The idea that compositing or blending may occur in human episodic memory stems from two sources: (1) distributed models of human memory, and (2) studies that have focussed on the distortions and mistakes that occur in eyewitness testimony. In this paper,data that have been uncovered within the eyewitness testimony paradigm are simulated by a distributed memory model-CHARM (composite holographic associative recall memory). Studies done by Loftus have been interpreted as indicating that blending does occur; modification of these experiments conducted by McCloskey and Zaragosa have been claimed to refute Loftus' interpretation. It is shown that both of these results are predicted by the composite-trace model

Metcalfe, Janet

English

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UC MercedProceedings of the Annual Meeting of the Cognitive Science SocietyTitleComposite Holohraphic Associative Recall Model (CHARM) and Blended Memories in Eyewitness TestimonyPermalinkhttps://escholarship.org/uc/item/54m9w1vgJournalProceedings of the Annual Meeting of the Cognitive Science Society, 11(0)AuthorMetcalfe, JanetPublication Date1989 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaC o m p o s i t e H o l o g r a p h i c A s s o c i a t i v e R e c a l l  M o d e l  ( C H A R M ) a n d B l e n d e d M e m o r i e s i n E y e w i t n e s s T e s t i m o n y Jane t  Metcalf e Departmen t  o f  Psycholog y Universit y o f  California ,  Sa n Diego . Abstrac t The idea that compositing or blending may occur in human episodic memory stems fro m tw o sources :  (1 )  distribute d model s o f  huma n memory ,  an d (2 )  studie s tha t  hav e focusse d o n th e distortion s an d mistake s tha t  occu r  i n eyewitnes s testimony .  I n thi s pa -per ,  dat a tha t  hav e bee n uncovere d withi n th e eyewitnes s testimon y paradig m ar e simu -late d b y a  distribute d memor y m o d e l - C H A R M (composit e holographi c associativ e re -cal l  memory) .  Studie s don e b y Loftu s hav e bee n interprete d a s indicatin g tha t  blendin g does occur ;  modificatio n o f  thes e experiment s conducte d b y McCloske y an d Zaragos a hav e bee n claime d t o refut e Loftus '  interpretation .  I t  i s show n tha t  bot h o f  thes e result s ar e predicte d b y th e composite-trac e model . Introductio n There has been considerable debate about the nature of human memory storage: whethe r  memorie s ar e store d discretel y o r  m a y interac t  o r  eve n blen d wit h on e another . Loftu s ha s argue d tha t  th e fac t  tha t  subject s w h o ar e give n misleadin g informatio n i n a realistic ,  eyewitnes s testimon y situatio n m a y b e mor e inaccurat e tha n ar e subject s no t give n th e misleadin g informatio n indicate s tha t  subsequen t  informatio n m a y distort , erase ,  o r  combin e wit h earlie r  informatio n abou t  th e targe t  event .  McCloske y an d Zaragos a sugges t  tha t  unde r  th e appropriat e testin g condiuons ,  n o evidenc e fo r  distortion , erasur e o r  blendin g i n m e m o r y i s found . Th e situatio n o f  primar y interes t  i n thi s debat e i s exemplifie d b y a  numbe r  o f experiment s b y McCloske y an d Zaragos a (1985) .  Subject s sa w a  serie s o f  colo r  slide s depictin g a n inciden t  i n whic h a  maintenanc e m a n enter s a n office ,  repair s a  chair ,  finds and steal s $20 ,  an d the n leaves .  Embedde d i n th e sequenc e wa s a  critica l  slid e i n whic h th e m a n picke d u p a  h a m m er  firo m a  too l  kit .  Afte r  viewin g th e slid e sequence ,  subject s rea d a  narrativ e i n whic h th e misleadin g informatio n wa s embedded ,  i n th e experimenta l condition ,  an d i n whic h neutra l  informatio n wa s give n i n th e contro l  condition .  