A task comparison of motor activation in online sentence comprehension.

Although motor activation has been observed during comprehension, establishing the functional role of such activation remains unclear. The current EEG study evaluates the functional issue in terms of task demands. Specifically, a semantic evaluation task and a lettermatching task were each expected to differentially engage the comprehension processes which, critically, may or may not reveal corresponding motor activation. Mu desynchronization (8 – 12 Hz) from the motor cortex was measured on critical verbs embedded in visually presented Dutch sentences (e.g., De winkelkarretjes die zij wegduwt zijn kapot./The trolleys that she pushes away are broken.). Manipulation of the verbs’ action specificity was intended to elicit differences in mu desynchronization (e.g., more action specificity for pushing trolleys than delivering trolleys). Half of the stimuli were constructed as semantically congruent sentences, the other half as semantically incongruent sentences to elicit an N400 effect, a measure of semantic comprehension, which was indeed observed in both tasks (e.g., The trolleys that she pushes away/sews are broken.). The preliminary results indicate that the motor system is activated in both tasks yet differently so in interesting ways. Whereas the semantic evaluation task shows the predicted main effect of action specificity, the letter-matching task shows an interaction of congruency and action specificity, with greater motor activation for action non-specific verbs than action specific ones in semantically incongruent sentences. Notably, the latter result was previously observed in a passive reading task using similar stimuli (Lam, Bastiaansen, Dijkstra, & Rueschemeyer, in preparation). This study underscores the claims of theories of embodied language by showing that (1) motor activation occurs even in a task that does not necessitate explicit retrieval of meaning, and that (2) the task-dependent patterns of motor activation reveal the different functional interactions between the motor system and comprehension processes