Implicit versus explicit memory: Definitions

1. Implicit versus explicit memory: Definitions • implicit memory: past experiences influence perceptions, thoughts and actions without awareness of person that any info from past is accessed • explicit memory: conscious access to info from past (“I remember that..” ) -> involves conscious recollection -> term generally used synonymously with episodic memory

2. Implicit memory:What studies in amnesia have told us • concept evolved out of neuropsychological research in patients suffering from amnesia; later studied in cognitive psychology, social psychology, developmental psychology etc. • first systematic study in denselyamnesic patient H.M. (Brenda Milner, 1960s, in Montreal) • H.M.: in 1953, bilateral surgical removal of medial temporal-lobes to stop his epileptic seizures, which couldn’t be treated with medication

3. Is normal implicit memory limited to motor learning in amnesia? No! • Warrington & Weiskrantz (1970) demonstrate that amnesic patients show preserved implicit memory on list learning with word stem completion task • Study: table, garden, telephone, lamp, umbrella etc. Test: - Free Recall - Yes/No recognition - Word stem completion: tab____? gar____? (Instructions: think of any word that fits stem) • Finding: amnesic patients show memory deficits on first 2 tests but normal performance on word stem completion

4. Repetition priming in amnesia: Lack of retrieval intentionality is important • -> normal performance of patients on completion task but impaired cued recall and free recall • -> type of access (implicit vs explicit) to stored info critical

5. Can repetition priming also be shown to be different from explicit memory in normal subjects? • Tulving, Schacter, & Stark (1982): • fragment completion task • study: incidental learning with semantic decisions; judge words in terms of animacy • (e.g. twilight, assassin, dinosaur, mystery) • test: complete fragments with first word that comes to mind • ch_ _nk • o_t__us • _ssa__in • repetition priming: more completions of studied than non-studied words

6. Repetition priming in normal subjects • Tulving, Schacter, & Stark (1982): • + repetition priming effects long-lasting (no ‘forgetting’ over a week or more) • + by contrast, recognition memory for previously studied words shows some forgetting • ->> even in normals implicit memory can be distinguished from explicit/episodic memory

7. Does repetition priming require attention at time of encoding? • informal (unethical!) observation with ‘mock crisis’ in 1960s: • faked crisis during surgery causes subsequent agitation in patients recovering from surgery, without their knowing why • systematic (ethical!) studies show that encoding under anesthesia produces repetition priming when patients are tested after surgery on word-fragment completion task • -> no allocation of attention required at encoding

8. Is repetition priming linked to semantic memory? • Does it benefit from semantic encoding ? • (LoP study; Graf & Mandler) • study: • - semantic decisions (animate /inanimate) • - physical decisions • (# of capital letters) • test: • cued recall • fragment completion Finding: no LoP effect on completion task -> not likely that semantic memory involved

9. Is repetition priming a perceptual type of memory? • two important findings: • reductions in repetition priming effects with • + changes in modality between study and test • (e.g. encoding of words in auditory modality • word-fragment completion test in visual modality) • + changes in perceptual characteristics of words between study and test (e.g. font, uppercase/lowercase)… • -> suggests that priming reflects a perceptual type of memory; fits with finding of no LoP effect • best term to capture phenomenon: perceptual priming

10. If it is perceptual, can priming be observed in other sensory modalities? • yes; evidence for perceptual priming on auditory word-stem completion task (after incidental encoding in auditory modality) • -> priming not limited to visual modality

11. Can perceptual priming be observed with non-verbal stimuli? • experiments with possible and impossible objects by Schacter & Cooper (early 90s) • Study: judge whether object faces left or right • Test: object decision task with 100 ms exposure • with studied and non-studied objects • Finding: more accurate performance with previously studied objects (priming)

12. Is perceptual priming on object decision task an expression of semantic memory? • Schacter & Cooper (early 90s) • comparison of encoding effects for recognition memory (explicit) and perceptual priming on object decision task (implicit) • + physical vs semantic judgements at encoding • (left-right facing vs what real object does it remind you of) • -> semantic encoding only improves recognition • -> finding suggests that priming perceptual in nature

13. Interpretation of perceptual priming: Perceptual representation systems (PRS) • theory proposed by Schacter & Tulving: • + perceptual representation systems: not dedicated memory systems but perceptual systems that keep memory as by-product of perceptual analysis • analogy: hot-tube effect with stove • + memory representations in PRS operate implicitly • (no conscious recollection possible)

14. Interpretation of perceptual priming: Perceptual representation systems (PRS) • Schacter & Tulving: • visual representation system for words • -> representation: visual word forms • visual representation system for objects • -> representation: structural descriptions of objects • auditory representation for words • -> representation: auditory word forms (phonology) • perceptual representation systems rely on brain structures that perform perceptual analyses • e.g. visual representation systems localized in visual cortex

15. Functional neuroimaging evidence for perceptual priming in PRS: reductions in brain activation C: unprimed objects D: primed objects activity reductions in visual cortex for primed objects effect at behavioural level: priming = facilitated performance

16. Problems for studying perceptual priming as type of implicit memory • typical set-up of priming study study: incidental encoding of word list (table, garden, telephone, umbrella etc.) priming test: word stem completion complete word stem with first word that comes to mind rea___?? gar___?? net___??

