Decomposition to the Root:

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Decomposition to the Root  MEG Studies of
Morphologically Complex Words

• Alec Marantz
• Olla Solomyak, Ehren Reilly
• NYU Depts. of Linguistics and Psychology
• KIT/NYU MEG Joint Research Lab

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Decomposition to the root(why the morphologist
cares about lexical access)

• Claim associated now with Distributed Morphology
• all lexical categories decompose at least to a
  root and a category-determining affix
• all relations between words or morphemes (e.g.,
  blocking relations) are computed at the syntactic
  level of terminal nodes. Thus a single item
  (e.g., undecomposed irregular past tense gave)
  cannot compete with a complex structure (e.g.,
  give pst) (Embick Marantz 2008)
• the grammar itself demands full decomposition to
  the root the existence of whole word roots to
  lexical access or processing would necessitate a
  different grammatical system for processing
  language as opposed to, say, computing
  grammaticality

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Decomposition to the root(why the morphologist
cares about lexical access)

• Tracking the ami in amiable, then, is one
  step along the way toward understanding how the
  root cat functions inside cat
• adj n
• vami adj vcat n
• -able
  ø

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(Overly) Simplified Models of Lexical Access
Pinkers Words and Rules

• Full storage model all complex words (walked,
  taught) stored and accessed as wholes
• only surface frequency effects predicted
• Reaction Time (RT) correlates with the surface
  frequency of a complex word
• Full decomposition model no complex words
  stored and accessed as wholes
• only stem frequency effects predicted
• RT correlates with the frequency of the stem of a
  complex word, not the frequency of the word as a
  whole (surface frequency)

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• Dual Route Model (Pinkers) irregular complex
  forms (taught) are stored and accessed as wholes
  regular complex forms (walked) are not
• surface frequency effects for irregulars (and
  high frequency regulars) RT to taught
  correlates with freq of taught, not teach
• stem frequency but no surface frequency effects
  on access for regulars RT to walked correlates
  with freq of walk, not walked

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• There are Stem Frequency effects in access for
  complex words
• RT to walked does correlate with freq of walk
• These effects are not attributable to post-access
  decomposition

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• But, surface frequency effects in lexical access
  are found in wide variety of cases, including
  completely regular morphology (e.g., for most
  inflected words in Finnish)

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E.g.

• Surface frequency effects even for transparent
  productive regular morphology like -less and for
  same words that yield base frequency effects
• surface frequency effects when surface frequency
  is varied and base frequency is held constant
• base frequency effects when base frequency is
  varied and surface frequency is held constant

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Additional Problems for Pinker-style Dual Route
Model

• The representation of irregular derived or
  inflected forms must be complex
• from the grammatical point of view, gave is as
  complex as walked
• no further affixation the gaving, the
  walkeding (note Pinkers appeal to irregular
  plurals inside compounds highlights his incorrect
  prediction here mice eater, but micey
  (mousey))
• alternations with do support Did he
  walk/walked, Did he give/gave

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• from the psycho and neurolinguistic point of
  view, irregulars contain the stem in the same way
  that regulars do
• taught-teach identity priming in long-lag priming
  (only identity (morphological) relations - not
  semantic nor phonological - survive in long
  distance priming)
• and for M350 brain response (e.g., Stockall
  Marantz 2006)
• taught-teach M350 (N400) priming equivalent to
  identity priming, although RT priming is reduced

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Whole Word Representations for Regulars, if
Surface Frequency effects imply whole word
representations(in some sense)

• Surface frequency effects on access are seen for
  a variety of completely regular derivations and
  inflections, implying whole word representations,
  in some sense
• Obligatory decomposition
• surface frequency effects could be tied to
  decomposition (the more youve decomposed a
  particular letter/sound sequence into stem and
  affix, the faster you are at it) and/or
• recombination (the more often youve put together
  a particular stem and affix, the faster you are
  at it)
• in either case, against Pinkers dual route
  model, such effects imply representation of whole
  word as complex structure, regardless of
  regularity

