Theories of embodied mental rotation suggest overlapping processes between real body and egocentric mental transformations. Corroboratory behavioral evidence showed interaction effects between vestibular stimulation and egocentric transformation. Yet, no study so far has investigated which cortical areas are involved in vestibular processing and/or illusory self-motion and mental transformation tasks within the same participants. This however seems crucial, as important individual differences exist for both mental transformation abilities as well as in subjective perception of artificial vestibular stimulation.~The primary objective is to reveal which brain area(s) are involved in the interaction of illusory self-motion (as induced by galvanic vestibular stimulation (GVS)) and egocentric mental transformation, as compared to no illusory self-motion or object-based mental transformation. It is hypothesized that the GVS induced illusory self-motion dampens the ability to perform egocentric mental transformation more than object-based mental transformation.~As previous behavioral studies on such an interaction were always done in a sitting position, a secondary objective is to first replicate previous behavioral mental rotation studies that used GVS, in the Magnetic Resonance (MR) -scanner comparable setting. Moreover, as no brain imaging study so far has investigated subjective illusory motion experience induced by GVS, illusory self-motion will be measured and included in the statistical model to find specific brain regions modulating the illusory self-motion perception.
Corroboratory behavioral evidence showed interaction effects between vestibular stimulation and egocentric transformation.~The investigators here examine in healthy participants, whether there are shared brain mechanisms underlying galvanic vestibular stimulation, illusory self-motion and egocentric transformation, as well as their interaction.~It is hypothesized that the GVS induced illusory self-motion dampens the ability to perform egocentric mental transformation.