Ž . International Journal of Psychophysiology 38 2000 21]41 The objective assessment of amnesia in dissociative identity disorder using event-related potentials John J.B. Allen U , Hallam L. Movius, II Department of Psychology, Uni ¤ ersity of Arizona, P.O.B. 210068, Tucson, AZ 85721-0068, USA Received 1 September 1999; received in revised form 2 April 2000; accepted 2 May 2000 Abstract Ž . Assessment of amnesia in Dissociative Identity Disorder DID typically relies on self-report, the veracity of which cannot often be independently verified. Memory in DID was therefore assessed using an objective method that Ž . involved event-related potentials ERPs as well as indirect behavioral measures of memory, and that provided statistically supported assessments for each participant. Four participants who met DSM-IV criteria for DID Ž . participated in an ERP memory assessment task, in which words learned by one identity identity A were then Ž . presented to a second identity identity B . All four participants } tested as identity B } produced ERP and behavioral evidence consistent with recognition of the material learned by identity A. While it would be premature to generalize all cases of DID, the results suggest that there may be reasons to question the veracity of reports by individuals who meet diagnostic criteria for DID on the basis of a structured clinical interview. Q 2000 Elsevier Science B.V. All rights reserved. Ž . Keywords: Amnesia; Dissociative identity disorder DID ; Memory 1. Introduction Ž . Dissociative Identity Disorder DID } formerly termed Multiple Personality Disorder Ž . MPD } is characterized by the presence of two or more distinct identities or personality states that recurrently take control of the individual’s U Corresponding author. behavior, accompanied by an inability to recall important personal information that is too exten- sive to be explained by ordinary forgetfulness Ž . 1 American Psychiatric Association, 1994 . The prevalence of DID has fluctuated widely over the last century, which some researchers have argued 1 The disturbance cannot be due to the direct physiological Ž . Ž effects of a substance e.g. alcohol or medical condition e.g. . complex partial seizures . 0167-8760r00r$ - see front matter Q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 1 6 7 - 8 7 6 0 00 00128-8
Transcript
Ž .International Journal of Psychophysiology 38 2000 21]41
The objective assessment of amnesia in dissociativeidentity disorder using event-related potentials
John J.B. AllenU, Hallam L. Movius, IIDepartment of Psychology, Uni ersity of Arizona, P.O.B. 210068, Tucson, AZ 85721-0068, USA
Received 1 September 1999; received in revised form 2 April 2000; accepted 2 May 2000
Abstract
Ž .Assessment of amnesia in Dissociative Identity Disorder DID typically relies on self-report, the veracity of whichcannot often be independently verified. Memory in DID was therefore assessed using an objective method that
Ž .involved event-related potentials ERPs as well as indirect behavioral measures of memory, and that providedstatistically supported assessments for each participant. Four participants who met DSM-IV criteria for DID
Ž .participated in an ERP memory assessment task, in which words learned by one identity identity A were thenŽ .presented to a second identity identity B . All four participants } tested as identity B } produced ERP and
behavioral evidence consistent with recognition of the material learned by identity A. While it would be premature togeneralize all cases of DID, the results suggest that there may be reasons to question the veracity of reports byindividuals who meet diagnostic criteria for DID on the basis of a structured clinical interview. Q 2000 ElsevierScience B.V. All rights reserved.
Ž .Keywords: Amnesia; Dissociative identity disorder DID ; Memory
1. Introduction
Ž .Dissociative Identity Disorder DID }formerly termed Multiple Personality DisorderŽ .MPD } is characterized by the presence of twoor more distinct identities or personality statesthat recurrently take control of the individual’s
U Corresponding author.
behavior, accompanied by an inability to recallimportant personal information that is too exten-sive to be explained by ordinary forgetfulnessŽ . 1American Psychiatric Association, 1994 . Theprevalence of DID has fluctuated widely over thelast century, which some researchers have argued
1The disturbance cannot be due to the direct physiologicalŽ . Žeffects of a substance e.g. alcohol or medical condition e.g..complex partial seizures .
0167-8760r00r$ - see front matter Q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S 0 1 6 7 - 8 7 6 0 0 0 0 0 1 2 8 - 8
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4122
reflects the influence of media and culture onsuggestible individuals who are already distressedŽ .Spanos, 1996 . The nature of DID has alsochanged over the last century, with early casesusually involving no more than three personalitiesand transitions between personalities occurringonly after a period of sleep; modern patients maydisplay an average of 15 personalities, and may
Ž .have up to 100 Ross et al., 1989b .Perhaps the most controversial part of this
diagnosis has been the debate over whether dif-ferent identities or ‘alters’ might truly be unawareof each other. Prior to 1994 intrapsychic amnesiawas not required as a criterion for MPD. In 1994} with the publication of the DSM-IV } the
name of the disorder was changed from MPD toDID, and amnesia ‘too extensive to be explainedby ordinary forgetfulness’ became necessary fordiagnosis. While some therapists have claimedthat a DID case could have several personalitieswho share consciousness, the ability to determinewhether personalities are truly amnestic for eachother has become a key theoretical and diagnosticissue. The present study therefore used an objec-tive and reliable method of assessing memory thatis able to identify recognized material, even incases where individuals deny knowledge of such
Ž .material Allen et al., 1992 .
1.1. Pre¨ious studies of MPD2 using ‘objecti e’measures
Anecdotal and case studies comprise the ma-jority of publications to date on MPD. Behavioralstudies of multiple identities date back to 1817,and psychophysiological studies date back nearlya century, to an investigation of galvanic skinresponses in a patient who displayed multiple
Ž .identities Greaves, 1980 . There have been, how-ever, surprisingly few controlled studies using pu-
2 Because the amnesia criterion was not present among theDSM-III and DSM-III-R criteria for MPD, we use the acronymMPD when reviewing studies that relied on DSM-III-R orearlier criterial for diagnosis. We reserve the acronym DID torefer to cases that meet DSM-IV criteria, and thereforenecessarlily involve reported amnesia.
Žtative MPD cases Miller and Triggiano, 1992;.Kihlstrom et al., 1993 . Reported behavioral cor-
relates of MPD include changes in handwritingŽacross personalities Thigpen and Cleckley, 1957;
.Coons, 1984 , changes in vocal expressionŽ .Putnam, 1984 , and changes in handednessŽ .Putnam, 1984 . Most, if not all, of these behav-iors fall under voluntary control, however, and
Ž .are therefore possible to simulate Spanos, 1996 .In addition to doubts about the reliability andvalidity of the reported observations, the lack ofadequate controls or comparison subjects in al-most all cases makes firm conclusions difficult, if
Žnot impossible Miller and Triggiano, 1992;.Brown, 1994 .
1.2. Psychophysiological correlates of DID
Previous studies have reported a number ofchanges in physiology that parallel reportedchanges in personalities. Such changes include a
Žchange in respiration rate Bahnson and Smith,.1975; Larmore et al., 1977 , differences in pat-
Žterns of galvanic skin responses Ludwig et al.,.1972; Brende, 1984 , differences in visual acuity
Ž .Miller, 1989 , and differences in patterns of EEGŽacross alleged personalities Ludwig et al., 1972;
.Larmore et al., 1977; Braun, 1983 . While it mightinitially seem that such responses are outside therealm of voluntary control, it is critical to keep inmind that substantial changes in physiologicalmeasures can covary with changes in behavior. Ifone is to appropriately infer that some physiologi-cal change is a marker of an identity change inDID, it would be necessary to show not only thatthis change necessarily occurs with putative iden-tity change in DID, but also that there is not asimilar change across ‘normal’ states among non-
ŽDID individuals cf. Cacioppo and Tassinary,.1990 . Moreover, many such changes could in
theory be simulated; EEG can vary markedly as aŽfunction of eye movement, for example Plotkin,
.1979; Perlini and Spanos, 1991 , and merely imag-ining different moods can induce a number of
Ž .autonomic shifts Sheikh and Kunzendorf, 1984 .In general, the strategy of looking for psychophys-iological differences across alleged personalitiesas markers of distinct identities is a poor one, as
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 23
Ž .such differences: 1 could represent nothing morethan normal change associated with changes in
Ž .emotional or cognitive state; 2 could be due to anumber of factors that fall under voluntary con-
Ž . Ž .trol such as muscle tension Coons, 1988 ; or 3could be due simply to capitalization on chance.In order to draw more convincing conclusionsabout behavioral correlates, it is necessary at aminimum to show that such changes are signifi-cantly different from those displayed by reason-able control groups or during control conditions.Unfortunately, studies that have employed eithercontrol subjects or control conditions are few innumber.3
1.3. Studies of psychophysiological correlates withcontrol groups
Ž .Putnam et al. 1990 examined electrodermaland cardiovascular responses to tones in nineMPD patients and five control subjects instructedto fake changes in personality, finding that therewas a non-significant trend for MPD patients to
Ž .show less habituation. Coons et al. 1982 foundthat a simulatorrcontrol case exhibited largerchanges in various EEG frequency bands whensimulating a personality change than did two pu-tative MPD cases. The researchers concluded thatthe pattern of changes in EEG were more consis-tent with changes in anxiety, muscle tension, andconcentration } perhaps reflecting changes inemotional states, expectancies, muscle tension, ortask demand } than with complete transforma-
Ž .tion in personalities. As Brown 1994 p. 107concluded, to date ‘‘there is neither consistentevidence for a distinctive EEG abnormality in
Ž .MPD patients trait nor a shift in EEG activityŽ .state when a patient experiences a ‘shift’between personalities’’.
