Data_Sheet_1_Automatic morpheme identification across development: Magnetoencephalography (MEG) evidence from fast periodic visual stimulation.docx

The present study combined magnetoencephalography (MEG) recordings with fast periodic visual stimulation (FPVS) to investigate automatic neural responses to morphemes in developing and skilled readers. Native English-speaking children (N = 17, grade 5–6) and adults (N = 28) were presented with rapid streams of base stimuli (6 Hz) interleaved periodically with oddballs (i.e., every fifth item, oddball stimulation frequency: 1.2 Hz). In a manipulation-check condition, tapping into word recognition, oddballs featured familiar words (e.g., roll) embedded in a stream of consonant strings (e.g., ktlq). In the experimental conditions, the contrast between oddball and base stimuli was manipulated in order to probe selective stem and suffix identification in morphologically structured pseudowords (e.g., stem + suffix pseudowords such as softity embedded in nonstem + suffix pseudowords such as trumess). Neural responses at the oddball frequency and harmonics were analyzed at the sensor level using non-parametric cluster-based permutation tests. As expected, results in the manipulation-check condition revealed a word-selective response reflected by a predominantly left-lateralized cluster that emerged over temporal, parietal, and occipital sensors in both children and adults. However, across the experimental conditions, results yielded a differential pattern of oddball responses in developing and skilled readers. Children displayed a significant response that emerged in a mostly central occipital cluster for the condition tracking stem identification in the presence of suffixes (e.g., softity vs. trumess). In contrast, adult participants showed a significant response that emerged in a cluster located in central and left occipital sensors for the condition tracking suffix identification in the presence of stems (e.g., softity vs. stopust). The present results suggest that while the morpheme identification system in Grade 5–6 children is not yet adult-like, it is sufficiently mature to automatically analyze the morphemic structure of novel letter strings. These findings are discussed in the context of theoretical accounts of morphological processing across reading development.

本研究将脑磁图（magnetoencephalography, MEG）记录与快速周期性视觉刺激（fast periodic visual stimulation, FPVS）相结合，旨在探究发展性阅读者与熟练阅读者对语素的自动化神经反应。研究招募了以英语为母语的儿童（N=17，五至六年级）与成人（N=28），向其呈现快速流状基础刺激序列（6Hz），并周期性插入偏差刺激（oddball），即每5个项目插入1个，偏差刺激呈现频率为1.2Hz。在操作检验条件中，为考察词汇识别加工，偏差刺激为嵌入辅音串（如ktlq）流中的熟悉词汇（如roll）。在实验条件中，研究者通过操纵偏差刺激与基础刺激的差异，以探究形态结构化假词中选择性词干与词缀识别情况，例如将词干+词缀类假词softity嵌入非词干+词缀类假词trumess的刺激流中。研究者采用基于非参数簇的置换检验，在传感器层面分析了偏差刺激频率及其谐波的神经反应。如预期所示，操作检验条件的结果显示，儿童与成人组均在颞叶、顶叶与枕叶传感器上出现了以左侧偏侧化为主的簇状反应，该反应反映了词汇选择性加工。然而，在不同实验条件下，发展性阅读者与熟练阅读者的偏差刺激反应模式存在显著差异。当追踪存在词缀的词干识别条件（如softity与trumess对比）时，儿童组在以中央枕叶簇为主的脑区出现了显著反应。与之相对，成人组在追踪存在词干的词缀识别条件（如softity与stopust对比）时，在中央与左侧枕叶传感器簇上出现了显著反应。本研究结果表明，尽管五至六年级儿童的语素识别系统尚未达到成人成熟水平，但已足够成熟，可以自动化分析新型字母串的词法结构。最后，本文结合阅读发展过程中形态加工的理论解释框架，对上述发现进行了讨论。