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Chapter 7- The Neuroscience of Personality .pdf

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Connie Boudens

Chapter  7:  The  Neuroscience  of  Personality       -­‐In  one  study,  participants  who  wanted  to  Learn  about  meditation  as  a  form  of   stress  reduction  were  randomly  assigned  to  either  a  meditation  group  or  a  control   group  .The  meditation  group  went  through  an  extensive-­‐8-­‐week  training  in   mindfulness-­‐based  stress  reduction  meditation,  whereas  people  in  the  control   group  were  put  on  a  wait  list  for  the  8  weeks  to  receive  the  training  at  a  later  time.   In  this  way,  both  groups  were  essentially  equivalent  except  for  participation  in  the   meditation  training.   -­‐  During  the  training,  participants  practiced  being  in  the  moment  instead  of   planning,  worrying,  thinking,  or  fantasizing  about  the  future,  the  way  most  of  us  do   when  given  a  few  moments  to  sit  still.  The  meditation  group  members  tuned  in  to   their  breathing  and  practiced  regulating  their  attention  to  not  think  about  these   things-­‐to  think  about  nothing,  in  fact.   -­‐  At  the  end  of  the  training  session  the  two  groups  were  compared  on  a  number  of   measures.  The  researchers  found  that  the  group  that  had  learned  meditation   showed  less  anxiety.  This  would  be  exciting  enough-­‐that  people  who  meditate  have   less  anxiety-­‐but  the  real  news  is  that  they  also  showed  differences  in  how  their   brains  responded  to  emotional  stimuli.  People  who  meditated  showed  greater  brain   activation  on  the  left  prefrontal  cortex  of  their  brains  both  at  rest  and  in  response  to   positive  and  negative  emotional  event.  As  a  special  bonus,  participants  in  the   meditation  group  also  showed  better  immune  functioning  than  participant  in  the   control  group.   -­‐  Overall,  the  data  suggest  that  regular  meditation  fundamentally  changes  how  our   brains  work  and  that  this  activation  is  related  both  to  the  emotions  we  feel  and  to   how  we  respond  to  stressful  events.  The  researchers  surmised  that  meditation   makes  people  more  open  to  experiencing  positive  emotions  and  less  reactive  to   negative  emotions  with  the  overall  effect  of  decreasing  their  anxiety  and  improving   immune  functioning  -­‐all  of  this  without  drugs!     What  Is  Neuroscience  and  How  Do  We  Study  It?   -­‐  Researchers  who  explore  the  neuroscience  behind  personality  focus  on  the  brain   and  the  nervous  system.   -­‐  The  nervous  system  is  made  up  of  the  central  nervous  system  and  the   peripheral  nervous  system.  The  central  nervous  system  includes  the  brain  and  the   spinal  cord  whereathe  peripheral  nervous  system  includes  the  somatic  nervous   system,  which  control  movements  of  the  muscles,  and  the  autonomic  nervous   system,  which  regulates  smooth  muscle  (e.g.,  inner  organs),  cardiac  muscle,  and   glands.  The  autonomic  nervous  system  is  further  divided  into  the  sympathetic   division  and  the  parasympathetic  division.  The  sympathetic  division  mobilizes   energy  (e.g.,  for  fight  or  flight),  whereas  the  parasympathetic  division  supports   systems  that  replenish  the  body's  energy  stores  (e.g.,salivation,  digestion,  etc.).   -­‐  The  brain  is  protected  by  a  bath  of  cerebrospinal  fluid  (CSF)  that  cushions  the   delicate  brain  and  also  flows  through  spaces  in  the  brain  called  ventricles.  CSF  is   similar  to  blood  plasma,  and  is  continually  produced,  circulated,  and  reabsorbed   through  the  brain  and  the  ventricles.   -­‐  The  brain  contains  a  number  of  structures  and  systems  that  control  everything   from  thinking,  reasoning,  learning,  and  memory,  to  breathing,  sleeping,  and  eating,   to  movement  and  the  processing  of  sensory  information,  to  the  experience  of   emotions.   -­‐  Because  all  of  these  part  are  crucial  for  basic  functioning,  we  should  not  expect  to   see  large  differences  among  people.   -­‐  However,  individuals  can  vary  in  all  kinds  of  ways,  from  how  they  may  respond  to   stress  (e.g.,  heart  palpitations,  sweating)  to  what  they  think  is  happy  or  sad,  to  how   they  respond  to  hormones  and  drugs.   -­‐  Researchers  hypothesize  that  differences  in  bodily  responses,  brain  structure,   brain  activity,  and  biochemical  activity  are  all  related  to  individual  differences  in   personality.     All  of  the  research  that  has  been  done  on  exploring  physiological  and  neurological   differences  in  personality  fit  into  one  of  these  four  categories:     Bodily  Responses   -­‐  When  our  body  responds  to  arousing  events  in  the  environment  it  is  the  autonomic   nervous  system  that  responds.  When  aroused,  the  sympathetic  division  responds  by   increasing  heart  rate,  blood  pressure,  blood  flow  to  the  extremities,  respiration,   sweating,  and  muscle  activity.  Essentially  the  body  curtails  some  of  its  regular   maintenance  functions  to  mobilize  an  immediate  response.   -­‐  Sweating  is  measured  by     Galvanic  skin  response  (GSR):  Which  is  a  measure  of  skin  conductance  or  how   quickly  a  slight  electrical  current  passes  through  two  points  on  the  skin.  The  faster   the  conductance  of  the  current,  the  more  moisture  is  present  that  indicates  greater   arousal.     -­‐  Muscle  activity  is  measured  by     Electromyography  (EMG)  :  or  myoelectric  activity,  which  estimates  the  electrical   impulses  of  the  muscles  during  contraction  and  relaxation.  EMG  is  often  used  in   biofeedback  to  train  people  to  perceive  muscle  contractions  so  that  they  can  learn  to   relax  their  muscles.     Brain  Structure   -­‐  Another  place  that  researchers  have  looked  for  differences  among  people  is  in  the   relative  size  and  weight  of  specific  part  of  the  brain  ,or  even  in  the  kinds  and   number  of  cells  found  in  various  parts  of  the  nervous  system.   -­‐  In  the  past,  the  only  way  of  studying  differences  in  brain  structure  and  cells  was   through  dissecting  the  brain  after  death.  During  an  autopsy  the  brain  may  be   removed  and  sections  of  tissues  preserved  for  cytological  (cell}  study.   -­‐  Today,  through  the  advent  of  more  sophisticated  techniques  we  can  study  the   structure  of  a  living  human  brain  through  noninvasive  procedures.  For  example,     Computerized  tomography  (CT)  :  called  a  CT  scan,  takes  a  high-­‐resolution  x-­‐ray   picture  of  the  brain.  By  looking  at  thin  cross  sections  of  the  brain-­‐often  less  than  a   millimeter!-­‐we  can  detect  abnormalities  or  differences  in  brain  tissue.(This  same   technique  was  once  called  computer  axial  tomography  [CAT),or  CAT  scan.}     A  similar  technique  involves  magnetic  resonance  imaging  (MRI}.  Here  radio   frequency  waves  are  used  instead  of  x-­‐rays.  First,  a  strong  magnetic  field  causes  the   nuclei  of  some  atoms  to  resonate.  Then  radio  frequency  waves  are  used  to  detect  the   activity  of  these  atoms.  Because  hydrogen  atoms  are  present  in  all  tissues  but  in   varying  concentrations,  the  pattern  of  resonance  formed  by  the  hydrogen  atoms   forms  a  multidimensional  picture  of  the  brain.     Brain  Activity   -­‐  Both  CT  scans  and  MRIs  can  detect  only  static  pictures  of  the  brain-­‐that  is,  pictures   of  brain  structure  at  one  moment  in  time.  Measures  of  brain  activity  are  ways  of   looking  for  differences  in  brain  structures  while  the  brain  is  stimulated.  