Decomposition to the Root: MEG Studies of Morphologically Complex Words

1. 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

2. 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

3. 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 √ami adj √cat n -able ø

4. (Overly) Simplified Models of Lexical Access: Pinker’s 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)

5. Dual Route Model (Pinker’s): 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

6. 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

7. 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)

8. 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

9. 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: Pinker’s 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

10. 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

11. 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 you’ve decomposed a particular letter/sound sequence into stem and affix, the faster you are at it) and/or • recombination (the more often you’ve put together a particular stem and affix, the faster you are at it) • in either case, against Pinker’s dual route model, such effects imply representation of whole word as complex structure, regardless of regularity

12. 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)

13. “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” [un[real]] White House UN+REAL (??) lemma (lexical entry) “not” REAL modality specific access lexicon (visual word form) unreal (??) un real form code (letters) u n r e a l

14. 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

15. Stages of Lexical Access:which 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)

16. 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

17. 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

18. Sequential processing of words

19. Sequential processing of words Pylkkänen and Marantz, 2003, Trends in Cognitive Sciences

20. Repetition Frequency (Embick, Hackl, Shaeffer, Kelepir, Marantz, Cognitive Brain Research, 2001) (Pylkkänen, Stringfellow, Flagg, Marantz, Biomag2000 Proceedings, 2000) Latency of M350 sensitive to lexical factors such as lexical frequency and repetition:reflects stage of lexical access

21. 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

22. Regions of interest derived from peak activity in grand averaged data across subjects

23. 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

24. 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

25. 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.

26. 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 word’s 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 word’s frequency to the frequency of words with the same suffix

27. hypothetical example:matched 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

28. Effect of “Dominance” on Lexical Access:view 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

29. Taft (2004): “Morphological Decomposition and the Reverse Base Frequency Effect”Obligatory 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.

30. 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):

31. Experiment: parallel behavioral and MEG processing measures • Lexical Manipulation (Baayen, Dijkstra & Schreuder, 1997, JML) • Lemma/stem frequency (CELEX database) • Stem vs. affix dominance

32. Stimuli: 3 Lexical Categoriesfully productive morphology • Nouns: singular/plural • bone • bones • Verbs: stem/progressive • chop • chopping • Adjectives: adjective/-ly adverb • clear • clearly

33. Experiment: behavioral measures • Reliable effect of stem frequency in RT in lexical decision

34. 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

35. M350 sensors chosen subject by subject

36. 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

37. 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

38. Analysis of M350 peak latency • No interaction between Dominance (base-dominant vs. affix-dominant) and Affixation (base vs. affixed) Behavioral RT M350 peak latency

39. 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.

40. 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

41. Grand Average All Stimuli All Subjects (11)

42. M170 sensors chosen on thebasis of field pattern, subject by subject

43. M170 Correlation with Dominance:Significant “parsing” effectThe higher the transition probability from stem to affix, the higher the M170 amplitude – for affix-dominant words

44. Recombination Effect?:Correlation with Conditional Probability of Stem, Given Affix, for Affixed Words at 450ms, after the M350

45. 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 Hay’s 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

46. 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)

47. Zweig & Pylkkänen(2008, LCP) Bimorphemic: farmer, Monomorphemic Orth: winter

48. 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

49. 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

50. Lexical access in early stages of visual word processing: A single-trial correlational MEG study of heteronym recognitionMarantz & 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