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Long-term memory (LTM)

Long-term memory: episodic and semantic memory

PS2016: Cognitive Psychology

John Beech

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LTM: episodic and semantic memory – a preview

1. An examination of earlier research on memory.– (e.g. Atkinson and Shiffrin, 1968)

2. An overview of the components of LTM (Squire, 1992)

3. Procedural memory– (e.g. about amnesia)

4. Encoding, storage and retrieval.– (e.g. levels of processing)

5. Relatedness vs. distinctiveness

6. Semantic vs episodic memory– Comparisons and contrasts

7. Retrieval in episodic memory

8. The cognitive neurospsychology of episodic memory

9. Conclusions

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Atkinson & Shiffrin (1968) and 3 memories

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Long-term memory (LTM)

Atkinson & Shiffrin proposed 3 types of memory:Sensory memory: We process information very briefly in its

raw form. Large capacity. Rapid decay.Short-term memory (STM): This has limited capacity for

period of 15-30 sec. Rehearsal maintains it. Forgetting slow.

Long-term memory (LTM): This has large (unlimited?) capacity that holds information for a long period. Perhaps all that can be remembered is held for virtually a lifetime, or at least while the brain is capable of retrieval.

It is believed that LTM is organised into components which contain different types of information.

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Working MemoryThe concept of Working Memory came later, which as its name

suggests, is a kind of STM involved in everyday mental activity.

Examples of Working Memory: • Listening to or reading text• Remembering a phone number. Known as working memory and can be used visually, spatially,

in mental arithmetic, in reasoning and problem solving as well.

It can be important for transferring information into long-term memory. It works as a temporary holding store during processing.

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LTM

Ryle (1949) proposed an important difference between remembering information based on “knowing that” and when we remember in terms of “knowing how”.

We know that: • our bike is currently parked in a bike shed• we had to take the cat to the vet last Wednesday• the capital of England is LondonWe know how:• to ride a bike• to swim

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Squire (1987, 1992) and her LTM distinctions

LTM

Declarative (fact) Procedural (skill)

Episodic Semantic Skills Priming Conditioning

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Declarative vs. procedural memory

Declarative (facts) memory – involves factual information, such as ‘Henry VIII had 6 wives’. It means that information is stored that is explicitly available for later—which is often referred to as explicit memory. It can be tested by free recall, cued recall and recognition memory. we are conscious of these memories.

Procedural (skills) memory – involves the knowledge we have for performing a skill such as using a computer mouse. Although we learn skills, they are implicit memories in that we don’t have access to how they work. In fact if you try to think about what you’re doing, your performance can get worse. (E.g. if you’ve learned to type, but then try to be more self-conscious about what you’re typing, you can make typing errors.) We are not conscious of information in implicit memory.

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Procedural memory• Amnesics are able to continue with their normal skills and

even develop new ones. Just to explain further—patient HM had his medial temporal lobe removed as part of an operation for epilepsy when 27 in 1953. He was the worst case in a series of 10 patients reported by Brenda Milner.

• Removal of HM’s medial temporal lobe, including the hippocampal formation, resulted in dramatic memory impairments, because it was bilateral.

• He remained of normal intelligence (IQ 112) and had no psychological illness. However, the surgery resulted in intense anterograde amnesia (Events taking place after surgery are never remembered for more than 60 sec).

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Procedural memory• But to return to the main point—if HM does a jigsaw,

he will get faster and faster each time he does it. In other words his implicit (or procedural) memory is intact. However, HM, like other amnesiacs would not remember doing that particular jigsaw before. In other words, explicit memory is severely affected.

• There a number of procedural memory skills that amnesiacs can do without difficulty: mirror drawing/writing; finger mazes; Tower of Hanoi—but what is the commonality across these tasks?

• This leads to the problem of circularity—if an amnesiac can do a task, then this is labelled as ‘procedural’.

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Procedural memory• Baddeley (1997) thinks that it is important to study the

sub-components of procedural memory. Squire (1992) thought that these were: (1) skills and habits; (2) priming; (3) simple classical conditioning and (4) non-associative learning (e.g. habituation). As shown in the previous fig.

