The Impersistence of
Running head: FALSE MEMORY IMPERSISTENCE
The Impersistence of False Memory Persistence
James M. Lampinen and Rachel M. Schwartz
University of Arkansas
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Abstract
When subjects study lists of thematically related words they sometimes falsely recognize
non-presented words related to the theme. The gist extraction account of these findings
provided by Fuzzy Trace Theory suggests that false recognition should decline
substantially more slowly than true recognition across a delay. Participants listened to six
lists of words with each being related to a non-presented critical lure. Participants then
took a recognition memory test immediately or after a 48-hour delay. Contrary to Fuzzy
Trace Theory corrected recognition of targets and critical lures decreased by equivalent
amounts across the 48-hour delay. Results are discussed in terms of their implications for
Fuzzy Trace and Source Monitoring accounts of false memories.
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The Impersistence of False Memory Persistence
A false memory is a memory for an event that never occurred and therefore
involves the creation of a psychological reality that is distinct from historical reality.
Recently, Roediger and McDermott (1995) have revived a paradigm introduced by Deese
(1959) that can be used to create compelling false memories for words (hereafter the
DRM paradigm). Subjects are presented with lists of words (e.g. bed, slumber, doze and
so on) that are all related to a non-presented critical lure (e.g. sleep). On later tests
subjects claim to remember the critical lure as having been presented with surprisingly
high levels of subjective confidence (Lampinen, Neuschatz & Payne, 1998; Payne,
Neuschatz, Lampinen & Lynn, 1997 for reviews).
One account of these results is the gist extraction account of Fuzzy Trace Theory
(Reyna & Brainerd, 1995). Fuzzy Trace Theory's core assumption is that in a wide
variety of tasks people tend to encode multiple representations in parallel and that these
representations vary in terms of their level of precision. Memory traces that represent
item level information including surface features of items are verbatim representations.
Memory traces that represent general senses and meanings including relational
information are gist traces.
An important assumption of the theory is that false recognition in many
paradigms (including the DRM paradigm) is produced when subjects base their
recognition memory judgment on gist representations (Brainerd, Reyna & Mojardin,
1999). The theory also assumes that verbatim traces decay more rapidly than gist traces
(Brainerd, Reyna, & Brandse, 1995). Combining these assumptions leads to the
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prediction that false memories will be forgotten more slowly than true memories (i.e. the
false memory persistence effect).
Payne, Elie, Blackwell, and Neuschatz (1996) provided evidence that false
recognition produced in the DRM paradigm sometimes does decline more slowly than
accurate recognition. Payne et al. presented subjects with lists of thematically related
words. After each list each subject sometimes attempted to recall the list and sometimes
did math problems before the next list was presented. Shortly after the final list was
presented or 24 hours after the final list was presented subjects took a recognition test.
Consistent with the gist extraction account there was a substantial decrease in recognition
of presented items across the delay but no significant decrease in the recognition of
critical lures.
An alternative account of false memories in the DRM paradigm focuses on the
possibility that the critical lure might sometimes be spontaneously generated by subjects
as an implicit associative response (IAR) while processing list items at acquisition
(Underwood, 1965). This account has been called the "source monitoring" account by
McDermott and Roediger (1998) and is based on the well established finding that
internally generated information is sometimes confused with externally presented
information (Johnson, 1997). It is important to note that Brainerd, et al. (1999) have
recently argued that if false memories were created in this manner they would be
verbatim based but they have also argued that current evidence does not support the
existence of such verbatim false memories.
