OTOLITHIC THRESHOLDS INFLUENCE THE PERCEPTION OF PASSIVE LINEAR DISPLACEMENT

The vestibular sensors are the necessary source of information for est imating self-displacement during passive linear transport. Displacemen t has to be computed from the otolith signal by means of an integratio n process (path integration), which provides a measure of linear accel eration. However, the onset of self-motion perception is delayed due t o perceptual thresholds. We investigated the effect of these threshold s on the estimation of passive displacement. Subjects seated on a line ar acceleration device (ESA-SLED) were displaced to their left or righ t. Two tasks were performed: (1) subjects pressed a button when they p erceived self-motion; (2) subjects pressed a button when they thought they had reached a previously seen visual target located above the sle d rail. Displacement estimation (task 2) was found to depend upon the acceleration magnitude and on the individual motion perception thresho ld measured in task 1. The results can be explained by assuming that s elf-displacement computation starts at the onset of self-motion percep tion and is initialised by a value that is independent of the amplitud e of acceleration, thereby compensating for the displacement informati on lost due to the thresholds.