The effect of mirrored visual feedback on the EEG correlates of pointing direction

Purpose. Looking through laterally mirroring prisms produces at least two changes in the phenomenal appearance of the world: When stretching your right arm, for example, visual feedback will indicate that it is your left arm that is moving. But not only will the 'wrong' limb seem to be moving, it will also move in the diametrically opposite direction. Usually output and feedback of an action 'fit' (i.e., go to and come from the same limb). But when looking through mirroring prisms, visual feedback comes from the opposite arm and opposite direction. In order to behave properly under these circumstances, some kind of recalibration has to occur. The contralateral hemisphere is more strongly involved in controlling these arm movements. It is possible that this recalibration alters the lateralization of the neural activity that controls these movements. To test for this, we recorded event-related potentials (ERPs) and event-related lateralizations (ERLs) of the EEG during pointing movements with and without laterally mirrored vision. Targets were presented either centrally or laterally. Results: We found effects of mirrored vision on the lateralization of neural activity. The relative involvement of the hemisphere ipsilateral to the SEEN target position (objective position is reversed with mirrored feedback) increased, especially around 300-400ms after stimulus onset. Additionally, differences in the ERPs around the same time after target onset were evident. Both effects were maximal around the parietal and parieto-occipital sites, suggesting modified stimulus processing.