Monsalve, I. 1 & Molinaro, N. 1, 2
1 BCBL, Basque center on Cognition, Brain and Language
2 Ikerbasque, Basque foundation for Science
Prediction of future events has been proposed to be a fundamental neurocognitive mechanism. However, the role of prediction in language processing is currently under debate. Most studies so far focus on post-target word effects, so that little is known about the neural mechanisms behind such predictions. In this magnetoencephalography study we aimed to find evidence for pre-activation of expected word-forms and to characterize the predictive processes supporting it. Participants were presented with a picture of an object and after a delay of 2 seconds with the corresponding written word. The target words could contain a 1-letter substitution, and participant's task was to respond if the word was correct or not. In order to explore anticipatory pre-activation we manipulated expected word length, generating two conditions (short: 3-4 letters, and long: 7-8 letters). Cluster-based permutations on event-related fields revealed significant differences (alpha = 0.05) between long and short words over posterior sensors before target word presentation. These differences had the same direction and a similar topography than those elicited by presentation of the actual word. To further characterize this effect we performed time-frequency analysis during the pre-target word interval. Differences over posterior sensors were maximal (albeit non-significant) over a low beta range, around 0.6 s after image onset, and were localised to the left fusiform gyrus (visual word form area). However, this effect was not sustained in time. Interestingly, visual inspection suggests that differences in the theta response to the actual words start shortly before word onset. Our results suggest that under high-predictability conditions it is possible to elicit word-form representations in sensory cortices before stimulation. We tentatively propose that top-down information in the beta band would lead to word-from preactivation as soon as possible, whilst just-before stimulus theta modulations would prepare sensory cortices for imminent stimulation.