Often,   participants  are  given  a  mental  task  to  work  on  or  other  stimuli  to  react  to  while   measures  of  brain  activity  are  taken.   -­‐  In  an  electroencephalogram  (EEG)  electrodes  are  placed  on  the  scalp  to  monitor   electrical  activity  of  the  brain.  When  electrical  activity  of  the  brain  or  other  part  of   the  nervous  system  is  measured  in  response  to  a  specific  stimulus,  this  is  called  an   evoked  potential  (EP).  Both  EEGs  and  EPs  indicate  amount  of  brain  activity  in   response  to  a  stimulus.  However,  newer  techniques  identify  the  exact  location  of   brain  activity.     -­‐  In  positron  emission  tomography  (PET),  called  a  PET  scan,a  slightly  radioactive   glucose-­‐  like  substance  with  a  very  short  half-­‐life  (rate  of  breakdown)  is  injected   into  the  brain  and  the  person  is  placed  in  a  scanner  similar  to  a  CT  scanner.  Active   regions  of  the  brain  use  up  more  glucose  than  inactive  regions  and,  with  the  aid  of   computer  enhancement,  scans  of  these  regions  appear  in  different  colors  related  to   their  activity  level.   -­‐  The  most  detailed  view  of  brain  activity  at  a  cellular  level  comes  from  functional   magnetic  resonance  imaging  (fMRI).  This  works  the  same  as  the  traditional  MRI   except  that  brain  activity  levels  are  monitored  over  time  by  tracing  blood  oxygen   levels  in  the  brain.  The  more  active  areas  use  up  more  oxygen  and  this  activity  is   translated  into  different  color  scans  of  the  brain.     -­‐  Though  the  use  of  fMRI  for  personality  research  is  on  the  rise,  there  are  some   notable  problems  with  fMRI  research.  One  problem  is  timing  of  response.  When   viewing  a  stimulus,  our  thoughts  react  within  milliseconds  whereas  blood  flow  takes   about  2  seconds.  This  makes  it  difficult  to  pinpoint  the  precise  area  that  fired  at  the   exact  moment  of  a  thought  or  reaction.  Another  problem  is  that  the  procedure  is   time-­‐intensive  and  the  equipment  expensive  so  that  often  experiments  use  only  a   small  number  of  participants.  Small  sample  sizes  make  it  difficult  to  find  a  reliable   and  significant  effect.  A  third  problem,  called  the  nonindependence  error,  is  that   researchers  may  unintentionally  bias  their  results  by  not  independently  selecting   which  brain  areas  to  correlate  with,  say,  personality  characteristics  or  other   variables.  Finally,  confounds  such  as  time  of  day  and  nervousness  of  participants   can  also  affect  the  results  of  neuroimaging  studies.   -­‐  One  of  the  newest  techniques  for  studying  brain  activity  is  transcranial  magnetic   stimulation  (TMS).  With  TMS  a  brief  electrical  current  passes  through  a  coil  placed   on  the  head.  The  magnetic  field  disrupts  the  regular  activity  of  the  neurons,   sometimes  impairing  and  some-­‐  times  enhancing  function.  By  carefully  mapping   parts  of  the  brain  that  are  stimulated  and  noting  what  kind  of  functioning  is   disputed,  researchers  are  able  to  pinpoint  with  greater  accuracy  than  cortical   stimulation  or  EP  the  exact  area  affected.  Essentially  TMS  mimics  a  brain  lesion,   which  allows  researchers  to  draw  inferences  about  cause  and  effect.   -­‐  What  exactly  does  it  mean  when  an  area  reacts  in  response  to  certain  stimuli?       1)  First,  it  could  mean  that  the  area  in  question  is  indeed  the  center  for  that   characteristic  or  response.  But  there  could  also  be  other  areas  that  are  less  active   but  of  equal  or  even  greater  importance  that  may  have  disinhibited  the  more  active   area.   2)  Also,  when  an  area  responds  to  stimulation  we  know  that  the  area  is  necessary,   but  we  don't  know  if  it  is  a  sufficient  cause  of  the  characteristic  or  response  that  we   have  observed.  