I n th e experimenta l  condition ,  i t  wa s suggeste d t o th e subject s tha t  th e too l  th e m a n ha d picke d up wa s a  screwdriver .  I n th e contro l  condition ,  a  generi c term -  tool-wa s use d t o refe r  t o th e detai l  i n question .  A t  tim e o f  test ,  subject s wer e aske d th e followin g question :  "Th e 307 M E T C A L FE man sli d th e calculato r  beneat h a i n hi s too l  box" . The tes t  consiste d o f  a  two-alternativ e force d choic e procedure .  I n wha t  wil l  her e be designate d th e "standard "  condition s th e labe l  o f  th e actuall y viewe d objec t  (i n thi s cas e th e ter m "hammer" )  wa s contraste d wit h th e suggeste d object s ("screwdriver") .  Th e pervasiv e finding  i n thi s testin g procedur e wa s tha t  correc t  selectio n o f  hammer  wa s impaire d i n th e experimenta l  bu t  no t  i n th e contro l  condition .  McCloske y an d Zaragos a modifie d thi s testin g procedur e suc h tha t  th e correc t  alternativ e wa s pitte d agains t anothe r  categor y member  ("wrench" )  bu t  no t  agains t  th e misleadin g informatio n itself . We wil l  her e designat e thi s testin g procedur e th e "Modified "  condition .  I t  wa s foun d tha t unde r  thes e testin g conditions ,  ther e wa s n o decremen t  i n performanc e fo r  th e ter m "hammer "  i n th e experimenta l  conditions . Table 1. The experimental paradigm. Standar d "Loftus "  Condition s Presentatio n Contro l Man-Hammer Misle d Man-Hammer Questionair e Tes t Hammer-Screwdrive r Man-Screwdrive r  Hammer-Screwdrive r Correc t 7 2 % 3 7 % Modifie d "McCloskey "  Condition s Presentatio n Contro l Man-Hammer Misle d Man-Hammer Questionair e Tes t Hammer-Wrenc h Man-Screwdrive r  Hammer-Wrenc h Correc t 7 5 % 7 2 % On th e basi s o f  thes e findings,  summarize d i n Tabl e 1 ,  McCloske y an d Zaragos a argu e tha t  ther e i s n o los s o r  distortio n o f  th e initial y encode d events .  Loftu s ha s usuall y 308 M K T C A L FE argue d fo r  a  blendin g vie w o f  memor y (rathe r  tha n fo r  simpl e los s o r  erasure ,  attributabl e t o th e misleadin g information) .  Abou t  thi s blendin g o r  integratio n view ,  McCloske y an d Zaragos a state : "What  sort s o f  dat a would ,  then ,  suppor t  o r  disconfir m th e integratio n claim ? Con -sideratio n o f  thi s questio n lead s quicld y t o th e realizatio n tha t  wha t  i s mean t  b y integra -tio n i s no t  a t  al l  clear .  On e migh t  sugges t  tha t  th e clai m simpl y assert s tha t  th e infomia -tio n fro m variou s source s i s store d togethe r  i n memory .  Althoug h thi s answe r  ma y b e satisfyin g a t  a n intuitiv e level ,  i t  lose s muc h o f  it s appea l  whe n w e ask .  What  doe s 'store d togethe r  i n memory '  mean? "  (p .  15) . In the model, that is outlined below, there is but a single memory trace which consist s o f  th e su m o f  th e association s tha t  ar e entere d int o it .  Thi s composit e o r superimpose d trac e i s a n exampl e o f  a  memor y syste m tha t  produce s blende d memories . I f  a  cu e ha s bee n associate d wit h mor e tha n on e item ,  tha t  cu e wil l  serv e t o retriev e al l  o f th e item s wit h whic h i t  ha s bee n associated ,  an d the y wil l  al l  b e produce d together ,  o r  i n a blend .  Mor e explici t  compute r  simulation s provid e prediction s an d postdiction s abou t exactl y wha t  thi s composite ,  o r  blendin g mode l  doe s i n th e situation s outline d above . Summary of the CHARM model The model that will be used to investigate the blending predictions under th e condition s outline d i n McCloske y an d Zaragosa' s experimen t  i s calle d th e C H A RM mode l  (composit e holographi c associativ e recal l  model) .  