CNS poster 2003

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Visual Word Form Recognition An MEG study using
Masked Priming

• Heejeong Ko1, Michael Wagner1, Linnaea Stockall1,
  Sid Kouider2, Alec Marantz1
• 1Department of Linguistics and Philosophy, MIT
  KIT-MIT MEG Laboratory, 2Ehess/CNRS, Paris

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Testing Identity Priming with MEG
Testing Morphological Priming with MEG

• Goals of the Study
• To establish the neuropsychological correlates of
  identity priming in visual word processing in the
  masked priming paradigm without conscious
  perception, using Magnetoencephalography (MEG).
• To identify the MEG components that dissociate
  the priming effects of morphological and
  orthographical relatedness in the masked priming
  paradigm.

• Stimuli. (240 Items 120 word targets, 120
  nonword targets) mostly taken from Rastle et al.
  (2000, 2003). (1) 40 tokens of control and
  identity condition (abyss - BOWEL (control)
  bowel BOWEL (identity)). 40 tokens of
  semantically related fillers (gut - BOWEL). (2)
  40 tokens of nonword target triplets (hora -
  ABOL, abol - ABOL, tomato - ABOL).

• Hypothesis. If morphological decomposition
  applies blindly to all potentially complex words
  in early visual processing (e.g broth-er), we
  expect to find identity priming effects when two
  words are potentially morphologically related in
  early visual processing (brother-BROTH).

• Procedure. DMDX presentation with masked priming
  (resolution 1024768 , 60Hz). Prime duration 34
  ms. ISI500ms. Items were divided in three blocks
  and counterbalanced in each block. Items were
  scrambled randomly by DMDX. Lexical Decision Task.

• Stimuli. (240 items120 word targets, 120 nonword
  targets) stimuli are mostly taken from Rastle et
  al. (2000, 2003). (1) 40 tokens of control,
  morphology, and orthography condition
  (trifle-BROTH (control), brother-BROTH
  (morphology), brothel-BROTH (orthography)). (2)
  40 tokens of nonword target triplets (supply-ANG,
  anger-ANG, angle-ANG).

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GIFT Target
Fixation 500ms
gift Prime 34ms
Forward Mask 500 ms
Early Visual Word Responses in the Brain

• Procedure, Subject, and MEG data analysis are the
  same as in our experiment 1 (see 4 in the
  poster).

M100 Early Visual Response
M170 Visual Word Activation

• Subjects. 14 right-handed native English speakers
  with normal vision gave informed consent to
  participate in the experiment. MEG data from 11
  subjects.

• M170 is sensitive to visual form processing in
  the brain (e.g. letter, symbol, face) (Tarkiainen
  et al. 1999). In our laboratory, M170 has not
  been sensitive to lexicality or frequency of
  words.

• M100 is the first large MEG time component evoked
  by visual stimuli. Generated by primary visual
  cortex bi-laterally. More activity for
  noisier/longer letter and symbol strings
  (Tarkiainen et al. 1999).

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Results Morphological Priming in the Brain

• MEG Data collection. Neuromagnetic fields were
  recorded using a 93-channel axial gradiometer
  whole-head system for 6 subjects and a
  157-channel system for 5 subjects (KIT, Kanazawa,
  Japan). Data were acquired in a band between DC
  and 200Hz, at a 1000Hz sampling frequency.

• Behavioral Results. N11. RT in the morphology
  condition is significantly faster than RT in the
  control condition (p0.019). No significant
  difference between the orthography and control
  condition in RT (p.310). The RT difference
  between the morphology and orthography condition
  is approaching significance (p 0.065),
  replicating Rastle et al. (2003).

p0.019

• MEG Data analysis. 25 sensors from 157 MEG
  channels, and 13 sensors from 93 MEG channels in
  the left hemisphere were selected as the Sensors
  of Interest (SOI). SOI had the negative field for
  M100 and the positive field for M170 (see 2 in
  the poster).15 data points from the time window
  for M100 (80ms-150ms) and 15 data points from the
  time window for M170 (155ms-225 ms) were included
  from each SOI for statistical analysis. Outlier
  data that do not match the typical polarity of
  the relevant components were filtered out.
  One-way ANOVA (DV amplitude at each time point,
  IV subject, time, condition) and planned
  comparisons for timecondition interactions were
  conducted through SPSS.

