Early effects of morphological complexity on visual evoked

fields in MEG

Eytan Zweig & Liina PylkkänenNew York University

80th Annual LSA meeting, January 7, 2006

Morphological decomposition -Two questions

• Do all affixed words decompose? Does semantic opacity play a role?

• What is the timing of lexical decomposition?

Semantic opacity• Transparent words generally taken to decompose

• Competing hypotheses about opaque words

“Farmer” Farm + -er

“Folder”Fold + -er

Folder ?

1. Opaque words decompose (Rastle & Davis, 2003; Davis et al., 2004)

2. Opaque words do not decompose (Marslen-Wilson et al., 1994)

Semantic opacity

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

Timing of decomposition

Decomposition Lexical access

1. Early decomposition (Taft & Forster, 1975; Rastle & Davis, 2003; Davis et al., 2004)

3. Race (Baayen, 1992)

Lexical access Decomposition

2. Late decomposition (Feldman et al., 2004)

farm + -er farm, -er

farmer farm + -er

Decomposition Lexical access

Lexical access

farm + -er farm, -er

farmer

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.

This study

• Takes advantage of the millisecond temporal resolution of MEG.

• Simple lexical decision task without priming.

Magnetoencephalography (MEG)

http://www.ctf.com/Pages/page33.html

EEGEEGMEGMEG

MEG analysis

MEG analysis

MEG analysis

MEG analysis

Typical MEG response to visual words

Experiment 1Suffixed words

Experiment 1 Stimuli

No SuffixNo Suffix Orth. -er

Opaque Suffix

Transparent

Suffix

SWITCH WINTER FOLDER FARMER

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.

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.

Prediction - Timing

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

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.

M170

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

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.

Prediction – Semantic opacity

• If opaque words decompose, they will pattern with transparent words.

• If they do not, they will pattern with orthographic controls.

-15

-10

-5

0

5

10

15

20

25

30

-50 -16 18 51 85 119 153 187 220 254 288 322 356 390

Suffixed

Not Suffixed

M170 - Left Hemisphere Grandaveraged waveform

n=16 no effect

Time

nAm

10

12

14

16

18

20

22

24

26

28

30

No Suffix No Suffix, Orth. Match Opaque Suffix Transparent Suffix

M170 - Left Hemisphere Amplitudes

SWITCH WINTER FOLDER FARMER

nAm

-15

-10

-5

0

5

10

15

20

25

30

-50 -16 18 51 85 119 153 187 220 254 288 322 356 390

Suffixed

Not Suffixed

M170 - Right Hemisphere Grandaveraged waveform

n=16 p < 0.001

Time

nAm

M170 - Right Hemisphere Amplitudes

10

12

14

16

18

20

22

24

26

28

30

No Suffix No Suffix, Orth. Match Opaque Suffix Transparent Suffix

SWITCH WINTER FOLDER FARMER

nAm

Other measures

• No M100 effects.

• No M350 effects.

• No response time effect.

Conclusions

• M170 activity is influenced by the presence of derivational suffixes.• Early lexical decompositon.

• No effect of opacity• All affixed words decompose.

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.

Why the right hemisphere?F

AR

ME

R

FA

RM

ER

FA

RM

ER

Experiment 2Prefixed words

Experiment 2 Stimuli

No Prefix No Prefix Orth. re-

Prefix

ROTATE RESUME REFILL

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.

M170 - Right Hemisphere Grandaveraged Waveform

-10

-5

0

5

10

15

20

25

30

35

-50 -16 18 51 85 119 153 187 220 254 288 322 356 390

Prefixed

No Prefix, Ortho re-

No Prefix

Time

nAm

n=10 p < 0.02

M170 - Left Hemisphere Grandaveraged Waveform

-10

-5

0

5

10

15

20

25

30

35

-50 -16 18 51 85 119 153 187 220 254 288 322 356 390

Prefixed

No Prefix, Ortho re-

No Prefix

n=10 p < 0.02

Time

nAm

Other measures

• No M100 effects.

• No M350 effects.

• No response time effect.

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.

/ta-ba-ko/

KanaKanji

smoke-weed

Nakamura et. al (2005)

FMRI activity in fusiform gyri

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.