Topic 6- Memory Flashcards
Explain the research of William James into memory.
He first conceptualised memory according to his own observations and he defined it in terms of two stores: primary and secondary memory. According to James primary memory, similarly to what we now refer to as working memory, was the kind of memory that is consciously available to people as it involved the thoughts they kept in their minds, for example whilst having a conversation with their friends. On the other hand, he thought of long term memory storage, including for example memory of a person’s childhood, as secondary memory which we are not always aware of and thus need to work harder to retrieve.
However, as James did not conduct any experiments on this it was unclear what the capacity of these stores would be and how we would access them
Explain Miller’s research into the primary memory store.
He wrote a review paper evaluating the findings of numerous studies on absolute judgements and the span of immediate memory and concluded that the mind’s capacity is limited to the mean of what he referred to as the magic number 7. According to Miller, we can hold approximately 7 numbers plus or minus 2 in working memory on average.
There is considerable debate surrounding the claims that Miller made and this number may be lower, possibly as low as four.
The key message message is really that, whatever the capacity of this store is, it is really quite limited.
How is work memory capacity usually measured?
The task often used to measure working memory capacity is the digit span task where participants are asked to repeat an increasing number of digits either in the same order or the reverse order as the experimenter.
Healthy participants can usually recall around 6 or 7 numbers in the forward version of this task without a problem, but less when they are asked to recall numbers backward due to the added computations this requires.
There is one exception to this rule which you probably have encountered before and, even in 1956, Miller already reported this. If I give a colleague my office phone number I usually chunk it so instead of saying 02078483490 I would say 020 7848 3490; this strategy breaks up what would normally be a digit span of 11 digits into three spans of three or four digits, making it a lot easier to retain in working memory as well as to memorise in general.
A similar principle can be applied to letters converted into words or words converted into sentences. In the literature, this process is called chunking.
What happens if the stimuli in an experiment exceed the capacity of working memory?
It is very unlikely that a minor detail from the middle would have come to mind instantly.
Studies reporting this phenomenon usually present participants with long lists of words and report two effects.
These effects are called the primacy effect for things at the beginning of a list and recency effect for things at the end of a list. The idea here is that, through rehearsal, the early items of the list have been committed to long term memory whilst the later items remain in working memory – there is no room in these limited capacity stores for the middle.
These effects can be manipulated by directly manipulating working memory for example and adding another task, disrupting the recency effect in turn. Therefore, similarly to last week when we talked about attention, this is another example demonstrating the limits of human cognition.
Explain the modal model of memory formulated by Atkinson and Shiffrin.
According to this model, sensory input is stored in sensory stores which are not able to retain information for very long at all. Some of this information then was thought to be transferred to a short term memory store at which point a person would have to consciously use a strategy, such as rehearsal, to translate a memory into a permanent one in a long term memory store, otherwise the memory would be displaced or in other words forgotten. This permanent memory would then have to be fed back to the short-term memory store in order to be recalled.
We now know that this is not how memory works as, for example, short term memory does not only have one store and memory does not operate in this sequential manner.
A study that supports this argument was published by Shallice and Warrington who tested patient K.F. who had a severe short-term memory impairment. They could not do the digit span task or keep a short list of words in memory; however, their long-term memory was intact. This was evidence in favour of a model in which short-term and long-term memory do not operate in a serial manner as the modal model of memory suggests, but rather independently.
Contradictory evidence from a dual task paradigm suggests that short term memory does not just contain a single store but rather has different stores for different types of information. Participants complete two task simultaneously in such a paradigm. Support for a multi-store short-term memory model was demonstrated in a landmark study by Baddeley and Hitch where people were asked to remember a string of digits whilst completing a simple spatial reasoning task, deciding whether or not a statement regarding the positioning of letters is correct. So in the example on the slide participants should see the letter C and G and be asked whether the statement that G is after C is true or false, with the correct answer obviously being true. What they found is that, whilst participants could perform the task accurately regardless of how many digits they were asked to keep in mind, the task became more effortful, in other words it took longer, as the number of digits increased. This indicates that it is very unlikely that the same resources that are being used to store these digits are also being used to complete the reasoning task.