It is important to note that Fuzzy Trace Theory's prediction of false memory
persistence is contingent upon false memories being produced by gist traces. For
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instance, Brainerd, et al. (1995, Experiment 3) found that false alarms that sounded like
targets did not produce the false memory persistence effect whereas false alarms that
were semantically related to targets did (Experiments 1 and 2). If false memories in the
DRM paradigm are sometimes verbatim based then it should be possible to establish
circumstances in which forgetting of false memories is equivalent to forgetting of true
memories. Payne et al. (1996) used a relatively fast presentation rate (one word per
second) and subjects were aware that after every list there was a good chance that they
would have to immediately recall that list. These two factors together may have favored
gist extraction over the spontaneous generation of the critical lure. It may be difficult to
explicitly generate the critical lure at a very fast presentation rate and knowledge that an
immediate recall test had a good chance of following each list may have caused subjects
to engage in organizational strategies that favored gist extraction. In Payne et al.'s study
it is also noteworthy that for lists that were followed by math problems there did appear
to be some decrease in recognition of critical lures across the 24 hour delay. It may be
that the significant item type by delay interaction they found was driven primarily by the
condition in which subjects attempted to recall items after the presentation of the list.
It is our aim to determine if, under some circumstances, recognition of critical
lures will decline at similar rates to recognition of targets across a delay. If this occurs it
could be interpreted as evidence either that gist based recognition and verbatim based
recognition sometimes decline at similar rates or that not all false memories in the DRM
paradigm are gist based. Because differential forgetting of gist and verbatim is an
important assumption of Fuzzy Trace Theory, a reasonable tentative hypothesis might be
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that such results would support the existence of verbatim false memories in the DRM
paradigm and lend credence to the source monitoring account.
In the present experiments we examined the effects of a 48 hour delay on
recognition of presented items and non-presented critical lures using a slower
presentation rate than that used by Payne et al. (1996) and without asking subjects to
perform interpolated recall/math tests after each list. In both experiments corrected
recognition of targets and critical lures declined at similar rates.
Method
Subjects
Eighty-four students participated for partial fulfillment of course requirements for
an introductory psychology course. We used a large number of subjects in the initial
experiment because we wanted to ensure that their was sufficient statistical power to
uncover the item type by delay interaction predicted by Fuzzy Trace Theory if it was
there.
Materials
Study Lists. Twelve of the 15 item lists from Roediger and McDermott (1995)
were used. Six lists were presented to subjects and six lists were used to select distractors
for the recognition test. Lists were counterbalanced such that each list served equally
often as a presented list and as a distractor list. The lists were presented at a rate of two
seconds per word on audio-tape.
Test List. An old/new recognition test consisting of 48 items was developed.
Four types of items were included on the test: targets, critical lures, distractors, and
distractor lures. Targets were items that had been presented at acquisition. Three targets
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were taken from each of the six studied lists (the first, eighth, and tenth items from each
list). The test also included 6 critical lures. These were the non-presented words to which
the targets were related. The test also included eighteen distractors and six distractor
lures developed in the same manner as the targets and critical lures but taken from lists
that were presented to other subjects.
Procedure
Subjects were randomly assigned to be tested immediately after the acquisition
phase of the experiment or after a 48 hour delay. After some initial instructions subjects
listened to the word lists. The subjects in the zero minute condition then took the
recognition memory test while subjects in the delay condition completed math problems.
All subjects were then dismissed and returned 48 hours later. The students who had
already taken the recognition test worked on math problems at this time while students in
the forty-eight hour delay condition took the recognition memory test.
Results
According to the gist extraction account recognition of targets should decline
much more rapidly than recognition of critical lures over a 48 hour delay. To test this
prediction we analyzed uncorrected recognition of targets and critical lures as well as
recognition corrected for response bias. To preview, whether we found any evidence for
false memory persistence depended critically on whether or not we corrected for response
bias.
Uncorrected target and critical lure recognition are depicted in Figure 1.
Consistent with the false memory persistence prediction uncorrected recognition of
targets declined by more (M = 13.4%) than uncorrected recognition of critical lures (M =
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5.1%). In absolute terms this difference is on the same order of magnitude as the
difference reported in the math condition of Payne et al. (1996). Arguably their math
condition is the condition most similar to the procedures used in the present experiment.
To test these predictions we conducted a 2 (Item Type: Target, Critical lure) X 2 (Delay:
0 minute, 48 hour) ANOVA. This analysis revealed that significantly fewer items were
recognized after the 48 hour delay than after the immediate test, F (1, 82) = 8.37, MSE =
.04. Recognition of targets and critical lures did not significantly differ, F < 1.
