Predictions in speech comprehension: fMRI evidence on the meter-semantic interface

When listening to speech we not only form predictions about what is coming next, but also when something is coming. For example, metric stress may be utilized to predict the next salient speech event (i.e. the next stressed syllable) and in turn facilitate speech comprehension. However, speech comprehension can also be facilitated by semantic context, that is, which content word is likely to appear next. In the current fMRI experiment we investigated (1) the brain networks that underlie metric and semantic predictions by means of prediction errors, (2) how semantic processing is influenced by a metrically regular or irregular sentence context, and (3) whether task demands influence both processes. The results are three-fold: First, while metrically incongruent sentences activated a bilateral fronto-striatal network, semantically incongruent trials led to activation of fronto-temporal areas. Second, metrically regular context facilitated speech comprehension in the left-fronto-temporal language network. Third, attention directed to metric or semantic aspects in speech engaged different subcomponents of the left inferior frontal gyrus (IFG). The current results suggest that speech comprehension relies on different forms of prediction, and extends known speech comprehension networks to subcortical sensorimotor areas.