Explain the Model of Working Memory (baddeley and hitch).
The model assumes that there is one store for visuospatial information, such as being able to process whether G is after C, and a separate store for phonological information, for example when we keep digits or words in memory by repeating them back to ourselves through subvocal articulation. The model also contains the central executive which serves as an attentional control component that the executive system we discussed in the previous lecture relies upon.
This broadly allows three things to happen: it allows the allocation of information to the other two stores, it allows us to manipulate things in working memory, for example if we complete a backwards digit span task, and it also seems to help us retrieve information from long term memory for conscious retrieval.
the working memory model makes two broad assumptions regarding dual task performance. That is, that if both tasks rely on the same part of the model they cannot be carried out well, whereas if they do not they should be carried out accurately, which in turn effects our ability to multitask in different situations.
Explain the phonological loop of the working memory model.
The phonological loop operates in the form of subvocal articulation. The fact that this operation actually takes place can be tested via the phonological similarity effect which is what Baddeley and some of his colleagues did when they asked participants to remember letters instead of digits. What they found is that a letter string containing phonologically similar letters, so letters that sound similarly such as P, V, C, and G, are much harder to remember than letters that are phonologically different such as X, R, F, and Y, indicating that our internal voice plays a role in the operations of working memory
A study using PET by Paulescu and colleagues recruited English participants with no knowledge of Korean and asked them to either remember a series of six English letters or six Korean characters on different trials. The idea here was that in the absence of knowledge of Korean no subvocalisation could take place. When contrasting brain activation in these two conditions they found activation in language-related areas of the brain in both hemispheres for the English letters. What Paulescu and colleagues could not demonstrate with this task is which of the activated areas was responsible for the rehearsal of items, so the articulatory loop, and which was responsible for their storage. They followed up on these questions by adding a rhyming task to the experiment in which participants had to decide whether a letter rhymed with another, so for example does ‘P’ rhyme with ‘B’. Participants completed both tasks in different blocks. What they found is that the activated area closer to the front of the brain was significantly more involved in the rhyming task and, therefore, specialised in functions of the articulatory loop.
Explain the visuospatial sketchpad of the working memory model.
We use this store when we imagine a visual space. A study by Postle and colleagues revealed the underlying operations of the brain when doing this.
Participants were told to fixate on a fixation cross whilst they were shown a target. They were told to keep the location of this target in mind. The location of this target changed from trial to trial. Following on from this there was a delay period featuring either a fixation cross or a fixation cross and a black and white checked pattern. Such a high contrast image is used in imaging research to elicit activation in the early visual cortex and we are particularly interested in these trials here. Following on from this, participants were shown two probes and, through pressing a button had to indicate whether they were closer to the fixation cross or farther away than the target.
What Postle and colleagues found was that, during the delay period, the side of the pattern that coincided with the location of the target was associated with significantly more activation in the primary visual cortex than the other side. This indicates that merely thinking about a location will activate the same areas that looking at it would. This is, of course, also very much related to attention as participants will pay attention to this space in particular.
Explain the visuospatial sketchpad of the working memory model.
We use this store when we imagine a visual space. A study by Postle and colleagues revealed the underlying operations of the brain when doing this.
Participants were told to fixate on a fixation cross whilst they were shown a target. They were told to keep the location of this target in mind. The location of this target changed from trial to trial. Following on from this there was a delay period featuring either a fixation cross or a fixation cross and a black and white checked pattern. Such a high contrast image is used in imaging research to elicit activation in the early visual cortex and we are particularly interested in these trials here. Following on from this, participants were shown two probes and, through pressing a button had to indicate whether they were closer to the fixation cross or farther away than the target.
What Postle and colleagues found was that, during the delay period, the side of the pattern that coincided with the location of the target was associated with significantly more activation in the primary visual cortex than the other side. This indicates that merely thinking about a location will activate the same areas that looking at it would. This is, of course, also very much related to attention as participants will pay attention to this space in particular.`
What are the critical stages associated with long-term memory?
