The  EEG  Signature  of  Same  Words  Spoken  by  Different  Speakers  S.  Elahi,  Professor  J.  Brennan  

Department  of  LinguisBcs  at  the  University  of  Michigan  

Results                                                              •  A:  n1  –  early  stages  of  acousBc  processing  à  possible  acousBc  priming  for  same  talk    •  B:  p2  –  later  stages  of  acousBc  processing  à  lack  of  acousBc  priming  for  diff  talker  •  C:  n400  –  semanBc  processing  à  lack  of  semanBc  priming  for  non  repeated  words  

         n400  –  semanBc  processing  à  reduced  for  both  repeBBon  condiBons  •  D:  possible  p300  à  unexpected  sBmuli  processing  –  with  diff  talker  

Conclusion    PaMerns  we  see  at  this  point  and  Bme:      •  repeBBon  effects  for  the  same  talker  appear  earlier,  ~100  milliseconds  •  repeBBon  effects  for  different  talkers  do  not  appear  later,  >300  milliseconds    

S4muli  Condi4ons  and  Hypothesized  Priming  Effect    R:  repeat;  NR:  non-­‐repeat;    +:  feature  is  repeated  in  sBmuli  pair;  –:  feature  is  not  repeated  in  sBmuli  pair              

       

 

Data  CollecBon  

 Materials  

 Experiment  

ParBcipants  

Our  study  obtained  data  from  X  parBcipants:  each  subject  was  right-­‐handed,  learned  English  as  his  or  her  first  language,  and  possessed  no  severe  neurological  impairments  or  disorders.  Sessions  lasted  for  an  hour  and  a  half  

and  all  took  place  in  the  ComputaBonal  NeurolinguisBcs  Lab  in  Lorch  Hall.      

Methods  

Introduc4on    •  Hearing   a  word   affects   an   individual’s   understanding   of   the  word   that   follows.   For  example,   if  one  was  to  hear  “dog”,  a  repeated  uMerance  “dog”  would  be  processed  quicker   than   another  word.   Priming   effects   occur   at   each   linguisBc   level   of   speech  percepBon-­‐acousBcally,  phoneBcally,  phonologically,  lexically,  and  conceptually.    

•  Furthermore,  we  understand  a  given  word  with  apparent  effortlessness  even  when  spoken   by   different   speakers.   Though   the   semanBcs   of   a   given   word   remains   the  same,  the  phoneBc  and  acousBc  aspect  of  the  word  varies  with  speaker  –  yet  we  are  sBll  able  to  understand  that  “dog”  means  dog.    

 •  At   issue   is   how   we   recognize   words   given   acousBc   and   phoneBc   variaBon.   The  prototype  theory  states  that  we  possess  the  same  mental  representaBon  for  a  given  object  and  compare  any  new  sBmuli  of  that  object  to  a  single  “prototype”  we  have  constructed   in   our   head.   AlternaBvely,   the   exemplar   theory   proposes   that   we  categorize  objects  by  comparison  of  any  new  sBmuli  with  instances  of  that  word  we  have  stored  in  memory.  

 •  Recent  research  indicates  that  more  rapid  processing  occurs  when  the  same  word  is  repeated   by   the   same   speaker   as   opposed   to   when   it   is   repeated   by   different  speakers.  We  use  electroencephalography  (EEG)  to  record  charges  in  scalp  electrical  potenBals   caused   by   neural   acBvity   while   the   parBcipants   perform   an   experiment  regarding  this  effect.  We  compare  the  Bme-­‐course  of  Event-­‐Related  Poten4als  (ERP)  between  condiBons  to  test  for  what  stage  of  processing  is  being  primed.    

