Presentation on theme: "Key points for lecture 4 Forgetting: good or bad?"— Presentation transcript:
1Key points for lecture 4 Forgetting: good or bad? How does the Deese / Roediger / McDermott (DRM) paradigm work?Which factors increase or decrease false memory?What are the actual underlying (cognitive) causes of false memory?Reisberg, Chapter 7.
2When Memories Go WrongWhat happens when your memory of an event does not correspond to what actually happened?In what ways can our decisions get warped by an inaccurate memory?Are we always aware when this happens?The readings from Reisberg for today’s lecture are in Chapter 7 (or chapter six if you are using the first edition). The chapter ranges quite widely over a number of topics, not all of which are directly relevant to today’s lecture. So to help you, pay particular attention to the following topics from the chapter :-‘Remembering what was said versus remembering gist’‘The Deese-Roediger-McDermott Paradigm’‘Interference: blurring of similar episodes’‘Rembering versus knowing’
3Forgetting Is Normal! And desirable! The Case of “S” (Luria, 1968) Perfect memories, photographic memories and so on, are few and far between. For the vast majority of us, forgetting things gradually over time is a normal part of life. And in some cases, being able to forget is very welcome - as I briefly mentioned a couple of lectures ago, patients who suffer post traumatic stress disorders would very much like to be able to forget the horrible events of their past but they simply cannot. So having the ability to recall everything perfectly, in other words never being able to forget anything, is not something that you should necessarily want to have.Reisberg briefly mentions a report from the Russian Neuropsychologist Luria, about a fellow called 'S', who couldn’t forget anything that happened to him.
4The Case of “S”“S” did not benefit a great deal from having a ‘perfect’ memory.Impaired ability to abstract general knowledge from his experiences.Related to his inability to forget specific details of each event?Almost the opposite of Varga-Khadem’s amnesic children.‘S’ found it extremely difficult to construct general knowledge, and reason about the world. But, he seemed to have perfect access to all the raw data of his experiences. He could state in minute detail just about everything that had ever happened to him, and Luria was able to verify that this was the case. But despite this, S wasn’t able to abstract any general knowledge out of all of this data. Reisberg mentions Luria's report that S was so incapable of abstracting out knowledge from his experiences, that he had difficulty understanding that two different dogs, seen on different occasions, were both DOGS, could both be thought of as instances of a 'DOG'.And it seems that 'S's problem in creating general knowledge was related to his inability to forget the specific details that distinguished between each and every DOG that he had seen.So in a sense, 'S' could find something novel in every experience, and very few things would have been just familiar to him, i.e. a repetition of the same kind of event or object. In a way, 'S's predicament is the opposite to the one afflicting the amnesic children reported by Varga-Khadem and colleagues I mentioned last week. These kids seemed to have lost all episodic details, and were reliant on familiarity information as a basis for their memory judgements.
5Episodic vs. Semantic Memory Baddeley’s MetaphorOur general knowledge is represented in a distinct ‘semantic’ Memory
6Episodic & Semantic Components of Autobiographical Memory Parker et al. (2006), Neurocase 12: pages (pdf available via my webpages)Case A.J. : ‘…highly superior semantic autobiographical memory’
7Sources of Error in Normal Memory Forgetting.A natural feature of our memory?Recollection and familiarity may have to trade off against one another all the time.How might their interaction distort our memory of the past, and mislead our judgement?In normal people forgetting goes on all the time, which I guess you could view as a kind of error, but only if our memory was meant to be perfect. What I mean is, the fact that we forget doesn’t mean that our memories are not working properly. There may have been no need for our memories to have evolved in that way. And in fact we have seen in the case of 'S' that perfect, total recall, can interfere with cognitive functioning in other domains. So our ability to reason and categorise things might be a positive and natural consequence of forgetting.In normal people who don’t have either a photographic memory, or amnesia caused by brain damage, episodic memory and familiarity are both working, they both interact and trade off against one another, probably all the time. A great deal of recent attention in the cognitive literature on memory has focussed on how this interaction might introduce bias or distortions into all, or potentially all, of our judgements and decisions. And one reason why this area of research has attracted such interest is because of the serious consequences that distortions of memory can have in real life, in all sorts of domains. This is particularly true within the legal system, where you own future, or that of someone else, might depend upon 1) the accuracy of your memory, 2) your confidence in your memory, and 3) the validity that the court assigns to your testimony.