Th e mode l was no t  devise d specificall y t o appl y t o thi s situation ,  an d has ,  i n fact ,  bee n ap -plie d wit h som e succes s t o a  variet y o f  othe r  classi c memor y situations ,  suc h a s paired-associat e learning ,  interferenc e a s a  functio n o f  similarity ,  encodin g specificit y effects ,  concep t  formation ,  elaboratio n effects ,  recognitio n failur e ef -fects ,  an d other s (Metcalfe ,  i n press ;  Metcalfe-Eich ,  1982 ,  1985) .  Th e mode l  i s associativ e i n nature ,  base d o n th e ide a tha t  items ,  represente d a s distribute d pat -tern s o f  features ,  o r  vectors ,  ar e associate d b y th e operatio n o f  convolution .  Thi s operatio n (denote d * )  i s give n b y th e followin g equation ,  fo r  th e mt h ter m o f  th e resultin g vector : (F*G)=  S fiSj' (1) where, F and G are the item vectors: (/•i,/2./3,-)and(^ 1,^2.^3,-) and Sim)=\(i,j)^^-^<iJ<^,andi+j=m -. The resulting vector is added into a single vector that is the composite memory trace .  A s eac h associatio n i s adde d int o thi s vecto r  th e value s fo r  eac h elemen t  o f  th e vecto r  ma y change .  Thus ,  th e trac e i s define d as : 309 M E T C A L FE T=iG*G)+(H*/)+(J*K)+.... (2) The initia l  ite m vectors ,  F,G ,  H ,  I ,  J ,  an d K  ma y bea r  an y similarit y relatio n t o on e another ,  an d ma y var y i n term s o f  thei r  initia l  strengt h o r  length .  Thi s summatio n a t  tim e of  storag e i s wha t  i s  mean t  b y blendin g o r  storin g togethe r  i n memory . The operatio n tha t  allow s retrieva l  fro m thi s composit e associativ e trac e i s calle d correlatio n (denote d # )  an d i s define d as : { F m m = z  /,o .  (3 ) wher e Sim) = , .  . .  I  n- 1 ^  .  .  ̂  n- \  ,  .  . O j )  — z — ^U J < — T —,  a.n d i-j= m The resul t  o f  retrieva l  i s  a  singl e vector .  Bu t  thi s vecto r  ma y b e broke n dow n int o th e component s tha t  contribut e t o i t  a s follows : R = F #T 1(4 ) =F# (F*G )+(//*/)+• •• =F#(F*G)+F# (//*/)+... =SppG+SpGF+errorp*Q+SpijI+Sp]H+errorijin+ • • • Here, S is a scalar giving the similarity value between F and F, for example, as measured by thei r  do t  product .  I n th e cas e wher e tw o item s ar e associate d wit h a  singl e cue ,  w e se e tha t  th e singl e vecto r  tha t  i s  retrieve d b y thi s syste m wil l  contai n component s o f  bot h o f th e origina l  items .  Thi s outpu t  fro m th e mode l  ca n b e simulated ,  an d th e resul t  ca n b e assesse d withi n th e framewor k o f  th e Loftus-McCloske y forced-choic e paradigm ,  b y simpl y providin g th e alternativ e the y allowe d i n th e experiment ,  an d lettin g th e mode l pic k th e bes t  matc h t o it s retrieve d output . Simulations A number of simulations were conducted on this and related paradigms. Only one serie s wil l  b e reporte d here . Metliod A lexico n o f  9 0 item s wa s constructed ,  wher e eac h ite m consiste d o f  6 3 feature s an d eac h featur e consiste d o f  a  valu e randoml y selecte d fro m a  truncate d Gaussia n distributio n wit h a n expecte d valu e o f  zero .  Th e item s wer e the n normahze d s o tha t  th e sel f  do t  product s wer e 1 .  Th e first  ite m i n th e lexico n w e wil l  hereinafte r  assig n th e nam e "man" ;  th e secon d ite m "hammer" ;  th e 22n d ite m "screwdriver" ;  th e 32n d ite m "tool "  an d th e 42n d ite m "wrench" .  I n th e Hig h Similarit y conditions ,  thes e exemplar s wer e reassigne d featur e value s s o tha t  8 0 % o f  thei r  feature s wer e th e sam e a s th e prototyp e ite m "tool" .  I n th e Moderat e Similarit y conditions ,  4 0 % o f  thes e feature s wer e reassigne d value s o f  th e prototype .  