Interactive and additive effects of word frequency and predictability: A fixation-related fMRI study

The effects of word frequency and predictability are informative with respect to bottom-up and top-down mechanisms during reading. Word frequency is assumed to index bottom-up, whereas word predictability top-down information. Findings regarding potential interactive effects, however, are inconclusive. An interactive effect would suggest an early lexical impact of contextual top-down mechanisms where both variables are processed concurrently in early stages of word recognition. An additive effect, to the contrary, would suggest that contextual top-down processing only occurs post-lexically. We evaluated potential interactions between word frequency and predictability during silent reading by means of functional magnetic resonance imaging and simultaneous eye-tracking (i.e., fixation-related fMRI). Our data revealed exclusively additive effects. Specifically, we observed effects of word frequency and word predictability in left inferior frontal regions, whereas word frequency additionally exhibited an effect in the left occipito-temporal cortex. We interpret our findings in terms of contextual top-down processing facilitation.