Can electrophysiological techniques help us understand reading in Chinese? Science of Learning SRT: Meeting of Minds Series

I-Fan Su Lab. for Communication Sciences, Division of Speech & Hearing Sciences 14-10-2015

Aims

Ø  What is EEG/ERP.

Ø  How these methods are used in our lab to understand which and when sub-lexical features in Chinese characters are processed in the brain.

Ø  Capturing the heterogeneity of developmental dyslexia in Chinese through behavioural profiles and event-related potentials (ERP) measures project

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What does EEG measure?

Ø Changes in electrical field potentials caused by neural activities.

http://psyphz.psych.wisc.edu/~greischar/BIW12-11-02/EEGintro.htm

•  EEG recorded from the scalp represents net electrical fields associated with a sizeable population of neurons

•  The individual neurons that comprise such a population must be synchronously active and have a certain geometric configuration

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Electroencephalography (EEG)

Ø EEG is the ongoing recording of electrical activity along the scalp produced by the firing of neurons within the brain

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Electroencephalography (EEG) vs. Event Related Potential (ERP)

Ø ERP’s are electrical brain potentials that are related to an event of some sort, usually stimulus perception and evaluation.

 

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ERP Setup

(Luck, 2005)

Electrode array

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EEG Recording

Taken from Luck, 2005

Conditions

EEG

Electrical activity scale

8 Taken from Luck, 2005

Conditions

EEG pattern of individual trials

ERP pattern of averaged trials

Differences in ERP waves tells us whether the brain honours the distinction between 2 conditions

The Time Course of Reading (single words)

Grainger & Holcomb, 2010

Together, the sequence of ERP peaks and troughs reflects the flow of information through the brain (Luck, 2005).

ERP Components

N170 Orthography / OàP (Eng.)

P200 Phonological

retrieval / OàP (Chinese)

N400 Lexical semantic access / retrieval

P100 Visual-

orthographic feature analysis

Spatial Specification of Radicals

Ø  Are radicals in Chinese Characters encoded for position? Ø  Most if not all models of Chinese character processing

recognize representations of radicals, but the theoretical frameworks have different assumptions about position specification of radicals

Ø  杏 /hang6/ - apricot vs. 呆 /daai1/ - foolish

Ø  Radicals are position general (Li & Chen, 1999; Taft et al., 2000; Tsang & Chen, 2009; Yeh & Li, 2002; 2004).

Ø  Configuration units provides spatial units/slots for position free radicals to fill in (Perfetti et al., 2005).

Ø  Radicals are spatially specified with independent position-specific radical representations (Ding et al. 2004; Taft & Zhu, 1997; Taft et al., 1999).

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Position-Specific Radical Representations

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Su, Mak, Cheung, & Law, 2012

Early Encoding of Radical Position legality

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Real characters introduce confounding phonological and semantic factors

Pseudo-characters allows greater flexibility to include only target radicals

Yum, Su & Law, 2015

N170

P100

Character detection task

Ø  Characters with radicals in subordinate positions showed larger N2/P2, associated with greater activation at radical-level processing.

Ø  Characters with radicals in dominant position elicited greater negativity at N400, suggesting greater lexical competition with other characters with similar radicals also in dominant position.

Ø  However, pseudo-character conditions in legal radical positions did not differ among themselves.

Ø  The early timecourse effects suggest that radical position legality was detected at the initial stage of visual processing (P100), which challenged theoretical models that assume primacy of position-general radical representations.

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Spatial Specification of Radicals

What is the basic unit of reading in Chinese?

Ø  Complex Chinese characters are automatically decomposed into sub-lexical components referred to as radicals during reading.

Ø  Yet writing error patterns in children and aphasic individuals suggest a smaller unit of representation, referred to as logographemes. Ø  碗 (/wun3/, “bowl”) à

Ø  In addition, how is the orthographic sub-system able to differentiate sub-lexical units in a character?