I n th e unrelate d conditions ,  th e item s wer e 310 M K I C A L FE statistically independent. T wo differen t  trace s wer e forme d t o depic t  th e experimenta l  an d th e contro l condition s o f  th e experiment .  Th e contro l  trac e was : Tc= (MAN*HAMMER)+ {MAN*T00L )+ 5 irrelevan t  convolutions . The experimenta l  trac e was : T^^ iMAN*HAMMER)+{MAN*SCREWDRIVER)+5 irrelevan t  convolutions . The irrelevan t  convolution s wer e include d her e t o indicat e tha t  ther e wer e othe r  event s store d i n th e trace ,  an d th e numbe r  i s no t  to o importan t  i n th e presen t  context .  (Se e Metcalf e &  Murdock ,  1981 ,  fo r  furthe r  detail s o n thi s point) . Retrieva l  wa s simulate d b y correlatin g th e vecto r  fo r  M A N wit h th e composit e trace .  Th e retrieve d vecto r  tha t  resulte d wa s the n compare d t o H A M M ER an d S C R E W D R I V E R,  i n th e standar d conditions ,  o r  t o H A M M ER an d W R E N C H,  i n th e modifie d conditions .  Th e compariso n consiste d o f  takin g th e do t  produc t  o f  th e retrieve d vecto r  wit h tha t  o f  th e lexica l  ite m i n question .  Th e matc h tha t  gav e th e highes t  valu e was th e winne r  an d wa s sai d t o b e th e choic e tha t  wa s mad e o n tha t  particula r  trial .  Th e entir e sequenc e o f  simulation s wa s ru n twice ,  th e first  tim e producin g 20 0 replication s o r observation s pe r  point ,  an d th e secon d time  100 0 observation s pe r  point . Results The patter n o f  result s produce d b y th e simulation s i s show n i n Tabl e 2 .  A s ca n b e seen ,  i n eac h o f  th e thre e manipulation s o f  similarity ,  th e mode l  produce d th e basi c patter n show n i n McCloske y an d Zaragosa' s data .  I n particular ,  unde r  Standar d testin g conditions ,  th e misleadin g informatio n i n th e Experimenta l  conditio n resulte d i n poore r performanc e tha n di d th e neutra l  informatio n i n th e Contro l  conditions ,  wherea s whe n th e Modifie d tes t  situatio n wa s simulated ,  ther e wa s n o differenc e betwee n th e Contro l and th e Misle d conditions . Conclusions It is clear that the simple blending model is able to generate data that have been construe d a s indicatin g tha t  ther e ar e distortion s i n memor y an d als o dat a tha t  hav e bee n ralie d t o rejec t  th e blendin g idea .  Wha t  ar e th e implication s fo r  real-worl d memory ? Ther e ar e som e situation s i n whic h on e migh t  expec t  blend s t o occur .  On e prerequisit e i n th e mode l  fo r  th e appearanc e o f  evidenc e fo r  suc h blend s i s tha t  ther e mus t  exis t  a  lexica l representatio n tha t  depict s o r  a t  leas t  i s  ver y simila r  t o th e composit e blende d entit y tha t i s  retrieve d fro m memory .  Figur e 1  show s a n exampl e wher e tw o object s tha t  ar e unlik e one anothe r  ar e superimposed .  Bu t  ther e i s n o rea l  worl d objec t  tha t  coul d correspon d t o th e blen d show n i n th e fa r  right  panel .  Figur e 2  show s a  secon d exampl e tha t  wa s create d i n exacti y th e sam e wa y a s th e first  example .  However ,  i n thi s cas e th e item s themselve s wer e highl y simila r  t o on e another ,  an d th e blende d entit y coul d plausibl y b e a  real-worl d entity . Positiv e blends -  wher e a  composit e mode l  wil l  predic t  a  compromis e betwee n th e presente d an d suggeste d items -  ar e difficul t  t o find.  However ,  Lxjftu s (1977 )  ha s 311 M E T C A L FE Tabl e 2 .  Simulatio n results . Categor y Similarit y Unrelate d Moderat e Hig h Test Conditio n Standar d (hammer-screwdriver ) Modifie d (hammer-wrench ) Standar d Modifie d Standar d Modifie d Informatio n Conditio n Contro l Misle d Contro l Misle d Contro l Misle d Contro l Misle d Contro l Misle d Contro l Misle d Percentag e Correc t 68. 0 32. 5 70. 5 62. 