Maybe  it's  sufficient  only  if  other  part  of  the  brain  are  also  involved.   3)  Finally,  when  a  PET  scan  finds  an  area  of  increased  glucose  use,  it  may  indicate   activity  or  it  may  also  indicate  a  neuron  that  is  working  less  efficiently  needing  more   glucose.     Biochemical  Activity   -­‐  Finally,  physiological  differences  may  appear  as  differences  in  how  the  brain  and   body  process  various  chemicals  including  neurotransmitters,  hormones,  and  drugs.   -­‐  Neurotransmitters  are  chemicals  released  by  neurons  to  inhibit  or  excite  the  next   neuron  into  action.  In  this  way,  neurotransmitters  do  just  that:  help  transmit  signals   through  the  nervous  system.   -­‐  Some  important  neurotransmitters  are  norepinephrine,  epinephrine,  dopamine,   and  serotonin.   -­‐  These  all  have  a  similar  molecular  structure,  so  that  drugs  that  affect  one  tend  to   affect  all  of  them.     -­‐Norepinephrine  (noradrenaline)  and  epinephrine  (adrenaline)  are  also  considered   stress  hormones.  They  help  the  body  deal  with  threat  by  increasing  blood  flow  to   the  muscles,  which  increases  heart  rate  and  blood  pressure.     Dopamine  is  related  to  feelings  of  pleasure,  and  helps  regulate  movement,  learning,   attention,  and  rewards.   Serotonin  is  involved  with  mood  regulation,  arousal,  the  control  of  sleeping  and   eating,  and  pain  regulation.  Depression,  anxiety,  and  other  mood  disorders  are   related  to  how  the  body  processes  serotonin.   -­‐  The  enzyme  monoamine  oxidase  (MAO)  regulates,  to  some  degree,  the  availability   of  dopamine,  norepinephrine,  and  epinephrine  in  the  system.   -­‐  Norepinephrine  and  serotonin  may  also  be  related  to  symptoms  of  depression  .   Some  antidepressant,  for  example,  work  by  blocking  the  reuptake  of  norepi-­‐   nephrine,  serotonin  or  both,  so  that  they  stay  in  the  spaces  between  the  neurons  a   bit  longer.   -­‐  Antianxiety  drugs  work  by  mimicking  another  neurotransmitter,  gamma-­‐ aminobutyric  acid(GABA),an  inhibitory  neurotransmitter.     Challenge  test:    in  which  researchers  administer  a  drug  that  is  known  to  either   increase  or  decrease  a  neurotransmitter's  functioning  and  monitor  the  impact  of   this  new  substance  on  reaction  presumed  to  be  related  to  the  neurotransmitter.     Scatterplots  or  scattergrams  :  they  show  the  scatter,  or  spread,  of  the  data.   -­‐  Many  brain-­‐imaging  studies  will  use  scatterplots  to  illustrate  their  results.   -­‐  As  you  can  see,  a  scatterplot  is  a  very  useful  graphic.  It  can  tell  us  at  least  three   things  abou  t  a  set  of  data.  First,  it  can  alert  us  to  outliers  ,or  participants  who  score   extremely  high  or  low  in  one  or  both  of  our  variables.   -­‐  Second  ,  a  scatterplot  can  tell  us  the  direction  of  the  correlation:  whether  it's   positive  (the  cloud  of  dots  points  upward)   or  negative  (the  cloud  points  downward).   -­‐Third,  the  thickness  of  the  cloud  or  scatter  of  the  dots  tells  us  the  strength  of  the   correlation.  More  oval  =  more  related.  Circle  =  less  related     Neurological  Theories  of  Personality   -­‐Maybe  biology  has  the  biggest  impact  at  a  broader,  more  general  level  of   personality,  called  temperament.  What  is  temperament?  Temperament  is  a  set  of   personality  characteristics  that  are:   1.  Relatively  stable  across  the  life  span   2.  Expressed  through  general  energy  level   3.  Present  from  early  childhood   4.  Similar  in  other  species  of  animals   5.  Present  at  birth,  at  least  in  a  general  way   6.  Determined  by  genetic  factors   7.  