ŽIn two studies, Miller and colleagues Miller,
3Even studies of DID symptoms have suffered from theŽ .absence of comparison groups. For example, Ross et al. 1989a
found that loss of hearing, reported by 18% of DID cases inŽ .one sample Bliss, 1980 , turned out to be equally prevalent
among control groups with eating disorders, panic disorder,and schizophrenia.
.1989; Miller et al., 1991 found that MPD patientsexhibited more variability in opthalmalogical re-sponses, including visual acuity, manifest refrac-tion, eye muscle balance, and visual fields. As
Ž .Miller and Triggiano 1992, p. 54 point out, how-ever, the obtained between-group differences mayhave been due to greater overall response vari-ability within the MPD group, independent fromvariability associated with specific changes in per-sonalities, and that these measures fail to ‘pro-vide evidence for the distinctiveness or unique-ness of individual personality states’.
In a study of cerebral blood flow patterns,Ž .Mathew et al. 1985 found increased blood flow
to the right temporal lobe during changes inpersonality in one MPD patient when comparedwith three control subjects. No statistical testswere performed that would allow inferences to bemade about the significance of reported changesin blood flow.
1.4. Experimental tests of memory in MPD cases
Ž .Nissen et al. 1988 investigated transfer ofmemory across identities in an individual whoreported intrapsychic amnesia. On several teststhere was little evidence of memory transfer, whileon others there was evidence of such transfer.
Ž .Nissen et al. 1988 concluded that assessing me-mory indirectly was a necessary, but not a suffi-cient, condition for demonstrating transfer of me-mory across personalities. Moreover, they sug-gested that implicit memory was seen in taskswhere the interpretation of stimuli was not likelyto differ between personalities, but no implicitmemory was seen where individual interpretation
Ž .of the stimuli was involved. Eich et al. 1997replicated some of these findings, again finding
Ž .that direct assessments of memory e.g. recallreveal inter-identity amnesia, and indirect meth-
Ž .ods picture-fragment completion show evidenceof inter-identity transfer of knowledge.
Ž .Silberman et al. 1985 adopted an interestingapproach to assessing memory, assuming that in-ter-personality amnesia should facilitate ‘com-partmentalizing’ memories, and thereby facilitatecorrectly discriminating lists of words learned asdifferent personalities. Two identities first learned
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4124
a list of words, and then both identities weresubsequently tested after a 2-h interval. Althoughtheir overall recall and recognition performanceswere similar to controls, MPD subjects did nobetter than controls in correctly assigning learnedwords to the personality that had learned them,suggesting that despite MPD subjects’ subjectivereports of compartmentalized memories, suchmemories had substantially ‘leaked’ between per-sonalities.
1.5. E¨ent related potentials as a method for assessingmemory
Ž .The use of event-related potentials ERPs withrespect to MPD has been very limited. Moreover,to the extent that ERPs have been utilized in
Ž .MPD e.g. Braun, 1983 , their use has not beenmotivated by a theoretical rationale to assessmemory or other symptomatology of MPD; rather,such investigations seem motivated by the erro-neous assumption that psychophysiological dif-ferences between identities can provide evidencein support of their veracity. ERPs, however, rep-resent a promising method by which to assessmemory and amnesia, a central symptom of DID.
1.5.1. ERPs and the assessment of memoryWhile several components of the ERP have
Žbeen shown to be sensitive to memory e.g. San-quist et al., 1980; Neville et al., 1986; Rugg andNagy, 1989; Smith and Halgren, 1989; Bentin andMoscovitch, 1990; Bentin et al., 1992; Paller andKutas, 1992; Rugg and Doyle, 1992, Rugg andDoyle, 1994; Smith, 1993; for a recent review see
.Rugg, 1995 , most research examining the rela-tionship of these components to memory haverelied on the assessment of groups of subjects,comparing components of ERPs for previously-seen and new items using conventional paramet-ric statistical procedures. While this approach isessential for understanding the theoretical sig-nificance of these components with respect tomemory, such procedures do not directly informclinical assessment. For clinical assessment, reli-able and valid decisions need to be rendered forindividual cases. For this purpose, a variety of
statistical methods have been used with event-related potentials.
In using ERPs to assess memory in individualcases, investigators are often interested in usingERPs to assess memory in situations where sub-jects are unable, or unwilling, to report theirrecollection for learned material. These assess-ment procedures are essentially variants of the
Ž .Guilty Knowledge Technique Lykken, 1959 andhave most often, but not exclusively, been applied
Žin the detection of deception Rosenfeld et al.,1988, 1991, 1998; Boaz et al., 1991; Farwell and
.Donchin, 1991; Allen et al., 1992 . In most ofthese paradigms, two classes of previously seenitems are presented, only one of which a subjectacknowledges recognizing. These previously seenitems appear infrequently among frequent itemsthat have not been previously seen. The previ-ously seen items will therefore stand out as rareand significant by virtue of having been learnedpreviously. This experimental design makes itlikely that the previously seen items, regardless ofwhether they are acknowledged as familiar, willelicit a larger P3 amplitude in the ERP than willthe frequent unfamiliar items.
Our previous work using this experimental de-Žsign Allen, 1992; Allen et al., 1992; Allen and
.Iacono, 1997 has shown that statistically sup-ported decisions can be rendered for individualsubjects with acceptably high rates of accuracy.
ŽUsing a Bayesian classification procedure see.Appendix A in three groups of 20 subjects each
Ž .Allen et al., 1992 , the ERP procedure was suc-cessful in correctly identifying previously-learnedmaterial } regardless of whether a person explicitlyacknowledged ha¨ing learned it } 94% of thetime. It was similarly successful in classifying un-familiar material 96% of the time.
This experimental procedure, and associatedanalytical strategy, lends itself readily to the studyof memory in DID. If one were to identify two
Ž .distinct identities identity A and identity B , eachof whom reported mutual amnesia for recollec-tions of the other identity, then each could learna set of material that should be familiar to onlythat identity and not the other. Because this ERPmemory assessment procedure identifies familiarmaterial regardless of whether a subject explicitly
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 25
acknowledges having learned it, the ERP couldserve as an objective way to assess the report ofamnesia in DID. If identity B were amnestic foritems learned by identity A, then the ERP proce-dure should only classify ERPs to identity B’sitems as familiar, while classifying ERPs to iden-tity A’s material as unfamiliar. If, by contrast,identity B in fact denied recognizing identity A’sitems despite being aware of these items, thisERP procedure should be sensitive to that aswell. In other words, as a clinical assessment tool,either outcome would prove informative. Theformer outcome would provide objective evidenceof amnesia, while the latter outcome would sug-gest that the reported amnesia was, in fact, fabri-cated.
2. Method
2.1. Participants
Five potential participants volunteered to par-ticipate. Participants were referred from commu-nity practitioners, or responded to an advertise-ment } in a monthly patient newsletter } de-scribing a study of memory and Dissociative Iden-tity Disorder being conducted at the University ofArizona.
Participants agreed to come to two separateappointments, one for diagnostic interviewing, anda second a few weeks later involving ‘brainwave’recording. During the first visit, all participantscompleted the Structured Clinical Interview for
Ž .Bernstein and Putnam, 1986 , the Folstein MiniŽMental State Examination MMSE; Folstein et
. Žal., 1975 , and several other measures earliestmemories, digit span, various personality mea-
.sures not reported here.From among these five potential participants,
four were able to complete testing and are de-scribed here. All four met DSM-IV diagnosticcriteria for DID according to their responses toquestions from the SCID-D. The fifth, who had arather remarkable claim of over 600 personalitiesand was judged not to provide reliable informa-
tion during the interview, did not complete theŽ .testing during session 2 see footnote 4 and did
not keep several rescheduled appointments. Eachof the remaining four cases is described in sum-mary format in Table 1. As can be seen in thetable, each of the four participants is rather typi-
Žcal of cases reported in the literature Spanos,.1994 in that they are female, they have a history
of other psychiatric problems that precede theirdiagnosis of DID, and that they report on averageabout eight identities.
2.1.1. College student comparison sampleSixty college student controls previously re-
Ž .ported in Allen et al. 1992 were used as acomparison sample for the present study. Al-though these college student controls were notspecifically asked to simulate DID, they weregiven instructions to deny knowledge of a recentlylearned list in the context of an ERP assessmentparadigm that was virtually identical to that usedin the present study. The college students wereasked to deny and conceal knowledge of a re-cently learned list in order to determine whetherERPs could detect recognized items even whenparticipants denied recognizing them as previ-ously learned.
