Introduction:
It is largely held that false memories from DRM lists
are created because of retrieval error rather than encoding error. The experimenters used two event-related
brain potential (ERP) experiments. These are potentials that are recorded at
the scalp and are recorded. They are generally sensitive to encoding processes.
They can show the difference between words that are remembered and words that
are not. The measure of an ERP is called a DM (difference due to subsequent
memory).
Method:
There were two experiments performed. Twenty DRM
lists were presented in the first experiment and after every fifth list a two
minute pencil and paper free recall was performed. Once all the lists had been
viewed, the experimenters gave a 200 word forced choice old/new test with
remember/know judgments. Experiment one participants had 14 electrodes attached
to their scalp.
In experiment two, 40 DRM lists were used. Twenty of
the lists came from experiments conducted by D. Payne. After each list was
presented, the participants had to conduct a 45s letter string matching task.
Immediately following that task, participants then took a 10 word test over the
list they just saw. Twenty-six
electrodes were used in experiment 2.
The experimenters looked at 2,048-ms recordings that
started 500ms before the onset of each studied word. The ERP and response were
only analyzed for participants with memory illusion rates between 10% and 90%.
Results:
Hit rates for studied words were fairly high (.80 in
exp. 1 and .91 in exp. 2) and false alarms were low (.10 for exp. 1 and .02 for
exp. 2). Experiment one had a higher memory illusion rate (.56) than experiment
2 (.47). ERPs were higher for words that did not lead to memory illusions that
the words that did cause a memory illusion (fig. 1 p. 20). This effect is
referred to as a DIM (difference in subsequent illusory memory). This effect
occurred approximately 400ms after the word was presented in experiment 1 and
even earlier in exp. 2. The times measured were split off into four categories:
P2 (100-300ms), N4 (300-500ms), Late Positive Complex (LPC; 500-800), and slow
wave (SW; 800-1,300). To equalize the differences
in memory illusion eliciting power of the DRM lists, the experimenters
subtracted the average ERP recorded by each word when it was studied as part of
a DRM list that induced a later memory illusion from the average ERP elicited
by the same word when it was studied as part of a list that did not induce a
later memory illusion. For both experiments, the midline electrodes showed that
ERPs for LPC and SW windows were reliably more positive. In experiment one, the
effect was more near the frontal lobe, while in experiment 2 the effect was
located more in the posterior. The
within-word DIM effect was positive at the posterior electrodes in experiment 2
and negative in the prefrontal electrode. In experiment 1, the only reliable
effect was an interaction between word type and electrode location in the
frontal plane during the P2 window.
Discussion:
The current study shows that some of the processing
leading to subsequent memory illusions occurred 500-1,300 ms after the
experience began. The DIM was found to be a precursor of memory illusions that
is observed while the encoding process is carried out. The DIM being positive could also reflect
encoding specific features of the studied words. This encoding would improve
the participants’ ability to discriminate between actually studied words and critical
lures. The DIM effect shows that encoding process do
play an important part of verbal memory illusions.
Important Legal
Disclaimer: The preceding are articles we read together in the Lampinen Lab Fall 2005 false memory reading group. By
clicking on the button next to the article you can see the summary of that
article. The summary was prepared by the student presenting that article and it
is of course the case that the views expressed in the summary do not
necessarily represent the views of the reading group as a whole, Dr. Lampinen, the Lampinen Lab,
Hugo's, the University of Arkansas, the Razorback Football or Basketball teams
(although we're not sure about cross country), people living down the street
from us, Bob Dylan, Jack Fate, our extended families, or anyone else for that
matter except for the student who wrote the summary (and they don't necessarily
believe what they wrote either).