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Abstract

Freud proposed that unwanted memories can be forgotten by pushing them into the unconscious, a process called repression. The existence of repression has remained controversial for more than a century, in part because of its strong coupling with trauma, and the ethical and practical difficulties of studying such processes in controlled experiments. However, behavioural and neurobiological research on memory and attention shows that people have executive control processes directed at minimizing perceptual distraction, overcoming interference during short and long-term memory tasks and stopping strong habitual responses to stimuli. Here we show that these mechanisms can be recruited to prevent unwanted declarative memories from entering awareness, and that this cognitive act has enduring consequences for the rejected memories. When people encounter cues that remind them of an unwanted memory and they consistently try to prevent awareness of it, the later recall of the rejected memory becomes more difficult. The forgetting increases with the number of times the memory is avoided, resists incentives for accurate recall and is caused by processes that suppress the memory itself. These results show that executive control processes not uniquely tied to trauma may provide a viable model for repression.
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19. Terborgh, J. Five New World Primates (Princeton Univ. Press, Princeton, 1983).
20. Leighton, M. Modeling dietary selectivity by Bornean orangutans: evidence for integration of multiple
criteria in fruit selection. Int. J. Primatol. 14, 257±313 (1993).
21. Gautier-Hion, A. et al. Fruit characters as a basis of fruit choice and seed dispersal in a tropical forest
vertebrate community. Oecologia 65, 324±337 (1985).
22. Davies, A. G. & Oates, J. F. in Colobine Monkeys (eds Davies, A. G. & Oates, J. F.) 229±249 (Cambridge
Univ. Press, Cambridge, 1994).
23. Wrangham, R. W., Conklin-Brittain, N. L., & Hunt, K. D. Dietary responses of chimpanzees and
cercopithecines to seasonal variation in fruit abundance: I. antifeedants. Int. J. Primatol. 19, 949±970
(1998).
24. Onishi, A. et al. Dichromatism in macaque monkeys. Nature 402, 139±140 (1999).
25. Struhsaker, T. T. Ecology of an African Rainforest (Univ. Florida Press, Gainesville, 1997).
26. Lucas, P. W. et al. Fieldkit to characterize the physical, chemical, and spatial aspects of potential
primate foods. Folia Primatol. 72, 11±25 (2001).
27. Osorio, D. & Vorobyev, M. Colour vision as an adaptation to frugivory in primates. Proc. R. Soc. Lond.
B 263, 593±599 (1996).
28. Darvell, B. W., Lee, P. K. D., Yuen, T. D. B., Lucas, P. W. Meas. Sci. Technol. 7, 954±962 (1996).
29. Newton-Fisher, N. E. The diet of chimpanzees in the Budongo Forest Reserve, Uganda. Afr. J. Ecol. 37,
344±354 (1999).
30. Gartlan, J. S., McKey, D. B., Waterman, P. G., Mbi, C. N. & Strusaker, T. T. A comparative study of the
phytochemistry of two African rainforests. Biochem. Syst. Ecol. 8, 401±422 (1980).
Acknowledgements
We thank D. Osorio for help with colour registration; E. Ting, P. Y. Cheng, I. C. Bruce,
R. T. Corlett, L. Ramsden, N. Yamashita and A. Walker for comments, P. Kagoro,
B. Balyeganira and M. Musana for ®eld assistance in Uganda; J. Magnay, R. W. Wrangham
and C. A. Chapman for logistic support in Uganda; and the Ugandan National Council for
Science and Technology, Ugandan Wildlife Authority and Makerere University Biological
Field Station for permission to work at Kibale. Supported by Research Grants Council of
Hong Kong, National Geographic Society, Sigma Xi, Explorer's Club and Croucher
Foundation of Hong Kong.
Correspondence and requests for materials should be addressed to N.J.D.
(e-mail: njdominy@hkusua.hku.hk).
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Suppressing unwanted memories by
executive control
Michael C. Anderson & Collin Green
Department of Psychology, University of Oregon, Eugene, Oregon 97403-1227,
USA
..............................................................................................................................................
Freud proposed that unwanted memories can be forgotten by
pushing them into the unconscious, a process called repression
1
.