2.2. Procedure
DID participants made two visits to the Univer-sity. The first visit was to a clinical interviewingroom within the Psychology Clinic, and entailedthe diagnostic interviewing and the administra-tion of the instruments listed above. The secondvisit, scheduled 2]4 weeks later, was to the Psy-chophysiology Laboratory. At the end of the firstvisit, the procedure for the second visit was de-scribed in order to help participants prepare forthe procedure, and to determine whether theywished to bring an assistant of their choosing.Ž .Only participant M03 did so. Participants weretold that one of the difficulties in DissociativeIdentity Disorder, as they themselves had alreadydescribed in the diagnostic interview, was thatsome identities had no awareness of the activitiesand experiences of other personalities. They werefurther told that we were specifically interested in
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4126
Tab
le1
aD
emog
raph
ic,
diag
nost
ic,
and
clin
ical
info
rmat
ion
for
DID
Par
tici
pant
s
M02
M03
M04
M05
Dem
ogra
phic
sI
P.K
.39-
year
-old
fem
ale
IM
.C.3
6-ye
ar-o
ldfe
mal
eI
M.D
.40
year
-old
fem
ale
IA
.J.5
1-ye
ar-o
ldfe
mal
eI
2ye
ars
colle
geI
2ye
ars
colle
geI
2ye
ars
colle
geI
2ye
ars
ofco
llege
ID
ivor
ced
=4
ISe
para
ted
from
only
mar
riag
eI
Div
orce
dI
Div
orce
d,w
idow
edI
Une
mpl
oyed
=2
year
sI
Une
mpl
oyed
=2
year
s;no
wst
uden
tI
Em
ploy
ed5
year
sI
Une
mpl
oyed
=3
year
sI
DE
Ssc
ore
s70
ID
ES
scor
es
47I
DE
Ssc
ore
s91
ID
ES
scor
es
65I
MM
SEs
29I
MM
SEs
29I
MM
SEs
28I
MM
SEs
30
Dia
gnos
tic
hist
ory
IH
isto
ryof
subs
tanc
eab
use
IH
isto
ryof
eati
ngdi
sord
erI
No
hist
ory
ofsu
bsta
nce
abus
eI
Con
vers
ion
reac
tion
’3ye
ars
ago
IC
urre
ntm
edss
proz
ac,m
elar
ilI
Cur
rent
med
sscl
onap
in,
IM
edss
clon
apin
,zol
oft,
afte
rse
izur
es,b
lindn
ess,
para
lysi
sI
Dia
gnos
eddu
ring
cour
seof
wel
lbut
rin,
synt
hroi
dpr
omaz
ine
subs
tanc
e-ab
use
trea
tmen
tci
rca
ID
iagn
osed
1991
,but
repo
rts
IH
isto
ryof
harm
tose
lf,
ISu
bseq
uent
diag
nosi
sof
DID
1988
,but
repo
rts
sym
ptom
sha
vesy
mpt
oms
date
back
toat
leas
tho
spit
aliz
atio
nsI
His
tory
ofho
spit
aliz
atio
ns,s
uici
deŽ
.be
enpr
esen
tsi
nce
atle
ast
teen
teen
year
sI
Inth
erap
yon
rof
fsi
nce
1983
atte
mpt
sea
rlie
stat
age
6ye
ars
IR
epor
tssy
mpt
oms
pres
ent
IC
urre
ntm
edss
effe
xor,
synt
hroi
dsi
nce
earl
ych
ildho
od
Dia
gnos
tica
llyre
leva
ntsy
mpt
oms
IR
epor
tsat
leas
t10
iden
titi
esI
Rep
orts
atle
ast
13id
enti
ties
IR
epor
tsat
leas
t4
iden
titi
esI
Rep
orts
atle
ast
6id
enti
ties
,one
ID
aily
gaps
inm
emor
yrm
issi
ngti
me
ID
aily
gaps
inm
emor
yrm
issi
ngti
me
ID
aily
gaps
inm
emor
yrco
nsis
tent
alte
rth
roug
hout
high
mis
sing
tim
esc
hool
,and
five
now
IH
asfo
und
unfa
mili
arcl
othe
sin
ID
escr
ibes
dram
atic
chan
ges
inab
iliti
esI
Dis
tant
trav
elw
itho
utkn
owin
gI
Dai
lyga
psin
mem
oryr
mis
sing
tim
eŽ
.cl
oset
e.g.
arti
stic
and
com
pute
rw
ork
why
IH
asfo
und
furn
itur
ere
-arr
ange
dI
Rep
orts
age-
regr
essi
onex
peri
ence
sI
Has
been
calle
dot
her
nam
esI
Rep
orts
inte
rnal
dial
ogue
sbe
twee
nw
itho
utkn
owle
dge
bype
ople
who
insi
stth
eykn
owhe
rid
enti
ties
IH
asfo
und
clot
hes,
jew
elry
,I
Des
crib
esin
tern
aldi
alog
ues
ID
escr
ibes
inte
rnal
dial
ogue
sbe
twee
nfu
rnit
ure
she
did
not
rem
embe
rI
Rep
orts
forg
etti
ngho
wto
dres
sse
lf,b
rush
Ž.
betw
een
iden
titi
esid
enti
ties
buyi
ngte
eth
whe
na
child
iden
tity
ID
escr
ibes
chan
ges
inI
Rep
orts
swit
chin
gun
der
dure
ss,e
spec
ially
hand
wri
ting
duri
ngjo
urna
lent
ries
duri
ngfa
mily
confl
icts
IR
epor
tsm
emor
ies
ofri
tual
abus
e
Obs
erva
tion
sof
test
edid
enti
ties
IR
epor
ts‘c
o-co
nsci
ousn
ess’
IR
epor
tsno
‘co-
cons
ciou
snes
s’I
Rep
orts
no‘c
o-co
nsci
ousn
ess’
IR
epor
tsth
aton
lyon
eof
the
lear
ned
betw
een
test
edid
enti
ties
betw
een
test
edid
enti
ties
test
edid
enti
ties
wor
dsw
asav
aila
ble
tobo
thte
sted
Ž.
IE
xper
imen
ter
had
clin
ical
iden
titi
eslim
ited
‘co-
cons
ciou
snes
s’im
pres
sion
that
part
icip
ant
IO
neid
enti
tym
anif
ests
Ger
man
acce
ntw
asex
peri
enci
ngI
Rep
orts
that
atle
ast
som
eof
her
depe
rson
aliz
atio
nid
enti
ties
are
not
‘co-
cons
ciou
s’
aŽ
.N
ote.
All
sym
ptom
sre
port
edby
the
part
icip
ants
.DE
S,D
isso
ciat
ive
Exp
erie
nces
Scal
em
axs
100,
scor
eov
er30
sugg
ests
poss
ible
diss
ocia
tive
diso
rder
;MM
SE,M
iniM
enta
lŽ
.St
atus
Exa
min
atio
nm
axs
30.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 27
that phenomenon, and therefore wished to testtwo distinct identities that were likely to be un-aware of each others’ activities. We asked themto think through whether it would be possible tofirst test one identity, and then ask them to switchto another identity that would be unlikely toknow anything that just happened to the firstidentity. We further stipulated that both identi-ties must be able to read common English wordson a computer screen.
Upon arrival to the Psychophysiology Labora-tory, participants were shown the control roomand equipment, and the adjacent sound-attenuated subject chamber. Participants were
Ž .then prepared for electroencephalographic EEGrecording by fitting a stretch lycra cap and sevenindividual electrodes. After preparation, partici-pants were escorted to the adjacent chamber tobegin the memory assessment procedure. Partici-pants were seated in front of a computer monitor,with an experimenter seated just behind and tothe left of the participant.
2.2.1. Identity A’s tasksEach participant was first asked to report her
identity. Once she confirmed that this was in factthe identity she had previously indicated shouldbe tested, identity A was shown a list of sixunrelated words and asked to learn them to acriterion of two perfect serial recitations. This listwas selected randomly from among a set of sevenlists of six high-frequency words that had beenmatched for word frequency using the word fre-
Ž .quency norms of Carroll et al. 1971 . For learn-ing, the words were presented at a rate of one
Ž .word every 2 s stimulus durations1530 ms on acomputer screen mounted on a movable arm andpositioned approximately 85 cm in front of theparticipant’s face. The experimenter recited eachword aloud as it appeared. Words subtended ap-proximately 0.348 of visual angle vertically and1.01]1.488 horizontally. Upon completion of thislearning task identity A performed a simple com-puterized recognition task in which she pressed abutton with the thumb of her dominant hand toindicate recognition of words she had learned andpressed a button with her non-dominant thumbfor words she did not recognize. Learned words
appeared on 1r5 of the trials and unlearnedwords appeared on 4r5 of the trials. These un-learned words were matched for frequency of
Ž .occurrence with the seven lists mentioned abovethat participants could learn, and these unlearnedwords were never seen subsequently in any othertasks.
