Neuroscience Letters 366 (2004) 254–258 Electrophysiological correlates of grapheme-phoneme conversion Koongliang Huang, Kosuke Itoh, Shugo Suwazono, Tsutomu Nakada ∗ Center for Integrated Human Brain Science, Brain Research Institute, University of Niigata, 1-757 Asahimachi-dori, Niigata 951-8585, Japan Received 17 March 2004; received in revised form 9 May 2004; accepted 19 May 2004 Abstract The cortical processes underlying grapheme-phoneme conversion were investigated by event-related potentials (ERPs). The task consisted of silent reading or vowel-matching of three Japanese hiragana characters, each representing a consonant-vowel syllable. At earlier latencies, typical components of the visual ERP, namely, P1 (110 ms), N1 (170 ms) and P2 (300 ms), were elicited in the temporo-occipital area for both tasks as well as control task (observing the orthographic shapes of three Korean characters). Following these earlier components, two sustained negativities were identified. The earlier sustained negativity, referred here to as SN1, was found in both the silent-reading and vowel-matching task but not in the control task. The scalp distribution of SN1 was over the left occipito-temporal area, with maximum amplitude over O1. The amplitude of SN1 was larger in the vowel-matching task compared to the silent-reading task, consistent with previous reports that ERP amplitude correlates with task difficulty. SN2, the later sustained negativity, was only observed in the vowel-matching task. The scalp distribution of SN2 was over the midsagittal centro-parietal area with maximum amplitude over Cz. Elicitation of SN2 in the vowel-matching task suggested that the vowel-matching task requires a wider range of neural activities exceeding the established conventional area of language processing. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Language; ERP; Literacy; Hiragana Phonological processing plays a crucial role in reading, even in the silent form of reading [3,4,6,7,14,15,24,27]. Characters are first converted to phonemes and syllables [7,9,24], which are then stored and manipulated in work- ing memory to form phonetic representations of words and phrases [4,6,15]. The importance of phonological process- ing, namely, grapheme-phoneme conversion and phonolog- ical manipulation in working memory, becomes explicit, for example, when reading unfamiliar words or appreciating rhymes in verses. Underdeveloped skills in either of the two fundamental stages of phonological processing impair literacy acquisition in children [6,7,24,25]. Although many studies [3,4,6,7,9,10,14–16,20,21,24–27], including those using event-related potentials (ERPs) [10,20,21,26], have investigated the phonological process- ing of grapheme-phoneme conversion and phonological manipulation, methodological difficulties have hindered clear and separate identification of the electrophysiologi- cal indices associated with these two stages of processing. ∗ Corresponding author. Tel.: +81 25 227 0677; fax: +81 25 227 0821. E-mail address: tnakada@bri.niigata-u.ac.jp (T. Nakada). Determining whether or not two English words rhyme, a type of vowel-matching task, has been effectively utilized to study phonological matching [20,21,26]. However, or- thographic priming represents a potential confounder of these studies, because word pairs that rhyme often share common graphemes (e.g. “a” and “l” in “pale” and “nail”). Semantic processing of the word may also contribute to and confound the observed ERPs. Utilization of single letters would alleviate these effects [10], but the ERP components prove difficult to be effectively separated due to the short processing time associated with converting single letters. The Japanese written system presents especially in- teresting opportunities for examining the cognitive com- ponents of reading because of its two co-existing or- thographic systems, kana and kanji. Simply stated, this dual system comprises a linearly combined phonetic character set of kana, and a “semantic” character set of kanji. Furthermore, there are two varieties of kana, namely, hiragana and katakana, each of which constitute a complete set of phonetic characters. A single hiragana character represents the equivalent of a single syllable con- sisting of a consonant and a vowel. Hiragana characters can rhyme with each other without sharing a common grapheme. 0304-3940/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2004.05.099