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.