Topic 4: Long-Term Memory Flashcards
What are the experimental challenges to studying long term memory?
early work geared towards better understanding long-term memory using imaging highlights some of the more general challenges associated with these methods, on both the design and analysis front
one obstacle relates to the constraints imposed by block designs typical of the time
What was the methodology of block design experiments like the Petersen et al. (1988) study?
Petersen et al. (1988) compared activation during word blocks with fixation blocks (i.e. used subtractive logic)
methodological note: not clear what (exactly) participants were doing during the fixation block, as well as the fact that they may have encoded things during those blocks
What is the approach to studying LTM using a comparison study?
compares neural activation during the presentation of novel stimuli with the same during familiar stimuli
this approach is based on the assumption that the inherently novelty would, on average, result in more robust encoding mechanisms being automatically recruited
“if we can’t devise a condition when it (encoding) is not active, perhaps we can at least devise one when it is less active”
note that this isn’t about recollection but encoding, and in fact you make rather different predictions if you were focused on testing a hypothesis related to recollection
What is the comparison study by Tulving et al. (1994)?
showed participants a set of photos on day 1, then brought them back for a follow-up session on another day (day 2)
two kinds of photos were presented on day 2: an “old” condition (involving photos that were shown on day 1), as well as a “new” condition (involving photos that were not shown on day 1)
it was predicted that more encoding would take place while viewing new stimuli, as compared to old, which would be reflected in differences in neural activation
they found greater hippocampus and parahippocampal activation during the presentation of “new” stimuli, as compared to “old”
What is the comparison study by Stern et al. (1996)?
another approach involves manipulating the amount of information participants need to encode (rather than manipulating when people are encoding)
showed 40 novel images with instructions to encode them for a later test
compared activation in a “one-item” condition in which only a single image is presented on each trial, to that in a “many-items” condition in which several images are presented on each trial (with the trial duration being held constant across conditions)
found greater activation in the “many-item” condition, as compared to the “one-item” condition, within several regions (including posterior hippocampus, parahippocampal gyrus, and fusiform gyri)
methodological note: could boredom be a confound in this design
What is incidental encoding?
is said to occur when encoding proceeds automatically, or without specific intention (e.g. have you ever read something that ruined a game, show, movie, etc. that you wanted to watch later?)
the vast majority of what we encode probably falls under this category
What does contextual reinstatement involve?
first activating knowledge about more general properties
then using that general knowledge to focus your memory search
related to the idea of mental time travel
What were the methods in the Polyn et al. (2005)?
- study phase: view 90 stimuli from 3 categories (famous people, famous locations, common household objects) while making various judgments, relied on incidental encoding meaning that participants did not know there would be a subsequent memory test
- training phase: a neural network pattern classifier was trained to distinguish between the distributed pattern of neural activity associated with each stimuli (in typical PDP fashion)
- free recall phase: during the (surprise) memory test, participants were instructed to recall as many items as possible while the pattern classifier attempted to “guess” what category an item being recalled belonged to
What were the results in the Polyn et al. (2005)?
their pattern classifier was able to successfully interpret which of three categories items that were being recalled belonged to
groups of items from a particular category were recalled in tightly packaged groups, or clusters
demonstrates contextual reinstatement
these clusters were presumed to underlie various kinds of shifts in brain state and suggest these kinds of large-scale fluctuations are important for facilitating retrieval
How can ERPs used to study incidental encoding?
- present a series of stimuli, one at a time
- average ERP’s time-locked to stimulus onset
- test memory of participants for stimuli
- compare ERP’s recorded during initial stimulus presentation, as a function of subsequent memory performance
What else can the paradigm used to study incidental encoding using ERPs be used for?
can also use the same general paradigm to measure changes in electrical activity related to both “remember” and “know” judgments (as well as “missed” or forgotten items)
note the advantage of having higher temporal resolution (with EEG) here
what could account for the differences across remember and know judgments? –> perhaps differences in which brain structures are involved in each kind of encoding, timing, etc.
What are “remember” judgments?
used for items associated with episodic memories and/or contextual details (i.e., “with context”)
What are “know” judgments?
used for items associated with semantic memory and/or a sense of familiarity but not necessarily any associated context (i.e., “without context”)
What were the methods of the Ranganath et al. (2005)?