The existence of repression has remained controversial for more
than a century, in part because of its strong coupling with trauma,
and the ethical and practical dif®culties of studying such pro-
cesses in controlled experiments. However, behavioural and
neurobiological research on memory and attention shows that
people have executive control processes directed at minimizing
perceptual distraction
2,3
, overcoming interference during short
and long-term memory tasks
3±7
and stopping strong habitual
responses to stimuli
8±13
. Here we show that these mechanisms
can be recruited to prevent unwanted declarative memories from
entering awareness, and that this cognitive act has enduring
consequences for the rejected memories. When people encounter
cues that remind them of an unwanted memory and they con-
sistently try to prevent awareness of it, the later recall of the
rejected memory becomes more dif®cult. The forgetting increases
with the number of times the memory is avoided, resists incen-
tives for accurate recall and is caused by processes that suppress
the memory itself. These results show that executive control
processes not uniquely tied to trauma may provide a viable
model for repression.
Executive control processes studied in behavioural
6,9,14
and
neurobiological
2,4,10±13,15±17
research on cognition may provide a
mechanism for the voluntary form of repression (suppression)
proposed by Freud
1
. To test this hypothesis, we adapted the go/
no-go paradigm used to study executive control over motor actions
in primates
18
and humans
15±17
for use in a memory retrieval task.
First, we trained subjects on 40 unrelated word pairs (for example,
ordeal±roach) so that they could recall the right-hand member of
each pair when provided with the left-hand member. Next, subjects
performed a critical task requiring them to exert executive control
over the retrieval process. On each trial of this think/no-think task, a
cue from one of the pairs appeared on the computer screen.
Depending on which cue appeared, subjects were told either to
recall and say (think about) the associated response word (respond
pairs), or not to think about the response (suppression pairs). For
the latter pairs, we emphasized that subjects should not allow the
associated memory to enter consciousness at all. If subjects acci-
dentally responded to a suppression pair, they heard a beep signal-
ling an error. To increase the need to recruit inhibitory control
mechanisms, we required subjects to ®xate on the cue word for the
entire time (4 s) that it appeared on the screen, discouraging
perceptual avoidance and generating a constant threat that the
associated memory might intrude into consciousness. Thus, sup-
pression trials required the stopping of both a prepotent motor
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g
b
c
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Figure 1 Final recall for respond and suppression items as a function of the number of
repetitions for the same-probe (SP) and independent-probe (IP) tests. a, b, Experiment 1;
c, d, experiment 2; e, f, experiment 3; g, averaged across experiments. Note the negative
slope for recall of the suppressed item, indicating increasing inhibition. Inhibition (0 vs 16
suppressions) was signi®cant (P , 0.01) in all experiments, and did not interact with type
of test cue (F , 1 in all cases; analysis of variance). Inhibition was signi®cant (P , 0.05) in
every SP and IP test for every experiment (a±f).
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response and the entrance of an unwanted memory into awareness.
Before this phase, we told subjects which cues would require
suppression so that they would recognize these words on sight.
Subjects performed suppression and respond trials on different
pairs that were intermixed. On each trial, no visual marking
indicated which cue words were suppression items, forcing subjects
to identify each cue to know whether to recall or suppress the
associated memory.
The objective of the think/no-think task was to determine
whether attempting to prevent awareness of an unwanted
memory would hinder its later retrieval. To evaluate whether this
occurred, the next phase required subjects to recall the response for
each of the cue words. We emphasized that the previous goal of
avoiding the associated items was no longer relevant and that a
response should be recalled for every cue. If trying to prevent a
memory from entering awareness recruits inhibitory control pro-
cesses that impair that memory's retrievability, recall for suppres-
sion items should be worse than for baseline pairs on this test. In all
experiments reported here, baseline items were studied pairs that
did not appear as either respond or suppression items during the
think/no-think phase.
In experiment 1, we varied the number of suppression or respond
trials given for each pair. Subjects received 0, 1, 8 or 16 trials for each
suppression and each respond item. If excluding unwanted mem-
ories from awareness recruits inhibitory control, recall should be
worse after 16 suppression attempts than after 0 attempts (baseline).