Identity A was then thanked for her participa-tion and the experimenter requested that sheswitch to identity B. Each participant had herown idiosyncratic method of switching identities,and in some cases, multiple attempts were re-quired in order for the participant to switch tothe intended identity. The switch from identity Ato identity B sometimes also occurred via another
Židentity i.e. identity A to identity X to identity.B .
2.2.2. Identity B’s tasksIdentity B was asked to recall what had hap-
pened during the experiment, and specifically ifshe remembered learning any words at this point.Participant M02 recalled identity A’s words, andparticipant M05 recalled one of identity A’s words.Neither participant M03 nor M04 could recall anywords, or even recall having learned any words.
Identity B then learned a list of six unrelatedwords other than that learned by identity A. Thislist was randomly selected from among the re-maining six of the original seven matched lists.This list was presented in the same manner as theearlier list. Once identity B had learned the list tothe criterion of two perfect serial recitations, shewas presented with the critical procedure in whichwords learned by identity A appeared on 1r7 orthe trials, words learned by identity B appearedon 1r7 of the trials, and words matched forfrequency but not previously seen by either iden-tity appeared on 5r7 of the trials.4 This arrange-ment made it likely that the learned lists, appear-ing relatively infrequently against a background
4 It was at this point } after instructions for this procedureŽwere administered } that the first potential participant the
one who claimed over 600 personalities and for whom we do.not report data reported that she suddenly developed an
incapacitating migraine and needed to discontinue testing.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4128
of unlearned material, would elicit a large P3 ifthey were recognized. Identity B was presentedwith five blocks of 42 words, with each blockcontaining a different random ordering of all six
Žwords from all seven lists two learned, and five. Žunlearned . At the beginning of each block in
.addition to the 42 words , three additional wordsappeared that were not included for purposes ofsignal averaging. Stimulus duration was 306 ms,and onset-to-onset interval was 1999 ms. Monitordistance and visual angles subtended by stimuliwere identical to those of the learning phase. Theexperimenter instructed identity B that she wouldsee a long list of words consisting of words shehad learned as well as other words. She wasinstructed to press the ‘YES’ button with thethumb of her dominant hand if the word on thescreen was one of the words she rememberedlearning today, and to press the ‘NO’ button withthe non-dominant thumb for all the other words.She was told to respond as quickly and accuratelyas possible.
2.2.3. Forced-choice recognition tasksFollowing this oddball recognition task, identity
B was given a forced-choice recognition task. Theintent of the forced-choice task was to provide anindex of whether participants were systematicallyavoiding acknowledging words learned by identityA, and whether words seen as distractors by iden-tity A would show evidence of transfer to identityB. Veritable amnesia would not result in syste-matic avoidance of learned material, but ratherwould show up as the tendency to respond withrecognition 50% of the time, because if one wereamnestic for previously learned words, one wouldchoose them 50% of the time by chance in thisforced choice task. Two words were presentedside-by-side on the computer screen simultane-ously, and identity B was instructed that sheshould indicate which of the two words she hadlearned. She was further instructed that if she wasunsure, she should guess, as we wanted her tomake a response for each and every pair of words.This task consisted of three different types of
Ž . Ž .stimuli: 1 Explicit Memory Probes ns6 , whichcontained words learned by identity A paired with
previously unseen items matched for frequency;Ž . Ž .2 Incidental Memory Probes ns12 , whichcontained words that had been previously seen asunlearned distractors by identity A paired withpreviously unseen items matched for frequency;Ž . Ž .3 Control Trials ns6 , which were two previ-ously unseen items matched in frequency to allother words. For the first two types of stimuli,words that had been previously seen appeared onthe left side of the screen for half the trials andon the right side of the screen for the other halfof the trials. Following this task, identity B wasthanked for her time and the experimenter onceagain requested to meet with identity A. Afterparticipants reported a successful switch to iden-tity A, a similar forced choice recognition taskwas administered to identity A to determinewhether identity A was aware of what identity B
Žhad learned. In this task, the learned words Ex-. Žplicit Probes and the previously seen words Inci-.dental Probes were those that were seen only by
identity B.Unfortunately, this forced choice recognition
task was implemented after the testing of partici-pant M02, and response apparatus problems ren-dered data from participant M03 useless. There-fore, only data for participants M04 and M05 areavailable.
2.3. Psychophysiological recording and analysis
2.3.1. Signal acquisition and analysisElectroencephalographic signals were recorded
from 26 scalp sites using tin electrodes mountedin an electrode cap with seven additional tinelectrodes outside the cap. Three of the additio-nal electrodes were placed to monitor electroocu-
Ž .lographic EOG activity: one at the nasion andŽone each directly below each eye 20% of the
.nasion]inion distance below FP1 and FP2 . Addi-tionally, an electrode was placed on the left andthe right mastoid and two of the electrodes wereused with FP1 and FP2 to create two bipolar
Ž .electromyographic EMG channels over the leftand right medial frontalis muscle. Recording sitesin the electrocap included FP1, FP2, F7, F8, F3,Fz, F4, FTC1, FTC2, C3, Cz, C4, T3, T4, T5, T6,
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 29
TCP1, TCP2, P3, Pz, P4, PO1, PO2, O1, Oz, andO2. All impedances were below 5 kV and allchannels were referenced online to the left mas-toid and amplified using a Grass model 12 Neuro-data system with a band-pass of 0.1]100 Hz anddigitized continuously at a sampling rate of 256Hz. All signals were amplified 20 000 times exceptfor FP1, FP2, the three EOG sites, and the EMGsites, which were all amplified 5000 times. Thecontinuous files were digitally filtered with a 12.5-Hz, 96-dB per octave low-pass filter, and thencorrected for ocular artifact using the approach
Ž .of Semlitsch et al. 1986 using a bipolar channelderived from the nasion and the site below theleft eye. The data files were then epoched from150 ms prior to stimulus onset to 1500 ms after
Žstimulus onset, linear detrended to remove any.prolonged DC shift in the waveforms , baseline
corrected to a prestimulus baseline of y150]0ms, and finally re-referenced off-line to linkedmastoids. Averaged ERPs were then created for
Žeach condition two learned and five unlearned.lists . For analyses involving the Bayesian predic-
tion, the waveforms were additionally filtered witha 5.75-Hz low-pass filter just as in Allen et al.Ž .1992 .
3. Results
Although most of the analyses involve the useof the Bayesian approach detailed in Appendix A,parametric statistics are presented to round outthe interpretation of the data. In cases whererepeated measures analyses of variance are re-ported, the Greenhouse]Geisser correction wasused. We report the P-values associated with theEpsilon-corrected degrees of freedom, but reportthe original degrees of freedom.
3.1. Beha¨ioral data during identity B’s recognitiontask
ŽTable 2 shows the number of times 30 maxi-.mum that identity B responded ‘YES’ to indicate
recognition of different word lists. As can be seenfrom the table, all four DID participants deniedrecognition on a majority of trials in which wordslearned by identity A were presented, and veryseldom indicated recognition for words that
Ž .should have been unfamiliar lists U1]U5 . Withthe exception of participant M04, these responsedata are virtually identical to the pattern seen in
Ž .college-student controls Allen et al., 1992 whoTable 2
aAffirmative responses by identity B indicating recognition of items from the various lists
aNote. Maximums30. U1 through U5 are five different unfamiliar lists. Identity B refers to words learned by identity B andŽ .identity A refers to words learned by identity A. The college student controls are the 60 participants reported in Allen et al. 1992 ,
Ž .who were instructed to deny knowledge of a previously learned list Conceal and to acknowledge learning a recently learned listŽ .NConceal .
