models of interaction

Notes

Study Notes

HCI Notes: Models of Interaction

Fundamental Models of Interaction

Conceptual frameworks explaining the interaction loop and process flow between human and computer.

1. Norman's Execution-Evaluation Cycle

This model describes the user's interaction process as a continuous loop of forming intentions, performing actions, and checking the system state. It identifies the two critical barriers to usability: the **Gulf of Execution** and the **Gulf of Evaluation**.

Gulf of Execution

The difference between the **user's intentions** and the **allowable actions** of the system.

  • **Problem:** The user doesn't know how to translate their goal into the system's language (e.g., "How do I print this?").
  • **Design Solution:** Improve the system's **Affordance** (what actions are possible) and **Mapping** (relationship between control and result).

Gulf of Evaluation

The difference between the **system's representation** of its state and the **user's expectations**.

  • **Problem:** The user can't tell if the action worked or what the new state is (e.g., "Did the file save? Is the process running?").
  • **Design Solution:** Improve the system's **Visibility** and **Feedback**.

2. The Interaction Framework

This formal model breaks down the communication process into four key stages or components, emphasizing translation processes at the interface.

Four Components of the Model:

  • **User:** The human seeking to perform a task.
  • **Input:** The mechanism by which the user articulates the command (e.g., mouse click).
  • **System:** The component that executes the task (the computational core).
  • **Output:** The system's visible/audible response (the display).

Four Translation Processes:

  • **Articulation:** The user expressing the task in the system's language (mental to physical).
  • **Performance:** The system executing the articulated command.
  • **Presentation:** The system rendering the result on the output device.
  • **Observation:** The user interpreting the system's presentation (physical to mental).

3. Linguistic and Conceptual Models

These models view interaction as a conversation, where the user issues commands and the system responds, defining the underlying conceptual structure of the interface.

Conceptual Model (User's Mental Model)

The user's internal idea of how the system works. Designers try to align the **Design Model** (how the system is built) with the **User's Mental Model** to achieve successful interaction.

  • **Metaphor:** Often used to bridge this gap (e.g., the "Desktop" metaphor, the "Shopping Cart" metaphor).

Command Language Grammar (CLG)

A formal grammar used to specify the syntax and semantics of the interaction language. Defines how objects, operations, and attributes are combined to form commands.

  • **Levels:** Defines components at semantic, syntactic, and lexical levels.

4. Predictive Models

These models allow designers to mathematically predict and compare the time it takes for an expert user to perform a task using different interface designs.

GOMS (Goals, Operators, Methods, Selection Rules)

A technique for measuring the efficiency of an expert user by modeling the task hierarchically:

  • **Goals:** What the user intends to achieve (e.g., Delete File).
  • **Operators:** Elementary cognitive or motor actions (e.g., Key Press, Mouse Click, Eye Movement).
  • **Methods:** Step-by-step procedures to achieve a goal (e.g., using a menu vs. a hotkey).
  • **Selection Rules:** Rules to decide which method to use when multiple are available.

Fitts's Law

A mathematical model used to predict the time ($T$) required to quickly move to a target area, based on the **distance** to the target and its **size**.

$$\text{MT} = a + b \log_2 \left( 1 + \frac{D}{W} \right)$$
  • **HCI Implication:** Large, close targets (buttons, icons) are easier and faster to click. This justifies the "pinning" of key controls to screen edges (which have infinite target size).

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