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• walked may stored as a complex form with a
  certain frequency in the same way that a saying
  like, And now for something completely different,
  is
• That is, any surface frequency effect may be
  connected to long-term effects of having computed
  a complex form and thus imply a representation
  of the complex form, no matter how regular
• This usage-based account of frequency effects
  holds no immediate implications for the grammar
  of morphologically complex words, nor for the
  issue of whether all complex words are recognized
  via decomposition (and recomposition)

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And now for something completely different
Encyclopedia Stored info about encountered
items (outside language system)
interactive dual route models and obligatory
decomposition models differ on the possible
presence of complex word forms in modality
specific access lexicons, and perhaps on whether
derived forms have lexical entries
unreal
White House
UNREAL (??)
lemma (lexical entry)
not
REAL
unreal (??)
modality specific access lexicon (visual word
form)
un
real
u n r e a l
form code (letters)
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Differences Between Realistic Dual Route Model
and Realistic Full Decomposition Model

• Both models require a (modality specific) word
  form lexicon
• for full decomposition model, this lexicon holds
  only forms of morphemes
• for dual route model, this lexicon holds some
  morphologically complex forms
• Dual Route but not Full Decomposition model
  allows whole word lexical entries and word form
  entries for morphologically complex forms

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Stages of Lexical Accesswhich computations in a
Full Decomposition Model affect RT?

• I. Decomposition (affix-stripping) no general
  effect on RT
• Taft cost-free
• Literature no evidence that ease or difficulty
  in affix stripping generally correlates with
  change in RT
• MEG studies (to be discussed) brain activity
  correlated with decomposition does not correlate
  with RT (more brain work associated with
  decomposition does not yield longer RTs)

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• II. Lemma access frequency of lemma (stem)
  correlates with RT
• Lemma (stem) access is modulated by frequency and
  by priming
• Morphological family size of a stem and number of
  related senses (polysemy) have been shown to
  modulate brain activity associated with lemma
  access at the same brain time/place (the M350)
  as stem frequency
• However, the relationship between an affix and a
  stem for a morphologically complex word has not
  been shown to affect the same brain response

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• III. Recomposition surface frequency
  statistics correlate with RT because of their
  role in determining the ease of recomposition of
  stem and affixes
• So, whole word representations (in the sense of
  Encyclopedia storage or simply in the sense of
  repeatedly used neural pathways) are accessed via
  decomposition and recomposition, where the
  surface frequency properties of these
  representations exert a late influence on lexical
  access

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Sequential processing of words
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Sequential processing of words
Pylkkänen and Marantz, 2003, Trends in Cognitive
Sciences
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Latency of M350 sensitive to lexical factors such
as lexical frequency and repetitionreflects
stage of lexical access
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Full Decomposition Model Related to MEG response
components

• M100 (Type I Tarkiainen et al.) response from
  primary visual areas
• visual feature analysis
• M130 (Type II) response from occipital-temporal
  junction
• abstract letter string analysis
• M170 (visual word from area) response from
  fusiform area
• affix stripping and functional morpheme
  identification
• visual word form recognition

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Regions of interest derived from peak activity in
grand averaged data across subjects
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• M350 (early N400m) response from temporal lobe,
  with possible (likely) contribution from inferior
  frontal cortex
• lemma activation
• Post-M350 N400m response from temporal lobe (and
  other regions)
• recombination of stem and affix, contact with
  Encyclopedic knowledge, integration into context

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Statistical Connections between Stem and Affix

• J. Hay proposes that the transition probability
  of the affix given the stem (so, from stem to
  affix) should correlated with ease of
  decomposition - the higher this probability, the
  harder the decomposition and the more affix
  dominant a complex word is

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• The transition probability of the stem given the
  affix (from affix to stem), on the other hand,
  could reflect the ease of recomposition.
• Note that for all but the most frequent regular
  English past tense verbs, the probability of the
  stem given the past tense suffix is vanishingly
  small.
• If RT that seems to correlate with surface
  frequency is actually correlating with the
  transition probability from affix to stem, this
  could explain why regular formations in English
  do not show surface frequency effects unless the
  frequencies are very high.

