In the book, Norman introduced the term
affordance as it applied to design, borrowing
James J. Gibson's concept from
ecological psychology. Examples of affordances are doors that can be pushed or pulled. These are the
possible interactions between an object and its user. Examples of corresponding signifiers are flat plates on doors meant to be pushed, small finger-size push-buttons, and long and rounded bars we intuitively use as handles. As Norman used the term, a door
affords pushing or pulling, and the plate or button
signals that it is meant to be pushed, while the bar or handle
signals pulling. He also popularized the term
user-centered design, which he had previously referred to in
User-Centered System Design in 1986. He used the term to describe design based on the needs of the user, leaving aside, what he deemed secondary issues like
aesthetics. User-centered design involves simplifying the structure of tasks, making things visible, getting the mapping right, exploiting the powers of constraint, designing for error, explaining affordances, and
seven stages of action. He went to great lengths to define and explain these terms in detail, giving examples following and going against the advice given and pointing out the consequences. Other topics of the book include: • The Psychopathology of Everyday Things • The Psychology of Everyday Actions • Knowledge in the Head and in the World • Knowing What to Do • To Err Is Human •
Human-Centered Design • The Design Challenge
Seven stages of action Seven stages of action are described in chapter two of the book. They include four stages of execution, three stages of evaluation: • Forming the target • Forming the intention • Specifying an action • Executing the action • Perceiving the state of the world • Interpreting the state of the world • Evaluating the outcome
Building up the Stages The history behind the action cycle starts from a conference in
Italy attended by Donald Norman. This excerpt has been taken from the book
The Design of Everyday Things: I am in Italy at a conference. I watch the next speaker attempt to thread a film onto a projector that he never used before. He puts the reel into place, then takes it off and reverses it. Another person comes to help. Jointly they thread the film through the projector and hold the free end, discussing how to put it on the takeup reel. Two more people come over to help and then another. The voices grow louder, in three languages: Italian, German and English. One person investigates the controls, manipulating each and announcing the result. Confusion mounts. I can no longer observe all that is happening. The conference organizer comes over. After a few moments he turns and faces the audience, who had been waiting patiently in the auditorium. "Ahem," he says, "is anybody expert in projectors?" Finally, fourteen minutes after the speaker had started to thread the film (and eight minutes after the scheduled start of the session) a blue-coated technician appears. He scowls, then promptly takes the entire film off the projector, rethreads it, and gets it working. Norman pondered on the reasons that made something like threading of a projector difficult to do. To examine this, he wanted to know what happened when something implied nothing. In order to do that, he examined the structure of an action. So to get something done, a notion of what is wanted – the goal that is to be achieved, needs to be started. Then, something is done to the world i.e. take action to move oneself or manipulate someone or something. Finally, the checking is required if the goal was made. This led to formulation of Stages of Execution and Evaluation. "Consider the movie projector example: one problem resulted from the Gulf of Execution. The person wanted to set up the projector. Ideally, this would be a simple thing to do. But no, a long, complex sequence was required. It wasn't all clear what actions had to be done to accomplish the intentions of setting up the projector and showing the film."
Usability has as one of its primary goals to reduce this gap by removing roadblocks and steps that cause extra thinking and actions that distract the user's
attention from the task intended, thereby preventing the
flow of his or her work, and decreasing the chance of successful completion of the task. This can be illustrated through the discussion of a
VCR problem. Let us imagine that a user would like to record a television show. They see the solution to this problem as simply pressing the
Record button. However, in reality, to record a show on a VCR, several actions must be taken: • Press the record button. • Specify time of recording, usually involving several steps to change the hour and minute settings. • Select channel to record on - either by entering the channel's number or selecting it with up/down buttons. • Save the recording settings, perhaps by pressing an "OK" or "menu" or "enter" button. The difference between the user's perceived execution actions and the required actions is the gulf of execution.
Gulf of evaluation The
gulf of evaluation reflects the amount of effort that the person must exert to interpret the physical state of the system and to determine how well the expectations and intentions have been met. The
gulf of evaluation is the degree to which the
system or
artifact provides
representations that can be directly perceived and interpreted in terms of the expectations and intentions of the
user. The
gulf of evaluation stands for the psychological gap that must be crossed to interpret a user interface display, following the steps: interface → perception → interpretation → evaluation. Both "gulfs" were first mentioned in
Donald Norman's 1986 book
User Centered System Design: New Perspectives on Human-computer Interaction. Usage as design aids The seven-stage structure is referenced as design aid to act as a basic checklist for designers' questions to ensure that the Gulfs of Execution and Evaluation are bridged. The seven stages of relationship can be broken down into four main principles of good design: •
Visibility – by looking, the user can tell the state of the device and the alternatives for action. • A good
conceptual model – The designer provides a good conceptual model for the user, with consistency in the presentation of operations and results and a coherent, consistent system image. • Good mappings – it is possible to determine the relationships between actions and results, between the controls and their effects, and between the system state and what is visible. •
Feedback – the user receives full and continuous feedback about the results of the actions. ==Reception==