• However as mentioned at the beginning, the focus of this topic is on episodic memory (and also how it compares to semantic memory), so examining procedural memory just serves as a contrast for our purposes.

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Encoding, storage and retrieval

Another perspective is that memory has 3 stages:• Encoding—inputting information• Storage—keeping in memory• Retrieval—pulling out of memory

Beginning with encoding—this is how we represent information (e.g. events). But this encoding also depends on how it is processed. This might be just perceptually, but information can be processed much further than this…

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Encoding: Levels of processing models

• A model to challenge the Atkinson and Shiffrin was one proposed by Fergus Craik and Robert Lockhart (1972).

• They proposed the levels of processing model in which items that were processed “deeper” were consolidated into LTM.

Written words were presented in 3 conditions:1. Ps had to identify if they were in upper or lower

case letters – this was a superficial level.2. Ps judged if words rhymed with each other – an

intermediate level as processing for meaning still not involved.

3. Ps had to make a judgement about a word (e.g. Lamp post -can it rotate?) – this was considered to be deep processing.

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Encoding: Levels of processing models

Written words were presented in 3 conditions:1. Ps had to identify if they were in upper or lower case letters

– this was a superficial level.2. Ps judged if words rhymed with each other – an

intermediate level as processing for meaning still not involved.

3. Ps had to make a judgement about a word (e.g. Lamppost -can it rotate?) – this was considered to be deep processing.

• Found that memory better if deep processing involving semantic processing was used. This is compared to information coded visually or phonologically.

• Thus there’s an incompatibility with the STM-LTM formulation of Atkinson & Shiffrin because it wasn’t about just holding information in STM long enough, it was instead about the type (superficial vs. deep) of processing taking place.

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Problems with levels of processing

• But the levels of processing model isn’t ideal. It’s major problem is one of circularity. What constitutes shallow versus deep processing? It comes down to the definition of the experimenter. This means that it is a theoretical formulation that can’t be falsified—one can always shift the definition to suit one’s findings. This is not actually too much of a problem as there are other formulations in psychology that are also very difficult to falsify.

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Problems with levels of processing

• Another problem is that it cannot explain all memory phenomena (see Rutherford, 2005); but again, this is perhaps not surprising. A relatively simple model is not going to explain phenomena outside its domain.

• At least the levels of processing model meant that researchers shifted from viewing memory as a structural phenomenon to one in which memory was regarded as a process, rather than residing in different storage areas. This is not to say that the concept of memory storage isn’t also viable.

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A paradox: relatedness vs. distinctiveness

Relational and item-specific processingResearch evidence in memory has a paradox: on the

one hand if items are distinctive in some way we tend to remember them. (E.g. we find it difficult to remember a set of faces if they are all very similar.) On the other hand, we know that if we organise items together they are easier to remember. (E.g. if you had to remember: “table, cat, chair, mouse, bed, cow, etc”. This is easier than this more disconnected list: “coat, pen, organ, broom, gun, car, etc.”)

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Relational and item-specific processing

• Hunt and McDaniel (1993) refer to relation processing for similarity in processing and item-specific processing for when there is distinctiveness.

• To illustrate relational processing vs. item-specific processing division consider a study by Hunt & Einstein (1981) that looked at this in the context of recall and recognition (which are both tests of explicit memory).

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Hunt & Einstein (1981) study

They used a 2 x 2 design looking at (1) categorised lists (6 words from 6 categories e.g. (a) “table, chair, bed…” (b) “cat, mouse, cow,… etc”) vs. a list of 36 unrelated words. And (2) relational processing vs item-specific processing—to be explained next.

Type of processing

Grouped Ungrouped

Relational 1 2

Specific 3 4

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Hunt & Einstein (1981) stages of the expt1. For relational processing two groups sorted their list

into categories (pretty difficult when dealing with the unrelated lists!). The other two groups had to undergo item-specific processing: they rated each word for pleasantness. Thus the relational group were processing for similarity – looking at how the items could be associated together, while the other group (the item-specific group) was processing distinctiveness by assessing its particular pleasantness.

