Ecological validity of experimental set-up affects parietal involvement during letter production.

Studies of symbol production using fMRI often use techniques that introduce an artificial pairing between motor production and visual perception. These techniques allow participants to see their own output by recording their pen trajectories using a touchscreen-only tablet and displaying these productions on a mirror placed above their head. We recently developed an MR-safe writing tablet with video display that allows participants to see their own hand and their own productions while producing symbols in real time on the surface where they are producing them-allowing for more ecologically valid fMRI studies of production. We conducted a study to determine whether the participation of posterior parietal cortex during symbol production was affected by the pairing of motor production and visual feedback associated with the two types of tablets. We performed ROI analyses in intraparietal sulcus while adult participants produced letters to dictation using either a touchscreen-only tablet (no visual guidance of the hand) (n = 14) or using a touchscreen-and-video-display tablet (visual guidance of the hand) (n = 14). We found that left posterior intraparietal sulcus was more active during production with the touchscreen-only tablet than during production with the touchscreen-and-video-display tablet. These results suggest that posterior parietal involvement during production tasks is associated with the somewhat artificial visual-motor pairing that is introduced by the techniques used in some studies of symbol production.