Lecture 24-25-26 Memory PDF

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Summary

This paper was primarily taught by Dr. Bart Ellenbroek, Dr. Gina Grimshaw, Dr. Tirta Susilo, Dr. Josh Faulkner. It deals with the cognitive and behavioural study of the mind. The paper is segregated into two parts wherein Part 1 of the course focusses on the behavioural concepts (Lectures 1-16) and ...

Description

Lecture 24: Short-Term and Working Memory Basics of Memory: 

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Defining memory o

Storage and recall. Encode and retrieve.

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Memory is the processing of information that is no longer present. Information from the past.

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Effect of past experiences on present or future thoughts or actions.

Modal model (Atkinson and Shiffrin) o

This model of memory was made of three main components – sensory memory (iconic and echoic), short term memory (15 – 20s) with a rehearsal loop, and long term memory (in which things can be stored and retrieved)

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Sensory memory here is all of the immediate information we receive in visual or auditory inputs. This long keeps information for a few hundred ms max, before it is either transferred into the STM or killed.

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Can pull things in and out.

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There are also a number of control processes that help maintain information in the STM – these include:

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Rehearsal processes

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LTM searches

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Attention

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Chunking

Our focus today will be on the STM component.

Short Term Memory: 

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Definition: o

Baddeley defined STM as a system involved in storing small amounts of information for brief periods of time

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This is an active, online process that is going on right now so is vulnerable to distraction.

How can we measure its capacity? o

Digit span, or word spans: you give a patient an increasing number of numbers or letters or words that they have to remember in order and say back to you. When they fail 2x in a row to say the correct numbers then you have their digit span which is a good indicator of their STM

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This task involves rehearsal, while you are telling the participant the new digits they must be able to hold in their heads the others that came before it.

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Speed can alter performance on this task, fast reading can make it harder because there is less time to rehearse.

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This task can be done with words, objects etc. and even when block tapping (point to the correct box etc)

Brain damage and verbal information:

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Here we look at KF who had a stroke, he was pretty much fine except for the fact that his short term memory in relation to learning new numbers or names was shocking. He had a selective short term memory impairment. His LTM was fine, just his verbal STM. He had a digit span of one. We find this kind of impairment is assocated with damage on the left parietal lobe.

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A second patient (EE) had a damaged verbal STM, but a functioning visual STM; his STM for non-verbal material was normal

Brain Damage and Spatial information: o

There are also patients who have normal digit spans, that have difficulty performing spatial tasks – they are unable to recall a pattern of blocks tapped instead.

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This group typically have damage to their right parietal lobe.

Double Disassociation! o

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There is now evidence that verbal and visual STM are two separate processes – patients with spatial issues might not have trouble with digit span and the injury tends to be on the right, whereas patients with verbal issues might not have issues with spatial span and have damage on the left.

Verbal Short Term Memory: Key Brain Bits: o

PET Study: look at the regions more active during the digit span compared to single digit repetition. The left parietal lobe and the inferior prefrontal cortex light up – note that there is more activation on the left than the right.

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The inferior prefrontal cortex seems to be key for rehearsal; if you do a delayed repetition task in which patients are delayed from being able to repeat the numbers back to you, you find that the PFC areas are active when the individual is rehearsing.

Visual Short Term Memory: Key Brain Bits: o

In visual STM and retention tasks, a network is also activated, but more strongly on the right. There are a large number of regions involved, including many prefrontal areas.

Problems with the Modal Model; 

Emphasis is on storage o

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We are not just storing information, we are also using the information in real time – this model does not account for that

Transfer from STM to LTM dependant on rehearsal o

We constantly hear about information like where a radio show is in terms of frequencies etc. but if we ask people if they actually recall that information they cannot tell you. It is not the case that whatever you hear often or rehearse you can recall it later.

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Note that STM is not a gateway to long term memory.

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Possibilities to carry on two tasks, digits and reading

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We need a better model

Working Memory: 

Definition (Baddeley and Hitch) o

A limited capacity system for temporary storage and manipulation of information for complex tasks such as comprehension, learning and reasoning

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Difference between STM and WM? o

WM is more about the manipulation of information we are holding onto, whereas STM is just holding on to that information

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An example might be a digit span – this is STM because all you have to do is recall it in that order. A backwards digit span is an example of a WM task – you have to maintain and manipulate the information.

WM and Brain Bits: o

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There is more activity in the dorsal prefrontal cortex when engaged in a WM task over an STM task.

