Morpheme-specific neural representations in skilled adult readers: Evidence from fast periodic visual stimulation


Society for the Neurobiology of Language (SNL) Annual Meeting, Helsinki, August 20-22, 2019


August, 2019


Maria Ktori, Mara De Rosa, Yamil Vidal, and Davide Crepaldi

Morphemes constitute the smallest meaning-bearing units of language that are combined to create complex words (e.g., kindness consists of the stem kind and the suffix -ness). Despite considerable behavioral evidence that morphologically complex written words are processed and represented via their constituent morphemes, the neural underpinnings of morphological processing remain poorly understood (Leminen, Smolka, Duñabeitia & Pliatsikas, 2018). The present study investigated whether morphemes are selectively represented in the brain of skilled readers as independent sublexical units in the absence of lexical context. Specifically, we used a fast periodic oddball paradigm (Lochy, Van Belle & Rossion, 2015) to measure EEG discrimination responses to morphological word endings (i.e., suffixes) presented in isolation. Skilled readers (N = 36; native Italian speakers) were presented with Italian suffixes (e.g., eria) appearing every five items in rapid streams of visual stimuli (F = 6 Hz) that varied in terms of their likeness to Italian word endings: non-alphabetic pseudofonts (e.g., wert), unpronounceable nonwords (e.g., pnsm), pronounceable pseudowords (e.g., beft), pronounceable pseudowords that would be legitimate word endings in Italian (e.g., enfa), and frequency-matched non-morphological word endings (e.g., enso). Participants engaged in a non-linguistic task by monitoring the color change of a central cross. Within a few minutes of visual stimulation, suffixes evoked a specific EEG response at their presentation frequency and its harmonics (i.e., nF/5: 1.2 Hz, 2.4 Hz, 3.6 Hz, 4.8 Hz), located predominantly over the left occipito-temporal cortex. This response was present in all experimental conditions and reflected the successful and, in the absence of explicit linguistic processing, automatic discrimination of suffixes from all other types of stimuli, irrespective of the degree to which they resembled Italian word endings. Critically, the discrimination response was significant even for the contrast between suffixes and other non-morphological sublexical units that occur equally frequently at the end of words in the lexicon, establishing, thus, its genuine morpho–semantic nature. The findings of the present study provide novel evidence for the selective neural representation of meaningful sublexical linguistic units and reveal the automaticity with which such representations are activated in the brain. They also inform us about the nature of the computations that may be carried out by the ventral occipito-temporal cortex in response to written input characterized by systematic correlations between orthographic form and meaning.