Lecture 18: Short-Term Memory Flashcards
Flow diagram for Atkinson and Shiffrin
Short-term memory
- Some people think of short term memory as our conscious access to the world. We feel that if we didn’t have this short term memory, we couldn’t access information in our world.
Atkinson and Shiffrin (1968)
First we have the input of our environment (visual, tactile auditory), when our receptors receive the information and transform into neural responses then it goes into our sensory memory. In order to get our information from the sensory memory to the short-term memory, we need to pay attention to the info that comes into your sensory world. To get our information from short term memory to long term memory, we need to rehearse to try to keep this information long enough and strong enough so that it can be transferred to our long term memory. When we are retrieving information, we need it to get back to our short term memory and then it can become an output.
• Three different types of memory:
1. Sensory Memory – Initial stage that holds all incoming information for seconds or fractions of a second (information will not stay long in our sensory memory).
2. Short-term Memory – Holds 7 +/- 2 items for about 15 to 20 seconds (George Miller). Brief period of time.
3. Long-term Memory – Can hold a large amount of information for years or even decades
• Control processes: active processes that can be controlled by the person (you can decide to use these strategies to make sure that the information we go to the long term memory)
• Rehearsal
• Strategies used to make a stimulus more memorable
• Strategies of attention that help you focus on specific stimuli
• The information that is really well consolidated no longer requires anymore the hippocampus then it was distributed across the cortex. If it is not consolidated properly, you might lose it.
Short term memory
• Capacity and duration
• Stores small amounts of information for a brief duration
• Includes both new information received from the sensory stores and information recalled from long-term memory
• Depends on the complexity of the information. Simpler information is easier to memorize
• Chunking: small units can be combined into larger meaningful units
• Chunk is a collection of elements strongly associated with one another but weakly associated with elements in other chunks
• We take all the items that we receive as inputs and then we group them in meaningful units. Ex: give 8 items, asked to recall them (difficult), then say ”recall all the vegetables that were said”, all of a sudden you will be able to remember more than just the vegetables because your brain grouped some items together in semantic groups. With a queue given (group vegetable)…allows u to retrieve.
• Proactive interference: occurs when information learned previously interferes with learning new information.
• Example: Your native language may make it more difficult to learn and remember a new foreign language
• Retroactive interference: occurs when new learning interferes with remembering old learning
• Example: After you get a new telephone number and use it for a while, you may have difficulty remembering your old phone number
This can affect our capacity and duration of short term memory and how we will recall information.
Working memory - Baddeley and Hitch Model
Baddeley and Hitch (1974)
Phonological loop = where verbal and auditory information are held into our memory
Visual spatial sketchpad = where visual and spatial information are held into our mind.
The central executive is how we are able to manage and process/manipulate information to do complex tasks: comprehension, learning, reasoning.
Working memory(WM):
• Similar concept to short-term memory (STM)
• limited capacity system for temporary storage and manipulation of information for complex tasks such as comprehension, learning, and reasoning
Working memory differs from STM
• STM holds information for a brief period of time
• WM is concerned with the processing and manipulation of information that occurs during complex cognition – DYNAMIC PROCESS
Sometimes in studies, they will refer to STM but it reality they will be talking about working memory.
**when referring to short term memory, she is referring to the static form of holding a formation in our mind. When talking about working memory, referring to the system associated with manipulation during complex cognition so during dynamic process.
Ex: Given a random sequence of 7 digits to recall. (Ex of STM)
Vs
Ask to give a random sequence of 7 digits with none of the digits repeating. Sp what you are doing is giving the first digit then keeping it in mind, then the second and keeping the first two in mind… (ex of WM)
What are the modifications made to the working memory model?
Episodic Buffer
- An episodic buffer has been added (next to the phonological loop and visuospatial sketch pad) and works with the central executive
- The episodic buffer is used to try to explain how we are able to use our working memory to do task that are very complex and that we cannot explain only by the phonological loop and the Visio-spatial Sketch-Pad.
- The episodic buffers ability is associated with our attentional system and inter individual capacity.
- We do not all have the same type of working memory, the same duration, the same capacity, strategies…
- We think that the episodic buffer is in the parietal lobe (the parietal lobe is really associated with attentional mechanisms)
- Perceptual processing will come from the phonological loop, and is also first processed by the occipital lobe when it is in the visual-spatial sketch-pad.
Prefrontal cortex
- it is essential to executive processes
- this is where the central executive is in place.
- the one that controls all of this information/modulates it
Anterior Cingulate Cortex (ACC)
- with the parietal lobe, is able to control the information with attentional abilities
Working memory, is all of that together with the dynamic monitoring and manipulation. You have to monitor the information that has been given in order to give you information. You need to manipulate some of the information to create something new, to know what you need to do next. Working memory is the reason we are able think, everything we have learned.
It is rare to have lesions to abolish working memory, if this happens it means it is a big damage to the brain and that the patient is no longer conscious of the world.
