Neurocognitive dimensions of lexical complexity in Polish

Neuroimaging studies of English suggest that speech comprehension engages two interdependent systems: a bilateral fronto-temporal network responsible for general perceptual and cognitive processing, and a specialised left-lateralised network supporting specifically linguistic processing. Using fMRI we test this hypothesis in Polish, a Slavic language with rich and diverse morphology. We manipulated general perceptual complexity (presence or absence of an onset-embedded stem, e.g. kotlet ‘cutlet’ vs. kot ‘cat’) and specifically linguistic complexity (presence of an inflectional affix, e.g. dom ‘house, Nom’ vs. dom-u ‘house, Gen’). Non-linguistic complexity activated a bilateral network, as in English, but we found no differences between inflected and uninflected nouns. Instead, all types of words activated left inferior frontal areas, suggesting that all Polish words can be considered linguistically ‘complex’ in processing terms. The results support a dual network hypothesis, but highlight differences between languages like English and Polish, and underline the importance of cross-linguistic comparisons.

► First neuroimaging study of speech comprehension in Polish.
► First cross-linguistic test of a novel neurobiological theory of the language system.
► Contrasts specifically linguistic complexity with general processing demands.
► We find substantial organisational parallels between Polish and English.
► All Polish words seem to be neurocognitively complex, engaging LIFG.