Changeable  with  maturation  and  experience     -­‐  In  their  search  for  the  biological  basis  of  personality  nearly  all  major  personality   typologies  converge  on  three  primary  temperaments  ,  or  clusters  of  related   personality  traits:     •  Extraversion:  Positive  emotion,  reward  sensitivity,  social  rewards,  sociability,   approach.   •  Neuroticism:  Negative  emotion,  anxiety,  punishment  sensitivity,  withdrawal.   •  Impulsivity:  Psychoticism,  lack  of  constraint,  sensation  seeking,  novelty  seeking,   lack  of  conscientiousness,  lack  of  agreeableness.   -­‐Indeed,  there  has  been  striking  similarity  in  the  various  models  that  researchers   have  pro-­‐  posed.  For  example,  Eysenck's  Psychoticism,  Extraversion,  and   Neuroticism  model  (PEN  model),  the  five-­‐factor  model,  the  Big  Five  ,  Gray's  RST  ,   and  Cloninger    all  posit  at  least  two  of  these  three  dimensions  as  part  of  their   theories.  However,  both  the  FFM  and  the  Big  Five  split  Eysenck's  Psychoticism   factor  into  Agreeableness  and  Conscientiousness  .  Other  researchers  write  about  an   approach  temperament  (i.e.,  Extraversion)  and  an  avoidance  temperament   (Neuroticism)  or  positive  emotionality  (Extraversion)  and  negative  emotionality   (Neuroticism).           -­‐To  understand  both  the  logic  and  the  evidence  supporting  this  assertion,  let's  take  a   close  look  at  two  important  biological  theories  of  personality:  Hans  Eysenck's  PEN   model  and  Jeffrey  Gray's  reinforcement  sensitivity  theory.     Eysenck's  PEN  Model   -­‐When  Eysenck  first  started  working  in  the  1940s,  he  was  unusual  in  his  desire  to   build  a  personality  theory  based  on  experimental  findings.   -­‐Further,  he  believed  that  a  comprehensive  theory  should  explain  how  people   developed  their  personalities  as  well  as  predict  consequences  and  outcomes  of   various  personalities.   Overview  of  Eysenck's  Three  Dimensions.   -­‐  The  first  of  Eysenck's  factors  is  Extraversion.  People  who  are  high  in  this  factor,   extroverts,  tend  to  be  sociable,  popular,  optimistic,  and  somewhat  unreliable.  Those   low  in  Extraversion-­‐introvert-­‐tend  to  be  quiet,  introspective,  reserved,  and  reliable,   and  to  have  a  few  close  friends.  Essentially,  Extraversion  refers  to  how  outgoing   people  are,  to  both  the  social  and  the  physical  environments.   -­‐Eysenck's  second  factor  is  Neuroticism,  which  we  might  contrast  with  emotional   stability.  People  high  in  this  factor  tend  to  be  distressed,  insecure,  and  upset  in  many   areas  of  life.  They  are  chronically  worried,  nervous,  and  moody,  hold  a  low  opinion   of  themselves,  and  find  it  difficult  to  get  back  on  an  even  keel  after  an  upsetting   experience.  In  contrast,  emotionally  stable  people  are  even-­‐tempered,  calm,  relaxed,   carefree,  unworried,  and  somewhat  unemotional,  and  return  to  their  natural  state   quickly  after  an  emotional  experience.   -­‐Eysenck  called  the  third  factor  Psychoticism.  We  might  think  of  Psychoticism  as   being  antisocial  and  contrast  it  with  ego  control.  People  high  in  Psychoticism  tend  to   be  loners,  egocentric,  troublesome,  manipulative,  impulsive,  uncooperative,  hostile,   and  withdrawn,  and  do  not  fit  in  anywhere.  In  contrast,  people  low  in  Psychoticism   tend  to  be  altruistic,  socialized,  empathetic,  and  conventional.  They  care  about   others  and  are  able  to  control  their  impulses  to  a  greater  extent  than  those  high  in   Psychoticism.   -­‐Eysenck  and  Eysenck  suggested  that  the  pathological  labels  of  Psychoticism  and   Neuroticism  be  dropped  in  favor  of  tough-­‐mindedness  and  emotionality  to   emphasize  that  this  is  a  theory  of  normal,  nonpathological  behavior  and  to  eliminate   the  negative  connotations  of  these  labels..   -­‐Eysenck  drew  on  at  least  three  pieces  of  evidence  to  support  his  view  that  these   differences  in  personality  are  genetic  and  biological.  