An Investigation into Kanji Character Discrimination Process from EEG Signals

The frontal area in the brain is known to be involved in behavioral judgement. Because a Kanji character can be discriminated visually and linguistically from other characters, in Kanji character discrimination, we hypothesized that frontal event-related potential (ERP) waveforms reflect two discrimination processes in separate time periods: one based on visual analysis and the other based on lexcical access. To examine this hypothesis, we recorded ERPs while performing a Kanji lexical decision task. In this task, either a known Kanji character, an unknown Kanji character or a symbol was presented and the subject had to report if the presented character was a known Kanji character for the subject or not. The same response was required for unknown Kanji trials and symbol trials. As a preprocessing of signals, we examined the performance of a method using independent component analysis for artifact rejection and found it was effective. Therefore we used it. In the ERP results, there were two time periods in which the frontal ERP wavefoms were significantly different betweeen the unknown Kanji trials and the symbol trials: around 170ms and around 300ms after stimulus onset. This result supported our hypothesis. In addition, the result suggests that Kanji character lexical access may be fully completed by around 260ms after stimulus onset.

Authors:

• Hiroshi Abe
• Minoru Nakayama

Keywords:

• Character discrimination
• Event-related Potential
• IndependentComponent Analysis
• Kanji
• Lexical access.

References:

[1] M.S. Gazzaniga, R.B. Ivry, and G.R. Mangun, "Cognitive Neuroscience,"
W.W. Norton & Company, Newyork, 1998.
[2] S. Thorpe, D. Fize, and C. Marlot, "Speed of Processing in the Human
Visual System," Nature, vol. 381, pp. 520-527, 1996.
[3] R. VanRullen, and S.J. Thorpe, "The time course of visual processing:
from early perception to decision-making," J. Cogn. Neurosci., vol. 13,
pp.454-461, 2001.
[4] R. VanRullen, and S.J.Thorpe, "Is it a bird? Is it a plane? Ultra-rapid
visual categorisation of natural and artifactual objects," Perception, vol.
30, pp. 655-668, 2001.
[5] S. Dehaene, L. Cohen, M. Sigman, and F. Vinckier, "The neural code for
written words: a proposal," Trends Cogn. Sci., vol. 9, pp. 335-341, 2005.
[6] A.P. Rudell, "Rapid stream stimulation and the recognition potential,"
Electroencephalogr. Clin. Neurophysiol. vol. 83, pp. 77-82, 1992.
[7] M. Martin-Loeches, J.A. Hinojosa, G. Gomez-Jarabo, and F.J. Rubia,
"The recognition potential: an erp index of lexical access," Brain and
Language, vol. 70, pp. 364-384, 1999.
[8] S. Makeig, M. Westerfield, T.P. Jung, J. Covington, J. Townsend and T.J.
Sejnowski, and E. Courchesne, "Functionally Independent Components of
the Late Positive Event-related Potential during Visual Spatial Attention,"
J. of Neurosci., vol. 19, pp. 2665-2680, 1999.
[9] T.P. Jung, S. Makeig, C. Humphries, T.W. Lee, M.J. McKeown, V. Iragui,
and T.J. Sejnowski, "Removing electroencephalographic artifacts by blind
source separation," Psychophysiol., vol. 37, pp. 163-178, 2000.
[10] J.L. Kenemans, P. Molenaar, M.N. Verbaten, and J.L. Slangen : "Removal
of the Ocular Artifact from the EEG: A Comparison of Time and
Frequency Domain Methods with Simulated and Real Data", Psychophysiology
28, pp.114-121 (1991)
[11] P. Berg, and M. Scherg : "Dipole Models of Eye Activity and Its
Application to the Removal of Eye Artifacts from the EEG and MEG",
Clinical Physics and Physiological Measurements 12(Supplement A),
pp.49-54 (1991)
[12] B. Rossion, C.A. Joyce, G.W. Cottrell, and M.J. Tarr, "Early lateralization
and orientation tuning for face, word, and object processing in the
visual cortex," Neuroimage, vol. 20, pp. 1609-1624, 2003.
[13] N. Amano and K. Kondo (ed.), "Moji Tokusei (Character charasteristics),"
Tokyo: Sanseido, 1999.
[14] M. Hayashi, Y. Kayamoto, H. Tanaka, and J. Yamada, "Semantic
activation by japanese kanji: evidence from event-related potentials,"
Perceptural and Motor Skills, vol. 86, pp. 375-382, 1998.
[15] M. Iwata, "Kanji versus kana neuropsychological correlates of the
japanese writing system," Trends Neurosci., vol. 7, pp. 290-293, 1984.
[16] A. Delorme and S. Makeig, "An Open Source Toolbox for analysis of
single-trial EEG dynamics," J. of Neurosci. Method, vol. 134, pp. 9-21,
2004.
[17] M.J. Taylor, "Non-spatial attentional effects on P1," Clin. Neurophysiol.,
vol. 113, pp.1903-1908, 2002.
[18] H. Abe and M. Nakayama, "Event-related potential study of kanji
perception process," J. Inst. Image Inf. Television Eng., vol. 60, pp. 397-
404, 2006.
[19] S. Bentin, Y. Mouchetant-Rostaing, M.H. Giard, J.F. Echallier, and J.
Pernier, "ERP manifestations of processing printed words at different
psycholinguistic levels: time course and scalp distribution," vol. 11, pp.
235-260, 1999.