Investigation of speech-planning mechanism based on eye movement and EEG

A major concern in the speech production research is how speakers make a plan for speech articulation, in which the latent time is an important index for evaluating the planning process. Previous researches on this topic using either isolated words or phrases found that the word length and familiarity could affect the latent time of speech planning. However, in continuous sentence processing, semantic prediction was found to be more influential from our previous eye movement investigation. To probe further into the underlying neural causes, this study combined eye movement and EEG techniques to analyze the behavior-locked brain activities during the speech planning process in a sentence reading task. The results showed that the latent time decreases gradually with ongoing reading process as the context information got richer. And the subjects tend to look ahead prior to the articulation of the current word. Functional network analyses for the visual and semantic processing were consistent with the behavior results and suggested that the look ahead phenomenon is a companying effect of speech coarticulation, and as speech prediction becomes easier, the latent time for speech planning tend to be shortened.