Lesson 16 covered what gets into memory via attention. This lesson covers what happens to it once it’s in — specifically, that “long-term memory” isn’t one thing, but several dissociable systems that can be damaged independently of each other, as the H.M. case makes starkly clear.
Terms (standalone):
- Episodic memory: memory for specific, personally-experienced events — “what happened, when, where.” Remembering that you practiced mirror-tracing yesterday is episodic.
- Semantic memory: memory for general facts and concepts, disconnected from any specific experience of learning them. Knowing “a mirror reverses left-right” is semantic — you likely can’t recall the specific moment you learned it.
- Procedural memory: memory for skills and how-to knowledge — how to perform an action, largely inaccessible to conscious, verbal report. Riding a bicycle, typing without looking at the keys, and (per this puzzle) getting better at mirror-tracing are procedural.
- Episodic and semantic memory are both forms of declarative memory — memory you can, in principle, consciously bring to mind and declare (state in words): “I remember doing X” or “I know that Y is true.” This is exactly the declarative memory from Lesson 10’s ACT-R chunks. Procedural memory maps onto ACT-R’s production rules (Lesson 3’s condition→action rules) — knowledge expressed as doing, not as a statable fact, and famously resistant to being put into words even by the person who has it (ask an expert typist to describe, without looking, exactly where the “F” key is relative to their fingers — many struggle, despite flawless performance).
- Dissociation: when brain damage impairs one memory system while leaving another intact, demonstrating that the two systems are at least partly independent, not just “harder vs. easier” versions of one unified memory. H.M.’s case is the textbook example: his hippocampal damage devastated new episodic (and largely new semantic) memory formation, while his procedural learning system remained fully functional.
The puzzle (MCQ above)
Think about what the mirror-tracing task requires (a motor skill, refined by practice) versus what H.M.’s specific damage impaired (forming new consciously-accessible memories of events).
Part 2 — Why this counts as evidence for separate systems, not just “partial amnesia”
If H.M.’s amnesia were simply “memory in general is a little worse,” you might expect his skill learning to also be somewhat impaired, just less severely than his event memory. Instead, his procedural learning curve was essentially normal — indistinguishable from a healthy person’s — while his episodic memory was essentially absent. Why does this specific pattern (one system fully intact, one fully devastated, rather than both partially impaired) make a stronger case for genuinely separate memory systems than a milder, evenly-distributed deficit would?
Part 3 — Reveal: predict a second dissociation
Given that episodic and semantic memory are both “declarative” but are still distinguishable from each other (specific events vs. general facts), predict: could a patient plausibly have damage that impairs new episodic memory formation while new semantic learning stays relatively more intact — or does the evidence you’d expect necessarily go the other way? Sketch a plausible real-world observation that would demonstrate this second, finer dissociation (episodic vs. semantic, not just declarative vs. procedural).
Part 4 — Connect to modern agents
In a modern LLM agent harness, an agent’s “knowledge” also fractures along related lines: facts baked into the model’s weights during training (closer to semantic memory — general, source-amnesic knowledge with no memory of “when I learned this”), a specific conversation’s context window (closer to episodic — this specific interaction, right now), and learned behavioral patterns like tool-use habits encoded in weights or in a system prompt (closer to procedural — how to act, not a statable fact). Pick one pair from that list and describe a concrete way an agent harness could “dissociate” them — i.e., a design where one kind of knowledge is lost or reset while the other persists, deliberately or as a bug.