EEG recording during list method directed forgetting of different

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EEG recording during list method directed forgetting of different
valenced words

Good memory is mostly associated with abilities to remember things. However, as we all
know there are certain memories that we would rather let go (e.g. embarrassing events,
irrelevant things…) than remember them forever. In this sense then effective memory would
imply forgetting of those events. The ability to forget on purpose has been studied in
laboratories with the directed forgetting paradigm. Two different methods are c
ommonly
used: In the item method in which a sequence of items is presented with each item being
followed by an instruction to either remember the previous stimuli or to forget it. Directed
forgetting occurs as less recall or recognition of to
-
be
-
forgotten
items compared to to
-
be
-
remembered ones. In the list method two lists are presented with the second one always to
remember while the first list is followed by an instruction to forget the whole previous list in
the experimental condition. In the control co
ndition both lists receive remember instruction.
In free recall, the first list is better remembered in the control group than in the experimental
group (also known as the costs of directed forgetting) while the second list is remembered
better in the expe
rimental condition than in the control condition (also known as the benefits
of directed forgetting). The two methods differ therefore in the retrieval tasks that show
effects of directed forgetting and therefore in the assumed underlying mechanisms
(e.g.
Basden & Basden, 1996; Basden, Basden, Coe, Decker, & Crutcher, 1994; Basden, Basden,
& Gargano, 1993; MacLeod, 1999)
. As the item method produces directed forgetting in recall
and recognition several studies sug
gested that to
-
be
-
remembered and to
-
be
-
forgotten items
are differentially or selectively rehearsed. In the list method on the other hand directed
forgetting only occurs in free recall and not in recognition, therefore it was suggested that
retrieval proces
ses are inhibited during recall while a representation of items in a recognition
task releases the inhibition and thus no effect occurs. Although retrieval inhibition is the most
prevalent theory for list method directed forgetting, there are several other

explanations. For
example, Sahakyan and co
-
workers
(Sahakyan & Delaney, 2003, 2005; Sahakyan & Kelley,
2002)

suggested that the costs are associated with change of mental contex
t and the benefits
with a change of encoding strategy

initiated by the forget instruction
. Sheard and

MacLeo
d
(2005)

argued that selective rehearsal is an sufficient account to explain list method directed
forgetting. Another account suggests that
attentional focusing
is a sufficient explanation for
list method
directed forg
etting
(Conway, Harries, Noyes, Racsma'ny, & Frankish, 2000;
Wessel & Merckelbach, 2006)
.

Conway and co
-
workers
(2000
)

related this account to the
idea of inhibitory mechanisms working on the reduced list 1 recall. Referring to selective
attention literature which showed that focusing the attention on an item leads to inhibition of
competing items, Conway and colleagues

assumed that the inhibition processes are triggered
through the attentional focusing on list 2 and that the “distribution of attentional resources at
encoding could be an important determinant of the extent of inhibition in the DF lists
procedure” (p. 412
).

So far, the underlying brain dynamics of the two paradigm were only studied for the item
method
(Paller, 1990; Paz
-
Caballero & Menor, 1999; Paz
-
Caballero, Menor, & Jimenez,
2004; Ullsperger, Mecklinger, & Muller, 2000; Wylie, Foxe, & Taylor, 2007)

while the
neural activity in the list method has still not been investi
gated.


In regard to emotional events, the literature showed that emotional material modulates
memory by enhancing it
(for an overview see: Dolcos, LaBar, & Cabeza, 2006; Hamann,
2001)
. This preferential memory processing for emotional material in found in recall
(Bradley, Greenwald, Petry, & Lang, 1992)
, recognition
(Dolcos, LaBar, & Cabeza, 2005)
,
passive viewing
(Palomba,

Angrilli, & Mini, 1997)
, and more elaborative processing
(Dolcos
& Cabeza, 2002)
.

