Human Computer Interaction (AL-804 (D)) - Unit 2 Short Notes

UNIT 2: FOUNDATIONS OF INTERACTION - THEORIES, MODELS, AND PRINCIPLES

2.1 Cognitive Foundations of HCI

This section explores how human cognitive systems process information, which directly informs effective interface design.

Mental Models

• Definition: A user's internal, simplified representation of how a system works. It guides prediction and operation.

• Norman's Model of Interaction: A cyclical model involving the Gulf of Execution (user's goal vs. system's allowed actions) and the Gulf of Evaluation (system's state vs. user's interpretation). Design aims to bridge these gulfs.

  • DiagramCANVAS: Simple cycle showing User Goal -> Execute Action -> System State -> Perceive System State -> Interpret -> User Goal

Key Cognitive Processes

• Attention: Limited capacity; design must manage distractions (e.g., highlighting important info).

• Perception: Interpreting sensory input. Influenced by Gestalt principles (see 2.2).

• Memory:

  • Sensory Memory: Very brief (<1 sec).

  • Working Memory (WM): Limited (~7±2 chunks), short duration. Critical for UI design – avoid overwhelming WM.

  • Long-Term Memory (LTM): Vast, stores knowledge and mental models.

• Learning & Problem-Solving: Skill acquisition moves from cognitive (rule-based) to associative (action-outcome) to autonomous (procedural) stages.

Cognitive Load Theory (CLT)

Design should minimize Extraneous Cognitive Load (poor design) and optimize Germane Load (effort for schema building).

Information Processing Models

• Stimulus-Response (S-R) Chain: Simple model: Stimulus -> Processing -> Response.

• Model Human Processor (MHP): A predictive model with three components (see 2.4 for formulas).

  • Perceptual System: Processes sensory input.

  • Cognitive System: Processes and decides (WM, LTM).

  • Motor System: Executes physical actions.

[!TIP] Exam Focus: Be prepared to define each cognitive process and give a UI example that reduces extraneous cognitive load (e.g., progressive disclosure).

2.2 Core Design Principles and Guidelines

Nielsen's 10 Heuristics (for heuristic evaluation)

1. Visibility of system status.

2. Match between system and real world.

3. User control & freedom (easy escape).

4. Consistency & standards.

5. Error prevention.

6. Recognition rather than recall.

7. Flexibility & efficiency of use.

8. Aesthetic & minimalist design.

9. Help users recognize, diagnose, recover from errors.

10. Help & documentation.

Shneiderman's Eight Golden Rules

1. Strive for consistency.

2. Enable frequent users to use shortcuts.

3. Offer informative feedback.

4. Design dialogue to yield closure.

5. Offer simple error handling.

6. Permit easy reversal of actions.

7. Support internal locus of control.

8. Reduce short-term memory load.

Norman's Principles of Design (from "The Design of Everyday Things")

• Affordance: Perceived and actual properties of an object that determine how it could be used (e.g., a button affords pressing).

• Signifier: Marks/indicators that communicate where the action should take place (e.g., a label, an arrow).

• Constraint: Limitations that restrict possible actions (physical, logical, cultural).

• Mapping: Relationship between controls and their effects (good mapping is intuitive).

• Feedback: Immediate and clear response to user action.

• Conceptual Model: The user's mental model; the system image (everything user sees) should support a good one.

Gestalt Principles of Perception (how we group visual elements)

[!TIP] Common Pitfall: Confusing affordance (what an object can do) with signifier (how we communicate what to do). A door handle affords pulling; a "PULL" sign is a signifier.

2.3 Interaction Styles and Paradigms

Emerging Paradigms:

• Tangible User Interfaces (TUI): Physical objects control digital information.

• Wearables & IoT: Interaction is contextual, often implicit or gesture-based, with limited I/O.

