -80 and 81- 100 years).
The high prevalence of mental and nervous diseases explains the loss of mental abilities in younger age groups. In addition, the high prevalence of musculoskeletal diseases in the 61 and older age groups explains the losses in the ability to move, stretch and stretch, and dexterity.
Chapter Summary
The IDC) wealth model provides a useful and simplified representation of wealth loss in the population. It masks the true picture that disability is a non-linear, discontinuous space of dependent factors.
Exploring Inclusive Interaction
Chapter Overview
Empirical Study with Two Toasters
- Empirical Study Design
- Data Analysis
- Results
- User Problems: Toasting Bread with Toaster 1 and Toaster 2
- User Problems: Toasting a Bagel with Toaster 2
- User Problems: Setting the Memory on Toaster 2
- User Preference between Toaster 1 and Toaster 2
- Issues Observed
- Summary
5 of the 7 participants had difficulty reading the numbers and the arrow on the heating control (task 1). In the case of Participant 5 with vision loss, a problem was encountered with the tactile feel of the heat control. All interface functions were on the front of the toaster for easy access and it indicated 'ON'.
Two participants also encountered problems with the lifting handle that lifts the bagel out of the slots. Users expected the bagel and crumpet button to be replicated on the right side of the toaster, as was done for some other controls, e.g.
Product demand analysis
- Sensory Demands
- Cognitive Demands
- Motor Demands
Different paths through the state-space of the toaster can be represented as shown in Figure 6-5. The state-action representation allows for the evaluation of feedback on each state of the device. The user is therefore only required to keep track of the condition of the bread.
Thus, the toaster's demands on users' knowledge and long-term memory are assumed to be relatively low. Most of the motor actions required to use the toaster controls can be performed with non-compound actions with one hand.
Discussion
Issues with lack of tactile support on controls (like problem 8 in the user survey) could be addressed as a standard control for each control or set of controls on the product. This could be addressed by developing a list of packaging types, expected product-to-plug distances and common surface types likely to be encountered. In order to make valid estimates, the relationship between pre-measured capacity values and product requirements must be carefully modeled and understood.
Both types of product evaluation methods lead to results that would be useful for product design, and both methods can be used in the Inclusive Design process. However, predictive analytics methods that rely on user proficiency data are less developed than empirical methods in the field of Inclusive Design.
Chapter Summary
The analytical evaluation performed by the author for toast 1 showed that the use of a systematic analysis coupled with tools such as state charts can also highlight important areas for design improvement. This included raising issues such as slider contrast, the lack of a power-on status indicator, and the lack of an alarm to indicate that the toast is complete. The analytical evaluation method would be further improved if it provided quantitative estimates of how many people would be excluded from the design and how many people would find it difficult to use in a given population.
Thus, there is room for further work in improving analytical evaluations with supporting data on user capabilities. The next chapter explores the issue of describing and modeling the relationship between pre-measured capabilities and product requirements in actual use cases as the next logical step.
Experiment: Four Consumer Products
Chapter Overview
Study Design
- Study Planning
- Selecting Products and Tasks
- Measuring Product Demands
- Measuring User Capabilities
- Sampling Users
- Study Procedure
The Usability Laboratory on the 1st floor of the William Gates Building (Computer Science) at the University of Cambridge was identified as an ideal location for the study, as the building is accessible with disabled parking spaces near the facility entrance (Figure 7-2). . For the clock radio, mixer and vacuum cleaner, the chosen task reflected the main function of the product. The letters were displayed in triplets with decreasing contrast from the top to the bottom of the screen.
Participants were asked to read the letters from top to bottom until they could no longer read two of the three displayed letters. At the beginning of the tasks, participants were informed that they could stop at any time for any reason.
Results
- Data Analysis Procedure
- Participant Characteristics
- Factor Analysis of Capability Variables
- Task Outcomes
- Capability-Demand Analysis
- Sensory Capabilities and Demands
- Motor Capabilities and Demands
- Cognitive Capabilities and Demands
- Effects of Multiple Variables
The next section discusses the data analysis procedures before presenting the analysis of the data. Second, the task outcome results are described (task success/failure, difficulty scores, times, and errors). Of the 13 participants who failed the cell phone task, all gave up after trying to complete the goal.
A linear model accounted for a significant portion of the variance for actions involving reading textual features on the products. The blender and vacuum cleaner tasks were the more physically demanding tasks of the four tasks, and the graphs show that there was a greater spread of points around the linear fit line. MAX The maximum of the four cognitive variables MAX(a,b,c,d) MIN The minimum of the four cognitive variables MIN(a,b,c,d) CITY-BLOCK The city block metric is the sum of the four .
MAX and MIN models used the maximum and minimum value of the four cognitive variables, respectively.
Discussion of results
- Key Findings
- Study Limitations
Chapter Summary
Conclusions
Answering the Research Questions
Recommendations and Further Work
Reflections on the Research Process
Thesis Contributions
Consent Form for Toaster Study
Participant Questionnaire for Toasters Study
Ethical Approval Letter
Study Consent Form
Difficulty Scale
Contrast Cards
Task Sequences
Product Demand Values
Experimental Study Checklist
Experiment Data Collection Sheets
Scatter Plots
Multiple Regression Models