Word   Non-­‐Word  Same    

Speaker  Different  Speaker  

Same    Speaker  

Different  Speaker  

R   NR   R   NR   R   NR   R   NR  Acous4cs   +   (+)   –   –   +   (+)   –   –  Phone4cs   +   –   (–)   –   +   –   (–)   –  Phonology   +   –   +   –   +   –   +   –  Seman4cs   +   –   +   –   –   –   –   –  

We  used  electroencephalography  (EEG)  to  record  electrical  acBvity  in  the  brain.  We  situated  each  subject  in  a  nylon  cap  containing  61  acBvely  amplified  electrodes  evenly  distributed  across  the  scalp.  These  electrodes  measured  electrical  potenBal,  which  reflected  the  current  generated  

by  the  summary  of  corBcal  neurons  in  the  brain.    

We  injected  electrolyte  gel  to  minimize  impedance  

while  it  is  being  monitored.  Low  impedances  means  the  

electrical  connecBon  between  the  skin  and  electrode  are  stabilized.    

 Hearing  threshold  was  idenBfied  for  each  subject  using  a  1000  Hz  tone.  The  volume  was  set  to  be  45  dB  above  this  

threshold.    

The  task  of  the  parBcipants  was  to  iden4fy  if  the  s4mulus  was  a  word  or  a  non-­‐word  as  quickly  and  accurately  as  possible.  This  

indicaBon  was  made  by  pressing  either  the  lei  or  right  buMon  on  a  gamepad  console.  Subjects  were  presented  with  a  total  of  700  

words,  separated  into  secBons  containing  50  words  each.  Each  word  was  separated  from  each  other  by  an  inter-­‐sBmulus  interval  that  

ranged  from  400  -­‐600  milliseconds.  The  image  to  the  lei  depicts  the  brain  signals  we  monitor  during  the  experiment.      

Abstract    Speech   percepBon   research   shows   that   individuals   with   normal   language  processing   rapidly  understand   the  meaning  of  a   spoken  word  despite   the   fact  the  arBculaBon  and  acousBcs  of   these  words  differ   -­‐   someBmes  significantly   -­‐  across  speakers  of  the  same  dialect.  While  the  semanBcs  of  the  word  spoken  by  two  separate  speakers  would  remain  the  same,  the  phonology,  phoneBcs,  and  acousBcs  of  the  word  are  different  among  the  two.  In  order  to  contribute  to  the  mapping   of   this   capacity   for   "speech   normalizaBon",   we   test   the   Bming   of  repeBBon   effects   within   and   across   speakers   using   electroencephalography.  This  allows  us  to  idenBfy  the  Bming  of  cogniBve  processes  that  allow  the  brain  to  recognize  that  the  same  word  uMered  by  two  different  speakers  are,  in  fact,  the   same  word.  We   used   electroencephalography   (EEG)   to   record   charges   in  electrical  potenBals  that  are  caused  by  neural  acBvity  while  the  human  subjects  listened   to:   words   or   non-­‐words,   either   repeated   or   no   repeated,   and   if  repeated,  by   the  same  speaker  or  by  different   speakers.  The   results   from  this  experiment   will   indicate   how   quickly   we   recognize   two   words   (that   are   the  same)  are  the  same  

Experimental  Design                        

No  rep  

grassx   dogA   catA   boMlex  

Diff  talk  

grassx   dogA   dogB   boMlex  

Same  talk  

grassx   dogA   dogA   boMlex  

Hypothesis  and  Objec4ves      Our  objecBve  is  to  discover  at  what  point  in  4me  is  the  difference  in  acous4cs  and  phone4cs  of  repeated  words,  spoken  by  different  speakers,  factored  out  seman4c  aUribute  of  the  word  manifests  within  our  minds.  We  do  this  by  looking  for  what  brain  signals  were  sensiBve  when  words  were  repeated  (either  by  the  same  speaker  or  by  different  speakers)  compared  to  when  they  were  not  repeated.      We  predict  that  early  components  will  be  reduced  for  within-­‐speaker  priming  due  to  repeBBon  effects  on  acousBc  and/or  phoneBc  processing.  In  contrast,  we  predict  that  between-­‐speaker  priming  will  only  show  aMenuaBon  on  later  components,  reflecBng  lexical  and/or  conceptual  priming.