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4130
aNote. Mean response latencies are calculated for ‘YES’ responses to words learned by identity B, and to ‘NO’ responses to allŽ .other words. The college student controls are the 60 participants reported in Allen et al. 1992 , who were instructed to deny
Ž . Ž .knowledge of a previously learned list Conceal and to acknowledge learning a recently learned list NConceal .bReaction time estimated as the ‘YES’ button failed to record latencies for this particular participant. This estimate was derived
by taking the ratio of ArB response latencies for the other three participants, and using this scaling factor to estimate thisparticipant’s response latency for this condition. Re-running the analysis without this participant yielded virtually identical results. It
Ž .is worth noting that this ratio of reaction times ArB for the DID participants was 0.95, and for the college student controls it was0.94.
were instructed to deny knowledge of a previouslearned list. To compare the DID participants
Ž .and undergraduate participants, a 7 List by 2Ž .Group: DID, Control repeated measures analy-sis of variance was conducted. Data were firstrecoded to express the number of ‘incorrect’ re-sponses, that is the number of times each partici-pant did not respond in accord with the expecta-tion of how someone who was amnestic for iden-tity A’s words would respond. This meant that‘NO’ responses for identity B’s words and the‘YES’ responses for identity A’s words were ana-lyzed. The rationale for analyzing the data in thisfashion was that this transformation put all listson a similar metric, rather than having one listwith a disproportionately large value. Moreover,the data expressed in this fashion serve as the
Žinput data for the Bayesian combination see.below of behavioral indicators. The anticipated
Ž .main effect for List F s24.8, P-0.001 indi-6,372cated that participants made more incorrect re-sponses to the learned lists than to the unlearned
Ž .lists P-0.05 by Student Newman Kuhls . Addi-tionally participants made significantly more er-
Ž .rors P-0.05 by SNK to the recently learned listŽ .identity B’s words than they did to the previ-
Ž .ously learned list identity A’s list . A main effectŽ .for Group F s5.3, P-0.05 indicated that1,62
DID participants made more errors overall, butŽ .the absence of a List by Group interaction F-1
indicated that their tendency to commit moreerrors was not isolated to any particular list.
Table 3 shows the mean response latency for‘correct’ responses; i.e. indicating ‘YES’ for iden-tity B’s items, ‘NO’ for identity A’s items, and‘NO’ for all unfamiliar items. The rationale forexamining response latencies for only such trials
Ž .was based on: 1 the fact that } in most cases} there were very few incorrect responses on
Ž .which to calculate a reliable response latency; 2the fact that this method was used in analyzingthe data from the college student control subjectsŽ . Ž .Allen et al., 1992 ; and 3 the fact that the ERPswere analyzed using only these trials. As shown in
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 31
Table 3, the DID participants’ pattern of re-sponse latencies were very similar to that demon-strated by the college-student control subjects.Because the DID participants were slower overallŽ .F s13.0, P-0.001 , we examined within sub-1,62ject Z-scores to determine whether the pattern ofresponse latencies was the same for the twogroups, after removing the overall difference in
Žreaction time. The main effect of list F s94.6,6,372.P-0.001 and the absence of a List by GroupŽ .interaction F s1.2, ns indicated that all sub-6,372
jects had longer response latencies to the learnedŽwords than to the unlearned words P-0.05 by
.SNK . Thus even though DID participants re-sponded ‘NO’ to words learned to identity A andto unlearned words, they were significantly slowerto responds to words learned by identity A thanto unlearned words. These response data can alsoinform whether } at an individual subject level} a list of words had been learned. In the
Ž .validity studies of Allen et al. 1992 , the Bayesiancombination of response latency and incorrectresponses accurately identified 96% of learneditems and 98% of unlearned items. As can beseen in Table 4, these behavioral indicators per-fectly identify word lists learned by both identities
Žas having been learned, and very seldom 2 times.among 20 chances identify unlearned words as
having been learned. On the basis of slowedreaction time and an increased propensity to make
Žincorrect responses i.e. indicating ‘NO’ to iden-tity B’s words, and indicting ‘YES’ to identity A’s
.words or to unlearned words , these behavioralmeasures suggest that identity A’s words are in-fluencing identity B’s behavior in much the sameway identity B’s words do. Moreover, these behav-ioral measures suggest that identity A’s words areinfluencing identity B’s behavior in much thesame way as previously learned words affect thecollege student controls } who deliberatelyconcealed their recognition of previously-learneditems.
3.2. Electrophysiological data during identity B’srecognition task
The upper region of Fig. 1 presents the ERPwaveforms for each of the four DID participantsand four selected control subjects, and the lowerpanel presents the grand average waveformsacross all four DID participants and all 60 collegestudent control subjects. Note the inter-subjectvariability in waveform morphology. Descriptively,while all DID participants exhibit a larger P3
Žamplitude maximum amplitude from 350 to 850.ms to words learned by identity B than to un-
learned words, only participants M02 and M05exhibit a larger P3 amplitude to words learned byidentity A than to unlearned words. ParticipantsM03 and M04 , on the other hand, do not exhibit
Table 4Bayesian posterior probability that a list was recognized as learned for DID Participants, calculated on the basis of behavioral
aresponses
Ž . Ž .Preditor Sensitivity C Sample Specificity C Sample Z Cutscore
aNote. Sensitivities and specificities of the indicators for the DID sample are presented, along with the values from theŽ . Ž .comparison sample C Sample . Z cutscore s the cutscore established in the study of Allen et al. 1992 and applied here. Values in
the lower panel of the table indicate the probability that a list of words was recognized as learned by identity B, based on responseŽ . Žlatency and the number of ‘incorrect’ responses see text . For example, for M02, there is an extremely high probability rounds to
. Ž .1.00 that words learned by both identity A and identity B appear recognized, and a very low probability rounds to 0.01 that any ofthe five unlearned lists appear recognized.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4132
Fig. 1. Left column shows identity B’s ERPs at site Pz for words learned by identity A and identity B, and for unlearned words.Note that participants M02 and M05 reported some degree of mutual awareness between personalities, while M03 and M04 did not.
Ž .Right column shows comparable data from four college student controls labeled C01]C04, selected from among the 60 . At thebottom of each column are grand average ERP waveforms at site Pz for DID participants and college-student controls. DIDparticipants were tested as identity B for recognition of words learned by identity A, identity B, and unlearned words. College
Ž .student controls were tested for recognition of words for which they denied and concealed knowledge labeled ‘Learned A’ , forŽ .which they acknowledged learning labeled ‘Learned B’ , and for words they had not learned. Only trials where participants
responded with recognition of ‘Learned B’ items and denied recognition of ‘Learned A’ items and unlearned items are included inthe ERP averages. Top panel plots each subject on a different microvolt scale to maximize viewing; Bottom panel plots DID andcontrols on the same scale. The Bayesian procedure identified both learned lists as recognized for all eight subjects depicted in thefigure, despite considerable inter-subject variability in the appearance of P3.
a clearly identifiably P3 peak, and the amplitudein the P3 range to words learned by identity Athat is in the range of amplitudes seen for un-learned words. These descriptive statements arebased not only on visual inspection of Fig. 1, butalso upon a comparison of the present data to thenormative data of the college student controls. In
Ž .the Allen et al. 1992 study, P3 amplitudes werefirst converted to within subject Z-scores in orderto observe the pattern of amplitudes within asubject, independent of between subjects’ varia-tions in amplitudes. A cutscore of a Zs0.114was then established to maximally separate ERPsto learned words from ERPs to unlearned words.ŽThis cutscore was derived on a sample of 20
individuals and cross-validated on two indepen-.dent samples of 20 individuals each. Using this
cutscore with the DID participants’ ERP data, P3Žamplitude maximum amplitude in the 350]850-
.ms range for identity B’s words exceeded thecutscore for all four participants,5 but P3 ampli-tude for identity A’s words exceeded this cutscorefor only 50% of the DID participants, specifically
5Subjects M03 and M04 fail to show a clearly identifiableP3 peak for words learned by identity B as well, but theamplitude in this region did exceed the cutoff for identity B’swords.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 33
Table 5Bayesian posterior probability that a list was recognized as learned for DID Participants, calculated on the basis of P3 amplitude
2 aŽ .and four communality H measures
Ž . Ž .Predictor Sensitivity C Sample Specificity C Sample Z Cutscore
aNote. Sensitivities and specificities of the indicators for the DID sample are presented, along with the values from theŽ . Ž .comparison sample C Sample . Z cutscore s the cutscore established in the study of Allen et al. 1992 and applied here. Values in
the lower panel of the table indicate the probability that a list of words was recognized as learned by identity B, based on the fiveERP indicators. Only epochs where identity B acknowledged learning identity B’s words, and denied recognizing identity A’s wordsor unlearned words were included in this analysis.
those reporting some degree of co-consciousnessŽ .M02 and M05 . For comparison, among the 60college control subjects, P3 amplitude to theconcealed list exceeded this cutscore for 88.3% ofthe subjects.
Although P3 amplitude was not uniformly sen-sitive to the words learned by identity A, otherfeatures of the ERP waveform were, as indicatedby the results of the Bayesian classification proce-
Ž .dure see Table 5 . Based solely on features ofthe ERP waveform that have proven sensitive torecognized items in previous work, there is agreater than 98% chance that ERPs to words
Ž .learned by either identity A or B are indicativeof recognized items. It is further important toreiterate that these ERP data were based only ontrials where identity B responded ‘YES’ to indi-cate recognition of identity B’s items, and re-sponded ‘NO’ to indicate non-recognition of iden-tity A’s items.
