Norman's Model of Interaction

Models of interaction

In the previous chapter, we learned that humans and computers are complex. Their ways of communication and perception are different. For a successful interaction between these two, an effective translation of information through an interface is required. Models of interaction can help us better understand how interaction and translation of information occurs, what difficulties can arise, and how to prevent them.

Before diving into the models of interaction, let’s first take a look at some common terms used in these models.

• Domain: The area of knowledge, work, and expertise under study
• Goal: The desired output
• Task: The set of actions or operations to be performed to achieve the goal
• Intention: A specific action or operation of a task required to meet the goal
• Core language: The language used by the system
• Task language: The language used by the user

Example: One task in a document writing domain can be to write a paragraph using a specific font and style. The goal would be to write a center aligned paragraph using black text color, font size 14, and font style Arial. The intentions may include selecting font size, selecting text color, etc. The task language will be the language used by the user to define actions such as “select font-size,” “select text color,” etc. The core language will be the language the system is using on its backend to perform each function.

Note: Interaction models focus on interactions from the perspective of a single user. In a multiple user environment such as a videoconference, other users are part of the system from one user’s perspective.

Norman’s model of interaction

Seven stages of Norman’s model

The whole process of interaction explained above can be divided into seven stages.

1. Establish the goal.
2. Formulate the intention.
3. Specify action sequence.
4. Execute action.
5. Perceive system state.
6. Interpret system state.
7. Evaluate system state.

Example

Consider the example where the goal was to write a paragraph with font size 14. Let’s say the paragraph has been written, but now the user wants to increase the size of a part of the text. Let’s break this task into the seven stages of Norman’s model.

Stages	Description
Establish the goal	Increase text font size.
Formulate the intentions	Select a font size a few sizes greater than the current font size from the font option of the toolbar.
Specify action sequences	Select the text to enlarge. Click on the current font size in the font option present in the toolbar. Select a font size from the dropdown menu.
Execute the actions	Execute all the actions specified in the last step.
Perceive system state	Perceive (in this case, look at) the selected text.
Interpret system state	Observe the text and look for any visible font-size difference from the previous version of the text.
Evaluate system state	Compare the current text size with the one you wanted. If the current size satisfies the user goal then the cycle stops. Otherwise, if the font is way larger than required, a new goal is formulated to decrease the font size. If the font is still not large enough then a new goal to increase font size is formulated.

Why do some interfaces cause problems for users?

Norman used this model to illustrate why some interfaces can cause problems for their users. He summed up the reasons with these two terms:

• Gulf of execution: The difference between actions formulated by the user and those allowed by the system. A smaller gulf of execution corresponds to an effective interface. More specifically, an effective interface is the one that allows a user to perform an action without being constrained by the system’s limitations.

• Gulf of evaluation: The difference between the presentation of system output and the user expectations. A smaller gulf of evaluation corresponds to an effective interface where the user can easily evaluate the output based on their goals.

Human error

Norman explained what problems can arise on the system’s side in an interaction, but the error can appear on the user side as well. We can distinguish between two types of human error, slip and mistake.

• Slip: When the user understands the system and goal, formulates correct actions but fails to execute them correctly. This can include mistyping, pressing the wrong button, etc. This can be avoided by improving interface design.
• Mistake: When the user does not understand the system, interface, and goal. This can include having the wrong understanding of icons. This can be avoided by having a better understanding of the system.

Limitations of Norman’s model

Norman’s model is clear and intuitive, thus providing us with a good understanding of interaction. However, it has some limitations such as:

• It considers the system just as an interface. Problems in an interaction can occur on the system’s side as well. Hence, considering how the system works is equally important.
• It concentrates only on the user’s view of interaction and ignores how the system perceives, processes, and translates the user’s actions and updates its state.

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