2. All Ps read a short story for one minute to stop rehearsal.

3. (3) They ‘free recalled’ the 36 words.4. (4) They were given a recognition test – the 36 words

were again presented along with 36 new words and they had to say whether each item was ‘old’ (i.e. previously presented) or ‘new’.

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Hunt & Einstein (1981) study-findings

LH figure shows the results of free recall (FR) and the RH figure for recognition. An interpretation for FR is that when items are related together, performance is better. Thus the one condition (the ungrouped – item-specific group) in which the items were unrelated and Ps were concentrated on individual properties, performance was the worst. In the other red condition, the items were grouped together, even though this wasn’t explicit, it helped recall.

In recognition there is an advantage for item-specific processing (red) as performance is best in both the pleasantness rating conditions.

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101520253035404550

grouped ungrouped

RelationalItem-specific

0102030405060708090

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grouped ungrouped

RelationalItem-specific

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Hunt & Einstein (1981) studyConclusions(1) In free recall it helps to relate the items with each

other. Trying to process each items by itself is not so helpful. Perhaps because when retrieving one item it helps you to retrieve others?

(2) In recognition, it helps to concentrate on the individual properties of the items to produce the best performance. This helps to differentiate it from others?

(3) Note that actual performance in free recall is much worse than in recognition. It is much more difficult trying to retrieve information “out of the blue” than judging if you have seen something before.

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Semantic vs. episodic memory (Tulving, 1972, 1983, Schacter et al. (2001)

Semantic memory is about facts, concepts and ideas;

whereas episodic memory is about personal experiences and is temporally dated. As the label implies, episodic memory about the episodes (i.e. autobiographical experiences) that have happened to us throughout life.

Evidence: Lefrancois (2000) KC, an amnesiac, plays chess and knows that he can, but cannot remember playing a game.

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Tulving’s distinction between episodic and

semantic memory

The distinction has plausibility:• Episodic, semantic and procedural

memories are interactive with one another: if we are learning a new language our first time we encounter a certain word it is within our episodic memory.

• Gradually its meaning assimilates into semantic memory and we may forget the first encounter. This makes for an efficient system—the less useful episodic information gets cleaned out gradually. What is left resides in semantic memory.

• Learning a new skill requires episodic memory while we consciously master, e.g. the gear positions in a car. But again, this information eventually gets cleared away. What is left resides within procedural memory.

• This is a system that has a built-in avoidance of redundancy, so that we disconnect the context in which we learned something. This is efficient in terms of storage.

Semantic

Episodic Procedural

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Comparing episodic and semantic memoryEpisodic1. It is organised in time.2. It makes a reference to me.3. I consciously retrieve events

in my life.4. My memories are subject to

forgetting.5. The context of what I

remember is important-to be shown later.

Semantic1. Time is irrelevant—I can’t

remember when I learned about Henry VIII.

2. It refers to my general knowledge—it is not about me.

3. These are ‘events’ that haven’t happened to me personally—I just know them.

4. This is permanent knowledge—unless my brain deteriorates or gets damaged.

5. The context of learning is not important.

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Episodic vs. semantic memory

However, Rutherford (2005) argues against making a case for independent episodic and semantic memories, contrary to the proposals of Tulving and Schacter. Although it is a useful heuristic, he thinks that a better way would be to think of semantic memory as ‘an abstraction of episodic experience’. That is, we are continuously have episodic experiences in everyday life and these continue to input into some form of distillation of these experiences, that we can refer to as semantic memory.

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Episodic vs. semantic memory

There are contrasting ways to test semantic and episodic memory:

Sentence verification tests semantic memory e.g. ‘a spaniel is a dog’ true or false?

Sentence recognition tests episodic memory—where you test if individual sentences had occurred earlier in the experimental session.

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Episodic vs. semantic memory

A study Rutherford cites to show this contrast between episodic and semantic memory comes from Anderson and Ross (1980):

Anderson & Ross found that the time to verify sentences (i.e. using semantic memory) was affected by episodic information that they gave them in previous sentences.

