Dear Halleh,

By visualizing the t-stats map you captured, my main concern would be the large t values around the brain, located in the sagital sinus and the meninges. Was there a large motion correlated with the task here ? I guess it's not too uncommon in motor paradigms but scary anyway. A collaborator of mine (Dr Pierre Orban) suggested that the coregistration between the EPI and the T1 maybe completely off, in which case the "motion artefacts" would fall in the sensorimotor cortex and the visual activation would be in the cerebellum. Certainly worth checking on the mean image ...

Regarding the visual component of the task, you can enter it in the model with a different duration than the motor task, and then regress out the visual regressor from the motor one. With this approach you will loose a lot of motor activation that cannot be disambiguated from the visual one, but you will clean-up the visual component of the task. However, the most classical way to adress your problem is to ignore it, and not to interpret the activations in the visual cortex. Usually, the contrasts of interest lie between a task and a control, and the visual component should be identical in both conditions. In this case, the visual activation will cancel itself out.

I hope this helps, good luck with your analysis,

Pierre Bellec