In general there are three critical stages associated with long-term memory: firstly, we need to encode a memory, and the processes underlying encoding are complex as, for some memories, we actively pay attention to them and try to keep them in mind, for example when studying for an exam, whilst for others we merely encounter and passively encode them in everyday life. Then we need to consolidate or stabilise the memory and, of course, we also need to be able to activate it to retrieve it. The latter process is related to operations of the central executive within working memory.
What is amnesia?
A large proportion of what we know about long-term memory comes from patients with amnesia this is a condition which, unlike for example dementia, is associated with a specific impairment to long-term memory where patients’ other cognitive functions remain intact. Causes of amnesia vary but it is sometimes caused by stroke, though syndromes such as neglect are more common as a result of stroke. More often it occurs after an accident or as a result of a neurological disease.
There are two types of amnesia though most patients experience a mixture of both. Anterograde amnesia is associated with an inability to form new memories and is the most common form of amnesia, for example following an accident. A patient who only has anterograde amnesia can remember everything before their accident perfectly well but really struggles to make new memories.
Retrograde amnesia on the other hand is when a patient cannot remember anything prior to their injury. Patients often also experience this but to a much lesser extent; in a way that they will often still remember their childhood and youth but might struggle with more recent memories closer to the amnestic incident.
On its own retrograde amnesia is a very rare occurrence and there is only one thoroughly documented case in the literature, patient L.T., who was reported to have dense retrograde amnesia but only very mild anterograde amnesia.
The few other cases in the literature that report retrograde amnesia in isolation usually address psychiatric reasons for this rather than damage to organic brain structures. The vast majority of patients with retrograde amnesia also have an anterograde impairment. The severity of retrograde amnesia is measured through the temporal gradient. As mentioned previously it is more common that patients cannot recall recent events, such as in the case of H.M., than not being able to recall very early memories. This suggests that more recent memories are less stable than older ones
The way in which the temporal gradient is assessed in hospitals is via the famous faces test where you give people batches of famous faces from different periods of their lives and see which ones they remember.
Explain the case study of patient HM.
H.M. had very severe epilepsy which was treated through a radical surgery in which Scoville, a neurosurgeon, removed his medial temporal lobes as shown in the image on the slide. As a result, they estimated that about two thirds of H.M.’s hippocampi were destroyed. The surgery did, in fact, treat his epilepsy but had severe consequences for his memory.
H.M. experienced very minor retrograde amnesia; there are varying reports, but it appears that he struggled mostly with memories from the two years immediately before his surgery. It is really new memories of people and events he could not retain. For example, even though he worked with neuropsychologist Brenda Milner for 40 years he could never remember having met her.
As mentioned previously, unlike in dementia, other cognitive abilities of amnesic patients are intact, so H.M. was aware of his deficit which was very much a struggle for him
When Brenda Milner tested H.M. she found that his short term or working memory was intact, as evidenced by typical digit span performance. She then gave him a version of the task which relies on longer-term memory where he had to remember one number in addition to the original digit span on every new trial. Healthy individuals can quite easily retain up to 15 digits this way whereas H.M. never got past 7 digits
H.M.’s spatial working memory was tested using the Corsi Block Tapping Task. In this task the experimenter sees blocks with numbers as shown on the slide. They tap these blocks in sequence and the participant who does not see the numbers needs to repeat this. Normally participants can repeat 5 or 6 moves and H.M. was able to complete this task without any problems, however, similarly to the previous task when they turned this into a longer term memory task by adding one location on each consecutive trial H.M. was not able to progress past six taps.
Once H.M.’s intact working memory capacity was established, they administered other tasks. In the mirror drawing task you are instructed to complete a drawing whilst looking at your hand in a mirror. This requires you to spatially remap your intentions in order to successfully complete the task. It is a difficult task, but people tend to get better at this over time. Here is where they found something very interesting with H.M. – he was asked to complete this task on three consecutive days and, similarly to a healthy participant, he made less errors as time progressed. Strikingly, however, on days 2 and 3 he did not remember having done this task on the previous day and required the instructions to be given to him as if this had been the first time he encountered it. In other words, learning occurred but he was completely unaware of this
They also presented H.M. with a fragmented picture task, an example of which will be presented to you on the next few slides. See how long it takes you to figure out what this picture shows. Similarly to the mirror drawing task H.M. made fewer errors, in other words, he could name images faster when reencountering them, however, he did not remember ever seeing them before.