REMEMBER THIS FIGURE
Lesions to the prefrontal cortex. Task that studied monkeys with lesions to the prefrontal cortex (Delayed Response Task)
Jacobsen, 1936
Procedure
• Tested monkeys with lesions within and around the sulcus principalis, on a Delayed Response Task
• Monkey sees two empty wells; One is baited with a reward (animal sees this) and both wells are covered with identical plaques. The animal observed this, so he knew which well the reward was in.
• The screen is lowered, and there is a delay (<30sec)
• Screen raised test to see if monkey remembers where
reward was
• Alternate reward between 2 wells
They did this task thinking that they were testing memory in general .
The monkeys had lesions within and around the sulcus principalis —> separates the areas that are associated with area 46. Lesions to area 46 in general. Monkeys with lesions there made more mistakes with this task then monkeys that did not have lesions .
What are the results to Jacobsen’s experiment (lesion to the prefrontal cortex)?
Results
• Monkeys with bilateral lesions to area 46 could not perform this task!
Interpretation
• Amnesia problem? It is associated with long-term memory.
Arguments against this hypothesis
• Frontal patients (damage to lateral frontal cortex) do not show amnesia (they can consolidate new information, they have long-term memory).
• Patients could remember lists of words or faces. No problem with consolidation (patient K.M. was contrasted against patient H.M. in the Milner reading).
• Monkeys with the same sulcus principalis lesions can distinguish novel from familiar stimuli in the DNMS task, unlike medial temporal lobe lesion monkeys.
So what’s happening? Why do monkeys with that sort of lesion cannot perform a task??
- The reason is that during the delay, the monkey is not able to keep the information in his mind. It is not about consolidating the information in his long term memory. It is about keeping the information in mind as the delay was just a few seconds and then being able to keep the information long enough for when the screen is no longer there they are able to go and localize the information.
Note in picture below: that area 46 in older maps covered the entire sulcus principalis. Area 9/46 is a more recent terminology of Petrides and Pandya (1994)
Task done by Goldman_Rakic
Cell recordings in the prefrontal cortex
Dr. Patricia Goldman-Rakic (1980’s)
Procedure
• Recorded from neurons in PFC (specifically area 46) during this task.
There was a cue, then a delay , then a response.
- The cue referred to the action needed by the monkey.
- The delay is the period of time where the info is held into memory.
- The information that is held in the delay is used in order for the monkey to respond. During this delay, while we are recording neurons from the prefrontal cortex, what we are seeing is activation of these neurons (firing). The neurons are super active during the delay (lots of AP), what they are doing is holding the information.
Results
• Discovered that neurons were firing specifically during the delay of the task.
• Could extend the delay and the neurons would fire until delay ended. As long as the delay is on, the formation is still in your memory/ still accessed, this neurons will still fire.
• Different neurons would fire depending on which well was baited. Specific neurons will fire if it is the right well that has the reward and different neurons will fire if it is the left well.
Conclusion
• These neurons are the neurophysiological signature of spatial working memory. The neurons are “holding the information online” until they have to make a choice. After they make the choice, no longer activity.
• Neurons in the pre frontal cortex are not just associated into general memory,long-term memory, amnesia. It is associated with spatial working memory
Cell recordings in the prefrontal cortex
Funahashi et al. (1989)
Monkeys fixated a cross in the middle of the screen and then the cue was presented in one of the 4 positions. Then cue goes off and monkey had to move his eyes to where the last cue was.
• Single cell recordings from monkey’s prefrontal cortex during a delay-response task.
• Neurons responded when stimulus was flashed in a particular location and during delay, fired when the cue was shown.
• Information remains available via these neurons for as long as they continue firing. After the response activity stops.
Working memory and the pre frontal cortex
• Monkeys without a prefrontal cortex have difficulty holding information in working memory. Not impossible just harder
• Area 46 is important for monitoring/tracking information within working memory.
• Dysfunction in specific WM processes can explain many of the behaviors and
impairments of frontal patients!
• Regular digit sequence test – “remember the sequence 4 5 1 8 9 2 7” vs “list numbers between 1 and 7 randomly and only once”
• Frontal patients can do the first task – this is just regular static STM
• Problems with the second task – monitoring and tracking information within working memory - placing a mental “checkmark” on the numbers they have said to avoid renaming them.
• Frontal patients will have lots of dysfunction associated with executive processes and higher order cognitive impairments. Working memory is also associated with attention, you need attention to hold information.
The self-ordered pointing task
Milner and Petrides
Interested in the working memory and how we maintain and track it.
Procedure
• Similar to a mental “to-do” list
• This test involves monitoring of information within working memory.
• We have to monitor our previous responses in order to give the next responses.
They had multiple images in card 1 and they had to point randomly at a couple images. In card 2, they had to point to the images that they did not point to in card 1.
Verbal and nonverbal material (you can do this task using verbal and non verbal)
• Concrete words
• Abstract words
• Representational drawings
• Abstract designs
What brain activity is associated with the self-ordered pointing task?
• “The epoptic process (monitoring) refers to the tracking of the relative status of stimuli/events in working memory” (Petrides, 2013).