- presented line drawings of novel 3D shapes for 7-13 seconds, followed by memory probe (that was the same as the sample on 50% of the trials)
- conducted a surprise memory test (i.e., incidental encoding)
- sorted the fMRI data as a function of performance on the memory test
What were the results of the Ranganath et al. (2005)?
found that activation in the left dorsolateral PFC and left hippocampus shortly after stimulus presentation predicted performance
objects presented during the memory test that were correctly responded to were associated with greater activation in those areas during initial processing
What is the role of functional connectivity analyses in the Ranganath et al. (2005)?
refers to two or more regions whose activity is correlated (implying that they are “talking” to each other)
general logic: given that trial-by-trial fluctuations in the activity of particular regions was predictive of memory performance, are there areas for which functional connectivity with the hippocampus predicted better performance?
found that more successful encoding (as indexed by behavior) was associated with greater function connectivity between the hippocampus and many other MTL regions
What are the possible confounds in fMRI studies involving LTM?
Wagner et al. (1998): left hemisphere activation (potential confound: related to verbal processing?)
Brewer et al. (1998): responses associated with higher confidence involved bilateral parahippocampal gyrus activation and right dorsolateral PFC (potential confound: related to visual processing?)
both of these results likely speak to the role that verbal and visual processing play in supporting encoding
highlights the difficulty in isolating signals related to a singular dimension of what may tend to be a multidimensional process
Why do studies find inconsistent evidence for hippocampal activation in LTM?
methodological confounds that don’t reflect it’s true activity level (e.g., subtractive logic may “wash out” contributions that happen throughout the entire experimental session)
limited neural resources: we can’t encode everything and things that we find more compelling, exciting, etc. may compete for those resources, leaving relatively little for whatever may be the intended target of encoding
hippocampal contributions to other kinds of processing (e.g., spatial navigation)
What was the method of the Maguire, Woolett, and Spiers (2006) study of the hippocampus in spatial cognition?
compared a group of London taxi drivers with a group of London bus drivers
provide a well-matched comparison (socioeconomic status, nature of work, various perceptual and physiological factors relating to driving, etc.)
the key difference is the requirement for taxi drivers to be able to flexibly navigating a complicated environment (which bus drivers don’t have to worry about, given the way bus routes work)
What were the results of the Maguire, Woolett, and Spiers (2006) study of the hippocampus in spatial cognition?
found that the taxi drivers had more gray matter in mid-posterior hippocampus and less in anterior hippocampus, as compared to the bus drivers
What is noetic memory?
knowing or self-knowing
i.e., similar to the “modern” category of declarative/explicit memory
What are the two general forms of noetic memory?
with context (can be broadly related to recollection, or episodic memory), associated with the idea off mental time travel
without context (can be broadly related to recognition/familiarity, or semantic memory)
What is anoetic memory?
not knowing
i.e., similar to the “modern” category of non-declarative/implicit memory
e.g., effects related to procedural memory, conditioning, priming, etc.
What is a prominent dual-process model in memory?
within the domain of memory, familiarity and recollection and often considered a relevant dual-process model
free recall is thought to depend on recollection
recognition can be supported by familiarity
What is recollection?
involved with the retrieval of various association involving qualitative information
a relatively slow process
an all or nothing process
closely associated with hippocampal processing
What is familiarity?
involved with a quantitive memory signal that gauges how likely it is that stimuli had been previously encountered
rapid and relatively automatic
something that varies along a continuum (not “all or nothing”, a quantitive signal)
supported by various neocortical regions of the MTL (including the perirhinal cortex)
What are the steps in the familiarity and recollection dual process model?
- you might recognize someone from a movie who looks familiar, without having made any effort to attend to or identify them (familiarity signal kicks in)
- associations with the person may start coming back to you (places, times, etc.) even before you can identify who they are and/or being trying to do so
- more controlled effort focusses your attention on memories related to those associations, beginning a more deliberate attempt to identify them (recognition processing kicks in)
- if successful, those recognition processes will match your perception of the person to something in memory, and lead you to interpret/impose some meaning on the stimuli
What is semantic memory?
memories for facts whose retrieval is not accompanied by information pertaining to how, when, or where that information was acquire - its retrieval is noetic
What is mental lexicon?
refers to our knowledge of word meaning
What did the HM case study show about semantic memory?
HM didn’t show semantic deficits after removal of his hippocampus
early evidence that semantic is a distinct memory system from episodic
also suggested an intact MTL system is not necessary for retrieving semantic representations
What is semanticization?
refers to the gradual shift in the nature of memories from episodic to semantic
most theories propose that semantic knowledge is initially encoded in an episodic form, which may then “lose” it’s episodic content over time
What is spreading activation?
we understand that semantic knowledge involves meaning, and is organized relationally
this is demonstrated by spreading activation: think about one experience at your elementary school and you may spontaneously start thinking about others without intending to
What is the cognitive model of semantic memory?
we could also relate spreading activation back to the idea of memories being retrieved in distinct “clusters”
What are some examples of case studies that demonstrate category-specific deficits?
