Early effects of morphological complexity on visual evoked fields in MEG

1. Early effects of morphological complexity on visual evoked fields in MEG Eytan Zweig & Liina Pylkkänen New York University 80th Annual LSA meeting, January 7, 2006

2. Morphological decomposition -Two questions • Do all affixed words decompose? Does semantic opacity play a role? • What is the timing of lexical decomposition?

3. “Farmer” Farm + -er Fold + -er “Folder” Folder Semantic opacity • Transparent words generally taken to decompose • Competing hypotheses about opaque words 1. Opaque words decompose (Rastle & Davis, 2003; Davis et al., 2004) ? 2. Opaque words do not decompose (Marslen-Wilson et al., 1994)

4. Semantic opacity • Previous experiments have produced contradictory results (as reviewed by Feldman et al., 2004).

5. Timing of decomposition • Early decomposition • (Taft & Forster, 1975; Rastle & Davis, 2003; Davis et al., 2004) Decomposition Lexical access farm + -er farm, -er 2. Late decomposition (Feldman et al., 2004) Lexical access Decomposition farm + -er farmer 3. Race (Baayen, 1992) Decomposition Lexical access farm + -er farm, -er Lexical access farmer

6. ERP evidence for early decomposition in sentence processing • Word category violations elicit an early left anterior negativity (ELAN)(Friederici, 2000; Friederici et al., 2002). • Category is determined through morphological cues. • Indirectly supports an early effect of morphology.

7. This study • Takes advantage of the millisecond temporal resolution of MEG. • Simple lexical decision task without priming.

8. Magnetoencephalography (MEG) EEG MEG http://www.ctf.com/Pages/page33.html

9. MEG analysis

10. MEG analysis

11. MEG analysis

12. MEG analysis

13. Typical MEG response to visual words

14. Experiment 1 Suffixed words

15. Experiment 1 Stimuli 34 words per condition Conditions were controlled for matched for length, surface frequency, orthographic neighborhood density and frequency, and syntactic category. Suffixed conditions were further controlled for stem frequency and orthographic regularity.

16. Testing for pre-lexical effects • M350 is the first component to show effects of lexical factors (Embick et al., 2001; Pylkkänen & Marantz, 2003). • Fiorentino & Poeppel (2003) found that the M350 is sensitive to constituent frequency in compounds. • Decomposition likely to happen before M350.

17. Prediction - Timing • If decomposition is pre-lexical, we should find effects before the M350.

18. M170 • The first component that has been found to be sensitive to the presence of letter strings (Tarkiainen et al., 1999). • Most research has found that the M170 is not sensitive to lexical factors such as frequency.

19. M170 • Fusiform gyri have been found to be the primary generators of M170 activity.

20. Fusiform Gyri • Functional asymmetry between hemispheres (Tarkiainen et al., 2002) : • The left fusiform gyrus sensitive to letter strings (Cohen et al., 2000; Dehaene et al., 2002). • “Visual Word Form Area” • The right fusiform gyrus primarily sensitive to faces.

21. Prediction – Semantic opacity • If opaque words decompose, they will pattern with transparent words. • If they do not, they will pattern with orthographic controls.

22. M170 - Left Hemisphere Grandaveraged waveform n=16 no effect nAm Time

23. M170 - Left Hemisphere Amplitudes nAm

24. M170 - Right Hemisphere Grandaveraged waveform n=16 p < 0.001 nAm Time

25. M170 - Right Hemisphere Amplitudes nAm

26. Other measures • No M100 effects. • No M350 effects. • No response time effect.

27. Conclusions • M170 activity is influenced by the presence of derivational suffixes. • Early lexical decompositon. • No effect of opacity • All affixed words decompose.

28. Conclusions • The right lateralization of the effect is surprising. • Early visual word processing may be bilateral, with distinct functional roles for the left and the right hemispheres. • However, there is a second hypothesis.

29. Why the right hemisphere? FARMER FARMER FARMER

30. Experiment 2 Prefixed words

31. Experiment 2 Stimuli 32 words per condition Conditions were controlled for matched for length, surface frequency, orthographic neighborhood density and frequency, and syntactic category. Prefixed condition was further controlled for stem frequency and orthographic regularity.

32. M170 - Right Hemisphere Grandaveraged Waveform n=10 p < 0.02 nAm Time

33. M170 - Left Hemisphere Grandaveraged Waveform n=10 p < 0.02 nAm Time

34. Other measures • No M100 effects. • No M350 effects. • No response time effect.

35. Conclusions • Experiment 1 replicated. • Stem lexicality cannot be the sole reason for the RH effect in Experiment 1. • Possibly a combined effect of morphological complexity and stem lexicality.

36. Kana Kanji /ta-ba-ko/ smoke-weed

37. FMRI activity in fusiform gyri Nakamura et. al (2005)

38. Conclusions • Morphological decomposition is a pre-lexical effect, and is not sensitive to semantic opacity. • The RH M170 source is sensitive to morphological complexity irrespective of the linear ordering between a stem and an affix. • A crucial role for the right hemisphere in early word processing.