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Transition Probabilities Affix dominance
tokens of merely
tokens of merely
tokens of words with -ly
tokens of words containing mere
transition probability from stem to suffix
correlates with ratio of a suffixed words
frequency to frequency of words with the same
stem, which is essentially equivalent to affix
dominance
transition probability from suffix to stem
correlates with ratio of a suffixed words
frequency to the frequency of words with the same
suffix
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hypothetical examplematched for stem frequency
(9), difference in surface dominant (mere(ly)) or
stem dominant (sane(ly))

• mere merely
• mere merely
• mere merely
• mere merely
• merely

• sane sanely
• sane
• sane
• sane
• sane
• sane
• sane
• sane

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Effect of Dominance on Lexical Accessview
from interactive dual route model

• Hay affix dominance leads to difficulty in
  parsing/decomposition, thus reliance on
  whole-word recognition and suppression of
  decomposition in favor of whole-word route
• So, words with high affix dominance should not be
  recognized via decomposition and should show only
  surface frequency effects

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Taft (2004) Morphological Decomposition and the
Reverse Base Frequency EffectObligatory
decomposition makes similar predictions as
interactive Dual Route model for RT in lexical
decision

• Base frequency effects
• RT to complex word correlates with freq of stem
• reflect accessing the stem of morphological
  complex forms whereas
• Surface frequency effects
• RT to complex word correlates with freq of
  complex word
• reflect the stage of checking the recombination
  of stem and stripped affix for existence and/or
  well-formedness.

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How can we distinguish these accounts of RT
differences?

• With brain evidence for the various stages of
  lexical access leading up to the RT
• Interactive dual route models no base frequency
  effects at lexical access for affix-dominant
  words
• Full decomposition base frequency effects
  across affix- and stem-dominant words at lexical
  access followed by surface frequency effects in
  RT associated with recombination

Reilly, Badecker Marantz 2006 (Mental Lexicon)
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Experiment parallel behavioral and MEG
processing measures

• Lexical Manipulation (Baayen, Dijkstra
  Schreuder, 1997, JML)
• Lemma/stem frequency (CELEX database)
• Stem vs. affix dominance

Stem Frequency Stem Dominant low surface freq Affix Dominant high surface freq
High desk desks crop crops
Mid deck decks cliff cliffs
Low chef chefs chord chords
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Stimuli 3 Lexical Categoriesfully productive
morphology

• Nouns singular/plural
• bone
• bones
• Verbs stem/progressive
• chop
• chopping
• Adjectives adjective/-ly adverb
• clear
• clearly

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Experiment behavioral measures

• Reliable effect of stem frequency in RT in
  lexical decision

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Experiment behavioral measures

• Interacting effects on RT of affixation (base vs.
  affixed) and dominance (base-dominant vs.
  affix-dominant)

This is a surface frequency effect for completely
regular morphology. Same words, both base and
surface frequency effects, undermining Pinker
theory
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M350 sensors chosen subject by subject
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Analysis of M350 peak latency(brain index of
lexical access)

• Reliable effect of Stem frequency for unaffixed
  words and for affixed words

Unaffixed Words
Affixed Words
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Analysis of M350 peak latency

• No effect of Dominance (base-dominant vs.
  affix-dominant) - no effect of surface frequency
  - on M350 peak latency Against prediction of
  interactive dual route theory

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Analysis of M350 peak latency

• No interaction between Dominance (base-dominant
  vs. affix-dominant) and Affixation (base vs.
  affixed)

M350 peak latency
Behavioral RT
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Analysis of M350 peak latency

• Evidence that early stages of access for affixed
  words is based on full parsing Stem frequency
  affects M350/lexical access while whole word
  frequency affects post-access (recombination)
  stage of word recognition.

