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Title: Simulator%20Adaptation%20Syndrome%20Discussion

Simulator Adaptation Syndrome Discussion
  • Dr. Michael A. Mollenhauer
  • Realtime Technologies
  • 6/12/2003

  • What is Simulator Adaptation Syndrome?
  • Measurement of Symptoms
  • Visual and Vestibular Systems
  • Simulator Design Issues
  • Simulator Application Issues
  • Potential Countermeasures

Whats the Problem?
  • Rates of Occurrence
  • 20 40 Fighter Pilots Drop Out of First
    Training Simulator Flights
  • 30 50 Moderate Symptoms in Ground Vehicle
  • 40 60 Older/Experienced Drivers in Ground
    Vehicle Sims
  • Implications for Validity of the Results,
    Participant Motivation, and Product Appeal
  • Do No Harm!

What is Simulator Adaptation Syndrome (SAS)?
  • Ill Feelings Associated With The Use Of
    Simulation Devices
  • Syndrome Because Both Polygenic And
  • Causes Discussion To Follow
  • Symptoms Eye Strain, Headache, Postural
    Instability, Sweating, Disorientation, Vertigo,
    Pallor, Nausea, And Vomiting

Motion Sickness vs. SAS
  • Different Causation
  • Motion Sickness 0.2 1 Hz Whole Body
    Oscillation, Particularly Up and Down
  • Can Get Motion Sick Without Seeing Anything
  • Can Get SAS Without Any Movement gt Fixed Base
  • SAS Requires Some Feeling of Vection
  • Wired to Same Response Processes In Sympathetic
    Nervous System
  • Must Have Working Vestibular System To Get SAS or
    Motion Sickness

Who Is Affected?
  • Older More Than Younger
  • Female More Than Male
  • Asian More Than Caucasian
  • Experienced More Than Novice

Theories of Simulator Sickness
  • Cue Conflict Theory
  • Poison Theory
  • Theory of Postural Instability

Cue Conflict Theory
  • Symptoms Caused by Mismatches Between Sensory
    Expectation and What Actually Occurs
  • Eyes Indicate Movement, Vestibular System Does
  • Problems
  • Doesnt Identify Why Mismatch is Bad
  • Cannot Explain Adaptation
  • Why Doesnt It Occur With Every New

Poison Theory
  • Evolutionary Point of View
  • Blurred Vision, Sensory Conflict, Uncoordinated
    Movement Indicate Recent Poisoning or
  • Natural Response is to Remove Poison Through
  • Problems
  • No Predictive Capability
  • Does Not Explain Many Aspects of SAS Including
    Adaptation, Age, and Experience Effects
  • No Accounting for Individual Differences

Theory of Postural Instability
  • Sensory Systems Are Constantly Trying To Maintain
  • Sickness Comes Attempting To Stabilize Under
    Conditions Where Strategies Have Not Yet Been
  • Postural Instability Is Requirement Preceding SAS
  • Accounts For Adaptation, Experience, Etc.
  • Problems
  • Why Does Emesis Occur
  • Why Is A Lack Of Strategy A Bad Thing

Measurement of Symptoms
  • Simulator Sickness Questionnaire (SSQ)
  • Kennedy, R., Lane, N., Berbaum, K., and
    Lilienthal, M. (1993).
  • 3 Subscales and Composite
  • Nausea Subscale
  • Oculomotor Discomfort Subscale
  • Disorientation Subscale
  • Total Severity
  • Scoring Formulas
  • Postural Instability
  • Measured With Force Plate
  • Individual Differences Pre-Exposure

Questionnaire Format Example
Pertinent Human Sensory Systems
  • Visual System
  • Vestibular System

Important Aspects of Visual System
  • Central vs. Peripheral Vision
  • Optic Flow
  • Perception of Depth
  • Movements of the Eye