8The Weight of Eyewitness Evidence An estimated 77,000 people annually in the USA are charged solely on the basis of eye witness evidence.Around three quarters of English cases result in conviction due to eye witness testimony (of which half were based on a single eye witness).
9Introducing Distortions into Memory Force subjects to experience very similar kinds of episodes, which become hard to discriminate from one anotherManipulating the familiarity of retrieval cuesTwo of the principle ways of confusing memory are as follows. You can get your subjects to remember lots of episodes that have very similar kinds of content. This makes the episodes difficult to discriminate from one another, and produces problems for your episodic memory as it tries to keep the representation of each individual episode distinct in your memory. A second manipulation is to vary the retrieval cues so that some of them are really familiar to the subject, even though they don’t belong to any actual episodes from the subjects past. And you can then examine whether the familiarity is fooling the subjects memory. In fact, one of the most powerful ways of distorting memory in the lab works by combining these two manipulations, making episodic memory and familiarity fight against one another.
10The Deese (1959) Recall Task SOURCANDYSUGARBITTERGOODTASTETOOTHNICEHONEYSODACHOCOLATEHEARTCAKETARTPIEQUEENENGLANDCROWNPRINCEGEORGEDICTATORPALACETHRONECHESSRULESUBJECTSMONARCHROYALLEADERREIGNTwo of the study lists used by Deese in his original recall intrusion experiments.
11The Deese (1959) Recall Task Deese constructed his lists using word association norms.Each item in a list is a strong associate of a particular TARGET word.Deese found high levels of recall intrusions by these unpresented TARGET items.
12Roediger and McDermott (1995) Modified and extended Deese’s basic result.Employing recall and recognition tasksUse of the Remember / Know (R/K) procedure.The full reference isRoediger, HL, and McDermott, KB. (1995) Creating false memories: remembering words not presented in lists, Journal of Experimental Psychology: Learning, Memory and Cognition. Volume 21, pages
13The Remember / Know Procedure Ask subjects to report on their experiences while recognising.Do they ‘Remember’ any episodic details?Or do they just ‘know’ the information was encountered at study?
14Recognition Test List PLACE SWEET TABLE PARTY GENERAL MEMORY CONSENSUS KINGCOMPUTERTREEFERRETBURGLARBOTTLEThe lure items from the two study lists earlier are shown here in red. The rest of the items are ‘new’.
15Roediger and McDermott (1995) Percent RecognitionRoediger and McDermott's subjects didn’t just find the target word familiar, they were prepared to state that they could recollect episodic details from a study episode where the word was presented.In fact, just as many TARGET items got a remember response as did the genuinely studied items. It looked like there was basically no difference in the level, or the kind of experience, associated with TRUE or FALSE memories.Now this is a really remarkable result. These subjects were college students, bright, educated people, paying close attention to these very simple materials who, moreoever, were warned that the experimenters were trying to trick their memory, so they should be on their guard. Yet they are claiming to remember little events that never happened.