Baddeley’s working memory model: o

According to him, working memory has 3 main modules

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We have the ‘phonological loop’ which deals with verbal and auditory information. The information for this model comes from the phonological store, and is maintained through articulatory rehearsal. The brain area involved is the left parietal lobe

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We also have the ‘visuospatial sketch pad’ which deals with visual and spatial information. This involves the right parietal lobe

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Between these two loops we have the central executive, which we will get into a little later? It is the master component.

The phonological loop o

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Basically a way to manipulate the STM information we are playing with.

Components and pathways: 

There are two main components – a store that allows us to keep verbal information for 2 seconds, and the articulatory rehearsal loop that allows us to keep information in the store for longer.

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If the information is heard, rather than read, it enters the store directly. If we read something, however, it must travel first through the visuospatial sketch pad for visual analysis, we then transfer it into an orthographic phonological encoding, and then it can enter the phonological store and be articulatorily rehearsed.

How can we show there is a phonological loop? 

Phonological similarity effect: if we have to recall similar sounding words, we find it more difficult because the words get mixed up in our minds

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Word length effect: we can recall more words if they are shorter, rather than longer, because the length of the word affects how often we can rehearse it, and how many words we can rehearse.

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Articulatory suppression effect: if we tell someone to repeat blah while being asked to recall a list of words, they will be much less able to than normal because you supress the participants ability to rehearse the words they are learning

Visuospatial sketchpad o

This stores visual information, like spatial block tapping, or where the information or colour might be etc. This is also where we are rotating and manipulating visual information

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Visual imagery is the creation of visual images in the mind in the absence of physical visual stimulus.

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Central Executive: o

This system coordinates how information is used by the two auxiliary systems

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It focuses attention on relevant information

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It helps divide information between elements in the environment

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It also helps switch attention from one item to another as well

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The prefrontal cortex is key for this element of WM, we see in patients with damage to the PFC that they have trouble switching between rules in the Wisconsin card sorting task – indicating difficulty with mental flexilbity.

Baddeley’s revisited WM model o

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We have an added bit now – the episodic buffer – this new component has to deal specifically with information you retrieve about personal past experiences.

Working Memory Experiments: o

N back task: 

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Results: 

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You must say yes when the number you see in front of you is the same as that which appeared two trials ago. This is very hard. You have to maintain and constantly update your memory – it gets more difficult the larger the number of trials you have to go back

There is greater activation the harder the task is; the more numbers that people have to keep in mind, the more the brain regions involved are active. There is a network of structures in the left and right pre-frontal cortex involved.

Working Memory in the Brain: o

Monkey study – they can record a single cell in the brain, and what is occurring in that cell during a certain task like recalling information

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They trained the monkeys to fixate on a central screen, with a visual cue that could appear on either side (they cannot turn their eyes yet), the monkey had to recall that cue and once signalled with an arrow they must move their eyes to the area that the cue was in.

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They found that there is activation when the cue is present, and then there is specific activation while the monkey is maintaining the information in WM – the cell is firing even when the visual information is no longer present. This is what is helping the monkey move their eyes to the correct place afterwards. This is all in the PFC.

Central executive in the brain o

ERP experiment with people, there are three conditions. People are told to recall whatever is presented on the left. Wither there is 2 items, or four items, or people are told to recall only two even if there are four.

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They looked at people with poor working memory and good working memory. When participants had to recall two items, they found both groups had lower activation. When participants had to recall four items, both groups had similar activation. The difference between the groups came when you looked at participants being told to remember 2 and ignore 2.

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People that have a good working memory, or a high capacity, performed the same in the distractor task as the only having to recall 2 items task. They were doing the task using less effort and requiring less activation.

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People with a bad working memory or low capacity, performed the same in the ignore 2 task, as in the remember four task. This showed that they were having to do more work in the same task.

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People with a low working memory capacity were worse at inhibiting information that should not be processed. They were doing too much work. Its not about storage, but the ability to inhibit some items that they don’t need to process.

Working Memory Problems: o

Neuroimaging studies support Baddeley’s idea that the central executive might be in the prefrontal cortex, but that the precise network depends on the task.

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Different kinds of WM engage different parts of the prefrontal cortex (like verbal v spatial)

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This indicates the Baddeley’s model might be too simple

Working Memory: Cowan’s Model o

Short term memory is not a separate system, or even a set of systems. Not a thing. It’s the same as long term memory. It is a pattern of activation from information stored in LTM.

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Rather, short term maintenance involved temporarily activating and maintaining representations from long term memory. The brain structures that are activated depend on the material maintained.