• Seems to involve specifically the mid-dorsolateral PFC: areas 9/46 and 46
• Specific lesions to this area in monkeys (Petrides, 1991) means cannot perform tasks that require self-ordering (i.e. tasks of monitoring)
• PET/fMRI studies with self-ordered pointing in healthy humans →activity in mid-DLPFC (Petrides, 1993).
• Not as clear-cut in terms of laterality effects. If they use words or languages they saw activation manly in the left part and also the right (it was not very clear).
The serial order task
This task also requires working memory
Procedure
• Subject is presented with 4 trial- unique (non-repeating) abstract stimuli. They used abstract stimuli because they didn’t want people to activate all the semantic part in the brain (keep it as objective as possible to localize the regions associated with morning memory.
• In the test phase, among two stimuli (Which of the two were presented first), subject needs to select the stimulus which was presented earlier in the sequence
• Control task just a basic recognition memory task. Control task is used to eliminate all the other variables and only keep working memory.
• Recruits mid-DLPFC
What are we looking at visual activation, motor activation, memory and formation (what kind of memory?- working memory, recognition). In order to remove all the other areas we don’t want to be looking at we can do a control task.
Patients with lesions to the mid-dorsolateral prefrontal cortex
• No difficulty with static short- term memory tasks
(can reproduce fixed digit sequences normally – “repeat after me: 215436 87”)
• BUT cannot monitoring/track information properly (“list numbers between 1-8 randomly and only once”), including perform poorly on the self-ordered pointing task or serial order task.
• It is not only the DLPFC that is important for the process of recalling information, it is also the VLPFC that is specific to the retrieval of information.
This is why it is important to develop models for your tasks and know what you are trying to assess.
Retrieving information
Retrieving information is crucial. If we do not retrieve the information is it useful to just keep in our brain and not have access to it?
Retrieval: process of transferring information from LTM back into working memory (consciousness)
• Most of our failures of memory are failures to retrieve
Cued-recall: cue presented to aid recall
• Increased performance over free-recall
• Retrieval cues most effective when created by the person who uses them
• Making links, making semantic associations is very important when you learn. When there is more connections, things get more solidified, they get stronger.
Active selective memory retrieval: when we ask someone to make an active effort full memory retrieval, it does not just pop up into their mind. They have to retrieve the information by themselves..
• Mid-ventrolateral PFC, areas 45 and 47/12, involved in active effortful memory retrieval.
• These areas are not involved in regular memory recall (that is automatic, bottom-up, often stimulus driven*)
• They are involved in a top-down control of retrieval, higher order control retrieval (need to actively remember a specific trace when lots of interference is present). “We decide that we need to retrieve the information”
• Active selective memory retrieval is initiated under conscious effort and guided by the subject’s goals/plans.
• “Active retrieval is required when stimuli in memory do not bear stable relations to each other and therefore retrieval cannot be automatically driven by strong, stable, and unambiguous stimulus or context relations” (Petrides, 2002).
• Area 45 has diffuse connections, especially to the parietal lobe and lateral temporal lobe (From the frontal lobe to these two lobes).
What task can we use to test active selective memory retrieval?
Procedure
In this task there are two types of conditions: the experimental condition and the control condition.
Experimental condition: fixate cross and then there was a period of encoding information. The person needed to remember the face that was presented and the position of the face (two types of information are encoded here). Then there is a delay (the information is no longer present) and then there is the question part. The question part is where they had this image appear either a yellow circle or blue diamond (so now they has two types of information). They only had to remember the face. When the question stimuli was present they had to say if the face shown was in the same position as the first face shown.
• Subjects shown a face (all verbalizable features removed) in a particular location on a screen
• Subject is given a cue: has to either recall the specific face regardless of the location (visual non-spatial) OR the location regardless of the face (visual spatial)
• Control task is simple passive recognition memory of the correct face in the correct location versus a novel stimulus
• Subject trains before getting into the scanner and then in the scanner performs dozens of trials…
The only difference between the 2 experimental trials is the retrieval part. Everything else is the same.They were able to contrast these two types of trials and go specifically look at the region that was activated during the difference between these two types of trial. They also had a control condition where the person just had to recognize if the face was presented at the same spot as the initial one. But the face was always in the adequate position = they didn’t play with the two variables at once.
What were the results of the active selective memory retrieval task?
• After performing so many trials, you have seen all possible combinations many times
• During testing, have to choose correct response by actively retrieving the particular trace and inhibiting traces of other trials
• fMRI data showed right mid-VLPFC activated the most during retrieval phase
• Kostopoulos and Petrides, 2008 did the same task but with verbal material→left mid-VLPFC most activated during retrieval phase (i.e. some laterality effects). Shown the laterality affect!
How can we improve learning and memory
• Which results in a stronger memory trace?
• Re-reading the material
• Being tested on the material
• Roediger and Karpicke (2006) had participants read a passage and then either
• Reread the passage (rereading group)
• Take a recall test (testing group)
• Then tested recall after a delay; testing
group performed better
• Testing Effect