2.4 Models of Interaction

Model Human Processor (MHP)

Predicts user performance with three processors in parallel. Key parameters (typical values):

• Perceptual Processor Cycle Time (P): ~100 ms

• Cognitive Processor Cycle Time (C): ~70 ms

• Motor Processor Cycle Time (M): ~70 ms

• Effective User Knowledge (K): ~0.28 sec (time to retrieve a familiar rule from LTM)

Simple Execution Time Formula:

$$ T_{execute} = T_{prepare} + n \times (P + C + M) $$

Where n is number of operators (e.g., eye movement, keystroke).

GOMS (Goals, Operators, Methods, Selection rules)

A predictive model for task time.

• Goal: What user wants to achieve (e.g., "Send email").

• Operators: Atomic actions (K = Keystroke, P = Point, H = Home hand to mouse/board).

• Methods: Sequence of operators to achieve a goal.

• Selection Rules: Decide which method to use if multiple exist.

Keystroke-Level Model (KLM)

Simplified GOMS. Total time = Sum of operator times + mental preparation time (M).

Fitts' Law

Predicts time to point at a target.

$$ T = a + b \times \log_2 \left( \frac{D}{W} + 1 \right) $$

• T = Average time to complete movement.

• a = Start/stop time of movement (intercept).

• b = Speed of movement (slope).

• D = Distance from start point to target center.

• W = Width of target (along axis of motion).

• Index of Difficulty (ID): $$\displaystyle ID = \log_2 \left( \frac{D}{W} + 1 \right) $$

• Implication: Make targets larger and place them closer to reduce pointing time.

Hick-Hyman Law

Reaction time increases logarithmically with number of choices.

$$ RT = a + b \times \log_2(n+1) $$

• RT = Reaction time.

• n = Number of choices.

• Implication: Limit menu items; group logically; use search for large sets.

[!TIP] Exam Calculation: You may be asked to calculate task time using KLM or compare target sizes using Fitts' Law. Always identify all operators (K, P, H, M) first.

2.5 Social and Contextual Factors in Interaction

The Role of Context

• Physical Context: Location, lighting, noise, device (mobile vs. desktop).

• Social Context: Presence of others, social norms, collaboration.

• Temporal Context: Time of day, urgency, frequency of use.

• Task Context: User's current goal and workflow.

CSCW (Computer-Supported Cooperative Work)

• Shared Spaces: Artifacts/data all can see/edit (e.g., Google Docs).

• Awareness: Knowing others' presence, actions, and location in a shared space (e.g., "who's typing" indicator).

• Articulation Work: Coordination of activities (e.g., locking a file).

Culture & Internationalization (Hofstede's Dimensions)

Accessibility & Inclusive Design (WCAG Principles)

• Perceivable: Provide text alternatives, captions, adaptable layout.

• Operable: Keyboard accessible, enough time, no seizures.

• Understandable: Readable, predictable, input assistance.

• Robust: Compatible with current/future tools (AT).

2.6 Usability and User Experience (UX) Fundamentals

Defining Usability (ISO 9241-11)

"The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use."

• Effectiveness: Accuracy & completeness.

• Efficiency: Resources (time, effort) to achieve goals.

• Satisfaction: Comfort & positive attitudes.

Defining User Experience (UX)

Broader than usability. Encompasses all aspects of the end-user's interaction with a company, its services, and products:

• Perception: What users see, hear, feel.

• Cognition: What they think & understand.

• Emotion: How they feel (frustration, delight).

• Behavior: What they do.

• Motivation & Values: Why they use it.

Utility vs. Usability vs. UX

User-Centered Design (UCD) Process

An iterative, multi-stage process:

1. Understand & Specify Context of Use: Who? What? Where?

2. Specify User Requirements: Goals, needs, constraints.

3. Produce Design Solutions: Sketches, prototypes.

4. Evaluate Design: Against requirements (usability testing).

5. Iterate: Repeat based on evaluation findings.

[!TIP] Key Distinction: A system can be usable but have poor UX (e.g., a very efficient but ugly or frustrating tool). A system can have great UX but poor utility (beautiful but doesn't do what user needs). Both are essential for success.