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But what about evidence for parsing and
recombination?RMS Correlations Across Subjects

• For some set of sensors, calculate at each time
  point in each experimental epoch the root mean
  square (RMS) the square root of the mean of the
  squares of the values at each sensor (after
  normalization of values)
• So, for each subject, for each item, an RMS
  wave can be provided for the correlational
  analysis
• At each time point, the RMS value for each
  stimulus is correlated with a stimulus variable

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Grand Average All Stimuli All Subjects (11)
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M170 sensors chosen on the basis of field
pattern, subject by subject
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M170 Correlation with DominanceSignificant
parsing effectThe higher the transition
probability from stem to affix, the higher the
M170 amplitude for affix-dominant words
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Recombination Effect?Correlation with
Conditional Probability of Stem, Given Affix, for
Affixed Words at 450ms, after the M350
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Summary of Dominance Exp

• Base and Surface Freq RT effects for same words
  again argues against simplistic (Pinker) Dual
  Route theory
• Affix dominance effect at M170 for high affix
  dominant words argues against Hays interactive
  Dual Route theory, where such words should be
  accessed via the whole word route as does lack
  of M350 latency effects for these words
• M350 latency effects for stem frequency but not
  surface frequency (and not affix dominance)
  followed by effect of transition probability from
  affix to stem post M350 argues that recombination
  dominates RT effect for surface frequency of
  affixed words

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Evidence for an orthographic word form lexicon

• Frequency of stem relative to full affixed form
  affix dominance correlates with M170 amplitude
  implies access to some kind of stem
  representation
• Zweig Pylkkänen (2008) show M170 effect of
  decomposition in the contrast between farmer
  (complex) and winter (simple), where the contrast
  implies access to a representation of farm at the
  M170 (wint lacks a representation)

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Zweig Pylkkänen (2008, LCP)

• Bimorphemic farmer, Monomorphemic Orth winter

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Modality-Specific Access Lexicon?

• Pulvermüller in a number of studies has found
  early (150ms) word frequency effects in evoked
  brain responses in the posterior brain regions
• These are found for monomorphemic words, and the
  effects seem limited to shorter words
• These could be explained by higher order n-gram
  frequencies - by the frequencies of letter
  strings, i.e., by features of word form
  representations that do not make contact with the
  (semantic) lexicon

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Modality-Specific Access Lexicon?

• Parsing at the M170 requires access to word
  forms (or to high-n n-grams)
• Dominance effects at the M170 suggest frequency
  information associated with word-forms
• dominance reflects the conditional probability of
  the affix given the stem, where notion of stem
  implies form representation of the stem
• Difference between visual word form
  representation and lexical entry?
• heteronyms like wind (moving air vs. twist)
• visual word form frequency is not the same as
  lexical frequency
• wind has one word form frequency but two
  lexical frequencies, one for each meaning

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Lexical access in early stages of visual word
processing A single-trial correlational MEG
study of heteronym recognition Marantz
Solomyak (2008, Brain Language)

• All (20) monomorphemic heteronyms (meeting other
  criteria) of English
• If M170 marks access to visual word form
  representations, but not lexical entries, then
  only form frequency variables associated with
  heteronyms should correlate with M170 brain
  activity
• If M170 marks lexical access, relative frequency
  of the 2 pronunciations of heteronyms should
  correlate with activity

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Regions of interest derived from peak activity in
grand averaged data across subjects
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Visual Word Form Area Left Hemisphere Ventral
View

• The white point represents the peak of the
  Visual Word Form Area, as identified by Cohen et
  al. (2002)
• The yellow line outlines the region of peak M170
  activation in an average of 9 subjects brain
  activity.