In regard to brain activity, the preferential memory processes are thought to be reflected in
d
eeper st
imulus processing and faster categorization of emotional items
. Increased negativity
in posterior regions for emotional items compared to neutral ones in an early time window
(about 180
-
250 ms) is called early posterior negativity (EPN) and thought to refl
ect fast
categorization of these items
(Schupp, Junghofer, Weike, & Hamm, 2003)
. Enhanced
positivity for emotional material in a mor
e

P3
-
like time window, called late positive potential
(LPP), is more related to deeper stimulus processing and
motivational relevance
(Schupp et
al., 2000)
.
This p
rocessing pattern has been found for a variety of items, including pictures
(Schupp, Flaisch, Stockburger, & Junghofer, 2006)
, sounds, and words
(Kissler, Herbert,
Peyk, & Junghofer, 2007)


Concerning

list
-
method

directed forgetting, the memory enhancing effect of emotion
led
to
the question whether the

successfully forgetting of irrelevant items would be diminished by
emotional material.
Wessel & Merckelbach
(2006)

investigated
the modulation of
directed
forgetting
by
emotion
. They used
lists c
ontaining
either

neural
-
only

or unpleasant
-
only

words
.
Then two
neutral or two unpleasant lists were presented to the subjects with a
n

instruction
after the first list
for half of the participants to forget the previous words and no such

instruction for th
e other half.

Irrespective of the words` valence more list 2 items were
recalled

within the group

with forget instruction than in the remember

group (benefits)
while
the remember

group recall
ed

more
of list 1 than
the forget

group

(costs).

Studies on
autob
iographical memories
(Barnier et al., 2007; Joslyn & Oakes, 2005)

also investigated list
method directed forgetting of memories varying in
emotionality and their data also support
the view that emotional material, here emotional memories, can be intentionally forgotten.

However, while pleasant and neutral memories produce a similar effect of directed forgetting,
Barnier and colleagues found t
hat for unpleasant memories the effect was reduced or even
absent .
Several other studies with a clinical focus used list method directed forgetting

of
emotional material

to compare healthy subject with various clinical
(e.g. Bohne, Keuthen,
Tuschen
-
Caffier, & Wilhelm, 2005; Power, Dalgleish, Claudio, Tata, & Kentish, 2000)

or
subclinical populations
(e.g. DePrince & Freyd, 2004)
.

Power and colleagues
(Power et al., 2000)

investigated directed forgetting in the context of
emotional modulation with lists of pleasant and unpleasan
t trait adjectives. Here again a
directed forgetting effect for both valences occurred in free recall when the adjectives were
processed during a pleasantness rating.

This effect however differed a little bit for the two
valences in that more pleasant to
-
b
e
-
forgotten words wer
e recalled than unpleasant ones

(Power et al., 2000)
. In

another clinical study
(Bohne et al., 2005)

list
s

of
intermixed
unpleasant and neutral words were presented and the healthy control subjects
recalled more
(although not significantly) to
-
be
-
remembered items for

both the unpleasant and the neutral
words.

Myers, Brewin, & Power
(1998)

and Myers & Derakshan
(2004)

used lists of
intermixed pleasant and un
pleasant words in their experiments

on repressors and repressive
style
.

They found a
more forgetting of

unpleasant material

when told to forget compared to
to
-
be
-
remembered items.
While in one study t
his effect did not occur
for pleasant items

(Myers & Derakshan, 2004)

it was even stronge
r than for unpleasant items in the other study
(Myers
et al., 1998)
. Mould & Bryant
(2005)

presented

words of three valences (
pleasant,
neutral, and unpleasant) randomly and
they found that

directed forgetting effects for pleasant
and unpleasant words and a trend for neutral words

in control participants
.
Using lists of
intermixed
trauma
-
related and neutral words
(DePrince & Freyd, 2004
; McNally, Ristuccia,
& Perlman, 2005)

revealed effects

of reduced recall of to
-
be
-
forgotten items

for the trauma
-
related words but not for the neutral words

while
(study 2, Devilly et al., 2007)

found more
recall of to
-
be
-
remembered items regardless of valence for subjects with low dissociation
levels under normal

conditions
.

All of the mentioned studies found directed forgetting for emotional material
.
However,

some
of the very same studies
additionally found some modulation for the different emotions
(DePrince & Freyd, 2004; McNally et al., 2005; Moulds & Bryant, 2005; Myers & Brewin,
1994; Myers et al., 1998; Power et al., 2000)

and there is one

stud
y

t
hat yielded
no directed
forgetting for
emotion
al stimuli:

Payne & Corrigan
(2006)

found di
rected forgetting only for
neutral
items

and not for unpleasant ones when
lists of either emotional (pleasant and
unpleasant) or neutral IAPS
(International affective pictures system, Lang, Bradley, &
Cuthbert, 2005)

pictures
were used
.



