Memory Systems, Forgetting & Applications in Tech

Memory Systems: How the Brain Stores Information

1. Types of Memory

Memory is not a single process but a multi-stage system with distinct storage types. The Atkinson-Shiffrin Model (1968) classifies memory into three stages:

graph LR
    A["Sensory Memory"] --> B["Short-Term Memory (STM)"]
    B --> C["Long-Term Memory (LTM)"]
    C -->|"Retrieval"| B
    C -->|"Encoding"| B
    A -->|"Attention"| B

• Sensory Memory: Brief (0.5–4 sec) storage of sensory input (e.g., iconic for vision, echoic for sound).

  • Example: When you glance at a license plate, you briefly "see" it even if you don’t focus.
  • Capacity: High (near-sensory limit), but fades instantly without attention.

• Short-Term Memory (STM): Holds 5–9 items for 15–30 seconds (Miller’s "7±2" rule).

  • Encoding: Phonological (sound-based) or visual.
  • Example: Remembering a phone number long enough to dial it.
  • Limitations:
    • Decay: Information fades if not rehearsed (e.g., forgetting a password after 30 sec).
    • Interference: New info displaces old (e.g., trying to recall a new PIN while thinking of the old one).

• Long-Term Memory (LTM): Unlimited capacity, stores info permanently (or near-permanently).

  • Types:
    • Explicit (Declarative): Factual knowledge (semantic) or personal experiences (episodic).
    • Implicit (Non-declarative): Skills, habits, conditioned responses (e.g., riding a bike, typing).
  • Encoding: Semantic (meaning-based) or visual/spatial.
  • Example: Remembering your first day at college (episodic) or the capital of Nepal (semantic).

2. Memory Processes

Memory involves three key operations:

1. Encoding: Converting sensory input into a storable format (e.g., turning a face into a mental image).
2. Storage: Retaining encoded info (STM vs. LTM).
3. Retrieval: Accessing stored info when needed (e.g., recalling a password).

Worked Example: Password Recovery

• Encoding: You type P@ssw0rd and your brain encodes it phonologically ("P-ass-word-zero").
• Storage: If you don’t rehearse it, STM decay causes you to forget it in 30 sec.
• Retrieval: Later, you retrieve it from LTM via cues (e.g., "I used a symbol for 'O'").

Forgetting: Why We Lose Memories

1. Theories of Forgetting

Forgetting is not just memory loss but often failure to retrieve. Key theories:

2. Interference: Proactive vs. Retroactive

• Proactive Interference: Old info disrupts new learning.
  • Example: Struggling to learn a new language because your native tongue’s grammar keeps interfering.
• Retroactive Interference: New info disrupts old memories.
  • Example: Forgetting your old phone number after getting a new one.

Worked Example: Daraz Order Confusion

• Proactive: You keep entering your old Daraz password (OldPass123) instead of the new one (NewPass@2024).
• Retroactive: After creating a new Khalti PIN, you forget your old one because the new digits keep popping into your head.

3. The Forgetting Curve (Ebbinghaus, 1885)

Ebbinghaus found that without rehearsal, we forget 50% of new info in 1 hour and 70% in 24 hours.

graph LR
    A["100% Retention"] -->|"1 hour"| B["~50% Retention"]
    B -->|"24 hours"| C["~30% Retention"]
    C -->|"1 week"| D["~20% Retention"]
    D -->|"1 month"| E["~10% Retention"]

Application in IT:

• Password Expiry Policies: Companies force password changes every 90 days to combat retroactive interference.
• Spaced Repetition: Apps like Anki use Ebbinghaus’ curve to schedule reviews before you forget.

Memory in Real-World Systems

1. How Tech Uses Memory Principles

2. Case Study: Ncell’s "My Ncell" App

• Problem: Users forget their MPIN (Mobile Payment PIN) due to:
  • Decay: Rare usage leads to forgetting.
  • Interference: Similar PINs from other apps (e.g., Khalti, eSewa).
• Solution:
  • Biometric Login: Uses fingerprint/face ID (reduces retrieval failure).
  • PIN Recovery via Security Questions: Acts as cues for LTM retrieval.
  • Spaced Reminders: Sends SMS prompts before the PIN expires.

Exam Tip: How to Score Full Marks

1. Define Clearly: Always start with definitions (e.g., "STM is a limited-capacity memory system that holds info for 15–30 seconds via rehearsal.").
2. Use Examples: Link theories to real-world IT systems (e.g., Daraz passwords, NTC traffic lights).
3. Compare Tables: For forgetting theories, use a side-by-side table with causes and examples.
4. Diagrams > Text: Draw the Atkinson-Shiffrin model or Ebbinghaus curve to visualize memory stages.
5. Apply to Exams:
   • Short Answer: "Explain proactive interference with a Daraz order example."
   • Long Answer: "Compare decay and interference theories using Ncell MPIN as a case study."

Common Pitfalls to Avoid:

• Confusing STM capacity (7±2 items) with LTM capacity (unlimited).
• Ignoring retrieval failure as a major cause of forgetting (not just decay).
• Forgetting to link psychology to IT (e.g., how memory principles improve UX design).

Final Visual Summary:

mindmap
  root((Memory & Forgetting))
    Types
      Sensory Memory
      STM["5-9 items, 15-30 sec"]
      LTM["Unlimited, semantic/episodic"]
    Forgetting
      Decay["Time-based fade"]
      Interference["Proactive/Retroactive"]
      Retrieval Failure["Cue-dependent"]
    Real-World
      Passwords["STM decay"]
      Algorithms["LTM associations"]
      Traffic Lights["STM attention"]