neural correlates of morphological decomposition in a morphologically rich language : an fmri study

Neural correlates of morphological decomposition in a morphologically

rich language: An fMRI study

Lehtonen, M., Vorobyev, V.A., Hugdahl, K., Tuokkola T., Laine M.

Morphologically Complefl Words• SING+ER+S• Most Indo-European languages, such as English or

French, use inflectional affixes to quite a limited extent.

• Finnish has abundant inflectional possibilities: a single noun in Finnish can have as many as 2000 different forms– HUONE+I+SSA+NNE+KIN– ‘room’ + plural + ‘in’ + ‘your’ + ‘even’– ‘even in your rooms’

Morphological Decomposition• When compared to otherwise matched

monomorphemic words, Finnish morphologically complex words– are usually processed more slowly – with a greater probability of error.

• This suggests that morphological decomposition takes place during recognition of these words

• The recognition process of inflected words is assumed to require two major processing steps– early morphological decomposition at the visual word

form level– integration of the meaning of the morphological

constituents at the semantic-syntactic level.

Where is the Processing Cost?• It could be at the early visual level or the semantic

integration level.• Hyönä et al. (2002)

– suggests that the morphological effect derives from the more central, semantic-syntactic level.

– They observed that the morphological effect seen with isolated inflected words vanished when the participants read the very same items embedded in neutral sentence contexts.

• This study uses fMRI data to answer this question.

Previous Neuroimaging Studies• Two specific brain areas were identified as being

involved in morphological processing.• The left OTC (occipitotemporal cortex), especially

the fusiform gyrus, involved in decomposition at the visual input level

• The LIFG (left inferior frontal gyrus) and/or the left pSTG/pMTG (posterior superior/middle temporal gyri), involved in integration of meaning of the morphological constituents that calls for semantic-syntactic processing

OTC and Fusiform Gyrus

left inferior frontal gyrusLIFG

posterior superior temporal gyruspSTG

posterior middle temporal gyrus pMTG

So…• Increased activation in the OTC should

indicate work on morphological decomposition at the visual input level.

• Increased activation in the LIFG and/or pSTG/pMTG should indicate work on integration of meaning.

Methods• Participants

– 12 right-handed students• Materials

– 85 monomorphemic words– 85 case-inflected nouns– 170 pseudowords (half w/ inflection-like endings)

Methods• Procedure

– Lexical decision task– ½ responded with left hand, ½ with right (why?)– The stimuli were projected onto a screen that the

participants saw through an angled mirror fixated on the head coil.

– Asterisk for 500 ms, 500ms blank, then stimulus work for up to 2000ms

Methods• Procedure

– 34 30s task blocks• 10 items per block (5 pseudowords, 5 words)• 17 monomorphemic (MM) blocks• 17 inflected (INFL) blocks

MM(30s)

INFL(30s)

INFL(30s)

MM(30s)

REST(20s)

REST(20s)

REST(20s)

REST(20s)

MRI Scanning• fMRI is the use of MRI to measure the

hemodynamic response related to neural activity in the brain

http://www.howstuffworks.com/mri.htmhttp://www.fmrib.ofl.ac.uk/fmri_intro/brief.html

Results: Behavioral Data• As expected, the inflected words elicited

significantly longer reaction times than the monomorphemic words– (mean for monomorphemic, 763ms, SD 80; for

inflected, 827, SD 88; t (11)D12.0, p<.001).• The inflected items received also significantly

higher error rates than the monomorphemic ones– (mean for monomorphemic, 2.84%, SD 3.93; for

inflected, 5.36%, SD 5.80; t (11)=2.75, p=.02).

Results: fMRI Data

Discussion• the contrast between inflected and

monomorphemic items elicited clear activation increases in two of the three VOIs: in the LIFG and in the left temporal region.

• Because the two stimulus groups were carefully matched and the only relevant difference between them was morphological complexity, it is plausible that the behavioral and activation differences between the two item types (inflected vs. monomorphemic words) were caused by morpheme-based processing of the inflected items.

Discussion• Semantic unification is assumed to be related to the function

of the LIFG– LIFG activation in the present study may reflect the operations

required for constructing a semantic-syntactic interpretation of the stem and affix combination on-line.

• Temporal areas have been assumed to play a crucial role in the memory component of language– Activation in the temporal VOI was expected to reflect activation of

the representations of the stem and the affix– may also reflect the activation of the rules of the stem+affix

combinability.– The fact that recognizing an inflected word involves accessing two

types of information may also bring about increased activation in temporal areas when compared to monomorphemic words.

Discussion• results do not rule out the possibility that the

left OTC is indeed involved in segmenting the orthographic patterns into morphemic units and relaying the information for temporal regions for further analysis

• This process may simply be very fast and automatic, and the main processing load with inflected words stems from the later stages.

Discussion• The neural correlates of morphological

decomposition reflect either form- or meaning-related lexical access processes that are part and parcel of the recognition of any given word (albeit more complex for inflected words).

Questions• In an fMRI study activation patterns seem to be

compared in between a baseline condition (do nothing?) and a task condition. Then how do we compare two (or more than) two different task type conditions directly?

• My only question was whether (and how much) it matters that the words were all low and medium surface frequency - that places considerable limit on the extension of the findings, I think.  They didn't really address the significance of that, rather, they just noted that high surface frequency helps predict full-form/decompositional processing.

Questions• I don't know Finnish at all. So, it is amazing that

Finnish can have as many as 2000 different forms of a single noun. How does it work?

• Why does Finnish benefit finding out the neural correlaton of morphological decomposition?

• Also, I am wondering if the effect could be resulted from working memory load but not morphology itself.

Questions• Compared with Finnish, which has lots of

inflectional possibilities, Mandarin, on the other hand, is inflection impoverished. Characters such as "LE", "ZHE" and "ZAI" is used in Mandarin to mark inflection. However, unlike other Indo-European languages, these characters in Mandarin are separate from the previous stem or words. Thus coming back to the topic of this paper, which states that left frontal regions and left superior or middle temporal areas the ones most commonly observed in studies of morphological processing, I was wondering if the same areas will be activated too?

Questions• Since this paper was aiming to look at the

morphological decomposition, I'm thinking maybe using words with similar orthography but different morphological structures would speak more to this issue?

• Other questions?