As shown in Fig. 1a, ®nal recall of suppressed items was worse than
of baseline items, and impairment increased linearly with suppres-
sion practice. In contrast, recall improved across repetitions for
respond items, demonstrating the established bene®ts of retrieving
memories on their later recall. These diverging patterns show that
controlling awareness not only terminated the powerful facilitative
effects of retrieval, but also impaired the recall of suppressed items
to below their baseline level (0 suppression attempts). The increas-
ing inhibition with repetition further indicates that unwanted
memories might be especially vulnerable in settings requiring
protracted avoidance, unlike the modest time (1 min over 16
suppressions) afforded by our task.
Impaired memory for suppression items indicates that there may
be an executive control process that suppresses (reduces activation
of) the unwanted memory itself (for example, roach in Fig. 2).
However, mechanisms other than inhibition may be at work
6
.For
instance, one strategy for avoiding an unwanted memory would be
to generate diversionary thoughts to environmental stimuli that
remind us of it. New associations between these stimuli and the
diversionary thoughts may interfere during later attempts to recall
the memory. Alternatively, terminating retrieval may degrade the
association between the cue and the response. Neither of these
alternatives requires us to assume that the unwanted memory itself
is inhibited and thus they do not require the postulation of an
executive inhibition process. To isolate the contribution of inhibi-
tion, we used the independent probe method
6
. If inhibition impairs
the unwanted memory itself, recall should be worse regardless of
whether that item is tested with the cue used to train suppression or
with a novel cue (Fig. 2). However, associative interference and
unlearning predict that forgetting should be limited to the originally
trained cue. To distinguish between these models, we retested
subjects from experiment 1 with cues not previously encountered
in the experiment (`independent probes'). For each item, we cued
subjects with a semantic category and the initial letter of the
response word (for example, for ordeal±roach, subjects received
`insect r___') and asked them to recall the studied word that ®t the
cues. On this new independent probe (IP) test, recall of suppressed
items was again worse than baseline (Fig. 1b), and the impairment
was higher when recall had been avoided more. The amount of
forgetting did not differ reliably from when the originally trained
cue was used in the test (for example, ordeal in the same probe (SP)
test condition, Fig. 1a). This ®nding rules out associative inter-
ference and unlearning and shows that impairment is localized to
the unwanted memory itself. This strongly supports the existence of
an inhibitory control mechanism
6
.
It was necessary to show that subjects did not recall and then
withhold suppression items on the ®nal test. They might have done
so out of confusion, given our emphasis on withholding responses
during the think/no-think phase. To address this, we expanded our
test instructions to emphasize that subjects should recall an item to
every cue regardless of earlier instructions, even if they were
guessing. To further encourage responding, we offered a monetary
reward for correct answers. These incentives had little impact on the
inhibition effect (Fig. 1c, d). Impairment was signi®cant overall,
increased with repetition, and did not vary with the type of test cue,
again supporting the inhibitory control view. Although the instruc-
tions to guess enhanced recall of suppression and baseline items
when the studied cue was given (P , 0.01), the linear trend for
inhibition did not differ reliably across experiments (F , 1).
Subjects might have guessed the hypothesis of the experiment and
tried to conform to the expectation of impaired memory by with-
holding items. To address this, we altered the ®nal test instructions
Ordeal
Roach
Insect r__
Alternative
associations
Diversionary thoughts
Trained cue Independent cue
Pre-experimental
association
(1)
(2)
(3)
Figure 2 Three mechanisms that can explain impaired recall in the same-probe condition,
illustrated with a stimulus pair. Associative interference posits that suppression training
leads subjects to generate diversionary thoughts (1) to the trained cue that interfere during
later attempts to recall the target. Unlearning assumes that suppression training weakens
the cue±target connection (2). The suppression hypothesis states that suppression
training inhibits the target (3). Note that testing the target with an independent cue
circumvents interference (1) and unlearning (2). Any impairment found with this test may
be attributed to effects localized to the target.
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to make subjects believe that we expected improved memory for
suppression items. We told subjects that research suggests that when
people try not to think about something, they ironically think about
it more, as when people try not to think about falling asleep at night
and then experience insomnia
19
. We noted that this research pre-
dicts that memory for suppression items should improve because
the avoided memories should intrude during suppression trials.