We
carried out two

experiments

on the influence of emotion on list
-
method and the
underlying brain dynamics. The list
-
method was chosen as an ex
perimental equivalent of
learning different episodes. We were interested in whether and how far the valence of a
second episode would influence the forgetting of a previous one and vice versa. EEG was
recorded during directed forgetting of

lists
containing

one

of

two emotional categories

(neutral and unpleasant)
.
In
experiment
1

the first list was unpleasant and the second one was
neutra
l while in

experiment
2

the first list was neutral and the second one unpleasant. These
two experiments were

thought to gi
ve insights

whether modifyi
ng valence of a whole list, or
episode, speaking of the equivalent, would
modify the directed forgetting effect.



The question was whether the directed forgetting effect would be modulated depending on the
emotionality assignmen
t of the lists. Additionally, we were interested in the neural activity
patterns after the mid
-
condition forget instruction compared to the mid
-
condition remember
instruction and the interaction with emotionality.



Experiment 1
: Negative list 1 and neutr
al list 2

Consistent with Wessel & Merckelbach

(2006)
, using pure lists of one valence leads to
similar results for both emotional categories. This outcome however might be depending on
the pure lists. As Hadley & Mackay
(2006)

suggested,
that differences in memory
performance for different valences would be observable in mixed list due to context
-
specific
binding processes. Therefore experiment
s with both valences were conducted.

Method


S
ubjects

28 subjects (15 male, 13

female) participated in this e
xperiment. The mean age was 23.74
(SE: 0.59
). The data of
three

subjects was excluded due to extreme alpha waves (n=
1
),
artefacts (n=1),
and depr
es
sive symptoms (n=1) leaving 25 (13 male, 12

female) data sets for
analysing. All subjects were right handed
(assessed according to Annett, 1979; Oldfield,
1971)

and had normal or corrected to normal vision. They provided informed consent and
received course credit or paym
ent for participation.


Material

From the word pool, again 80 words were chosen.
Half of the words
were

unpleasant

and half
neutral. The
unpleasant

words achieved a mean valence score of 2.5 (SE: 0.17) on a scale
from 1 (very unpleasant) to 9 (very pleasan
t) and a mean score of 6.17 (SE: 0.16) on an
arousal scale ranging from 1 (very unarousing) to 9 (very arousing). Analogous the neutral
words were rated on average as 5.3 (0.17) on the valence dimension and had a mean arousal
score of 2.66 (SE: 0.16). The
unpleasant

and neutral words differed significantly in regard to
their valence [
F
(1, 78)
=131.95, p<.0001
] and arousal scores [
F
(1, 78)
=256.52, p<.0001
] while
they were matched for concreteness, frequency, and word length.

All
unpleasant

nouns were arrange
d into two lists consisting of 20 words each with no
differences concerning the characte
ristic dimensions
. The same was done for
the neutral
nouns resulting in two unpleasant and two neutral lists
.



Design

Prior to the experiment the subjects were given v
erbal and written instructions: “
Several word
lists are going to be shown to you. You shall remember some of them for later. After each
word list you receive a cue whether the previous list is one to remember or one you can
forget”
.

The experiment consist
ed of two experimental conditions: the F (forget) condition
and the R (remember) condition. All subject received both conditions, with their order being
counterbalanced. Each condition started with the presentation of
list

1 which was
subs
equently
followed

by
an instruction to either forget
in the F condition
or to remember
in
the R condition

all
previous
words. Then
list 2 was
shown and followed by the instruction to
remember all previous words
in both conditions
.
Then a distractor task was given to the
su
bjects (
counting backwards in steps of three

for 2 min) before they
were asked to re
call

as
many words as possible of the previously shown nouns irrespective of the initial instruction
s.
After the
2

min
free recall test, the remaining condition was present
ed. The

procedure
of the
remaining condition was

identical to the first
condition

with one exception: all participants
who had
started with the F condition received then the R condition and vice versa.