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Mean Activity in LH M170 Region for 9
Subjects(Dotted line shows average across
subjects)
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Grand averaged activation over time from M170 and
M350 ROIs
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Only the form property (bigram frequency) showed
significant correlation with brain activity in
the M170 ROI while only the semantic property
(ratio of frequency of meanings) showed a
significant correlation in the M350 ROI
A Monte Carlo procedure was used to test for
significance in the face of multiple comparisons
(across time points)
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Evidence so Far

• Decomposition even for affix-dominant words
• evidence at M170 that high transition probability
  between stem and affix makes affix-stripping
  harder
• evidence post-M350 and at RT that surface
  frequency makes recomposition easier

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• Evidence for visual word form lexicon accessed
  at M170
• transition probability effects at M170 depend on
  frequencies over word form representations
• complexity effects at M170 (Zweig Pylkkänen)
  depend on wint vs. farm word form contrast farm
  is a word form but wint (in winter) isnt

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• Evidence that word form effects involve word
  forms, not lexical entries
• open bi-gram frequency (representational form for
  word forms) correlates with activity at M170
• but frequency ratio for heteronyms doesnt
  correlate with activity at M170
• but does correlate with activity at M350

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What about the status of bound stems?Can MEG
help settle a disputed linguistic issue

• Bound stem durable
• same root in duration
• predicts durability
• Unique stem amiable
• no other uses of root
• but, predicts amiability

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tracking the -able in amiable

• If words like durable with a recurring root and
  amiable with a unique root nevertheless are
  parsed and computed as is workable with a free
  root, then
• M170 parsing effects should be visible for
  these opaque words, since effects are strong
  for affix-dominant words
• M350 effects should be observed for stem
  frequency for bound stems

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Crucial contrasts

• To show effect of affix processing, need to show
  correlation with, e.g., affix frequency that is
  not equally explained by the positional frequency
  of the letters at end of the affixed word
• distinguish able as affix from a-b-l-e
• To show effect of parsing variable transition
  probability of affix given the stem, need show
  correlation with transition probability that is
  not equally explained by the transition
  probability between the last letters of the stem
  and letters of the suffix.

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Categories of Affixed Words for New Experiment

• 1. Free Root-Affix
• taxable
• 2. Bound Root-Affix
• tolerable
• 3. Unique Root-Affix
• capable
• Morphological parsing as from English Lexicon
  Project

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Nine Affixes(All derivational suffixes in
English that yielded reasonable number of
examples for each category)

• able
• ary
• ant
• ity
• ate

• ic
• er
• al
• ion

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The ROIs determined again from the grand average
across subjects.
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Decomposition Effects at M170

• Positional letter string freq effects at M130
• Affix freq effects but no letter string effects
  at M170
• Morph trans probability effects but no
  orthographic trans probability effects at M170
  Multiple regression, taking out first
  (non-significant) orthographic parsability leaves
  significant effect of morphological parsability
  at M170

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Summary

• At M130, form property of final letter frequency
  correlates with activity
• At M170, affix frequency but not final letter
  frequency correlates with activity for all
  groups, including bound and unique root groups
• At M170 transition probability between stem and
  affix, but not between last letters of stem and
  letters of affix, correlates with activity for
  both free and bound stems
• At M350, stem frequency effects for both free and
  bound root stems

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bound stems

• For transition probability results, bound stems
  pattern with free stems
• For affix frequency results, all stems, including
  unique bound stems, pattern alike
• Thus we find evidence for full decomposition for
  free, bound, and unique stems

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Conclusions

• All evidence massively disconfirms a Pinker-style
  dual route theory in which some morphologically
  complex words are recognized as undecomposed
  wholes
• Full Decomposition theories of lexical access are
  completely consistent with (in fact predict)
  surface frequency effects for morphologically
  complex words
• Surface frequency effects reflect statistics of
  composition rather than the frequency of whole
  word access

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• MEG data confirm the existence of a visual word
  form lexicon that enters into morphological
  decomposition in the recognition of complex words
• MEG confirms the morphologists claim that
  decomposition extends to bound and unique roots

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• Thanks to the audience and the colloquium
  organizers!