Importantly there was also a marginally significant interaction between item type
and delay, F (1, 82) = 3.10, MSE = .02, p = .082. Thus Experiment 1 produced results
that were very similar to the results obtained by Payne et al. using uncorrected
recognition scores. Although the interaction between item type and delay was not
significant at conventional levels, the trend is in the direction of more forgetting of
targets than critical lures.
These results however do not tell the full story because they fail to account for
possible response bias differences between conditions. Although there are several
possible ways of correcting for response bias the corrections we used in these
experiments are given by the equations:
Corrected Target = (Target - Distractor) / (1-Distractor)
Corrected CL = (Critical Lure - Distractor Lure) / (1-Distractor Lure)
These corrections were used because they assume that the contributions of memory based
and response bias based processes to recognition memory judgments are statistically
independent. This assumption is one of the assumptions included in the theory of
recognition memory recently proposed by Brainerd, et al. (1999) and so it seemed like the
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most reasonable correction to use as a test of a prediction arising out of Fuzzy Trace
Theory. 1
We applied these corrections to the data from the present experiment to derive
corrected recognition scores for targets and critical lures. These corrected recognition
scores are displayed in Figure 2. We performed a 2 (Item Type: Target, Critical Lure) X
2 (Delay: Immediate, 48 hour) mixed factorial ANOVA on the corrected recognition
scores of targets and critical lures. Results indicated a significant main effect of delay
with lower corrected recognition scores when subjects were tested after 48 hours than
when subjects were tested immediately after the presentation of the lists, F (1, 82) =
11.84, MSE = 0.07. Corrected recognition of targets and critical lures did not
significantly differ, F < 1. Importantly, and contrary to the prediction of the gist
extraction account, there was no significant interaction between delay and item type, F<1.
General Discussion
Recent theoretical accounts of false memories in the DRM paradigm have
contrasted two major explanations. One account is the gist extraction account of Fuzzy
Trace Theory. Fuzzy Trace Theory is a broad theoretical framework that has been used
to explain results in child and adult cognition, in reasoning and in memory, and which
has made a number of interesting and sometimes counter-intuitive predictions that have
later been confirmed (Reyna & Brainerd, 1995). The other account is the Source
Monitoring Account which claims that false memories are produced when subjects
spontaneously generate the critical lure as an implicit associative response at time of
acquisition and then later become confused about the source of their memory
(Underwood, 1965). Fuzzy Trace Theory would treat false memories created in this way
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as verbatim false memories with the same forgetting function as other verbatim
memories.
Interpretation of the present results depends on whether one believes the
appropriate way of addressing the false memory persistence question is to rely on
corrected or uncorrected recognition scores. If one relies on corrected recognition scores
then the present experiment paints a consistent picture of false memory impersistence.
Corrected recognition declined by approximately the same amount for targets and critical
lures. The most recent version of Fuzzy Trace Theory explicitly acknowledges that
response bias contributes to performance on recognition memory tests (Brainerd, et al.,
1999) and this suggests that some method must be used to correct for response bias if one
is to evaluate claims of false memory persistence.
If, however, one relies on uncorrected recognition scores the story becomes
somewhat more complex. The trend in the results supported the claim of false memory
persistence. Uncorrected false recognition appeared to decline more slowly across the
delay than did uncorrected recognition of targets although the interaction was not
significant at conventional levels.
Thus one interpretation of the present experiments is that they provide evidence
for false memory impersistence, at least in corrected recognition. There are at least two
possible accounts of false memory impersistence in corrected recognition. One account
is that under some circumstances gist based recognition and verbatim based recognition
decline at equivalent rates. This interpretation would be somewhat troublesome for
Fuzzy Trace Theory because the theory treats slower forgetting of gist as one of the
central predictions of the theory. The results also leave open the possibility that false
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memories in the DRM paradigm might be verbatim based. The existence of verbatim
false memories is not a new concept. Fuzzy Trace Theory acknowledges the existence of
verbatim false memories in cases in which experimenters create false memories through
suggestions and subjects confuse the suggested information with explicitly presented
information (Brainerd & Poole, 1997). An addendum to that proposal might be that
verbatim false memories are also sometimes created in the DRM paradigm.