In the episodic part of the experiment people were given sentences to learn (e.g. “A spaniel retrieves a ball”) and later verified sentences (e.g. “A spaniel is a dog”). Retrieval time in this later semantic part was affected by the nature of the episodic information given beforehand.

If episodic memory was affecting retrieval time from semantic memory, this suggests a relationship between them.

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Retrieval in episodic memory

Retrieval – let’s examine further aspects of episodic memory

How good is our ability to retrieve from LTM (or how permanent is our storage)?

• It depends on the type of retrieval. Tulving & Pearlstone (1966) showed that after presenting lists of words from categories (e.g. furniture, cooking, colours, etc) that if they used cued recall—by giving the category names performance was 75% compared with just free recall which produced 40%.

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Retrieval in episodic memory

How good is our ability to retrieve from LTM (or how permanent is our storage)?

• Willem Wagenaar (1986) kept a diary for 6 years and put down 1 or 2 events a day => 2400 entries altogether—without ever looking back. Each given cue: who, what, where and when. Every day he did 5 retrievals using 1, 2 or 3 of these cues. After 5 years recall was down to about 30% and when was least effective, probably because least visual.

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Retrieval in episodic memory

Example (invented)Who: My Aunty VeraWhat: I went with her to an art gallery during a visit Where: The local art galleryWhen: Monday, January 15, 1983

Question: Who did we encounter just outside the art gallery?Answer: A nurse who’d spotted that she’d dropped a glove.

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The permanence of semantic memory

• By contrast how well is information stored in semantic memory – if we can make a distinction with episodic memory?

• According to Bahrick (1984) semantic memory is pretty stable. He found that 40% of Spanish vocabulary was retained 50 years later.

• For this reason it has been called a ‘permastore”.

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Retrieval in episodic memory

• Retrieval takes place when information held in memory becomes available. There appears to be an element of activation as part of this retrieval process.

• The encoding specificity hypothesis was introduced by Tulving and Osler (1968). Ps were given a list of 24 cue-target pairs (e.g. thimble-HAND).

• Then they had immediate recall in one of 3 conditions; (1) thimble-HAND—same cue as at encoding; (Thus they were given the cue word “thimble” and they had to say “hand” to be correct.) (2) thumb-HAND—another weakly associated cue (3) just free recall—ie no cue. Condition (1) was best relative to (3), but (2) was ineffective.

• Thus these retrieval cues need to be stored at the time of initial learning to be effective.

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Retrieval in episodic memory

Transfer appropriate processing (TAP):

Morris, Bransford and Franks (1977) gave Ps words to learn under one of two different processing tasks followed by one of two different tests:

• Two processing tasks:

rhyme: Does the word rhyme with…

semantic: e.g. Can you feed it?• Two types of test

standard yes/no recognition test

rhyming test: e.g. Were you given a word that rhymes with cable?

Test

Encoding task Standard Rhyme

Semantic 83% 33%

Rhyme 62% 49%

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Retrieval in episodic memory

Transfer appropriate processing (TAP):

Morris, Bransford and Franks (1977)

• The result was that the Ps did better in the tasks that matched (ie. semantic encoding better in standard test [83 v 62] & rhyme better in the rhyme test [49 v 33]) .

• This supports the TAP hypothesis. In other words, performance appears to be best if the processes one undertakes while learning are the same type of processes that one uses during retrieval. An implication would be if you are going to be given an exam needing recall, you would be better to revise by testing yourself using recall, rather than by recognition or cued recall.

Test

Encoding task Standard Rhyme

Semantic 83% 33%

Rhyme 62% 49%

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Retrieval in episodic memory

Transfer appropriate processing (TAP):Morris Bransford and Franks (1977)

• A slight problem with the Morris et al. study is that performance levels on the standard vs. the rhyming tests are not matched—but matching is not likely to change the interaction.

Test

Encoding task Standard Rhyme

Semantic 83% 33%

Rhyme 62% 49%

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Retrieval in episodic memoryEncoding specificityAnother aspect is the importance of context during encoding. Grant et al. (1998) had Ps

read an article in noise or silence followed a test of reading comprehension under noise or silence and found the following results…

The top figure shows the design for Grant et al.’s (1998) “studying” experiment. The bottom shows the results of the experiment. Asterisks indicate situations in which study and test conditions matched. This suggests an advantage if one studies in quiet conditions.

