Project Summary Dizziness, vertigo, motion sickness, and simulator sickness are common clinical problems rooted in abnormal perception of movement. Clinical testing of the vestibular system and understanding of vestibular physiology has historically focused on reflex function and perception of isolated vestibular stimuli. However, vestibular reflex function is poorly correlated with perceptual symptoms. Perception of self-motion is at the root of understanding navigation, dizziness, motion sickness, and simulator sickness. Self-motion perception is also multi-sensory and primarily involves the vestibular and visual systems, although auditory and proprioception also may play a role in some situations. In many common clinical disorders, perceptual testing is the first line of clinical investigation. For instance an evaluation of vision usually begins with having the patient report what they are able to see and evaluation of hearing begins with testing what the patient is able to hear. However, understanding of self-motion perception is not yet at a state where perceptual testing is clinically meaningful. Most of the previous work on vestibular perception has focused on unimodal stimuli of perceptual thresholds and tests of visual vertical which do not address the more complex multisensory situations in which self-motion is usually experienced. The current proposal aims to advance understanding of human motion perception into a clinically and physiologically relevant arena by examining this perception in an appropriate, multisensory context. The project will measure visual-vestibular integration and define the conditions where it occurs. Visual motion can be ambiguously interpreted as self-motion through a fixed environment, environmental motion relative to a fixed observer, or inaccurate sensory calibration. The project will examine all of these possibilities but determining the factors involved in determining common causation which is essential for knowing if visual motion is a result of self-motion and can be integrated with vestibular cues or is the result of external motion and should be segregated. The project will also look at mechanism adaptation in two contexts – exposure to consistently offset visual and inertial stimuli and exposure to a rotating environment. This will be examined in normal controls but also individuals with unilateral loss of vestibular function. Developing a method of adaptation that is effective in vestibular pathology will be helpful in developing tools that are potential methods of future vestibular rehabilitation.