It is important to note that it appears that this finding of approximately equivalent
forgetting of targets and critical lures is not limited to our laboratory. Recently
Neuschatz (1999 Experiment 3) compared recognition of targets and critical lures across
a 48 hour delay and failed to find an interaction between item type and delay. Although
corrected recognition scores were not reported examination of his means for targets,
critical lures, distractors and distractor lures makes it is possible to estimate that corrected
recognition of targets declined by 0.28 and corrected recognition of critical lures declined
by 0.26 when using Schacter et al.'s (1996) high threshold correction procedure and by
0.21 and 0.18 when using the correction procedure adopted in the present article. This
independent finding provides some confirmation that false memories can at times be as
impersistent as true memories.
None of this is meant to gainsay the importance of gist extraction processes in
creating false memories or the importance of Fuzzy Trace Theory's broad account of false
memories. There is some evidence consistent with false memory persistence in recall in
the DRM paradigm (e.g. Toglia, Neuschatz & Goodwin, 1999). Additionally, the overall
pattern of forgetting in Payne, et al. (1996) suggests that there are conditions in which
delay affects recognition of targets and critical lures in very different ways. This was
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particularly true in their recall condition. It is possible that the differences between our
results and their results hinge on both the relatively fast presentation rate they used as
well as the fact that subjects were aware that they might have to immediately recall each
list. These differences may have caused a greater proportion of gist based false memories
in their study than in ours.
Another salient difference between our experiments and Payne, et al.'s experiment
is that subjects in the delay condition of our experiment performed an interpolated task
while subjects in the immediate testing condition were taking their test. All subjects were
then dismissed at the same time. This immediate interpolated task may have prevented
consolidation of the gist trace. Interestingly Neuschatz (1999) also had subjects in the
delayed recognition condition perform an interpolated task before dismissing them.
The present results provide some evidence consistent with the claim that two
mechanisms are at play in the creation of false memories in the DRM paradigm. On the
one hand, evidence from Payne et al. (1996) suggests that subjects sometimes rely on gist
traces that lead them to falsely recognize items on recognition tests. On the other hand,
evidence from the present study, and from Neuschatz's (1999) study, suggest that at other
times true and false memories may be forgotten at an equivalent rate, opening up the
possibility that verbatim traces may play a role in the creation of false memories for
words not presented in lists.
Brainerd and Poole (1997) have suggested that the relative rate of forgetting of
true and false memories may be dependent on the relative contribution of verbatim and
gist processes to these memories. An important avenue for future research therefore is to
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examine systematically the factors that lead to false memory persistence and those that
lead to false memory impersistence.
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Author Notes
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It is important to note that the overall pattern of results did not change when we instead
used the high threshold correction procedure that has been used by Schacter (Israel &
Schacter, 1997; Schacter, Verfaellie & Pradere, 1996) and other false memory
researchers (Payne, Lampinen & Cordero, 1996; Seamon, Luo & Gallo, 1998). In this
procedure corrected recognition of targets is given by the equation: Corrected Target =
Target - Distractor; and corrected recognition of critical lures is given by the equation:
Corrected Critical Lure = Critical Lure - Distractor Lure. Thus our results are not an
idiosyncratic function of the particular correction procedure we adopted.
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We'd like to thank the members of the false memory lab at the University of Arkansas
for their help with this project (http://comp.uark.edu/~lampinen/lab.html). We'd also like
to thank David Payne, Chuck Brainerd and an anonymous reviewer for their helpful
comments on earlier versions of this manuscript.
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Figure Captions
Figure 1. Uncorrected Recognition Scores for Targets and Critical Lures.
Figure 2. Corrected Recognition Scores for Targets and Critical Lures.
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0.75
0.7
0.65
Recognition
0.6
0.55
Targets
Critical Lures
0.5
0.45
0.4
0.35
0.3
Immediate
48 Hours
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0.7
0.65
Corrected Recognition
0.6
0.55
Targets
Critical Lures
0.5
0.45
0.4
0.35
0.3
Immediate
48 Hours