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Working memory involves brining some of these representations into the focus of attention (what you are thinking about, event or information), and operating on them. So think of long term memory housing a pen called ‘activated long term memory representations’ which is where you have highlighted some relevant facts, and your attention moves within that pen and focuses on one or two specific points to allow you to hold onto and play with that information

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Problem with this idea: people have some capacity limitations. Contrary to long term memory which is infinite, short term and working memory are limited. Response might be is what appears like limitations might be part of other mechanisms like inhibition (thinking of one thing then wont be able to think of other things.

Conclusion o

We are starting to see theories that view STM and WM as properties of the same brain structures that store relevant information, rather than as separate systems

Lecture 25: Long Term Memory I Types of Memory: 

Explicit Memory: o

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Autobiographical Memory: 

This is the overlaying label that applies to both of the categories below.

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This is a conscious form of memory

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This is what we know about our lives – both events and facts.

Episodic memory: events of life 

Recollection,

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Autonoetic

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Awareness

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Semantic Memory: 

Familiarity

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Noetic

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Awareness

Implicit Memory o

Procedural memory 

The ability to play the piano

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Priming

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Conditioning

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Properties of the three 

Not conscious – can do without knowing

Explicit Memory 

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Basics: o

Ability to mentally time travel forward and backward – recollecting environmental and contextual elements of the original event (episodic). Semantic is more factual – all the things we know but don’t know how we know.

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Knowledge affects experience

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Autobiographical memory overlies episodic and semantic – both interact with it.

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Autobiographical memory has aspects of both: (all we know about our own lives – facts about ourselves and events that we recall about ourselves) 

Multidimensional

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Spatial

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Emotional

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Sensory (good vision memory associated with it)

Brain Bits: o

Prefrontal Cortex and Hippocampus

The Medial Temporal Memory System (MTS) 

The Medial Temporal Memory System (MTS) o

It is a complex structure that also includes the hippocampus – attached to other structures – we discuss those below. Injury to any of these structures can lead to severe memory problems – the frontal lobes, the fornix, mamillary bodies, thalamus and hippocampus specifically.

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Hippocampus and Parahippocampal Gyrus 

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Medial surface of temporal lobes curl inwards – the hippocampus and parahippocampal gyrus is at the tip of this curled lip. Its readily accessible from a coronal section.

Associated subcortical structures (mammillary bodies, fornix)

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Surrounding reigns (entorhinal, perirhinal cortex and parahippocampal gyrus

Damage to the MTS: Medial Temporal Amnesia: o

Example: HM

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Other etiologies:

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Hypoxia (oxygen deprivation)

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Infection (herpes simplex)

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Alzheimer’s disease

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Korsakoff’s disease: damage to mammillary bodies.

Two Components of Medial Temporal Amnesia:

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Affects facts/events both before and after illness:

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Retrograde amnesia: loss of memories for at least a year before the illness

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Anterograde amnesia: cannot remember new facts or events

Retrograde Component: o

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Surgical removal of the hippocampus and surrounding areas to treat seizures – couldn’t recall new things and he couldn’t recall things from his past to a point.

Features: 

Impaired period at least one year prior to illness

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Can be more extensive if damage extends to prefrontal and or lateral temporal cortex

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Example: HM given a series of cue words – like holiday. All of HM’s recollections were from before the age of 16, even though he had the surgery at 27.

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Example Jimmie: He had Korsakoff, he was 49 but thought himself 19 and couldn’t understanding why everyone looked old. He believed he was in the navy because he enlisted young. He couldn’t understand why he looked so old.

Tests 

Autobiographical Memory Interview: this is where you get participants to give you a cued recall of experiences from three different time periods. 1. Childhood (primary etc.) 2. Early Adulthood and 3. Recent events.

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The more detailed the description the higher the score.

Results 

In practice, the pattern may be more continuous than an absolute – it shows a temporal gradient. The more recent the memory, the poorer it is remembered rather than it being all or nothing.

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Example: PZ – they have a progression in how clear their memory is starting in 1930 at most clear, and decreasing slowly until 196p when it drops down to very low by 1970. There is this progressive gradient drop

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Memory for semantic facts learned before the illness may be largely spared – we look at this next class.

Anterograde Component: o

Features:

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Much more severely impaired

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Knowledge and personal history are effectively frozen in time

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Patients may be unable to recall event from 5 minutes beforehand

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Example HM: He cannot recall what he just said before – its like being in a dream. Worries he’s said the wrong thing but cannot recall

Tests Episodic: 

Free recall 

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Recognition 

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Present list of words and a...