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(/ho1/, “to breathe out”) 呵

呵 呵

(/ho1/, “to breathe out”) 呵

呵 呵 呵

Radicals (2) Logographemes (3)

Logographeme Number Effect Ø  Greater P1 activation

for characters containing 6 logographemes than 3 logographemes, after controlling stroke number

Ø  N170 Logographeme Number x Frequency interaction showed greater sensitivity to the number of logographemes in a character for low frequency characters

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3Logo 6Logo

Lexical decision task

Logographeme Independence

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Lexical decision task

What is the Basic Unit of Reading in Chinese?

Ø The logographeme number and logographeme independence effects both suggest that logographemes contribute to word recognition.

Ø Effects were mainly found at the P100 component indicating that their impact on reading is short lived and only during the early visual-orthographic analysis stage.

Ø Based on theoretical models of Chinese character recognition, it is proposed that logographemes are represented between the level of strokes and radicals (Perfetti, Liu, & Tan, 2005; Taft, Zhu,& Peng, 1999).

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Sublexical processing in Dyslexics

Ø Reading aloud è processing or analysis of visual form to extract the appropriate orthographic units and later map onto phonemic units during phonological processing.

Ø Radicals play important role in the literacy development. However, few studies have directly examined how sublexical features influence the recognition of Chinese characters in poor readers (Chung et al., 2012).

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Regularity: Phonological (P200)

Regularity effect, Group effect

*Reg X Gp: CA àIR > R

Regular – 伴 /bun6/ à 半 /bun3/ Irregular – 秘 /bei3/ à 必 /bit1/

* *

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Regularity effect, Group effect

*Reg X Gp: PR àIR > R

Regularity: Lexical-Semantic (N400)

Regular – 伴 /bun6/ à 半 /bun3/ Irregular – 秘 /bei3/ à 必 /bit1/

* N400

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* *

Regular – 伴 /bun6/ à 半 /bun3/ Irregular – 秘 /bei3/ à 必 /bit1/

Regularity: Lexical-Semantic (N400)

Capturing the Heterogeneity of Developmental Dyslexia

Ø  Deficits in processing speech sounds and phonology are closely related to reading disorders.

Ø  Similar results reported in Chinese, but also additional evidence for poor morphological and orthographic awareness skills that may be specific to the Chinese orthography.

Ø  As many as 7 subtypes can be found in Chinese (Wu et al., 2009).

Ø  Approximately 43% of children with reading difficulties also have deficits in language development (Liu et al., 2010; Wong et al., 2010). Poor morphological awareness may be confounded by the high co-morbidity rate of SLI and developmental dyslexia.

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Lexical Quality Hypothesis

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Hypothesis: Dyslexic individuals may have weaker representations or lack of tight integration of the three lexical constituents that consequently lead to poor reading.

High quality lexical representations essentially means (almost) synchronous activation of the three lexical constituents, i.e. orthography, phonology, and semantics, and their integration (Perfetti & Hart 2002; Perfetti 2007).

Perfetti & Stafura, 2013

Aims Ø Do children with SLI and developmental dyslexia show

a profile different from those with dyslexia only?

Ø  Is there a relative dominance of certain dyslexia profile(s)?

Ø Can the nature of deficit(s) contributing to impaired reading be explained within the lexical quality hypothesis (as abnormal processing of particular lexical constituent(s) and/or integration of these constituents)?

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Behavioural and Neural Predictors of Reading Skills

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Can electrophysiological techniques help us understand reading in Chinese?

Ø  Modify existing models of Chinese character recognition. Ø  Identify different levels of sub-lexical representations Ø  Understand character decoding processes in individuals with

developmental dyslexia Ø Phonological regularity Ø  Lexicality

Ø  Address the issue of heterogeneity in developmental dyslexia Ø  Identify neural and cognitive indices of reading skill in Chinese

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Acknowledgements

Ø Dr. Sam-Po Law Ø Prof. Brendan Weekes Ø Dr. Dustin K.Y. Lau Ø Dr Cherry Y.N. Yum Ø Renee Fung

Ø Rachel Lee Ø Mak Sin-Ching Cassie Ø Cheung Lai-Ying Milly Ø Ko Sin Emily

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Lab for Communication Sciences Members: