Writing systems differ in how they represent spoken language in written form. For alphabetic writing systems such as English, orthographic units (i.e., letters) represent phonemes. For morphosyllabic writing systems such as Chinese, orthographic unites (i.e., symbols) represent syllables. These differences have consequence, as studies show that writing systems with different orthography to phonology mapping are processed via different underlying cognitive processes (Coltheart et al. 2001
; Perfetti et al. 2005
Recent progress in the development of techniques for recording brain activity has opened doors for researchers who wish to examine the brain areas that are involved in visual word recognition for different writing systems. A primary concern in these studies has been determining the neural substrates of phonological processing. Two recent meta-analyses of neuroimaging studies (Bolger et al. 2005
; Tan et al. 2005
) identified several brain areas related to phonological processing. With English writing, brain activation was pronounced in the left dorsal temporoparietal system, including posterior regions of the left superior temporal gyrus (BA22), the angular gyrus (BA39), and the supramarginal gyrus (BA40). These areas are thought to mediate grapheme-to-phoneme conversion and fine-grained phonemic processing in alphabetic writing systems (Bolger et al. 2005
; Tan et al. 2005
). With Chinese writing, strong activation was found in the left middle frontal gyrus (BA9), which has been suggested to relate to “look-up” processes of addressed phonology (Bolger et al. 2005
; Tan et al. 2005
). Further, the left inferior prefrontal gyrus (BA44,45,46,47), suggested to relate to subvocal rehearsal functions, is relevant to both Chinese and English readers (Tan et al. 2005
Although these findings are suggestive, few neuroimaging studies have examined phonological processing in different writing systems in a single study. An exception was an fMRI study by Tan et al. (2003)
, whose findings suggested activation of the middle frontal region for Chinese and of the superior temporal region for English. Unfortunately, this study did not present the data in a way that allowed for a fine-grained analysis of hemodynamic responses.
In the present study, we compared brain areas involved in phonological processing for English and Chinese using the hemodynamic measure of near-infrared spectroscopy (NIRS). NIRS measures changes in the concentration of oxy-hemoglobin and deoxy-hemoglobin in the brain regions of interest after near-infrared light penetrates the scalp, is absorbed and then scattered. NIRS is a more portable and affordable alternative to fMRI, providing reasonable temporal and spatial resolution (Hochman 2000
; Strangman et al. 2002a
). Previous studies suggest that NIRS data are highly consistent with fMRI data (Strangman et al. 2002a
), but it is an empirical question whether analysis of phonological processing will converge in this instance, using this alternate method.
To examine the processing of different writing systems in a single study, our task was modified in important ways from prior work. Tan et al.'s (2003)
fMRI study compared Chinese and English readers on a rhyme judgment task, which is the typical task used in studies with English (Tan et al. 2005
). We suggest, however, that rhyme judgment is a less natural task for Chinese speakers, since it forces them to segment sounds into phonemes, which are not represented in the Chinese writing system. We thus used a homophone judgment task for both Chinese and English readers, while acknowledging that this task may be somewhat more difficult than rhyme judgment for English readers. Our decision to use homophone judgment was based on it being a more natural task for Chinese readers since it calls on whole word phonology (Chen et al. 2007
Our study also differed from previous work in terms of experimental design. Whereas previous NIRS studies of language have used a block design, our study employed an event-related design. Although a block design may have superior statistical power to detect subtle differences (Friston et al. 1999
), event-related designs allow randomized presentation. This is desirable in investigations where carryover effects introduce response artifacts (Chee et al. 2003
). Using such a design in the present study also allows us to determine whether event-related designs are in general sensitive to the subtle changes typically observed in word recognition experiments. Because the NIRS method does not permit monitoring of blood flow change of the whole brain, it was important to identify the brain region(s) of interest (ROI) at the outset. Four ROIs in the present study were identified, all in the left hemisphere. We report findings for each of these four regions, as outlined below.