从字形到语义：跨语言Stroop效应的ERP研究

According to the influential dual-route model of reading (Coltheart, Rastle et al. 2001), there are two routes to access the meaning of visual words: one directly by orthography (orthography-semantic) and the other indirectly via the phonology (phonology-semantic). Because of the dramatic difference between written Chinese and alphabetical languages, it is still on debate whether Chinese readers have the same semantic activation processes as readers of alphabetical languages. In this study, the semantic activation processes in alphabetical German and logographic Chinese were compared. Since the N450 for incongruent color words in the Stroop tasks was induced by the semantic conflict between the meaning of the incongruent color words and color naming, this component could be taken as an index for semantic activation of incongruent color words in Stroop tasks. Two cross-script Stroop experiments were adopted to investigate the semantic activation processes in Chinese and German. The first experiment focused on the the role of phonology, while the second one focused on the realative importance of orthography. Cultural differences in cognitive processing between individuals in western and eastern countries have been found (Nisbett & Miyamoto, 2005). In order to exclude potential differences in basic cognitive processes like visual discrimination capabilities during reading, a visual Oddball experiment with non-lexical materials was conducted with all participants. However, as indicated by the P300 elicited by deviant stimuli in both groups, no group difference was observed. In the first Stroop experiments, color words (e.g., “green”), color-word associates (e.g., “grass”), and homophones of color words were used. These words were embedded into color patches with either congruent color (e.g. word “green” in green color patch) or incongruent colors (e.g. word “green” in either red or yellow or blue color patch). The key point is to observe whether homophones in both languages could induce similar behavioral and ERP Stroop effects to that induced by color words. It was also interesting to observe to which extent the N450 was related to the semantic conflicts. Nineteen Chinese adult readers and twenty German adult readers were asked to respond to the back color of these words in the Stroop experiment in their native languages by pressing the corresponding keys. In the behavioral data, incongruent conditions (incongruent color words, incongruent color-word associates, incongruent homophones) had significantly longer reaction times as compared to corresponding congruent conditions. All incongruent conditions in the Geman group elicited an N450 in the 400 to 500 ms time window. In the Chinese group, the N450 in the same time window was also observed for the incongruent color words and incongruent color-word associates. These results indicated that the N450 was very sensitive to semantic conflict-even words with semantic association to colors (e.g. “grass”) could elicite similar N450. However, the N450 was absent for incongruent homophones of color words in the Chinese group. Instead, in a later time window (600-800 ms), incongruent homophones elicited a positivity over left posterior regions as compared to congruent homophones. Similar positivity was also observed for color words in the 700 to 1000 ms time window in the Chinese group and 600 to 1000 ms time window for incongruent color words and homophones in the Geman group. These results indicate that phonology plays an important role in Geman semantic activation processes, but not in Chinese. In the second Stroop experiment, color words and pseudowords which had similiar visual shape to color words in both languages were used as materials. Another group of eighteen Chinese and twenty Germans were involved in the Stroop experiment in their native languages.The ERPs were recorded during their performance. In the behavioral data, strong and comparable Stroop effects (as counted by substract the reaction times in the congruent conditions from reaction times in the incongruent conditions) were observed. In the ERP data, both incongruent color words and incongruent pseudowords elicited an N450 over the whole brain scalp in both groups. These results indicated that orthography played an equally important role in semantic activation processes in both languages. The results of the two Stroop experiments support the view that the semantic activation process in Chiense readers differs significantly from that in German readers. The former rely mainly on the direct route (orthography-semantic), while the latter use both direct route and incirect route (phonology-semantic). These findings also indicate that the characteritics of different languages shape the semantic activation processes.

Stroop效应中的N450被认为是因色词语义干扰而产生的成分。本研究以双通路模型为理论基础，采用N450为ERP (event-related potentials)指标，通过两个跨文字的Stroop实验比较中文和德文熟练读者的语义激活过程。研究目的一是考察语音在语义通达过程中的影响。研究目的二是考察字形在语义通达过程中的影响。 第一个Stroop实验使用的关键材料是四种颜色词（红、绿、黄、蓝）和色词的同音词（中文：洪、律、皇、栏）。德文中的同音词为假词，按照德文的发音规则，这些词和色词的发音一样。实验重点是观察同音词是否引起和色词相似的行为效应和ERP效应。 为了考察N450对语义冲突的敏感程度，实验使用了和颜色有语义联系的词（中文：火、草、橙、海；德文：西红柿、草、香蕉、天空）。十九名中文被试和二十名德文被试用按键的方式完成Stroop实验（中文被试看中文，德文被试看德文）。实验后设置了一个视觉Oddball实验，旨在考察中文和德文被试的基本视觉辨别能力是否相同。 两组被试在视觉Oddball任务中产生的P300没有组间差异，表明他们的基本视觉辨别能力相似。在Stroop实验中，色词、色词的语义联想词和色词的同音词在两组被试中均引起显著的行为Stroop效应：不一致条件的反应时明显比一致条件的反应时长。在德文被试中不一致色词、不一致语义联想词和不一致同音词均引起了非常显著的N450。这表明语音在德文的语义通达过程中扮演着非常重要的角色。中文中不一致的色词和不一致的语义联想词引起了非常显著的N450。但是在N450的时间窗口上一致和不一致的同音词却没有差异，它们的差异出现在一个更晚的时间段。在600—800毫秒的时间窗口，和一致的同音词相比不一致的同音词引起了一个非常明显的正波。这个正波还从中文不一致色词、德文不一致色词和不一致同音词中观察到。因此这个成分可能反映了正常的语义通达后，被试意识到一致的同音词与色词和需要反应的颜色的发音相同，因而二次激活了色词的语义。 中文和德文同音词的结果表明语音在汉语正常的语义通达过程中的作用有限，而在德语的语义通达过程中有着重要作用。此外，基于语义联想词的实验结果还表明N450对语义冲突确实非常敏感——和颜色有语义相关的词在两组被试中都能够引起N450。 第二个Stroop实验主要考察字形在语义通达过程中的作用。实验用到的关键材料是中文和德文的色词和色词的词形相近词。同研究一的Stroop实验一样，使用了红、绿、黄、蓝四种颜色词。十八名中文被试和二十名德文被试（均未参加研究一的任何实验和调查）用按键的方式完成实验。 为了确认中文被试能够正确区分色词和色词的形近词，所有中文被试在Stroop实验后还完成了一个快速呈现的视觉辨别任务。视觉辨别任务的结果表明中文被试能够正确区分色词及其形近词。Stroop实验结果表明两组被试的色词和形近词均引起了显著行为和ERP的Stroop效应：不一致条件下的反应时比一致条件的反应时长，且不一致条件均引起了显著的N450。这表明词形在两组被试的语义通达过程中均起到重要的作用。 结合两个实验，本研究的发现为汉语单字词直接的词形—语义通路和德文词语的词形—语义和语音—语义两条通路提供了来自ERP的数据。