Many previous studies have focused on how humans combine inputs provided by different modalities for the same physical property.
However, it is not yet very clear how different senses providing information about our own movements combine in order to provide
a motion percept. We designed an experiment to investigate how upright turns are stored, and particularly how vestibular and
visual cues interact at the different stages of the memorization process (encoding/recalling). Subjects experienced passive
yaw turns stimulated in the vestibular modality (whole-body rotations) and/or in the visual modality (limited lifetime star-field
rotations), with the visual scene turning 1.5 times faster when combined (unnoticed conflict). Then they were asked to actively
reproduce the rotation displacement in the opposite direction, with body cues only, visual cues only, or both cues with either
the same or a different gain factor. First, we found that in none of the conditions did the reproduced motion dynamics follow
that of the presentation phase (Gaussian angular velocity profiles). Second, the unimodal recalling of turns was largely uninfluenced
by the other sensory cue that it could be combined with during the encoding. Therefore, turns in each modality, visual, and
vestibular are stored independently. Third, when the intersensory gain was preserved, the bimodal reproduction was more precise
(reduced variance) and lay between the two unimodal reproductions. This suggests that with both visual and vestibular cues
available, these combine in order to improve the reproduction. Fourth, when the intersensory gain was modified, the bimodal
reproduction resulted in a substantially larger change for the body than for the visual scene rotations, which indicates that
vision prevails for this rotation displacement task when a matching problem is introduced.
Keywords Self-motion - Yaw rotations - Spatial orientation - Vestibular - Multisensory integration