First,  cross-­‐cultural   universality  in  traits  implies  a  strong  biological  component.  After  all,  we  would   expect  that  large  differences  in  culture  and  environment  would  produce  different   kinds  of  personality  factors.  However,  this  is  not  the  case,  as  one  study  of   personality  in  25  diverse  countries.  The  fact  that  three  factors  of  Psychoticism,   Extraversion,  and  Neuroticism  occur  in  such  diverse  cultures  suggests  a  biological,   rather  than  cultural,  explanation.   -­‐Second,  people  show  tremendous  consistency  in  these  three  trait,  Over  time,   despite  changing  environment.  Responses  and  habits  might  change  over  time  and   situations,  but  traits  do  not.  This  consistency  suggests  a  strong  biological   component  to  these  traits.   -­‐The  third  piece  of  evidence  is  the  robust  finding  that  Extraversion,  Neuroticism,   and  Psychoticism  each  have  moderate  heritability.     Neurology  of  Extraversion.   -­‐Eysenck  thought  that  the  main  difference  between  introverts  and  extravert  had  to   do  with  arousal,  and  on  that  score  he  was  right.   -­‐Eysenck  thought  that  introverts  had  greater  cortical  arousal  than  extraverts,   particularly  in  the  ascending  reticular  activating  system  (ARAS),  a  pathway   transmitting  signals  from  the  limbic  system  and  hypothalamus  to  the  cortex.   -­‐The  ARAS  processes  the  more  cerebral  aspects  of  arousal  or  emotion  (e.g.,  thinking   about  a  difficult  calculus  problem).  Activation  in  the  ARAS  can  make  a  person  alert   and  mentally  sharp  or  sluggish  and  mentally  dull.   -­‐There  is  only  a  tiny,  if  any,  difference  in  arousal  level  between  extraverts  and   intraverts  at  rest.  However,  there  is  a  significant  difference  in  how  extraverts  and   introverts  respond  to  moderate  stimulation,  suggesting  that  the  key  difference   between  them  is  in  their  arousability  or  sensory  reactivity.   -­‐Given  these  differences  in  arousability,  we  would  expect  introvert.and  extraverts  to   differ  in  their  choice  of  situations:  noisy  versus  quiet.  One  study  found  that  people   studying  in  the  quiet  study  spaces  of  their  college  library-­‐spaces  with  individual   carrels,small  tables-­‐tended  to  be  introverted.  Where  did  the  extraverts  prefer  to   study?  In  the  noisy  but  highly  sociable  areas  of  the  library:  big  rooms  with  open   spaces  and  large  tables   -­‐But  here's  a  question:  Who  performed  better  on  their  exams?  Does  noise  level   really  matter  when  it  comes  to  learning  and  performance?  YES!   -­‐Participant.  Were  given  two  words,  one  that  fit  a  rule  and  the  other  that  didn’t.  By   observing  a  number  of  such  pairs,  participant  had  to  figure  out  the  rule.  For   example,  the  rule  might  be  animal  words  or  words  that  start  with  vowels.   -­‐While  participants  were  viewing  the  words  and  trying  to  figure  out  the  rule,  they   were  bombarded  with  random  bursts  of  white  noise.  Participants  were  randomly   assigned  to  one  of  three  conditions.  In  the  choice  condition,  they  were  told  that   although  they  couldn’t'  t  turn  off  the  noise,  they  could  select  the  volume  that   was"Just  right  for  you?'  In  the  second  and  third  conditions,  participants  were  unable   to  control  the  volume.  Instead,  they  were  assigned  the  level  of  volume  that  matched   what  a  participant  in  the  first  condition  chose.   -­‐In  the  assigned-­‐same  condition  their  volume  was  matched  to  the  volume  chosen  by   a  personality  just  like  them,  either  introverted  or  extraverted.  However,  in  the   assigned-­‐different  condition  they  were  subjected  to  the  volume  chosen  by  a  person   different  from  them:  an  introvert,  if  they  themselves  were  extraverted,  or  an   extravert  if  they  were  introverted.   -­‐Who  do  you  think  chose  the  lower  volume?  the  choice  condition  chose   a  lower  volume  than  extraverts  in  the  choice  condition.  The  difference  was  about   that  between  a  private  office  and  a  noisy  group  office.  Second,  who  do  you  think   experienced  greater  arousal  a  measured  by  heart  rate  and  skin  conductance?  Well,it   depended  on  which  level  of  noise  they  were  faced  with.  Both  extraverts  and   introverts  with  noise  level  sat  their  optimum  level  of  arousal-­‐in  either  the  choice   condition  or  the  assigned  same  condition-­‐had  similar  levels  of  arousal  as  measured   by  heart  rate  and  skin  conductance.  However,  when  faced  with  a  level  of  noise  not  to   their  liking,  introverts  showed  greater  arousal  and  extraverts  showed  lower  arousal.   Essentially,  introverts  were  over  aroused  by  the  loud  "extraverted"  level  of  noise   whereas  extraverts  were  under  aroused  by  the  soft,  boring  "introverted"  level  of   noise.   -­‐Finally,  how  well  did  participants  perform?  By  now  you  get  the  drill:  It  depended   on  if  they  were  working  at  their  optimum  level  of  noise.  Introverts  assigned  to  the   extravert's  noise  level  performed  the  worst,  needing  more  trials  to  Jearn  the  rule.   Next  came  extraverts  assigned  to  the  introvert's  noise  level.  The  choice  and   assigned-­‐same  conditions  performed  best,  learning  the  rule  in  the  fewest  number  of   trials.  As  you  can  see  in  Figure  7.3,  what's  just  right  for  introverts-­‐leading  to  their   optimum  performance-­‐is  too  little  for  extraverts  and  what's  just  right  for  extraverts   is  too  much  for  introverts.  People's  noise  preferences  and  performance  outcomes   depend  on  their  optimal  level  of  arousal  as  determined  by  their  personality.     Neurology  of  Neuroticism.   -­‐Eysenck  hypothesized  that  physiological  arousal  could  also  account  for  individual   differences  in  Neuroticism.  In  contrast  to  Extraversion,  which  was  related  to   activation  of  the  ARAS,  he  thought  that  Neuroticism  had  to  do  with  stability  or   instability  of  the  sympathetic  nervous  system.   -­‐Basically,  the  vulnerability  of  people  high  in  Neuroticism  to  negative  emotions  such   as  fear  and  anxiety  was  due  to  an  extrasensitive  emotional  or  drive  system.   -­‐Whereas  postulating  separate  physiological  processes  to  account  for  Extraversion   and  Neuroticism,  Eysenck  acknowledged  that  the  cortical  and  sympathetic  systems   were  interconnected.  THINK  OF  SMOKE  DETECTOR!   -­‐How  did  Eysenck's  theory  about  Neuroticism  fare  in  the  face  of  research  evidence?   Well,  it  appears  that  Eysenck  was  on  the  right  track.  Simple  measures  of   sympathetic  nervous  system  activation  (e.g.,  heart  rate,skin  conductance),  both  at   rest  and  during  stressful  situations  do  not  show  any  relationship  with  Neuroticism,   but  people  who  are  high  in  Neuroticism  do  show  an  increase  in  heart  rate  in   response  to  an  intense  stimulus  .So  do  introverts!  However,  people  high  in   Neuroticism,  but  not  introverts,  show  greater  startle  response  to  fearful  pictures.   Together,  these  findings  suggest  that  people  high  in  Neuroticism  may  be  more   sensitive  to  negative  emotions  in  particular,  and  not  to  arousing  situations  in   general,  the  way  that  introverts  are.  All  in  all,  there  is  no  support  for  Eysenck's   hypothesis  that  Neuroticism  is  related  to  activation  in  the  sympathetic  nervous   system.     Reinforcement  Sensitivity  Theory  (RST)   -­‐An  alternative  theory  was  proposed  by  Jeffrey  Gray.  For  Gray,  personality  is  the   variation  in  the  functioning  of  brain  systems.  Indeed,  the
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