- Episodic memories differ from semantic memories by containing circumstantial info (who, what, when, where, etc.) Remembering episodic memories is generally more complex than recalling semantic memories, involving the evaluation of cued memories based upon the current goal.
- According to source monitoring framework (SMF), episodic memory retrieval can be either
- heuristic: fast and effortless
- systematic: more deliberate, controlled, based on specific features
- Retrieval and evaluation prcesses are mediated by the prefrontal cortex (PFC) (Shallice et al., 1994)
- Nolde, Johnson, and Raye (1998)
- Found dual-hemisphere PFC activity more likely in difficult (systematic) memory tasks
- Example: old/new recognition judgements with successively presented items
- Found right hemisphere PFC only activity in easier (heuristic) memory tasks
- Example: two-item forced choice
- Cortical asymmetry of reflective activity (CARA) hypothesis
- Heuristic processing more likely to be found in right PFC only
- Systematic processing more likely to be found in both PFC hemispheres
- Other experiments have found greater left PFC involvement in source monitoring tasks than in old/new tasks
Experiments
1A, 1B, 1C:
- Letter designations seem to indicate different fMRI scanning methods used
- All participants saw pictures, words, and heard other words at study.
- Three conditions:
- O: Old/new blocks – respond “yes” to old items regardless of presentation during study
- P: Picture blocks – respond ‘yes’ to any items presented as pictures during study
- PH: Picture/heard blocks – ‘yes’ to any pictures or heard words
- Hypothesis: Expected greatest left or bilateral PFC activation in the PH condition and least in the O condition
- 180 words, 45 assigned to each of the three sources, 45 served as new items on the test list
- After 45 min. interval, participants were placed in a scanner for the memory test
Results and
Discussion:
- In experiments 1a, 1b, and 1c, found increased left PFC activity with increasing reflective demands (i.e. more demand for specific feature memory)
- Increased right PFC activity in 1c.
- Didn’t find any cases of increased activity solely in right PFC.
- Also found in 1A and 1C activation in the anterior cingulated cortex.
- Greater ACC activation in experiments 1A and 1C in PH condition.
- Results indicate while PFC is responsible for task control, the ACC may respond to competition or conflict b/t tasks.
Experiment
2:
-Sought to vary the reflective complexity of the memory task by comparing two-alternative forced choice recognition and new/old recognition
- Forced choice: Two items presented at a time. Participant says which is old and which is new. (simple)
- New/old recognition: One item at a time. Participant indicates old/new. (complex)
- Textures and words used for study items
- Based on previous research, using textures and words as opposed to other items allows the experimenters to check whether left PFC activity relates only to general task complexity, or to the the subject matter of a task.
Method:
- Two 144 item study lists – 72 textures and 72 abstract words
- Procedure virtually identical to Experiment 1
Results and
Discussion
- Participants did significantly worse on the successive item test than the forced choice.
- Forced-choice condition, the textures > words contrast showed right PFC activity, whereas the W>T contrast showed left PFC activity.
- Experiments 1A, 1B, 1C showed that increased demands to consider more specific features of memory resulted in increased left PFC activity
- Experiment 2 resulted in increased dorsal and ventral PFC activation, indicating that those areas may help bridge the gap across successive trials.
- E2 also found strongly lateralized PFC utilization depending on item type (right for textures vs. left for words).
- Conclude that there are some modality effects (i.e. pictures vs. words) that determine how hemispheres are utilized, as well as some effects based on how much processing a task requires.
- When viewed with data from other experiments, increased left PFC activity might not reflect the actual amount of data retrieved, but rather it is more likely to reflect processes involved in biasing or evaluating retrieved information.
- ACC seems to be involved in modulating/initiating reflective activity, as well as detecting conflicts between memory representations and tasks.
- Processes used
in going from forced-choice to successive recognition are probably not
the same as those that go from recognition to source identification. That
explains why there were different areas of activity in experiment 1 vs.
experiment 2.
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