Human-Computer Interaction for CSAI

by Albert Major

Task Analysis and Prototyping in HCI

This lecture covers two main topics within User-Centered Design (UCD): Task Analysis (how to assess user goals) and Prototyping (how to build iterative models).

Part 1: Task Analysis

To design effective interfaces, we must first define a Task: a set of activities performed to achieve a specific goal (e.g., booking a vacation or copying a file). There are two primary tools for analyzing tasks.

The two ways to analyze a task

1. GOMS (Goals, Operators, Methods, Selection Rules)

GOMS is a formal, quantitative way to analyze tasks based on the "Input/Output machine" view of humans. It predicts human behavior in terms of time and efficiency.

• Goals: What the user wants to achieve (e.g., "Send a message").
• Operators: The specific cognitive or physical actions required (e.g., click mouse, press 'C' key, verify highlight).
• Methods: The sequence of operators used to achieve the goal. There can be multiple methods for one goal.
  • Example (Copying text):
    • Method A: Right-click -> Select Copy -> Right-click -> Select Paste.
    • Method B: Ctrl+C -> Ctrl+V.
    • Method C: Ctrl+D (Duplicate).

• Selection Rules: The logic a user applies to choose a specific method (e.g., "If I am a pro gamer/expert, I will use Ctrl+D because it is faster; if I am a casual user, I will use the mouse menu").

Pros of GOMS:

• Quantifiable: You can measure keystrokes and predict exactly how long a task takes (e.g., 5 seconds vs. 10 seconds).
• Comparison: Useful for comparing efficiency between devices (e.g., a smartwatch requiring 2 taps vs. 5 taps).
• Prediction: Can predict the behavior of an "average" user without needing to test every single person.

Cons of GOMS:

• Ignores Cognitive State: It assumes the user is a machine. It does not account for memory load, attention span, fatigue, or distractions.

GOMS Examples

2. CTA (Cognitive Task Analysis)