Early morphological decomposition: MEG evidence from Fast Periodic Visual Stimulation


Workshop on Australiasian Magnetoencephalography (WAM), Sydney, Australia, December 10-13, 2019


December, 2019


Valentina Pescuma, Maria Ktori, Elisabeth Beyersmann, Paul Sowman, Anne Castles and Davide Crepaldi

Morphemes are the smallest linguistic units that carry meaning (e.g., a complex word such as artist is composed of a stem, art-, and a suffix, -ist). Behavioural evidence suggests that complex written words are decomposed into their constituent morphemes (Amenta & Crepaldi, 2012) and that reading development benefits from the morphological structure of words, especially from the presence of stems (e.g., Grainger & Beyersmann, 2017). Relying on previous EEG evidence for selective word (Lochy, Van Belle & Rossion, 2015) and morpheme (Ktori, De Rosa, Vidal & Crepaldi, in preparation) representations in the brain, the aim of this study was to investigate selective neural responses to morphemes embedded in pseudowords. Using Fast Periodic Visual Stimulation (FPVS) with an oddball paradigm (base frequency: 6 Hz, oddball frequency: 1.2 Hz) and MEG recording, we presented skilled adult readers (N=28, native English speakers) with pseudoword combinations of 12 stems (e.g., soft), 12 suffixes (e.g., ity), 12 non-stems (e.g., trum) and 12 non-suffixes (e.g., ust). Participants engaged with the unrelated task of monitoring the colour change of a fixation cross. Sensor-level analysis revealed successful discrimination response at oddball frequency (1.2 Hz) and its harmonics (2.4, 3.6, 4.8 Hz), in a left occipito-temporal region of interest, only for those experimental conditions in which the oddball stimuli were fully decomposable into stems and suffixes (e.g., softity). This provides evidence for automatic morpheme identification and is in line with accounts of morphological decomposition (e.g., Crepaldi, Rastle, Coltheart & Nickels, 2010; Taft & Nguyen-Hoan, 2010; Grainger & Beyersmann, 2017). Critically, these findings suggest that morpheme identification can be modulated by the context in which the morphemes appear. Further analyses will provide more refined spatial information and help shed light on the brain mechanisms underpinning morpheme identification. Particularly, involvement of the occipito-temporal cortex will be explored, in line with previous literature (e.g., Gold & Rastle, 2007; Leminen, Duñabeitia & Pliatsikas, 2019).