3.3. Forced-choice task data
As shown in the top panel of Table 6, it ap-pears that participant M04 } when tested asidentity B } systematically avoided all of the
Žwords learned by identity A binomial probability.- 2% . Participant M05, by contrast, ac-
knowledged 2 of the 6 words learned by identityA, a result not significantly different from chanceŽ .i.e. 50% . In terms of evidence of transfer ofincidentally learned information, neither M04 norM05 } when tested as identity B } showed anycompelling evidence of incidental learning, ac-knowledging 6 of 12 and 5 of 12 items, respec-
Ž .tively chance s50% .Following this first forced choice task, partici-
pants were asked to switch again to identity A,and where then tested for words learned by iden-tity B. While participant M04 did not perform
Table 6Percentage of times identity B and identity A responded
aindicating recognition of items seen by the other identity
Explicit probes Incidental probes
As identity B, responding to probes for identity AM04 0% 50%M05 33% 42%
As identity A, responding to probes for identity BM04 33% 75%M05 83% 42%
aNote. Explicit probes contain words learned intentionallyby the other identity, while incidental probes contain wordsthat were seen as distractors by the other personality. Chancein each case is 50%.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4134
significantly different from chance performance,M05 recognized 5 of 6 words learned by identity
Ž .B binomial probability -10% , suggesting thather identity A may have been aware of some ofthe words learned by identity B. For neither par-ticipant was there clear evidence of transfer ofincidental learning.
4. Discussion
Amnesia is a central descriptive and diagnosticfeature of Dissociative Identity Disorder, and onethat is typically assessed on the basis of clients’reports of memory disturbance. The present studywas designed to provide an objective and inde-pendent evaluation of memory in DID, usingevent-related potentials and indirect behavioralmeasures.
Virtually every measure provided evidence con-sistent with the hypothesis that DID participantsdid not have amnesia between tested identities.
Ž .In one case M02 , the participant clearly ac-knowledged this by reporting ‘co-consciousness’;nonetheless, her identity B responded during theERP task as if she did not recognize the itemslearned by identity A. For participants M03 andM04, neither participant reported that there wasany sharing of memory between personalities. Forparticipant M05, she denied ‘co-consciousness’,but did } as identity B } recall one of thewords learned by identity A. But similar to partic-ipant M02, she did not acknowledge this wordconsistently during the ERP task.
4.1. ERP results
While the appearance of a large P3 seems tocovary with the subjective report of ‘co-conscious-
Žness’ as only M02 and M05 had P3 amplitudes toidentity A’s words that were outside the range of
.P3 amplitudes to unlearned words , other fea-Žtures of the ERP waveforms empirically derived
.features detailed in Appendix A suggest that theERPs were elicited by recognized items.
It is provocative that P3 amplitude elicited byidentity A’s words was reduced in those partici-pants reporting no co-consciousness. P3 ampli-tude, however, was smaller overall in DID patients
Ž .see Fig. 1 , suggesting that P3 amplitude alonemay not be the most reliable index in thesepatients. Moreover, the two subjects reporting no
Ž .co-consciousness M03 and M04 failed to pro-duce clearly definable P3 peaks to any items. Thesmaller P3 amplitude among DID patients com-pared to controls, and the lack of a clearly de-fined P3 peak in two of the patients, could be dueto the fact that the DID patients are older or that
Ž .they were on medication see Table 1 , or couldreflect information processing deficits associatedwith their psychopathology.
Ž .One of the two subjects M04 with a small P3to identity A’s words showed a clear pattern ofmalingering on the test designed to assess syste-matic avoidance of identity A’s words. It is un-likely therefore that the small P3 to identity A’swords could indicate amnesia in this subject. It isworth noting that P3 amplitude alone has a rea-sonably high false negative rate, with 12% of thecollege-student subjects with intact memory fail-ing to show a large P3 amplitude to learneditems. These caveats, considered in the context ofthe entirety of the findings, suggest that the smallP3 amplitude in response to identity A’s wordsamong those without reported co-consciousness isintriguing, but far from definitive.
The results of the Bayesian classification, whichuses features of the ERP that have been empiri-cally derived to be sensitive to previous learning,provide strong evidence that in all cases identityB was familiar with material learned by bothidentity A and identity B. The procedure has abuilt in control so that one can determine whetherit is vulnerable to false positive or false negativeoutcomes. The former would be indicated by theproportion of times that the procedure mistakenly
Židentifies unlearned items as learned 4% in thecollege student sample, and 10% in the DID
.sample . The latter would be indicated by thenumber of times the procedure mistakenly identi-
Žfies the overtly acknowledged list the recently. Žlearned list as unlearned 3% in the college
.student sample and 0% in the DID sample .
4.2. Beha¨ioral response data
Behavioral responses also suggest in all cases
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 35
that the words learned by identity A were familiarto identity B. Just like the college student com-parison sample, identity B showed slower ‘NO’responses to words learned by identity A relativeto unlearned words. In the college student con-trols we have conceptualized this as a responseconflict associated with the requirement to say‘YES’ to recently learned words, but ‘NO’ to
Ž .previously learned words Allen and Iacono, 1997 .Previously-learned words involve priming of bothresponse channels: ‘YES’ by virtue of beinglearned, and ‘NO’ by virtue of the instruction todeny and conceal knowledge. Note that this re-sponse conflict would only arise if the previouslylearned words were in fact recognized. The mag-nitude of the slowing is virtually identical in theDID participants and the college student controlsŽ .see note in Table 3 . It would therefore appearthat identity B has knowledge of words learned byidentity A. The response data in Table 2 furthercorroborate this interpretation, as identity B doesclassify identity A’s words as learned more oftenthan she classifies unlearned words as learned.Again, the pattern of results is remarkably similar
Žto the college-student comparison sample see.Table 2 , and is consistent with the hypothesis
that DID participants } as identity B } wereaware of, but denied knowledge of, words learnedby identity A.
4.3. Implicit memory ¨s. intentional production ofamnesia
Whereas previous authors have concluded thattransfer of information across personalities may
Žbe indicative of implicit memory e.g. Nissen et.al., 1988 , the present study suggests that this is
not always the case. For the two participants forwhom the forced-choice task was operative, onedisplayed a rather clear malingering profile whilethe other did not. Yet in both cases, the ERP andbehavioral data are strongly suggestive of inter-personality recognition. In the report of Nissen etal., 1988, the MPD participant did not show evi-dence of malingering, as she responded at orabove chance in a forced-choice face recognitiontask to items seen by a different identity, such as
Ž .faces. So while the Nissen et al. 1988 data are
consistent with, but do not unequivocally support,the interpretation of, implicit memory, the pre-sent data do not support the interpretation thatthere is implicit memory across identities.
ŽOf additional interest are the two cases M02.and M05 where identity B, upon inquiry, recalled
some of identity A’s words prior to learning iden-tity B’s words. One would expect, then, that iden-tity B would acknowledge identity A’s words inthe recognition task. But as the data in Table 2reveal, this was clearly not the case. Rather, forthese participants identity B responded as if shewere amnestic for the items learned by identity A.It is possible that in the short interval betweenthe recall inquiry and the recognition task thatidentity B became amnestic for identity A’s words,but the preponderance of evidence in this reportsuggests that this possibility is unlikely. The alter-native is that identity B interpreted our instruc-tion } to respond yes to any words on the screenthat she remembered learning today } to indi-cate that she should respond yes to only wordsidentity B learned, even if she recognized thewords learned by identity A. Upon debriefing, thisis in fact what M02 reported. This observation issupportive of the sociocognitive perspectiveŽ .Spanos, 1994 of DID that holds that the symp-toms of DID are context bounded, goal-directed,social behavior produced in response to demandcharacteristics. It is worth cautioning, however,that simply because the symptoms of DID can beproduced in response to demand characteristics,it in no way implies they must always be. On theother hand, the scientific community can viewSpanos’ perspective as an hypothesis with con-siderable support, but one that has the potentialto be falsifiable if one could find cases that hadunequivocal and profound inter-identity amnesia,and that emerged in the documented absence ofsocial demand. While the assessment paradigmdetailed in this report could assist in documenting
Žamnesia, the latter stipulation absence of social.demand is admittedly difficult to conclusively es-
tablish.
4.4. Limitations to generalizability
At present, it would be premature to generalize
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4136
to all diagnosed cases of DID. There may existsome cases that in fact show a dramatically dif-ferent pattern than that evidenced by the fourparticipants in this study. On the other hand, thedemographic profile of the four DID participantsin the present study is not that different than
Žmany of the case reports in the literature Spanos,.1994 . It is also worth noting that the present
study did not, and likely could not, test all possi-ble pairs of identities for any given participant. Itmay be the case that, even among the four partic-ipants tested in this report, some pairs of identi-ties may demonstrate a mutual amnesia thatwould produce dramatically different results thanthose seen here.
4.5. Concluding remarks
The present study details an objective methodof assessing amnesia in those who meet diagnos-tic criteria for DID. These results suggest theneed to be cautious in making the diagnosis ofDID based on self-report, even with the use of astructured clinical interview. The present findings,electrophysiological as well as behavioral, indicatethat individuals who appear } by self-report anddiagnostic interview } to meet diagnostic criteriafor DID may not be assumed to show unequivocalevidence of inter-identity amnesia.
