Electroencephalography theta differences between object nouns and action verbs when identifying semantic relations

Nouns and verbs differ in their semantic properties and relationships with other words in the lexicon. This study uses electroencephalography (EEG) to investigate how word class differences influence semantic retrieval and identification of semantic relationships. Participants identified whether the final word in a triplet (noun or verb) was related to the first two words (both nouns). Time frequency analysis of the EEG revealed word class and relatedness effects in theta, beta and gamma. Decreases in beta power were found during action verbs, which may be related to motor processing. Theta exhibited a word class by relatedness interaction in which unrelated verbs elicited a greater power increase compared to other conditions. These data indicate that action verbs require more neural activity when identifying the absence of relationships than object nouns, likely due to the abstract, flexible nature of verb meanings and the shallow structure of verb organisation.