Thus, each
participant received four lists containing
20 words each, two corresponding to the F condition
and to corresponding to the R condition. Using such a within
-
participants
1

design in the list
method is not expected to vary from using a between
-
participants design
(Zellner & Bauml,
2006)

and therefore offers the possibility of enhancing the power without a huge number of



1

Such within design offers an experimental and control condition and should not be confused with a wit
hin
design without control condition in which simply the forget list (first list) and the remember list (second list) are
compared

participants.

During presentation each of the words appeared for 2000

ms on the display
followe
d by a fixation cross for 1500

ms.

All

instructions were visible for 4

s.



The EEG recording was done with 65 Ag/AgCl electrodes. All impedances were kept below
5

kΩ. The EEG activity was recorded using soft
-

and hardware of Neuroscan (Scan,
SynAmps, Comp
umedics, El Paso, USA). The data was acquired with a sampling rate of
500

Hz, an o
nline filter

from, and Cz as the online reference. The experimental stimulation
was presented with Presentation 0.61 (Neurobehavioral Systems, Albany, USA). Prior to the
exp
eriment vertical, horizontal, and blink related eye movements were systematically
recorded for later eye correction of the experimental EEG data.


Data analysis

The recorded EEG data was processed with Brain Electrical Source Analysis (
Besa

®,
MEGIS Sof
tware GmbH, Gräfeling, Germany, www.besa.com). The recorded Cz reference
was offline changed into an average reference. The EEG
was corrected for eye movements,
artefact
were
reject
ed

(EEG>220

µV)
,

and the

data was filtered with a 0.3

Hz highpass and a
30

Hz lowpass filter. The corrected and filtered data were then split into epochs (
-
200

ms
-
2000

ms), baseline corrected, and averaged
. As any influence of the mid
-
condition
instructions will only be observable in the lists following these instructions, only t
hose lists
were compared. Thus, electrophysiological activity elicited by list 2 of the F
-
block and list 2
of the R
-
block was compared and analyzed
. The ERP analyses of the resulting grand means of
each condition were done using EMEGS

(ElectroMagnetic EncephaloGraphy So
ftware,
Junghofer & Peyk, 2004)
. The ERP data was visually inspected and time windows of
interest

were extracted. For those time segments groups of relevant electrodes were chosen for
statistical analyses.




Statistical analysis

All statistical calcul
ations were done with Statistica 6.1© (StatSoft, Inc. 2003,
www.statsoft.com). The statistical analyses of the behavioural and electrophysiological data
were done using repeated measure ANOVAs and for the post
-
hoc testing Fisher’s LSD. A
significance level

of 0.5 was used for all calculations.

The directed forgetting effect is here
calculated as poorer recall of list 1 in the F
-
condition compared to the R
-
condition (costs) and
better recall of list 2 in the F
-
condition compared to the R
-
condition (benefits)
, according to
Sahakyan and Delaney
(2005)
.


Results

Due to the experimental design the terms list factor and valence factor describe the very sa
me
condition and therefore can be used interchangeably. Depending on the focus of interest
sometimes the list characteristics of the conditions are highlighted and sometimes the valence
attributes are emphasized by using the corresponding factor name.



Re
call data

Table 2.2.2 displays the mean numbers of recalled words for the different conditions
. A two
-
way ANOVA with the factors block (F block, R block) and list (list1, list2) was calculated and
yielded a list
/valence

main effect [F
(1, 24
)
=5.80
, p<.05]

a
nd a significant interaction [F
(1,
24
)
=10.89
, p<.01]

reflecting

benefits of directed forgetting (p<.01) and a tendency for costs
(p=.148) as well as
more recall for list 2 tha
n for list 1 of the F block (p<.001) and than for list
1
of the

R block

(p<.05).

T
he scatterplot (fig. 2.2.2) reveals that most subjects recalled more
list 1 items in the R block than in the F block (costs, more blue dots above the linear line) and
that also most subjects recalled more list 2 items in the F block than in the R block (be
nefits,
more red dots beneath the line).


table
0
.
1
:

D
etails for immediate recall data. Including mean number of recalled words (standard error in
brackets) and significant results
for costs and benefits (p<.0
5*, p<.01**, p<.001***).


