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