plt.0001
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p.031
Results Identity Priming in the Brain

• Behavioral Results. N11.
• Planned comparisons show that RT in the identity
  condition is significantly faster than RT in the
  control condition (p0.009).

p0.009
plt.0001
plt.0001
Discussion

• MEG Results. N11. The M100 shows significantly
  more activation for the morphology condition
  than the control (p lt. 0001) and the orthography
  conditions (p lt. 0001). The M170 shows
  significantly less activation for the morphology
  condition than the control (p.031). The
  amplitude in the orthography condition is
  significantly lower than the control condition in
  M100 (plt.0001). No significant difference between
  orthography and control in M170 (p.073) or
  between morphology and orthography in M170
  (p.737).

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Masked Priming Paradigm

• The Masked Priming Paradigm provides a method to
  examine priming effects without conscious
  perception in early visual word form processing
  (Forster Davis 1984, Rastle et al. 2000, 2003,
  among others).
• In masked priming, a prime is sandwiched between
  a forward mask () and a target. With short
  prime duration, the prime cannot be consciously
  perceived by the subject.
• Identity and morphological priming effects in the
  Masked Priming Paradigm have been observed in the
  absence of semantic and orthographic priming
  effects (cf. Rastle et al. 2000, 2003 for
  behavioral studies Dehaene et al. 2001 for a
  fMRI and EEG study).
• In the current study, we investigate the effects
  of marked priming without conscious perception in
  the brain by examining the early MEG time
  components (M100 and M170). In particular, the
  effects of identity priming (experiment 1) and
  morphological priming (experiment 2) are of
  special interest.

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• Our MEG data show that the M100 and M170
  components are sensitive to identity and
  morphological priming effects in the masked
  priming paradigm.
• The identity and morphological priming
  conditions show the same pattern in the M100 and
  M170 components. This supports our hypothesis
  that morphological decomposition occurs prior to
  lexical access.
• Unlike RT results, orthographical and
  morphological priming show a significantly
  different pattern in the brain (M100). This
  suggests that priming due to morphological
  decomposition significantly differs from priming
  due to pure graphemic overlap in visual word
  processing in the brain.
• Localization and source activation analyses are
  required before we can definitely assign effects
  from masked priming to either the M100 (visual
  cortex) or M170 (letter string/visual word form
  area).

p.029
plt.0001

• MEG results. N11. The amplitude in the identity
  priming condition is significantly lower than the
  amplitude in the control condition (plt.0001) at
  the M100 (negative polarity, more activation).
  The amplitude in the identity condition is also
  significantly lower than the control condition
  (p.029) at the M170 (positive polarity, less
  activation).

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• Dehaene, S., L. Naccache, L. Cohen, D. L.Bihan,
  J-F. Mangin, J-B. Poline, and D. Rivière (2001).
  Cerebral mechanisms of word masking and
  unconscious repetition priming. nature.
  neuroscience 4(7) 752-758.
• Feldman, L. B. (2000). Are morphological effects
  distinguishable from the effects of shared
  meaning and shared form? Journal of Experimental
  Psychology Learning, Memory, and Cognition 26.
• Forster, K.I. and C. Davis (1984). Repetition
  priming and frequency attenuation in lexical
  access. Journal of Experimental Psychology
  Learning, Memory, and Cognition, 10, 680-698.
• Rastle, K., M.H. Davis, W.D Marslen-Wilson and
  L.K. Tyler (2000). Morphological and semantic
  effects in visual word recognition A time-course
  study. Language and Cognitive Processes, 15
  (4/5), 507-537.
• Rastle, K. and M.H. Davis (2003). Reading
  morphologically-complex words Some thoughts from
  masked priming. In Kinoshita, S. Lupker, S.J.
  (eds.) Masked priming State of the art.
  Psychology Press.
• Tarkiainen, A, P. Helenius, P.C. Hansen, P.L.
  Cornelissen, R. Salmelin (1999). Dynamics of
  letter string perception in the human
  occipitotemporal cortex. Brain 122 2119-2131.