The behavioral data from the present studysuggest the utility of screening additional DID
Žcases using only behavioral response and not.ERP data. Two behavioral indicators } slowed
responses to learned items and increased misclas-sifications of learned items } can be used toderive statistically supported classifications ofitems as recognized or not recognized. While notmany investigators with access to DID patientsmay have access to an ERP laboratory, most suchresearchers could certainly implement the pre-
Žsent protocol using the behavioral measures. Thepresent task, as programmed, can be run on anyPC computer, and is available from the first au-
.thor. If, through such screening, a DID partici-pant or participants were identified that appearedto show objective evidence of mutual amnesiabetween identities, then a follow-up study with
such individuals in an ERP protocol could proveworthwhile.
Acknowledgements
This research was supported, in part, by a grantfrom the McDonnell-Pew Program in CognitiveNeuroscience. The authors wish to thank the par-ticipants for volunteering of their time to partici-pate in the study, and to thank James A. Coan,John Polich, and Cyma Van Pe for helpful com-ments on an earlier draft of this manuscript.Portions of this data set were presented at theannual meeting of the Society for Psychophysio-logical Research, Vancouver, BC, Canada, Octo-ber 1996.
Appendix A. Using Bayesian procedures to arriveat statistically-supported inferences for eachindividual
Bayesian analysis can be used to compute theprobability that items from each of several listsare familiar to a subject. In the procedure de-tailed in the manuscript, two sets of items arethose that subjects have learned, while substan-tially more sets are those that have not beenlearned. ERPs are derived for each set of items.Our analytical approach uses several ERP indica-
Ž .tors e.g. P3 amplitude , each of which may im-perfectly distinguish previously-seen from newmaterial. While any given indicator may distin-guish such items very well, it would seldom do soperfectly. These particular ERP indicators in-cluded P3 amplitude and four measures derivedfrom within-subject factor analyses of different
Ž .ERP waveforms for each subject see below .These latter factor-analytic measures were de-vised because they take into account the entirewaveform rather than a single feature such as P3amplitude. Moreover, even among unselected col-lege students, P3 can be rather variable on in
Žindividual subject level of analysis Allen and.Iacono, 1997 and it imperfectly discriminates
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 37
Žlearned from unlearned material Allen et al.,.1992 .
In order to provide statistically informed deci-sions concerning whether a single subject’s ERPsare likely to be in response to items that thesubject recognizes, we have taken a statisticalapproach that involves combining several featuresof the ERP waveform that tend to distinguishERPs to recognized items from ERPs to unfamil-iar items. The essential features of this approachŽ . Ž .detailed fully in Allen et al., 1992 , involve: 1using each participant as his or her own control;Ž .2 examining patterns within each participantafter removing mean differences between sub-
Ž .jects; 3 using measures that are not dependenton any single component of the ERP but thatcapture aspects of the entire waveform’s mor-
Ž .phology; and 4 combining information inBayesian fashion to arrive at the posteriorprobability for any given individual that an ERPis indicative of recognition. This approach usesERP data from site Pz, as adding informationfrom additional sites did not significantly improvethe overall accuracy of classifying recognized and
Ž .unfamiliar material Allen et al., 1992 . This maybe due, at least in part, to the fact that data froma single site provided highly accurate classifica-
First, each participant serves as his or her owncontrol in that the participant sees words thathave been previously learned, as well as newwords. By comparing ERPs elicited by these twoclasses of stimuli, one can assess how ERPs tolearned items differ from those to unlearned itemsfor a gi en participant rather than with respect tonormative data. Additionally, the ERPs elicitedby the unlearned items provide an opportunity toassess the extent to which the procedure producesfalse positive outcomes, that is erroneously con-cluding that ERPs to unlearned words were likelyto have been elicited by learned stimuli.
A.2. Patterns within participants
Second, the pattern across ERPs to different
conditions can be examined for a given subject byfirst computing an ERP to each list: that learnedpreviously, that learned recently, and each of thefive unlearned lists. Each of the resultant ERPs isthen in response to a single list of words, andcomprised of roughly the same number of trials.Any given index, such as P3 amplitude, is calcu-lated for each of these seven ERP waveforms,and is then transformed to a Z-score for eachparticipant. Between-subject differences in P3 am-plitude are then removed, leaving scores thatcapture within-subject variations between theseven ERP waveforms.
A.3. Measures that capture the morphology the ofthe entire wa¨eform
Third, the approach involves deriving measuresof the ERP waveform that are not dependent on
Ž .any single component e.g. P3 amplitude , butthat rely instead on a comparison of the entirewaveforms between conditions. This is accom-plished by a conducting a factor analysis for eachsubject, using as variables the ERP waveformselicited by each of the seven lists, and using asobservations time points from y100 ms to q1050ms. The resultant 7=7 variance-covariance sum-marizes the similarities and differences amongthe waveforms, and serves as the input matrix for
Žthe factor analysis. In our previous work Allen et.al., 1992 we noted that ERPs elicited by learned
items tended to have larger variance and covari-ance, and would often load highly on the first orsecond extracted principal components, althoughsometimes on the third principal component. The
Ž .communality sum of squared loadings of a vari-Ž .able i.e. an ERP waveform across the first three
principal components is a convenient way to sum-marize the results of the factor analysis and in-dexes the extent to which that ERP waveform has
Žimportant variance. Incidentally, the communal-ity across these three extracted components is
.unchanged by rotation. In our previous work, weconducted such a factor analysis not only on theoriginal ERP waveforms, but also on three trans-
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4138
formations of those waveforms that highlight dif-ferent aspects of the morphology. The firstderivative of the waveform highlights the slope ofthe waveform at any point, the second derivativehighlights the change in slope, and the ‘deviation’
Žwaveform calculated as a given ERP minus thegrand mean ERP for that subject; cf. Farwell and
.Donchin, 1991 highlights how an ERP deviatesfrom the average for that subject.
A.4. Bayesian combination
Finally, each of these five indictors } P3 am-Ž .plitude maximum amplitude from 350 to 850 ms ,
and the four communalities from the factor anal-yses } are combined in Bayesian fashion. For agroup of subjects, each indicator will have an
Žassociated sensitivity i.e. the proportion of allERPs to learned items that show this particular
.characteristic, such as large P3 amplitude andŽspecificity i.e. the proportion of all ERPs to
unlearned items that do not show this particular.characteristic . The sensitivity and the specificity,
along with the base rate of ERPs elicited byŽ .learned items i.e. 2r7 of the ERPs will de-
termine the probability that a given ERP waselicited by learned items given the presence ofthe indicator. This is determined by:
LlLlqUu
where:
v L is the base rate of ERPs elicited by learnedŽ .items 2r7 ;
v l is the sensitivity of the indicator;v U is the rate of occurrence of the ERPs
Ž .elicited by unlearned items 1yL ; andŽv u is the complement of the specificity 1y
.specificity of the indicator, which is simplythe rate at which unlearned items produceERPs with the indicator.
The numerator indexes the proportion of allERPs that are in response to learned items and
Ž .show the presence of the indicator e.g. large P3 .The denominator indexes the proportion of all
Ž .ERPs learned as well as unlearned that showthe presence of the indicator.
For example, take the single indicator P3 am-Žplitude. In the validation studies Allen et al.,
.1992 , 92.5% of ERPs elicited by learned itemsŽ .had a large P3 sensitivity s0.925 and 92% of
the ERPs elicited by unlearned items did notŽ .have a large P3 specificitys0.92 . In these stud-
ies } like the current study } learned wordsŽ .comprised 2r7 0.2857 of the trials, and un-
Ž .learned words comprised 5r7 0.7143 of the tri-als. Thus if an ERP has a large P3, the probabilitythat it was elicited by learned items is:
With the single indicator of P3 amplitude, whichhas reasonably high sensitivity and specificity,there is still only an 82% chance that an ERPwith such an amplitude was in fact elicited bylearned items. For this reason, it is often helpfulto combine multiple indicators, which can in-crease the statistical confidence with which onecan identify ERPs elicited by learned items. Ex-tending the approach to multiple indicators, theprobability that any particular list is learned, givena particular combination of n indicators, is thendetermined by the formula:
Ž .Prob Learnedrcombination of n indicators
Ž .Ll l l . . . l1 2 3 ns Ž . Ž .L q Ul l l . . . l u u u . . . u1 2 3 n 1 2 3 n
where
v Lsproportion of ERPs elicited by learnedŽ .items i.e. the ‘base rate’ of 2r7 ;
v Usproportion of ERPs elicited by unlearnedŽ .items 1yL ;
v l ssensitivity of indicator i if indicator i indi-icates the ERP was in response to learneditems; or
Ž .v complement of sensitivity 1ysensitivity forindicator i if indicator i indicates the ERPwas in response to unlearned items;
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]41 39
Ž .v u scomplement of specificity 1yspecificityifor indicator i if indicator i indicates the ERPwas in response to learned items; or
v specificity for indicator i if indicator i indi-cates the ERP was in response to unlearneditems.