Post-experimental questionnaires indicated that subjects believed
that this was our rationale (average rating of 4.2 on a 5-point belief
scale) and most endorsed the theory on the basis of experience.
These new test instructions had little effect on the inhibition pattern
(Fig. 1e, f).
Success in our think/no-think task is de®ned by participants'
subjective awareness of the unwanted memory during suppression
trials, a state which cannot be measured. Efforts to control this state
nevertheless left their mark on memory. However, the apparent
memory de®cit may re¯ect suppression of the overt motor response
associated with the unwanted memory. To test this, we removed the
instruction to suppress awareness of the memory during the think/
no-think phase. We instead asked subjects to recall the memory,
but not say it aloud, rendering this an episodic go/no-go task.
Recall did not decline with the number of verbal suppressions, and
this pattern did not vary with the cue used to test items (Fig. 3a,
b). In contrast, when experiments 1±3 are combined, the linear
trend for inhibition was reliable for the SP and IP test conditions
(P , 0.001, Fig. 1g) and these effects did not vary reliably across
experiments. Importantly, the linear inhibition effect was statisti-
cally larger in the think/no-think task (experiments 1±3) than in
the go/no-go task (experiment 4). These ®ndings isolate impaired
recall of unwanted memories to cognitive operations directed at
keeping them out of awareness.
Our results imply that a process exists that impairs the retention
of memories when they are deliberately kept out of consciousness.
When people encounter a stimulus that is known to cue an
unwanted memory, this process can be recruited to prevent aware-
ness of the memory. The regulation of consciousness is accom-
plished by an inhibitory control mechanism that suppresses the
unwanted memory itself (as shown by our independent probe data),
and not merely by the momentary ®lling of working memory with
diversionary thoughts. Delayed recall of the unwanted memory is
worse than a baseline condition in which no reminders of the
memory were presented in the interim. This paradoxical pattern
arises because repeated exposure to reminders makes it necessary
for people to adapt their patterns of thought internally with
executive control processes. Thus, frequent encounters with remin-
ders should make an unwanted memory less accessible, a ®nding
noted in some clinical studies of psychogenic amnesia
20
.
Our results clarify the nature and scope of inhibitory processes
previously shown to impair episodic recall, and link those processes
to behavioural and neurobiological research on executive control.
Work on retrieval-induced forgetting
6
has shown that memories
that interfere with the retrieval of other targets are inhibited, but it
has not previously been established whether inhibition is under
strategic control. Research into directed forgetting
7,21,22
suggests a
controllable inhibition process, but one limited in scope to an
immediately preceding temporal interval. The present ®ndings
show a controllable inhibition process that can be ¯exibly targeted
to a speci®c prepotent memory after intervening memories have
been acquired. These ®ndings do not support the popular idea that
attempting to suppress an unwanted thought makes it hyperac-
cessible, at least as this idea applies to suppressing episodic
memories
19
.
The need to terminate retrieval in the think/no-think paradigm
can be viewed as one instance of the need to override prepotent or
habitual responses when they are inappropriate, a function pre-
sumed to require executive control
4,8±10,12,13,23,24
. Related tasks such as
the go/no-go procedure are widely used to study this executive
function and have been shown to recruit dorsolateral prefrontal
cortex (DLPFC) and anterior cingulate cortex (ACC) (with ventral
PFC)
15±17
. Other studies show a speci®c role of DLPFC in over-
coming interference from competing representations in working
memory
4
, in selecting one item in working memory as the basis for
responding
26
and in on-line manipulation of information
27
. The
sustained regulation of awareness required by our procedure is likely
to use such processes. This suggests that the think/no-think task
recruited DLPFC and ACC, perhaps with medial temporal regions,
to control awareness of the memory
28,29
. If this is true, the present
memory de®cits provide a behavioural marker of the action of this
network on rejected memories and suggest that this network exerts
control through inhibition
4,6,11,12,25
.
