Modulation of spatial orientation processing by mental imagery instructions: A MEG study of representational momentum

Under appropriate conditions, an observer's memory for the final position o f an abruptly halted moving object is distorted in the direction of the rep resented motion. This phenomenon is called "representational momentum" (RM) . We examined the effect of mental imagery instructions on the modulation o f spatial orientation processing by testing for RM under conditions of pict ure versus body relation perception and imagination. Behavioral data were g athered via classical reaction time and error measurements, whereas brain a ctivity was recorded with the help of magnetoencephalography (MEG). Due to the so-called inverse problem and to signal complexity, results were descri bed at the signal level rather than with the source location modeling. Brai n magnetic field strength and spatial distribution, as well as latency of P 200m evoked fields were used as neurocognitive markers. A task was devised where a subject examined a rotating sea horizon as seen from a virtual boat in order to extrapolate either the picture motion or the body motion relat ive to the picture while the latter disappeared temporarily until a test-vi ew was displayed as a final orientation candidate. Results suggest that per ceptual interpretation and extrapolation of visual motion in the roll plane capitalize on the fronto-parietal cortical networks involving working memo ry processes. Extrapolation of the rotational dynamics of sea horizon revea led a RM effect simulating the role of gravity in rotational equilibrium. M odulation of the P200m component reflected spatial orientation processing a nd a non-voluntary detection of an incongruity between displayed and expect ed final orientations given the implied motion. Neuromagnetic properties of anticipatory (Contingent Magnetic Variation) and evoked (P200m) brain magn etic fields suggest, respectively, differential allocation of attentional r esources by mental imagery instructions (picture vs. body tilt), and a comm unality of neural structures (in the right centro-parietal region) for the control of both RM and mental rotation processes. Finally, the RM of the bo dy motion is less prone to forward shifts than that of picture motion evide ncing an internalization of the implied mass of the virtual body of the obs erver.