17. Problems for studying perceptual priming as type of implicit memory • does performance on priming task always reflect implicit memory? • no! -> problem of ‘explicit contamination’ • e.g. subjects may rely on conscious recollection to perform stem completion task even when no explicit memory instructions are given • -> presumed implicit memory task may not always measure concept of implicit memory • L. Jacoby’s approach to purify measures of implicit memory: • process dissociation procedure (method of opposition)

18. Process dissociation procedure to purify measures of implicit memory • experiment by Jacoby et al. with word-stem completion task • Study: incidental encoding of words under full or divided attention • Test: word-stem completion task under Inclusion or Exclusion instructions • Jacoby’s terminology: • implicit memory = automaticity • explicit memory = recollection

19. Process dissociation procedure • inclusioncondition: • try to generate a word that begins with stem; simply take first word that comes to mind; you can take one presented earlier • -> implicit and explicit memory work in same direction • exclusioncondition: • try to complete stem but avoid completions of words presented earlier • -> implicit and explicit memorywork in opposite direction • Inclusion = e + i (1-e) -> formula allow to get Exclusion = i (1-e) purified estimates for implicit (i) and explicit • e = Inclusion – Exclusion (e) memory contributions • i= Exclusion/(1-R)

20. Process dissociation procedure finding: attention only affects estimates of explicit not of implicit memory -> procedureoffers powerful way to study implicit and explicit memory processesseparately explicit implicit

21. Types of implicit memory other than perceptual priming • motor skill learning (e.g. mirror drawing task) • + normal in amnesic patient H.M. • -> does not rely on medial temporal lobe structure • + patients with Huntington’s disease (neurological disease of motor system; brain damage in basal ganglia) show impaired motor skill learning but normal perceptual priming • -> does not rely on PRS either • -> type of implicit memory that is different from perceptual priming

22. Types of implicit memory other than perceptual priming: Conceptual priming • can be shown with category instance generationtask • study: incidental encoding of words • (e.g., cycle, tree, mail, elephant, tulip etc.) • test: name as many members of the following category in 1 min • e.g., flowers -?? (note: no perceptual cue from study phase) • priming effect: previously studied category members more likely generated than others • conceptual priming typically normal in amnesic patients

23. Types of implicit memory other than perceptual priming • is conceptual priming different from perceptual priming? • yes!! • + it benefits from semantic encoding (LoP effect) • + not affected by switch in perceptual modality between study and test • + dissociation in patients with Alzheimer’s disease: • normal perceptual priming but impaired conceptual priming • -> suggests that they rely on different brain structures • -> conceptual priming not based on PRS; • instead builds on semantic memory

24. Are they really different types of implicit memory? • perceptual priming • conceptual priming • motor skill learning • -> research suggests that each of them relies on different brain structures and has different functional characteristics (e.g. modality, LoP effect, forgetting curve) • BUT commonality: • implicit access to information from past • -> unconscious form of memory!!

25. Does implicit memory occur in everyday life? • yes, most certainly • BUT difficult to grasp given its unconscious nature • applied research shows: • +mere exposure toadvertisementsinfluences subsequent affective judgments of these ads (attitudes), although subjects don’t remember seeing them (Perfect & Askew, 1994) • Schacter’s examples: • + unintentional plagiarism (conceptual priming?) • e.g. George Harrison’s ‘My sweet lord’ • + motor skills, e.g. in sports and music

26. Amnesia / Amnesic Syndrome:selective LTM impairments caused by neurological condition retrograde amnesia anterograde amnesia remote past recent past time onset of neurological condition

27. Neurological conditions that can produce amnesia • temporal lobe resection (neurosurgery) • traumatic closed head injury (massive blow to head) • herpes simplex encephalitis (viral infection) • ischemia (vascular problem; interruption of blood flow to brain) • stroke, ruptured aneurysm (bleeding from blood vessel) • Korsakoff’s syndrome (Vitamin B1 deficiency) • Alzheimer’s disease (type of dementia) Milder, more limited memory impairments also with: • epilepsy (brain seizures) • brain tumors • chronic alcoholism

28. Neuroanatomical basis of anterograde amnesia: Where is brain damage typically localized?

29. Selective memory impairments of H.M. and other patients suffering from anterograde amnesia • in neuropsychological testing: + normal IQ + normal perceptual and language functions + severe deficits on episodic memory tasks; not specific to particular info / material: e.g. problems with - learning of word lists - recognition of faces and other non- verbal info (scenes, houses etc.)

30. How can anterograde amnesia be explained?What is the nature of the memory impairment? • general findings in amnesic patients: • + normal STM capacity on digit-span task • + normal forgetting curve on Brown-Peterson task • + normal recency effect in serial position curve

31. Additional evidence showing that memory deficit is specific to LTM in amnesic patients: lists larger than STM span extremely difficult to learn for patients (Drachman & Arbit, 1966)

32. How can anterograde amnesia be explained?What is the nature of the memory impairment? • STM / WM intact -> problem in long-term memory (LTM) but does it affect all aspects of LTM?

33. Motor-skill learning: a type of implicit memory that is normal in H.M. • mirror tracing task: builds on procedural memoryfor skills • improvement in tracing performance with practice but no recollection of previous training sessions (i.e. episodes) -> suggests that H.M. retains some info over long-term and can access it implicitly

34. Normal perceptual priming on word-stem completion task in anterograde amnesia • -> normal performance of patients on completion task but impaired cued recall and free recall • -> type of access (implicit vs explicit) to stored info critical

35. How can anterograde amnesia be explained?What is the nature of the memory impairment? • STM / WM intact -> problem in long-term memory (LTM) • implicit memory intact + perceptual priming + conceptual priming + motor-skill learning procedural memory (learning how to) -> problem in explicit memory (consciously processed info in LTM)