Questions: Declarative and Procedural Memory Systems

Question 1

Patient H.M. undergoes mirror-drawing practice across multiple sessions. Which pattern of results is actually observed, and what does it demonstrate?

• A. No improvement across sessions, confirming that his amnesia prevents all forms of new learning
• B. Improvement across sessions, which he attributes to his growing confidence and memory of previous practice
• C. Improvement across sessions at a normal rate, even though he has no conscious memory of ever having practiced
• D. Improvement only when reminded of previous sessions, showing that cuing can restore declarative memory

Answer: (C)

H.M. showed normal procedural learning — his performance on mirror-drawing improved session to session at the same rate as control participants. Crucially, he had no declarative memory of the task: each session, he believed it was his first attempt. This dissociation is the central evidence for separate memory systems. The procedural memory system (basal ganglia, cerebellum) was intact despite total destruction of declarative memory capacity via bilateral hippocampal removal. Option A reflects the common misconception that amnesia prevents all learning.

Question 2

A patient has severe bilateral damage to the basal ganglia following a stroke, but the hippocampus and medial temporal lobe are fully intact. Which profile is most likely?

• A. Cannot form new episodic memories but can acquire new motor habits normally
• B. Can form new episodic memories and semantic knowledge, but struggles to acquire new motor habits and stimulus-response routines
• C. Neither declarative nor procedural learning is possible, since the two systems share neural substrates
• D. All memory is intact because the cerebral cortex compensates for basal ganglia damage

Answer: (B)

The basal ganglia are the primary neural substrate for procedural (habit and skill) learning. With basal ganglia damage, the patient will struggle to acquire new motor routines and stimulus-response associations — procedural memory is impaired. However, the intact hippocampus and medial temporal lobe preserve declarative memory: the patient can form new episodic memories (what happened today) and semantic memories (new facts). This is the reverse dissociation from H.M. and is exactly what patients with Huntington's disease demonstrate.

Question 3

Procedural memory is simply an unconscious, automatic form of declarative memory — information stored in the same hippocampal system but not accessible to verbal report.

• T. True
• F. False

Answer: False

This is the most important misconception to dispel. Procedural memory is not a weak or inaccessible version of declarative memory — it is a genuinely distinct system with different neural substrates, different encoding mechanisms, and different operating principles. Declarative memory depends on the medial temporal lobe (hippocampus); procedural memory depends on the basal ganglia and cerebellum. The double dissociations (H.M. and Huntington's patients) prove this: you cannot get selective impairment of one system while the other is intact if they share the same neural machinery.

Question 4

Consciously trying to analyze the details of a well-practiced motor skill — such as focusing on exactly how each finger moves while typing — can interfere with performance of that skill.

• T. True
• F. False

Answer: True

This 'centipede's dilemma' effect occurs because procedural memory operates most efficiently outside conscious attention. Once a skill is automatized, its execution is handled by basal ganglia and cerebellar circuits that bypass conscious deliberation. Attempting to retrieve the movements as declarative knowledge ('what exactly am I doing with my left hand?') forces the procedural system to compete with the slow, serial declarative system, degrading performance. Expert performers often report that thinking too hard about technique during execution hurts them — the skill works best when procedural memory is left to run without interference.

Question 5

What does a 'double dissociation' between declarative and procedural memory demonstrate, and why is it more convincing evidence than a single dissociation alone?

Model answer: A double dissociation occurs when two patient groups show opposite patterns: one group has impaired declarative but intact procedural memory (e.g., H.M.), while another has impaired procedural but intact declarative memory (e.g., Huntington's patients). A single dissociation — one system impaired, the other intact — could be explained by arguing one system is merely harder or more sensitive to damage, not truly separate. A double dissociation rules this out: if A can be damaged while B is preserved, and B can be damaged while A is preserved, then A and B must be genuinely independent systems. This is the gold standard for inferring neural and cognitive modularity.

The single-dissociation alternative interpretation is that declarative memory is just 'harder' than procedural — so it fails first under damage. If true, we'd only ever see declarative impaired with procedural spared, never the reverse. The double dissociation refutes this by showing the pattern can be reversed, confirming true independence.