Conceptually, this probability ratio is equal tothe proportion of ERPs elicited by learned itemswith a gi en combination of indicators di ided bythe proportion of all ERPs showing this combinationof indicators. If all indicators suggested the ERPwas in response to learned items, the probabilitywould be high, but disagreement between indica-tors would lower the probability.
A final word concerning the indicators is inorder. In the example, the magnitude of the P3indicators was simply discussed in terms of largeor not large. One needs to determine a cutpointsuch that P3 amplitude greater than some crite-rion is considered large. While this could be es-tablished based on the raw microvolt values of P3,this approach is less than optimal because indi-vidual differences between persons in their meanP3 amplitude } regardless of which list elicited it} are likely to be substantial. An alternative tothis normative approach would be to use anintra-individual approach to determining whetheran indicator is ‘large’. By using within-subjectZ-scores as mentioned above, between-subjectvariation in overall level are removed, and theresultant scores reflect the pattern across theERPs elicited by the learned and unlearned lists.
Ž .In the validation studies Allen et al., 1992 , aZ-score cutpoint was chosen for each indicatorthat optimally separated ERPs to learned fromERPs to unlearned material. This cutpoint wasselected based on data from the first of thesethree validation studies, and cross-validated in
Ž .the two additional studies Allen et al., 1992 .These are the cutpoints that are used in thepresent report.
References
Allen, J.J., 1992. The development and validation of an event-related potential memory- assessment procedure: applica-tion to hypnotically-induced amnesia. Diss. Abstr. Int. 53,05B.
Allen, J.J.B., Iacono, W.G., 1997. A comparison of methodsfor the analysis of event-related potentials in deception-detection. Psychophysiology 34, 234]240.
Allen, J.J., Iacono, W.G., Danielson, K.D., 1992. The develop-ment and validation of an event-related-potential memoryassessment procedure: a methodology for prediction in theface of individual differences. Psychophysiology 29,504]522.
American Psychiatric Association, 1994. Diagnostic and Statis-tical Manual of Mental Disorders, 4th ed. American Psy-chiatric Association, Washington.
Bahnson, C.B., Smith, K., 1975. Autonomic changes in amultiple personality. Psychos. Med. 37, 85]86.
Bentin, S., Moscovitch, M., Heth, I., 1992. Memory with andwithout awareness: performance and electrophysiologicalevidence of savings. J. Exp. Psychol.: Learn. Mem. Cogn. 18Ž .6 , 1270]1283.
Bernstein, E.M., Putnam, F.W., 1986. Development, reliability,and validity of a dissociation scale. J. Nerv. Ment. Dis. 178,727]735.
Bliss, E.L., 1980. Multiple personalities: a report of 14 caseswith implications for schizophrenia. Arch. Gen. Psychiatry37, 1388]1397.
Boaz, T.L., Perry, N.W., Raney, G., Fischler, I.S., Shuman, D.,1991. Detection of guilty knowledge with event-relatedpotentials. J. Appl. Psychol. 76, 788]795.
Braun, B.G., 1983. Neurophysiologic changes in multiple per-sonality due to integration: a preliminary report. Am. J.Clin. Hypn. 26, 84]92.
Brende, J.O., 1984. The psychophysiologic manifestations ofdissociation: electrodermal responses in a multiple person-ality patient. Psychiatry Clin. North Am. 7, 41]50.
Brown, P., 1994. Toward a psychobiological model of dissocia-tion and post-traumatic stress disorder. In: Lynn, S.J., Rhue,
Ž .J.W. Eds. , Dissociation: Clinical and theoretical perspec-tives. The Guilford Press, New York.
Ž .nary, L.G. Eds. , Principles of Psychophysiology: Physical,Social, and Inferential Elements. Cambridge UniversityPress, New York, pp. 3]33.
Carroll, J.B., Davies, P., Richman, B., 1971. The AmericanHeritage Word Frequency Book. Houghton Mifflin, Bos-ton, MA.
Coons, P.M., 1984. The differential diagnosis of multiple per-sonality: a comprehensive review. Psychiatry Clin. NorthAm. 7, 51]64.
Coons, P.M., 1988. Psychophysiological aspects of multiplepersonality disorder: a review. Dissociation 1, 47]53.
Coons, P.M., Milstein, V., Marley, C., 1982. EEG studies oftwo multiple personalities and a control. Arch. Gen. Psy-chiatry 39, 823]825.
( )J.J.B. Allen, H.L. Mo¨ius, II r International Journal of Psychophysiology 38 2000 21]4140
Eich, E., Macaulay, D., Loewenstein, R.J., Dihle, P.H., 1997.Implicit memory, interpersonality amnesia, and Dissocia-tive Identity Disorder: comparing patients with simulators.
Ž .In: Read, J.D., Lindsay, D.S. Eds. , Recollections ofTrauma: Scientific Evidence and Clinical Practice. PlenumPress, New York, pp. 469]474.
Farwell, L.A., Donchin, E., 1991. The truth will out: interroga-Ž .tive polygraphy ‘lie detection’ with event-related poten-
hensive Handbook of Psychopathology, 2nd ed.. Plenum,New York.
Larmore, K., Ludwig, A.M., Cain, R.L., 1977. Multiple person-ality: an objective case study. Br. J. Psychiatry 131, 35]40.
Ludwig, A.M., Brandsma, J.M., Wilbur, C.B., Bendfeldt, F.,Ž .Jameson, D.H. 1972 . The objective study of a multiple
personality: or, are four heads better than one? Arch. Gen.Psychiatry, 26, 298]310.
Lykken, D.T., 1959. The GSR in the detection of guilt. J.Appl. Psychol. 43, 385]388.
Mathew, R.J., Jack, R.A., West, W.S., 1985. Regional cerebralblood flow in a patient with multiple personality. Am. J.Psychiatry 142, 504]505.
Miller, S.D., Triggiano, P.J., 1992. The psychophysiologicalinvestigation of multiple personality disorder: review andupdate. Am. J. Clin. Hypn. 35, 47]61.
Miller, S.D., 1989. Optical differences in cases of multiplepersonality disorder. J. Nerv. Ment. Dis. 177, 480]486.
Miller, S.D., Blackburn, T., Scholes, G., White, G., Mamalis,N., 1991. Optical differences in cases of multiple personal-ity disorder: a second look. J. Nerv. Ment. Dis. 179, 132]135.
Nissen, M.J., Ross, J.L., Willingham, D.B., Mackenzie, T.B.,Schachter, D.L., 1988. Memory and awareness in a patientwith multiple personality disorder. Brain Cogn. 8, 117]134.
Neville, H.J., Kutas, M., Chesney, G., Schmidt, A.L., 1986.Event-related brain potentials during initial encoding andrecognition memory of congruous and incongruous words.J. Mem. Lang. 25, 75]92.
Paller, K.A., Kutas, M., 1992. Brain potentials during memoryretrieval provide neurophysiological support for the distinc-tion between conscious recollection and priming. J. Cognit.
Rosenfeld, J.P., Reinhart, A.M., Bhatt, M., Ellwanger, J.,Gora, K., Sekera, M., Sweet, J., 1998. P300 correlates ofsimulated amnesia on a matching-to-sample task: topo-graphic analyses of deception vs. truth-telling responses.Int. J. Psychophysiol. 28, 233]248.
Ross, C.A., Heber, S., Norton, G.R, Anderson, G., 1989a.Differences between multiple personality disorder andother diagnostic groups on structured interview. J. Nerv.Ment. Dis. 179, 487]491.
Ross, C.A., Norton, G.R., Fraser, G.A., 1989b. Evidenceagainst the iatrogenesis of multiple personality disorder.Dissociation 2, 61]65.
Rugg, M.D., 1995. Event-related potential studies of humanŽ .memory. In: Gazzaniga, M.S. Ed. , The Cognitive Neuro-
sciences. MIT Press, Cambridge MA, pp. 789]802.Rugg, M.D., Doyle, M.C., 1992. Event-related potentials and
recognition memory for low- and high-frequency words. J.Cogn. Neurosci. 4, 69]79.
Rugg, M.D., Doyle, M.C., 1994. Event-related potentials andstimulus repetition in direct and indirect tests of memory.
Rugg, M.D., Nagy, M.E., 1989. Event-related potentials andrecognition memory for words. Electroencephalogr. Clin.Neurophysiol. 72, 395]406.
Sanquist, T.F., Rohrbaugh, J.W., Sydulko, K., Lindsley, D.B.,1980. Electrocortical levels of processing: perceptual analy-sis and recognition memory. Psychophysiology 17, 568]576.
Semlitsch, H.V., Anderer, P., Schuster, P., Presslich, O., 1986.A solution for reliable and valid reduction of ocular arti-facts applied to the P300 ERP. Psychophysiology 23,695]703.
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