Full Body Motion and Full Body Motion and Locomotion InterfacesLocomotion Interfaces

OutlineOutline

• Physiology and Psychology

• Types of displays

• Motion platforms and their control

Stability and Self-MotionStability 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 headThe 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 ArmsThe 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

LocomotionLocomotion

• 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 motionIllusions 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 StuffStimulating 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 SicknessMotion Sickness

Notes about SicknessNotes 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 SyndromeSopite Syndrome

• Chronic fatigue

• Lack of initiative

• Drowsiness

• Lethargy

• Apathy

• Irritability

The InterfacesThe 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 SimulatorThe Dynamic Flight Simulator

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

HexapodHexapod

Rotation RoomRotation Room

Motion Control LogicMotion Control Logic

Good motion control depends on: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 SystemThe 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 AlgorithmThe Classical Algorithm

Critical FactorsCritical 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