0 58. 5 38. 0 67. 0 65. 0 52. 5 37. 5 54. 5 58. 0 64. 2 34. 1 64. 8 66. 3 63. 1 37. 9 63. 1 64. 7 55. 8 42. 0 56. 7 57. 0 provide d on e suc h exampl e i n whic h a  ca r  tha t  ha d i n fac t  bee n gree n i n a  slid e sequenc e was guesse d mos t  frequentl y a s havin g bee n a  blue-gree n colo r  afte r  misleadin g blu e informatio n abou t  it s colo r  wa s given .  I n thi s color-shif t  experiment ,  th e intermediat e color s coul d an d d o exis t  i n th e rea l  worl d an d s o ther e woul d b e n o a  prior i  restrictio n agains t  th e possibilit y  tha t  suc h a  colo r  ha d occurred .  I n man y othe r  cases ,  however , ther e ar e n o real-worl d object s tha t  compris e a  blend .  Fo r  instance ,  ther e i s n o rea l  worl d objec t  tha t  consist s o f  a  blen d betwee n a  screwdrive r  an d a  hammer .  Thus ,  a  litera l  blen d coul d b e rule d ou t  immediately ,  eve n i f  suc h wer e retrieve d fro m memory . Face recognitio n pose s a n interestin g puzzle ,  an d on e tha t  ma y hav e practica l significance .  A s Figur e 2  ilustrates ,  ther e ma y b e case s i n whic h th e superimpositio n o f tw o face s coul d produc e a  plausibl e blend .  I n suc h a  situatio n eve n i f  w e wer e t o eliminat e fro m th e testin g altemativ e th e fac e tha t  wa s use d a s th e misleadin g informatio n th e possibilit y  exist s tha t  a  thir d fac e (o r  actually ,  i n th e model ,  a  whol e famil y o f  intermediat e faces )  migh t  nevertheles s b e accepte d b y th e subjec t  a s plausibl e interpretatio n o f  th e blen d tha t  i s retrieve d fro m memory .  I n conclusion ,  then ,  th e composit e mode l  doe s a  goo d jo b o f  predictin g th e dat a fro m bot h th e McCloske y an d th e Loftu s testin g conditions .  I t  als o make s furthe r  prediction s tha t  ma y b e o f  bot h practica l  an d o f  theoretica l  importance . 312 M E T C A L FE '".''••''  '  •. « •  "• -  •*':.'• • ;•  .•~v-'4,-u«»i.ii.rf| •  •  -  >• '•'•li -  •'•'•' •  •  •  •  /\''' .  :-" ' • m M m m S ,  •  . •  .. .  6  /. .  •.••• :  VI. ' Figur e 1 .  Th e superpositio n o f  tw o nonintegrabl e object s tha t  d o no t  yiel d a  po -sitiv e blend . •  •  \  c u^ I ' • :;li|$i;,:::: : .,-;-;̂-•;•'•'•' •  <! '  -.' .  •  :'•'• • •'.- . •':;•. . •,̂ 'n; ' .  •-: . •-  :• ' -•yl- ' '  v v '•'̂''-•:?. . •:''•'/•''':• : •;•;; ;  ̂  ii-'ŷl : -  '•"'I' '  ; • "̂•*"•' '  •  /• • Figur e 2 .  Th e superposito n o f  tw o integrabl e object s producin g a  positiv e blend . 313 M E T C A L FE References Loftus, E. F. (1977). Shifting human color memory. Memory & Cognition, 5, 696,699. McCloskey, M., & Zaragosa, M. (1985). Misleading postevent information and memory fo r  events :  Argument s an d evidenc e agains t  th e memor y impairmen t  hypothesis . Journa l  o f  Experimenta l  Psychology :  General ,  114,3-\S . Metcalfe, J. A composite holographic associative recall model (CHARM) and blended memorie s i n eyewimes s testimony .  Journa l  o f  Experimenta l  Psychology : General ,  i n press . Metcalfe, J. & Murdock, B. B., Jr. (1981) An encoding and retrieval model of free recall. Journa l  o f  Verba l  Learnin g an d Verba l  Behavior,20 ,  161-189 . Metcalfe-Eich, J. (1982). A composite holographic associative recall model. Psychologica l  Review ,  89 ,  627-661 . Metcalfe-Eich, J. (1985). Levels of processing, encoding specificity, elaboration, and C H A R M.  Psychologica l  Review ,  92 ,  1-38 . 314 

Composite Holohraphic Associative Recall Model (CHARM) and Blended Memories in Eyewitness Testimony

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Composite Holohraphic Associative Recall Model (CHARM) and Blended Memories in Eyewitness Testimony

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