Models and Types of Memory: Sensory, STM, and LTM

Memory is the cognitive system that enables human beings to encode incoming sensory information, store it over time, and retrieve it when needed. Without memory, we would have no language, no personal identity, no relationships, and no capacity to learn from past experiences.

1. The Three Fundamental Processes of Memory

Before information becomes a permanent part of your mind, it must pass through three distinct operational phases:

2. The Information Processing Model (Atkinson & Shiffrin, 1968)

Richard Atkinson and Richard Shiffrin proposed the most famous structural model of human memory, known as the Stage Model or Modal Model. They drew an analogy between human cognition and modern computer systems:

3. Deep-Dive into the Three Memory Stores

A. Sensory Memory (Sensory Register)

Sensory memory acts as an ultra-brief buffer that holds an exact copy of sensory stimuli just long enough for the brain to decide whether to pay attention to it.

• Iconic Memory (Visual): Holds visual snapshots for approximately 0.25 to 0.5 seconds (discovered by George Sperling’s partial-report experiment, 1960). This allows you to perceive smooth motion when watching a film instead of individual photographic frames.
• Echoic Memory (Auditory): Holds sound echoes for 2 to 4 seconds. Example: When someone asks you a question while you are distracted, you say “What did you say?”, but before they repeat it, your brain replays the audio echo and you answer.

B. Short-Term Memory (STM) & Working Memory

Information that receives focused attention passes from sensory registers into Short-Term Memory.

• Capacity: George Miller (1956) showed that STM can hold 7 ± 2 items (between 5 and 9 discrete units).
• Technique of Chunking: You can dramatically increase STM capacity by grouping individual bits into meaningful units. For example, remembering a 10-digit Indian mobile number: 9826012345 is much easier when grouped as 98260 - 12345 (2 chunks) rather than 10 isolated digits.
• Duration: 20 to 30 seconds without active rehearsal (demonstrated by Peterson and Peterson’s Brown-Peterson task).
• Maintenance Rehearsal: Mentally repeating an OTP or phone number over and over keeps it active in STM, but does not guarantee permanent storage.

C. Long-Term Memory (LTM)

Information transferred through Elaborative Rehearsal (connecting new information to existing knowledge and understanding its meaning) enters LTM.

• Capacity: Virtually unlimited.
• Duration: Days, months, decades, or a full lifetime.

4. Classification and Types of Long-Term Memory

Cognitive psychologists classify Long-Term Memory into two major branches: Explicit (Declarative) and Implicit (Non-Declarative) memory.

5. Working Memory Model (Baddeley & Hitch, 1974)

Alan Baddeley and Graham Hitch replaced the simple passive “box” of STM with an active multi-component system called Working Memory:

6. Why Do We Forget? Major Theories of Forgetting

1. Decay Theory (Trace Decay): Physical memory traces in the brain (engrams) naturally fade away over time if not refreshed (Hermann Ebbinghaus Forgetting Curve).
2. Interference Theory:
   • Proactive Interference: Old memories block the recall of new information (e.g., dialing your old phone number instead of your new one).
   • Retroactive Interference: Newly learned information overwrites older memories (e.g., memorizing this semester’s psychology syllabus makes you forget last semester’s sociology topics).
3. Retrieval Failure (Cue-Dependent Forgetting): The memory is safely stored in LTM, but the right retrieval cue is missing. Manifests as the Tip-of-the-Tongue (TOT) phenomenon.
4. Motivated Forgetting (Repression): Sigmund Freud’s concept that the unconscious mind represses traumatic or emotionally threatening memories to protect the self from anxiety.