Human Factors and Ergonomics Design of Displays and Controls

Introduction

The term “control” can be used as noun or verb and both have important meaning in the field of human factors and ergonomics.Control (as verb) refers to the activities of one or more people directly or indirectly guiding a system or process to achieve pre-determined goal(s) or perform according to certain specification(s). Control (as noun) refers to a device which is used to control a system or process. Humans control their limbs in the most sophisticated ways when they make movements. It is done automatically and most of the time people are not aware of how they do it. (e.g. picking up a pen) In more complex settings, people control their movement more consciously. (e.g. driving)

Human factors interaction, Source: https://sites.tufts.edu/bethkrikorian/

Introduction In order to control a system, it is necessary to have:

One or more goals or objectivesObservations or measurements of how close the current situation is to meet the goals/objectivesMeans to adjust the improve the performance of the systemUsually, systems are made of multiple components and controls and each of them have their own inter-related goals/objectives.CarCooling SystemFuel SystemSuspension SystemPower Transmission

Environmental factors

Control SystemExample of a control systemThere is always time-lag between input and outputControl activitiesGoals and informationPower sourceEnvironmental factorsControllersControl junctionControlled variablesControl effectorsDetectorsControl signalsSensed signalsConditioned signalDisplays and ControlsPeople interact with machines, tools, computer, equipment in order to perform tasks.The controller component of control systems (previous slide) is where people communicate with machines to determine what should and what should not be done.Information are provided to operators by machines using displays, dials, lights, audio signals and etc. and operators enter inputs using keys, switches, keyboards and etc.In order to have an effective display and control, the designer must first have a well-defined objective. (what information are supposed to be displayed and why)

Displays and ControlsDesign of displays and controls are closely related. Visual characteristics of controls show:What they are for.What the current status of the system is.Multiple displays and controls are usually provided together to create an interface (a point where two systems, subjects, organizations, etc., meet and interact).The arrangement of displays and controls is an important factor in interface effectiveness and usability.User-Centered Interface Design
The main goal of user-centered interface design is to make interaction with the system as simple, effective and efficient as possible.The designer develops different forms of arrangements of displays and controls and tests their efficiency and usability.In some interface designs the displays and controls are distinguishably separate (displays on dashboard and controls in a car), and in some systems the displays and controls are integrates into one component (touch screen displays).User-Centered Interface Designs are focused on:Selecting the type of displays and controlsDetermining the arrangement of displays and controlsBeing appropriate for the task and usersNatural MappingsNatural mapping is one way to design user-centered interfaces.It systematically considers the display-like properties of the function and control elements of the system.It can lead to designs that eliminate the need for additional displays or labels or instructions.In other words, the arrangement of controls can be mapped similar to the actual configuration of components of a system which are supposed to be controlled, so the operator can understand which control belongs to which component without using additional displays or labels.

Population stereotyping and stimulus-response compatibility

A population stereotype design corresponds to a strong tendency for people from a particular group/culture to behave in similar ways in certain situations.It can be measured by exposing people to certain condition with no prior warning or explanation and observe their first reaction. The strength of a particular stereotype can be estimated as:𝑆𝑡𝑒𝑟𝑒𝑜𝑡𝑦𝑝𝑒 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ= 𝐻𝑖𝑔ℎ𝑒𝑠𝑡 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑢𝑠𝑒 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 1−𝐻𝑖𝑔ℎ𝑒𝑠𝑡 𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑢𝑠𝑒 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦For example, if 80% of people use the right valve for cold water, the stereotype strength would be:𝑆𝑡𝑒𝑟𝑒𝑜𝑡𝑦𝑝𝑒 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ= 0.8 1−0.8 =4

Population stereotyping and stimulus-response compatibility

Interface design will be more effective if natural mapping is consistent with population stereotype.This can cause a problem if a different group of users with different or conflicting stereotypes like to use the system.Population stereotypes indicate that stimulus-response correlation can be different from one group to another and it can be explained based on the operator’s mental model.If natural mapping of an interface is compatible with stimulus-response (mental model) of the operator, it results in quicker and more accurate performance.

Message Meaning and Comprehension

There are two inter-related aspects of display signs and controls:ContentComprehensionLinguistic model is one of the commonly used models with three important factors:SemanticSyntacticContextThe level of details and scope of coverage is a complicated issue and it depends on the users’ level of knowledge.

Message Meaning and Comprehension

Semantic factors refer to the fundamental meaning of symbols have for particular receivers. They can be:Verbal – verbal symbols used in language to express messages.Non-verbal – abstract symbols and pictographs.Syntactic factors (or syntax) refer to the way or pattern symbols are arranged (rather than the symbols themselves).The importance of syntax depends on the ratio of number of desired messages to the number of symbols.In other words, syntax become very important when we use small and limited number of symbols to convey large number of messages.Context factors refer to the meaning of individual symbols or strings depending on the exact environment, within which they are introduced, or the particular receiver, or the event that have taken place.This dependency exist because most of the verbal and non-verbal symbols have multiple semantic meanings.WalkingDrivingIndoorOutdoorTemperature

Testing the Comprehension of Symbols

Generic Approaches to evaluate comprehension of symbols and display elements include:Symbol recognition/matching – participants (from target population) answer open ended questions about what each symbol might mean or match the symbol to the statement that best describes the meaning of the symbol.Message recall – it measure how well participants were able to recall the meaning of the symbol sometimes after viewing the symbol.Psychometric scales – participants subjectively rate the symbols on very specific criteria, such as, how easily the symbol is understood, how the symbol was able to convey the importance of the message, or how likely and event will happen.Sometimes these criteria do not consider the contextual aspect of the symbols.