F block

R block

Directed forgetting

list 1 (neg)

list 2 (ntr)

4.24 (0.48
)

6.80 (0.63
)

5.20 (0.41)

4.76 (0.60)

costs (p=.148)

benefits**






figure
0
.
1
:
S
catterplot display of
the
individual recall data. The linear line describes a hypothetically symmetrical
recall list 1 and 2 in the different block.



To control for influences of gender and blockorder (F block first, R block first) additional
ANOVAs were calculated with these
factor as between factors. For gender, an
interaction
with

list was revealed [
F
(1, 23
)
=8.16
, p<.0
1
]
indicating that female participants recalled more

of
list 2 than of list 1 (p<.00
1) and more than males of list 1 (p<.0
1
)

and list 2 (p<.05)

whereas
the mal
e subjects showed no difference betw
een recall of list 1 and 2. No interactions
occurred for blockorder.




EEG data


EPN


LPP


Directed forgetting


Discussion

Experiment 2
: Neutral list 1 and negative list 2


Method


Subjects

Thirty subjects particip
ated in this experiment (14 male, 16 female) with a mean age of 22.79
(SE: 0.69). Two data sets were excluded due to extreme alpha waves and another set due to
extreme artefacts leaving 27 data sets (13 male, 14 female) for analysing.
All subjects were
rig
ht
-
handed
(assess
ed according to Annett, 1979; Oldfield, 1971)

and had normal or
corrected to normal vision. Informed consent was provided and all received payment or
course credit for participation.


Material

The identical stimulus material was used as in experiment

3
.


Design

The

design was the same as in experiment 1 except that within a block, the first list always
consisted of neutral words and the second list of unpleasant ones.


EEG recording, data and statistical analysis

The
EEG recording, data and statistica
l analysis
were identical to those used in experiment 1.


Results


Recall data

The mean numbers of recalled words for the different conditions are displayed in table 2.2.4
.
A two
-
way ANOVA with the factors block (F block, R block) and list
/valence

(list1
/n
eutral
,
list2
/unpleasant
) was calculated and yielded a list
/valence

main effect [F
(1, 26
)
=14.80
, p<.0
01
]

and a significant interaction [F
(1, 26
)
=7.49, p<.05
]

reflecting

trends for both costs and benefits
of directed forgetting as well as
more recall for li
st 2 tha
n for list 1 of the F block (p<.001)
and than for list 1
of the

R block

(p<.0
1
)

and less recall for list 1 of the F block than for list 2
of the R block (p<.01)
.

The scatterplot (fig. 2.2.4) reveals that most subjects recalled more list
1 items in t
he R block than in the F block (costs, more blue dots above the linear line) and that
also most subjects recalled more list 2 items in the F block than in the R block (benefits, more
red dots beneath the line).


table
0
.
1
:

Details for immediate recall data. Including mean number of recalled words (standard error in
brackets) and significant results
for costs and benefits.


F block

R block

Directed forgetting

list 1 (ntr
)

list 2 (n
eg
)

3
.
89 (0.62
)

7.18 (0.45
)

5.
25 (0.63
)

5.86 (0.46
)

costs (p=.061)

benefits (p=.068)



figure
0
.
1
:
Scatt
erplot display of the
individual recall data. The linear line describes a hypothetically symmetrical
recall list 1 and 2 in the diff
erent block.


To control for influences of gender and blockorder (F block first, R block first) additional
ANOVAs were calculated with these factor as between factors. Neither gender nor blockorder
interacted with any of the effects.


EEG data


Discussion

Replication Wessel & Merckelbach

Can be generally explained by retrieval inhibition, context change and attentional focusing.
Context change and attentional focusing can add up on the effects.

Contest change can be initiated through the forget instruction
but also through the change of
valence of a whole list. Then the recognition of the change would not be as abrupt as with the
forget instruction but be a little slower. Thus, the context change initiated through valence
change in the remember condition sho
uld be weaker than the context change in the forget
condition.

Due to this, the perfect interactions found with pure valence material are distorted in these
experiments as in pure valence experiments, no context change is assumed for the remember
condition
.


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