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Retrieval in episodic memory

Encoding specificity – state dependent memoryEich & Metcalfe (1989) looked at the effects of mood in this

context.Musical mood induction- they tested on mood several times

each session:happy mood Ps – rated happier and more arousedsad mood Ps- rated sadder and less aroused.

Later they studied a word list either in a happy state or in a sad state.

E &M found that the best performances were either (1) when they encoded while happy and were tested while happy, or (2) when they encoded when sad and tested when sad.

Here’s the data…

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Retrieval in episodic memory

The top figure is the design of Eich and Metcalfe’s (1989) “mood” experiment and the bottom shows the results. Asterisks show when encoding and retrieval sessions match.

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Retrieval in episodic memoryConclusion of encoding specificity – state dependent

memory

The concepts of encoding specificity and Transfer Appropriate Processing (TAP) give importance to the relationship between the processes involved in encoding and retrieval. It seems that performance is improved considerably if there is a similarity in information and indeed a similarity in the mental state of the individual.

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The cognitive neuropsychology of episodic memory

• Earlier we look at the case of HM who had amnesia because of bilateral surgery to the hippocampus. This demonstrates how new episodic memories need the hippocampus. Thus when this structure is damaged on both sides of the brain, new procedural memories can be learned, but new events (episodes) in one’s life cannot be retained.

• There is evidence that the prefrontal cortex (PFC) is also needed for the establishment of new episodic memories. Patients have such damage due to aneurisms or head injury (esp. car accident).

• When the PFC is damaged new information can be learned but it tends to be disordered.

• Incidentally, there is also evidence (Nyberg et al., 2000) from studying the PFC that women are better than men in retrieval from episodic memory.

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The prefrontal cortex and episodic memory

• Janowsky et al. (1989) showed how patients with PFC damage could recognise an object seen before, but could not say where or when it had been seen.

• Nyberg et al.’s (1996) HERA model (hemispheric encoding/retrieval asymmetry) is based on a meta-analysis of many neuroimaging studies. The left PFC is more involved in episodic memory encoding than the right PFC. On the other hand, the right PFC is more important for retrieval within episodic memory.

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The hippocampus and episodic memory

• Although there is general agreement that the hippocampus is involved in episodic memory, due to the amnesic evidence, there is controversy about how long such memories are stored for normal people.

• Views range from the hippocampus storing information only for a brief period before being processed elsewhere to episodic memories being stored permanently in the hippocampus.

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Conclusions on the relationship between episodic and semantic memory

• As a reminder, episodic memory is a ‘one-off’ learning situation. An episode happens (e.g. I post a letter) and then it moves away in time, perhaps repeated later, perhaps not. But only one occurrence is all that is required.

• Tulving (2002): “An event happens, a person experiences it, memory traces are laid down representing the event, the past vanishes and is replaced by the present.”

• With semantic memory there could be several exposures, but not necessarily. E.g. we can have a flash-bulb memory of “9/11”.

• When there is a repetition, there is an update and perhaps a modification of semantic memory, if we learn something to add to this.

• Some think of episodic memories as transmuting into semantic memory over the passage of time. This is done by making some generalisations from these similar events, while the specific context in which these encounters occurred is lost.

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Conclusions on the relationship between episodic and semantic memory

• Others think that episodic memories remain in that form, so what is retrieved is still an episodic memory. Nevertheless they also help semantic knowledge. Thus the destiny of episodic memories is NOT inevitably to become semantic memories.

• There is a plausibility in the notion of an episodic-semantic distinction, although many are skeptical (e.g. Rutherford, 2005). It feels like one is undergoing different types of task when comparing what one ate in the evening 3 nights ago (episodic) with retrieving the name of the prime minister (semantic).

• But there is not strong evidence that there are two completely different memory systems.

• At the moment, it looks like the controversy will continue…