Neural estimates of language comprehension of sentences with selected action verbs in a non-literal context in the Polish language studied by permutation cluster-based analysis and decoding of the event-related potentials.

BACKGROUND: This work examines how the human brain processes mental metaphors in Polish verbal phraseologisms (a fixed, non-compositional combination of at least two elements that conveys a single meaning distinct from its parts and functions as a pragmatically expressive, semantically metaphorical, and syntactically unified unit) by studying dynamic changes in brain electrical activity using electroencephalography (EEG). The study aimed to investigate how figurative motor expressions (known and unknown) and known literal motor and mental expressions are processed via event-related potentials (ERPs). METHODS: EEG was recorded from 34 participants using a 32-channel active EEG system in an extended 10-20 montage. We used two advanced biomedical information processing methods: (1) the nonparametric cluster-based permutation analysis, which doesn't require specifying a priori time and spatial boundaries of the anticipated effects, and (2) machine learning (ML) using multivariate pattern analysis (MVPA) to decode the ERPs between the studied conditions. RESULTS: The comparison of the ERPs elicited by short sentences with an action verb in literal and non-literal (phraseological and unknown figurative) contexts, and a mental literal verb as a control condition, presented to participants on the computer screen, showed a decrease in amplitude from phraseological -> unknown figurative -> motor literal -> mental literal. The first effect was a robust and stable difference between the phraseological and literal conditions, corresponding to a spatiotemporal cluster maximal over frontal and central scalp areas, starting around 550 ms after noun phrase onset, as confirmed by machine-learning decoding. This effect likely represents a late frontal positivity (LFP). The second one showed a weaker difference between the non-literal and mental literal conditions, corresponding to a spatiotemporal cluster maximal over the midline central area around 250-350 ms after noun phrase onset. This effect relates to a higher P2-N2 complex in both figurative conditions compared to the mental one. CONCLUSIONS: Our results suggest a specific way in which the human brain processes action verbs in non-literal contexts, thereby filling a gap in neurocognitive research by providing a deeper understanding of how the brain processes language. They may aid neuroengineering research in designing more ecologically valid biomedical engineering solutions, such as more accurate language models or human-robot interactions.