Whatever their neural basis, our results establish a direct link
between internal operations that control phenomenal awareness
of a memory and its later accessibility. These ®ndings thus
support a suppression mechanism that pushes unwanted mem-
ories out of awareness, as posited by Freud. Research on retrieval-
induced forgetting shows that suppression can have a lasting
impact on a memory's accessibility
6
. Suppression in the current
paradigm may be similarly enduring. Furthermore, if retrieving
diversionary thoughts becomes habitual, inhibition may be sus-
tained without any intention of avoiding the unwanted memory
30
.
Together, these factors provide a viable model of repression, and
its potential evolution from an intentional to an unintentional
process. If so, repression may not be tied uniquely to psycho-
logical defence, but may rather re¯ect the action of a general
executive control process, directed at declarative memories of past
experience.
M
Methods
Thirty-two neurologically normal college students participated in each experiment, except
experiment 4, in which there were sixteen. Each participant was trained on 40 critical and
10 ®ller word pairs. The stimulus and response members of each pair had a weak pre-
experimental relationship, and were unrelated to words in other pairs. The response
members were chosen so that each was a member of its own category (for example,
insects), to permit later testing of that item with an extralist category cue. The word pairs
were exposed individually for 5 s in the centre of a computer screen with the response
printed to the right of the stimulus. Test±feedback cycles followed in which subjects were
presented with the stimulus member and asked to say the response aloud as quickly as
possible. The correct answer was given visually if the response was omitted. Test±feedback
cycles on all the pairs continued until a minimum of 50% of the pairs were correctly
recalled.
After initial study, subjects were given the think/no-think phase instructions, and were
then presented with the 15 stimulus members from the to-be-suppressed pairs without
their responses. Subjects familiarized themselves with the stimuli so that they could
identify them during suppression trials and prevent the associated memory item from
coming to mind. After a brief practice session on the think/no-think task using ®ller items,
subjects were given 377 trials in which respond and suppression stimuli were randomly
65
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Withhold
Respond
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01 816
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Withhold
Respond
Same probe
Independent probe
a
b
Figure 3 Final recall of withhold and respond items as a function of the number of
repetitions. a, Performance in the same test probe (SP) condition. b, Performance in the
independent probe condition (IP). In both conditions, withhold item performance does not
decrease with repetition. None of the inhibition effects were signi®cant (F , 1 in all
cases). There was reliably more inhibition in experiments 1±3 than in experiment 4
(P , 0.05), and a reliably greater linear trend for inhibition (P , 0.05). Neither of these
tendencies interacted with type of test cue (F , 1).
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intermixed. On each trial, a ®xation cross appeared for 200 ms, followed by a stimulus
member in the centre of the screen. For respond trials, the stimulus was presented for
up to 4 s, or until the subject responded, and subjects had to report the response as
quickly as possible. For suppression trials, the stimulus remained on the screen for 4 s.
If a subject responded, a loud error beep sounded. Trials were separated by a 400-ms
intertrial interval. Suppression and respond trials were conducted on different word
pairs, with ®ve pairs participating in each of the 0 (baseline), 1, 8 and 16-repetition
conditions for both the respond and suppression conditions. Respond trials on ®ller
pairs were also included so that 67% of the trials in the think/no-think phase required a
response, encouraging a strong mental set to respond that had to be overridden, as in
go/no-go tasks.
After the think/no-think phase, we tested the subjects' memory for all of the word pairs
in two ways. In both tests, a cue for each word pair was presented in the centre of the screen
for up to 4 s, or until subjects spoke the response. Pairs for the different respond and
suppress conditions were intermixed pseudo-randomly, with the constraint that the
average test position for each condition was equated. In the same-probe test, subjects'
recall for each pair was cued with the stimulus member that was paired with the response
throughout the experiment. In the independent probe test, subjects were cued with the
category name for each exemplar along with its ®rst letter. In each case, subjects were asked
to recall the studied item that ®t the cues and not to withhold any items. Half of the
subjects in each experiment got the same-probe test ®rst, and half were given the
independent probe test ®rst.
Subjects in experiment 2 were given 25 cents for each correct answer, up to a maximum
of $4. Subjects in experiment 3 were given a questionnaire after the experiment in which
they were asked about their impressions of our (false) hypothesis that memory would
improve with attempts to suppress an item.