16Some Factors that increase or decrease DRM False Memory Increase: the number of associates presented for studyIncrease: the strength of association between study list items and their TARGETDecrease: (in young people) multiple study-test cycle.Decrease: the ‘distinctiveness heuristic’A brief summary of some further results investigating the DRM paradigm. For a good review and discussion of the paradigm, you SHOULD make a point of reading the following paper:-Dodson, CS., Koutstaal, W., and Schacter, DL. (2000) Escape from illusion: reducing false memories. Trends in Cognitive Sciences, volume 4, number 10, pages
17‘Distinctiveness Heuristic’ Two study conditionsWords from the DRM listsWords from the DRM lists paired with a pictureFalse recognition was almost absent when words had been paired with picturesThe ability to recollect picture information was ‘diagnostic’ for studied items.More recently, other researchers, notably Daniel Schacter and his colleagues, have adapted and extended the basic DRM paradigm to investigate these two accounts in more detail (you can read about this work in the Dodson et al review in Trends in Cognitive Sciences). Schacter and colleagues used pictures instead of words, finding that if you study lots of pictures, lets say of different cats, or different cars, and you then do a recognition test which contains pictures you’ve studied along with new cats and new cars, you false alarm like crazy, just like in the original DRM paradigm with words. So the DRM findings are not just peculiar to words and their associations.The level of false memory, however, drops dramatically if the subjects are given different instructions at test. So if the subjects are allowed to make a three way distinction between 'new' pictures, pictures that are 'new but from the same category as old items, and old pictures that were actually studied, they false alarm much less often. So false memory responses drop if you adopt a retrieval ‘orientation’, where you have to make a more fine grained discrimination between the test items. In other words, where you have to retrieve specific details from the study episodes, rather than just relying on the familiarity of the test items - familiarity alone could not support correct responding in this retrieval orientation.
18A triple whammy! 3 Reasons for ‘DRM’ False Memory (1) Implicit associative responsessubjects themselves generate the target items while studying each list.Then experience ‘source confusions’ at test(2) Familiarity of ‘lure’ itemsBut what about the ‘Remember’ responses?(3) A loss of encoding specificityMore than one explanation of these effects has been given. A popular one is that during the study phase, the subjects might think of the target item themselves, which is reasonable given that the study items were picked precisely because of their ability to bring the target item to mind through word association. So if you see more associates at study, or if they are very strong associates, then the target may be more likely to come to mind. And then what might happen at test, according to this account, is that the subjects get confused about the source of their memories, they know that they experienced the word at study, its just that they forget that it wasn’t actually on the list, they just generated it themselves. So they are confused about the proper source of their memory. They have recollected episodic details, that’s why they make R responses, but they get the fine details wrong. And the finding that false memories decrease with multiple study test cycles could be because you are simply getting more opportunities to encode specific features of the items on the study list marking them out more strongly.
19The puzzle raised by false memory Within the consensus view, how is it possible to recollect events that never took place?That is, what might causeSource errors?Familiarity-based confusions?Loss of encoding specificity?
20CMF Explanations for DRM False Memory The hippocampal formationPattern separation failure at encodingPattern completion failures at retrievalTherefore: source errors, & loss of encoding specificityThe frontal lobesStrategic control over memoryFailure to adequately focus on cues and/or monitor retrievalThe entire ‘association’ neocortexRepresents very similar content across a succession of episodes
21SummaryJudgements are most accurate when they are made on the basis of information whose source has been recollected.But if retrieval instructions allow it, judgements may be based, by default, upon potentially less accurate familiarity.The impression from all these studies is that you have to almost force subjects to interrogate their memories for information that is diagnostic, information that specifies the source of the memory. And if the retrieval task instructions don’t emphasise this, then the subjects appear to rely on an easier, default strategy, responding on the basis of familiarity. But in the laboratory at least, you can get past this strategy if the retrieval instructions emphasise the particular feature of the episode which is diagnostic of its source. You can also get round the use of familiarity if the encoding episode has really distinctive information that the subject can use to guide their responses.So the two important conclusions coming out of this work for the applied setting is not to let your eye witnesses rely on any easy, default use of familiarity, and second, to believe what they say only if they have recollected the source of the information they are telling you, and can state the source explicitly. But of course, even this isnt sufficient, if they confuse the source of their memories, then they will get their decisions wrong, like the DRM subjects who made remember responses to the lure items, possibly because they generated the items themselves instead of perceiving them on the study lists. And if your single eyewitness gets the source wrong there is unfortenately nothing that you can do, to verify their story independently. So to my mind at least, the importance or weight that is given to eye witness testimony, has to be balanced by this appreciation that witnesses' confidence in their recollections could all too easily be misplaced.