Distinction between implicit and explicit memory

Question 1

Suggested two separate LTM systems:

• Explicit: requires conscious recollection of previous experience.
• Implicit: facilitated in the absence of conscious recollection

Answer 1

Schacter 1987

Question 2

Examined effects of different levels of processing at encoding.

• Deeper level of processing improved explicit memory (as previously shown by Craik & Tulving 1975), had little effect on implicit memory.
• Also examined effects of modality differences between study and test: changing modality between study and test had no effect on explicit memory but significantly reduced implicit memory.

Answer 2

Jacoby and Dallas 1981

Question 3

Implicit but not explicit memory for events heard under general anaesthesia? Priming can occur when patients are unconscious. Salient intra-operative stimuli may cause more priming than neutral experimental stimuli

• Examined priming following presentation of primes during anaesthesia. Instructed ear vs nose touching, then counted touches in post op interview
• ‘Correct’ touches (vs ‘incorrect’ as control) increased in both duration & number following priming

Answer 3

Block et al 1991

Question 4

Normal & amnesiacs given a word list to study, then tested for explicit & implicit memory

Amnesiacs impaired relative to controls on first 3 tasks (explicit)

Amnesiacs & normals showed equal priming of stem completion (implicit)

Answer 4

Graf, Squire and Mandler 1984

Question 5

On pursuit rotor or mirror tracing tasks: performance of amnesiacs improves over trials (implicit- procedural) but they don’t recall having done test before.

Answer 5

Warrington and Weiskrantz 1970

Question 6

Neurophysiological double disosciation between implicit and explicit memory:

• Patients with MTL amnesia are impaired (compared to controls) at explicit but not implicit memory (consistent with Graf 1984)
• Patient MS (lesion of occipital cortex): performed as well as contorls on explicit memory, but severely impaired on implicit memory.

Taken together: these results suggest that dissociable brain regions support explicit and implicit memory, and thus that they are functionally separate memory systems.

Answer 6

Gabrielli et al 1995

Question 7

Reviewed evidence reporting activity in the medial temporal lobe during explicit encoding and/or retrieval
fMRI studies; converge on the conclusion that posterior MTL is associated with episodic encoding
PET studies: recent meta-analysis by Lepage et al 1998

Based on their analysis of the rostrocaudal distribution of activations reported during episodic encoding or retrieval, conclude that anterior MTL is strongly associated with episodic encoding, whereas posterior MTL is strongly associated with episodic retrieval.
S & W consider the evidence reviewed by Lepage et al along with additional studies- condlude that PET studies of encoding reveal both anterior and posterior MTL activations.

Conclude that contradiction between fMRI and PET studies of encoding was more apparent than real. However, PET studies have reported anterior MTL encoding activations more frequently than fMRI studies

Answer 7

Schacter and Wagner 1999

Question 8

• Review 275 PET and fMRI studies of attention, perception, language, working memory, semantic memory retrieval, episodic memory encoding and retrieval, priming, and procedural memory.
• Attention and working memory: activations usually found in prefrontal and parietal regions
• Language and semantic memory retrieval: left preftontal and temporal
• Episodic memory encoding: left prefrontal and medial temporal regions
• Episodic memory retrieval: prefrontal, medical-temporal, and posterior midline reguisn
• Priming: deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions consistently seen.
• Proceedural memory: motor cortex as well as non-motor brain areas.

Answer 8

Caheza & Nyberg 2000