Received 10 October; accepted 21 December 2000.
1. Freud, S. in The Standard Edition of the Complete Psychological Works of Sigmund Freud 1
(ed. J. Strachey) 117±128 (Hogarth, London, 1966).
2. Chao, L. L. & Knight, R. T. Human prefrontal lesions increase distractibility to irrelevant sensory
inputs. Cog. Neurosci. Neuropsychol. 6, 1605±1610 (1995).
3. Dagenbach, D. & Carr, T. H. (eds) Inhibitory Processes in Attention, Memory, and Language (Academic,
San Diego, 1994).
4. Smith, E. E. & Jonides, J. Storage and executive processes in the frontal lobes. Science 283, 1657±1661
(1999).
5. Hasher, L. & Zacks, R. T. Working memory, comprehension and aging: A review and a new view.
Psychol. Learn. Motiv. 22, 193±225 (1988).
6. Anderson, M. C. & Spellman, B. A. On the status of inhibitory mechanisms in cognition: Memory
retrieval as a model case. Psychol. Rev. 102, 68±100 (1995).
7. Bjork, R. A. in Varieties of Memory and Consciousness: Essays in Honour of Endel Tulving (eds Roediger,
H. L. & Craik, F. I. M.) 309±330 (Lawrence Erlbaum Associates, Hillsdale, 1989).
8. Luria, A. R. Higher Cortical Function in Man (Basic Books, New York, 1966).
9. Logan, G. D. & Cowan, W. B.On the ability to inhibit thought and action: A theory of an act of control.
Psychol. Rev. 91, 295±327 (1984).
10. Posner, M. I. & Peterson, S. E. The attention system of the human brain. Annu. Rev. Neurosci. 13,
25±42 (1990).
11. Knight, R. T., Staines, W. R., Swick, D. & Chao, L. L. Prefrontal cortex regulates inhibition and
excitation in distributed neural networks. Acta Psychol. 101, 159±178 (1999).
12. Cohen, J. D. & Servan-Schreiber, D. Context, cortex, and dopamine: A connectionist approach to
behavior and biology in schizophrenia. Psychol. Rev. 99, 45±77 (1992).
13. Carter, C. S., Botvinick, M. M. & Cohen, J. D. The contribution of the anterior cingulate cortex to
executive processes in cognition. Rev. Neurosci. 10, 49±57 (1999).
14. Mayr, U. & Keele, S. W. Changing internal constraints on action: The role of backward inhibition.
J. Exp. Psychol. Gen. 129, 4±26 (2000).
15. Casey, B. J. et al. A developmental functional MRI study of prefrontal activation during performance
of a go-no-go task. J. Cogn. Neurosci. 9, 835±847 (1997).
16. Garavan, H., Ross, T. J. & Stein, E. A. Right hemispheric dominance of inhibitory control: An event-
related functional MRI study. Proc. Natl Acad. Sci. USA 96, 8301±8306 (1999).
17. de Zubicaray, G. I. et al. Motor response suppression and the prepotent tendency to respond: A
parametric fMRI study. Neuropsychologia 38, 1280±1291 (2000).
18. Sakagami, M. & Niki, H. Spatial selectivity of go/no go neurons in the monkey prefrontal cortex.
Exp. Brain Res. 100, 165±169 (1994).
19. Wegner, D. M. Ironic processes of mental control. Psychol. Rev. 101, 34±52 (1994).
20. Freyd, J. J. Betrayal Trauma: The Logic of Forgetting Childhood Abuse (Harvard Univ. Press, Cambridge,
MA, 1996).
21. Geiselman, R. E., Bjork, R. A. & Fishman, E. L. Disrupted retrieval in directed forgetting: A link with
posthypnotic amnesia. J. Exp. Psychol. Gen. 112, 58±72 (1983).
22. Conway, M. A, Harries, K., Noyes, J., Racsmany, M. & Frankish, C. R. The disruption and dissolution
of directed forgetting: Inhibitory control of memory. J. Mem. Lang. 43, 409±430 (2000).
