The design of everyday things
Good design relies on affordances (interactions between people and their environments) and signifiers (signs that communicate which actions are possible and how they should be performed). Because not all affordances are perceivable, designers must focus on signifiers to create usable objects. Mappings, feedback, and conceptual models contribute to an effective design by communicating effectively to the user.
The Design of Everyday Things by Donald Norman
The first edition of The Design of Everyday Things was written in 1988 and titled The Psychology of Everyday Things. The book featured examples of film projectors, overhead slide projectors, video cassette recorders, and telephone answering systems. Responding to his publisher’s feedback author Don Norman re-titled a subsequent edition The Design of Everyday Things. Norman writes that no one would think to find a book on industrial design in the psychology section of a book store so he took his own advice and listened to his audience with the new title. Noting the fast pace of technological change, the most recent edition of the book attempts to depict human-centered design principles without as much reliance on contemporary technology examples as previous editions.
What makes good design?
Two of the most important characteristics of good design are discoverability and understanding.
Discovery is the ability of the person using the product to determine what is possible to be done with the object and how to do it. Understanding is the user’s comprehension of meaning of controls within the product. Norman writes that design is an act of communication. Because of this, information on usage and goals must be contained within the object itself. The person using the product needs to understand what actions are possible to achieve with the object and how to perform them. Most failures of design stem from the inability of the object to convey its intended usage and operations.
Design is concerned with how things work, how they are controlled, and the nature of interactions between people and technology.
Designing for human error
We have to accept human behavior the way it is, not the way we wish it to be.
Many stories and illustrations within the book are concerned with poor design that led to a bad, or really bad (Three Mile Island) outcome. To account for the characteristics of people, “we must design our machines with the assumption that people will make errors.” This resilience is often overlooked as designers assume that their customers will logically follow a correct set of steps.
Affordances and Signifiers
Affordances determine what actions are possible. Signifiers communicate where the action should take place.
Affordances are relationships between objects and the agents that interact with and use them. Affordances are not properties of objects; rather, they depend on the properties of the objects and agents. Chairs afford sitting and lifting, but may afford lifting and sitting for only certain people. It is important for affordances to be discoverable–that’s the role of signifiers. Signifiers communicate appropriate behavior to people. A sign that says “Pull” is a signifier as is a line of people waiting near a cash register. Many design and usability problems are a result of poor or non-existent signifiers. Norman gives extended examples of doors which have either ambiguous, non-existent, or contradictory signifiers.
In design, signifiers are more important than affordances, for they communicate how to use the design.
Mappings are a key feature of everyday things because they typically form the conceptual model of controls to functions. Switches which control a device or electrical component can be presented in a natural or arbitrary mapping. If lights are installed in a row, light switches can be aligned in a row with each switch corresponding to a light in spatial correspondence. A natural mapping like this accelerates a person’s understanding of how the overall system works. Mappings are frequently cultural and need to be tested to ensure that assumptions are correct.
Given the importance of feedback, it is amazing how many products ignore it.
Feedback is critical in directing behavior and communicating success or failure. A combination of poor signifiers with misleading feedback is deadly for a product. Norman points out that feedback must be immediate. Even a minuscule delay can be disorienting to the user and lead to incorrect interactions. Additionally, feedback should convey appropriate information. A blinking light draws our attention, but does not tell us what has happened or what to do next. A beep can be useful if our attention is elsewhere, but it may not be clear what device or what part of a device made the sound.
Conceptual Models and the System Image
Good conceptual models are the key to understandable, enjoyable products: good communication is the key to good conceptual models.
People use available information to create a model in their mind of how a device or system works. If the available information is inconsistent or misleading, the product becomes unusable and results in frustration. As a person attempts to operate a product, the gather information based on their interactions, available documentation, and analogues to other products. Designers assume that the conceptual model in the user’s mind will be identical with the design model they used to create the product, but unless the signifiers and feedback are clear, it is likely not the case.
So many things to control, so little space for controls or signifiers.