Warrington and McCarthy (1983) suggested that brain damage can result in a selective impairment related to animacy (i.e., living things vs. objects)
patient VER had a left hemisphere stroke, demonstrated severe linguistic impairments, and showed relative impairments in identifying various non-living things
4 patients with herpes encephalitis showed relative impairments in identifying living things
What conclusions can be drawn from the case studies that demonstrate category-specific deficits?
the pattern of results for these case studies represent a double dissociation for living and non-living things
led to various theories that propose knowledge is represented in taxonomic categories
one example is the domain-specific knowledge hypothesis
What is an explanation for knowledge being represented according to taxonomic categories?
evolutionary pressures have resulted in specialized mechanisms for perceptually and conceptually distinguishing animate and inanimate kinds… leading to a categorical organization of this knowledge in the brain
What was the idea proposed by Warrington and Shallice (1984) regarding perception and action?
suggested the case studies may be more accurately described as involving a distinction related to action and perception
according to this view identifying living things primarily involves vision, while identifying non-living things tend to rely on our knowledge of how we use those objects
What is a modality-specific knowledge hypothesis?
it suggests a key organizational factor in the use of semantic information is the “functional modality”
can use motor images to represent action and imagine
one line of supporting evidence comes from self-reported ratings indicating what properties participants feel they rely on to identify various kinds of objects
What were the results of the PET study by Martin et al. (1996)?
contrasted brain activity during the silent naming of animals and tools
animal naming was associated with greater activation in visual cortex (due to a role in processing low-level visual features)
tool naming was associated with greater activation in areas related to action generation: posterior middle temporal gyrus (due to a role in processing motion) and premotor cortex (due to a role in processing movement, and/or mirror neuron activity)
What is the category-specific model proposed by Caramazza and Shelton (1998)?
suggested distinctions between animals vs. fruits/veggies vs. artifacts (e.g., tools)
What are some drawbacks of these category specific models?
they represent a significant departure from everything else we know about brain organization, according to which subsystems are delineated by function or modality but not by semantic content
these models are entirely post-hoc and there doesn’t seem to be any obvious way to test them
there is difficulty in generating generalizable and meaningful principles on the basis of case studies
What are repetition suppression effects?
can sometimes be observed in fMRI data, in which the BOLD response gradually declines with the repeated presentation of stimuli that have some kind of commonality (e.g., the same color, shape, from the same conceptual/semantic category)
although somewhat distinct in terms of the neurological mechanisms involved, this is conceptually similar to desensitization and habituation
What are fMRI adaptation paradigms?
can be used to attempt to determine what properties a given brain region responds to, based on the presence (or absence) of these effects
What was the repetition suppression study by Grill-Spector et al. (2006)?
used repetition suppression effects to make inferences about what parts of the brain are sensitive to higher-level meaning (e.g., conceptual category), as compared to low level stimulus properties (e.g. color)
in other words, they were looking for parts of the brain that recognized (“treated”) pictures of things from categories of stuff that were previously presented as belonging to that same category
What were the two phases in the repetition suppression study by Grill-Spector et al. (2006)?
study phase: 32 items were shown, all of which were also presented again during the test phase, referred to as “same” items
test phase: three types of stimuli presented, described on the next slide
What was the test phase in the repetition suppression study by Grill-Spector et al. (2006)?
some items were the same: pictures that were shown during the study phase
some items were slightly different: exemplars from the same category as something that was shown in the study phase
some items were completely novel: pictures that were unrelated to anything shown during the study phase
What was found in three regions of the brain in the repetition suppression study by Grill-Spector et al. (2006)?
suppression for same items
release from suppression for the different and novel items
interpreted as indicating they were sensitive/responding to low-level visual features of stimuli (e.g., shape, lighting, etc.)
What was found in the left fusiform gyrus in the repetition suppression study by Grill-Spector et al. (2006)?
suppression for same items
release from suppression for novel items
a partial release from suppression for the different items
interpreted as indicating that region’s role in recognizing the conceptual similarity (somewhat independent of low-level visual features)
may implicate a role for that region in a modality-independent form of semantic representations
What were the general results of the repetition suppression study by Grill-Spector et al. (2006)?
all regions showed repetition suppression for same items, and release from suppression for novel items
critically, the left fusiform gyrus was the only region that showed any evidence for continued repetition suppression for different items, which was take as evidence this region is sensitive to concepts