23. Norman, D. A. & Shallice, T. in Consciousness and Self-Regulation: Advances in Research and Theory
(eds Davison, R. J., Schwardz, G. E. & Shapiro, D.) 1±18 (Plenum, New York, 1986).
24. MacDonald, A. W., Cohen, J. D., Andrew-Stenger, V. & Carter, C. S. Dissociating the role of the
dorsolateral prefrontal and anterior cingulate cortex in cognitive control. Science 288, 1835±1838
(2000).
25. Shimamura, A. P. The role of the prefrontal cortex in dynamic ®ltering. Psychobiology 28, 207±218
(2000).
26. Rowe, J. B. et al. The prefrontal cortex: Response selection or maintenance within working memory.
Science 288, 1656±1660 (2000).
27. D'Esposito, M. et al. Functional MRI studies of spatial and nonspatial working memory. Cogn. Brain
Res. 7, 1±13 (1998).
28. Schacter, D. L. & Wagner, A. D. Medial temporal lobe activations in fMRI and PETstudies of episodic
encoding and retrieval. Hippocampus 9, 7±24 (1999).
29. Schacter, D. L. Memory and awareness. Science 280, 59±60 (1998).
30. Anderson, M. C. Active Forgetting: Evidence for functional inhibition as a source of memory failure.
J. Agression Maltreatment Trauma (in the press).
Acknowledgements
The research reported here was supported by a grant from the US National Institute of
Mental Health.
Correspondence and requests for materials should be addressed to M.C.A.
(e-mail: mcanders@darkwing.uoregon.edu).
.................................................................
Masking unveils pre-amodal
completion representation
in visual search
Robert Rauschenberger & Steven Yantis
Department of Psychology, The Johns Hopkins University, Baltimore,
Maryland 21218, USA
..............................................................................................................................................
When one object is partly occluded by another, its occluded parts
are perceptually `®lled in', that is, the occluded object appears to
continue behind its occluder. This process is known as amodal
completion
1
. The completion of a partially occluded object takes
about 200 ms (ref. 2), and pre-completion information (that is,
information from before amodal completion has occurred) exists
in the visual system for that duration
2,3
. It has been suggested,
however, that observers cannot make use of this information, even
when it is bene®cial to do so: visual search for a target that appears
to be partly occluded, for example, is slower than for a target that
does not undergo occlusion, despite both targets being physically
identical
4±6
. Here we show that visual search does have access to
pre-completion representations, but only for a limited time that
depends on the size of the occluded region.
Early investigations of visual search focused on discovering the
elementary features available in early vision
7±12
, whereas more
recent work has demonstrated that the input to visual search is
much more complex than previously assumed
4±6,13,14
. Although it
seems that the entry level for vision (that is, entire objects or
individual features) can be quite high in many cases, questions
remain about the nature of the information available at earlier stages
of processing. In the case of amodal completion, for example, it
seems that visual search relies on a post-completion representation
even when this impairs search
4±6
. This ®nding can be interpreted in
at least three ways. First, it could be that there is no pre-amodal
completion stage in processing. This is unlikely because other
studies have shown that pre-completion information is available
for certain perceptual judgements
2,3
. Second, it is possible that pre-
completion information exists only implicitly, as an `ingredient' in
the computation of a completed representation, and is not explicitly
available for all perceptual judgements. Examples of this include
monocular information during binocular rivalry
15
, and very high
spatial frequency information
16
, both of which are present in
Table 1 Percentage of mean target-absent error rates
Experiment Number of items in display
2468
.............................................................................................................................................................................
Medium notch (100-ms SOA) 11.4 17.7 20.3 12.3
Medium notch (250-ms SOA) 3.5 4.6 5.5 3.0
Small notch 18.7 19.8 22.5 15.6
Large notch 2.0 4.0 3.0 1.9
.............................................................................................................................................................................
© 2001 Macmillan Magazines Ltd
... To examine this question, we used multivariate decoding of EEG recordings to track memory intrusion during the Think/No-Think (TNT) task, 35 based on bottom-up capture during an attention task (see Figure 1). The TNT paradigm is designed to induce intrusive memories triggered by a cue whose long-term accessibility is reduced after several suppression attempts. ...
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