HM's case contributed to the understanding that memory consists of which two systems?

• A. Declarative and Nondeclarative memory
• B. Short-term and long-term memory
• C. Semantic and episodic memory
• D. Procedural and semantic memory

Answer: (A)

Memory is organized into separate systems, and HM’s case helped reveal that distinction: conscious, reportable memory (declarative or explicit memory) versus nonconscious, skill-based memory (nondeclarative or implicit memory). After his hippocampal damage, HM could not form new declarative memories, meaning he couldn’t consciously recall events or facts. Yet he could learn new motor tasks and improve with practice even though he had no recollection of practicing them, showing that nondeclarative memory operates independently of the hippocampus. This two-system view—declarative vs nondeclarative—fits HM’s pattern far better than the idea of short-term vs long-term memory, or the idea that semantic and episodic are the two halves, since semantic and episodic are both forms of declarative memory, not separate systems.