AUTHOR=Pescuma Valentina N. , Ktori Maria , Beyersmann Elisabeth , Sowman Paul F. , Castles Anne , Crepaldi Davide 

TITLE=Automatic morpheme identification across development: Magnetoencephalography (MEG) evidence from fast periodic visual stimulation

JOURNAL=Frontiers in Psychology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2022.932952

DOI=10.3389/fpsyg.2022.932952

ISSN=1664-1078

ABSTRACT=<p>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 (<italic>N</italic> = 17, grade 5–6) and adults (<italic>N</italic> = 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., <italic>roll</italic>) embedded in a stream of consonant strings (e.g., <italic>ktlq</italic>). 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 <italic>softity</italic> embedded in nonstem + suffix pseudowords such as <italic>trumess</italic>). 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., <italic>softity</italic> vs. <italic>trumess</italic>). 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., <italic>softity</italic> vs. <italic>stopust</italic>). 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.</p>