Full Body Motion and Locomotion Interfaces

Outline Physiology and Psychology Types of displays Motion platforms and their control

Stability and Self-Motion We don’t realize how precious it is until we have lost it We ignore (or are adapted to) forces on the feet, head movement, eye movement Virtual Environments can disrupts this adaptation Persistence from SE adaptation may lead to performance decrements and simulator sickness with real world stimuli

The head Almost anything to do with the head and eyes can be provocative Coriolis forces seem to be automatically accomodated and adapted for with active head movements; passive movements can induce unexpected forces and create nausia Visual stimulation can elicit a sensation of self motion

The Arms Expectations about object properties are important -- size should correlate to weight New assumptions (changing the laws of physics in a SE) can lead to adaptation effects For example, reaching and Coriolis forces

Locomotion Visual flow depends on step frequency and stride length The mind makes interesting remappings when relationship between flow and stride is disrupted –Moon walking –Hand rail comes to life

Illusions of self motion Circular vection –Perception of rotation in response to a rotating visual field Linear vection –Perception of motion in response to linear motion of visual field Head movements during these effects can cause disorientation Sound may also work

Stimulating Stuff Pedaling a platform, turning a circular railing can create a strong illusion of motion Somatosensory stimulation is as important (more important?) than vestibular stimulation Tonic vibration reflex of the spindal receptors can create an illusion of motion in a restrained limb. Eye movements and posture changes are automatically affected by illusions of motion

Motion Sickness

Notes about Sickness Attributed to sensory conflict, but that theory is not predictive Seems uncorrelated with heart rate, blood pressure, peripheral blood flow, electrogastrogrom activity, etc. Not related to vestibular sensitivity Sensitivity varies among people and stimulation types Gradual intensity increases helps mediate

Sopite Syndrome Chronic fatigue Lack of initiative Drowsiness Lethargy Apathy Irritability

The Interfaces Inertial Displays –Full inertial display –Partial inertial display –Variable gravity displays Locomotion Displays –Active sensations: treadmills, bikes –Individual feet displays? Noninertial displays –Vestibular displays –Proprioceptive/Kinesthetic displays

The Dynamic Flight Simulator Up to 40 G’s (when the Navy says “Dynamic” simulator, they mean it

Hexapod

Rotation Room

Motion Control Logic

Good motion control depends on: Simulator sickness –Caused by cue conflict –Motion bases can help Visual gaze stability –Vestibulo-ocular reflex –Optokinetic nystagmus Face validity (realism and fidelity) Validity

The Vestibular System 3 orthogonal semicircular canals –Endolymph fluid flows through the canal deflecting the gelatinous cupula, which is detected by sensory cells. –Angular rate sensors Utricle –The gelatinous otolith rests on a bed of sensory cells (the macula). Shearing force is detected. –Linear accelerometer

The Classical Algorithm

Critical Factors Tilt coordination to recover low-frequency acceleration cues Tilt must be adjusted below 3.0 deg/sec Tilt can create a force at the driver’s head Must tune scaling and filters for realistic feel Tuning depends on specific scenario