The differences between what H.M. could and could not remember tells us something about differences in types of long-term memory. He struggled recalling explicit or declarative memory (conscious memory), but he could indeed rely on implicit or nondeclarative memory when performing these tasks. This demonstrates that the hippocampi are not responsible for implicit memory but rather long-term memory we are explicitly aware of. Again, this demonstrates that memory, whether it is short- or long-term, is not a unitary function.
Explain research into the role of the medial temporal love in the encoding of memories.
The temporal gradient encapsulates the idea that, the longer we know something, the more likely we are to remember it. This is because memories are better consolidated. Work on the medial temporal lobes has taught us a lot about how new explicit memories are formed and there is also strong evidence for their involvement in the consolidation of these memories
The first imaging study to look at the role of the medial temporal lobe in the encoding of memories was published by Wagner and colleagues. They presented participants with words that they should remember whilst in an FMRi scanner. This was to observe activation during encoding. They then gave participants a memory test to see how many words they remembered. This allowed them to contrast encoding activity for remembered and forgotten words. They found that the remembered words were associated with a significantly stronger BOLD signal in the left medial temporal lobe at the time of encoding
Haist and colleagues looked at consolidation using famous faces. Again, the idea here is that the longer we have known something, the longer we have consolidated it. They wanted to look at activity in the right medial temporal lobe, specifically the fusiform cortex which is responsible for the processing of faces, the hippocampus, and the entorhinal cortex which is close to the hippocampus. They found that activity in the fusiform face area was similar across faces regardless from what decade they were. A similar trend was observed in the hippocampus, indicating that the hippocampus is consistently involved in memory processing, regardless of consolidation. Activation in the entorhinal cortex, however, reduced significantly the older the pictures were, implicating this area in the consolidation of memory in particular in a way that processing in this area is not as required for well-consolidated memories as opposed to new ones.
Explain the two different types of explicit long-term memory.
Semantic: memory for facts such as those you have learned in school or read in the newspaper
Episodic: memories for events such as holidays or birthday parties
This explicit memory distinction was proposed by Tulving based on his observation that episodic memory appears to be a much greater issue associated with amnesia, as opposed to semantic memory. This was reinforced by his work with patient K.C. who had sustained severe medial temporal lobe damage following a motorcycle accident. As a result he had severe retrograde and anterograde amnesia and had no episodic memory whatsoever, whilst his intelligence, short-term memory and language remained intact. In other words, he could make use of his semantic memory.
Explain the two different types of explicit long-term memory.
Semantic: memory for facts such as those you have learned in school or read in the newspaper
Episodic: memories for events such as holidays or birthday parties
This explicit memory distinction was proposed by Tulving based on his observation that episodic memory appears to be a much greater issue associated with amnesia, as opposed to semantic memory. This was reinforced by his work with patient K.C. who had sustained severe medial temporal lobe damage following a motorcycle accident. As a result he had severe retrograde and anterograde amnesia and had no episodic memory whatsoever, whilst his intelligence, short-term memory and language remained intact. In other words, he could make use of his semantic memory.
There was some scepticism regarding this idea of differentially affected types of explicit memory, namely, saying that this might be a product of encoding as semantic memory tends to be reinforced a lot more through studying for example than episodic memory. Vargha-Khadem and colleagues tested this idea by testing young children with very early hippocampal damage which meant they did not have a lot of time to reinforce semantic memories. The three participants they tested all had severely reduced hippocampal volume they went to schools but required a lot of support due to their episodic memory deficit compared to a healthy control. The participants really struggled to recall a story 20 minutes after listening to it and they also struggled copying the complex figure we talked about in the previous lecture after a short delay period. Crucially, however their semantic knowledge was intact