Central vs. Peripheral Vision
  • Central Vision
  • Answers What Is It
  • Small Stimulus Patterns, Fine Detail
  • Central Retina Only
  • Well Represented In Consciousness
  • Object Recognition And Identification
  • Peripheral Vision
  • Answers Where
  • Large Stimulus Patterns
  • Image Quality And Intensity Not Important
  • Peripheral And Central Retina
  • Not Well Represented In Consciousness
  • Spatial Localization, Orientation, And Motion

Optic Flow
  • Perceived From Movement Of Objects In Optic Array
  • Locomotor Flow Line Derived From Flow Of Objects
    Beneath Observer
  • Used To Determine Current Path Of Travel
  • Implications For Geometric Accuracy Of Displayed

Locomotor Path Determination
Perception of Depth
  • Oculomotor Cues
  • Given By The Position Of Our Eye And Tension On
    The Muscles Within The Eye
  • Binocular Cues
  • Slightly Different Scenes Are Formed On The
    Retina Of Our Eyes
  • Pictoral Cues
  • Can Be Deduced From Looking At Still Picture
  • Motion Cues
  • Deduced By How Objects Appear To Move When
    Observer Moves

Oculomotor Depth Cues
  • Proprioceptive Cues Interpreted By The Brain
  • Convergence
  • Inward Angular Positioning Of The Eyes To Keep An
    Object Focused On The Fovea As The Object Is
    Moved Closer To The Observer
  • Range 0 14 Ft
  • Accommodation
  • Flexing Muscles In The Eye To Change The Shape Of
    The Lens As An Image Is Brought Into Clear Focus
  • Range 0 5 Ft

Binocular Depth Cues
  • The Eyes See The World As Two Slightly Different
    Pictures Due To The Slightly Different Vantage
    Points Created By The Distance Between Them
  • The Brains Ability To Fuse These Disparate
    Images Into A Single Visual Image Produces Strong
    Perception Of Depth

Pictoral Depth Cues
  • Pictorial Cues Give The Illusion Of Depth To
    Two-dimensional Art
  • Brain Uses Pictorial Cues To Turn Two-dimensional
    Image On Retina Into A 3D Image
  • Absence Of Cues Can Cause Uncertainty

Pictoral Depth Cues
  • Relative Size
  • Smaller Objects of Same Shape Appear Further Away
  • Interposition
  • Obscured Objects Seem Further Away

Pictoral Depth Cues
  • Texture Gradient
  • Detailed Texture Appears Closer to Observer

Pictoral Depth Cues
  • Linear Perspective
  • Parallel Lines Converge at Greater Distances from

Pictoral Depth Cues
  • Shades and Shadows
  • Orientation and Intensity of Shadows Convey Depth
  • Relative Height
  • The Higher the Object in a Viewing Plane, The
    Further Away it Appears

Pictoral Depth Cues
  • Atmospheric
  • The Washing Out of Objects and Object Detail
    Due to Haze Makes them Appear Further Away

Motion Depth Cues
  • Objects That Are Further Away Appear To Move
    Slowly In The Direction Of The Observers
  • Closer Objects Appear To Move More Rapidly In The
    Direction Opposite The Observers Movement
  • Accretion And Deletion Are Related To Motion
    Parallax And Interposition Object That Moves To
    Cover Another Is Closer

Movements of the Eye
  • Consist of Saccade, Smooth Pursuit, Vergence,
    Opto-Kinetic Reflex (OKR), and Vestibulo-Ocular
    Reflex (VOR)
  • OKR and VOR Work to Stabilize Image on Retina
  • OKR Evaluates Image on Retina to Identify Slip,
    If Found it Triggers an Opposite Saccadic Eye
  • VOR Has a Similar Goal But is Triggered By
    Information from the Vestibular System
  • More Discussion of These Provided Later

Important Aspects of Vestibular System
  • Responsible for Identifying Orientation and
    Acceleration of Head
  • Drives Balance, Motor Control, and Eye Movements
  • Semi-Circular Canals
  • Utricle and Saccule
  • Vestibulo-Ocular Reflex
  • Very Fast Operation
  • (lt 10 ms latency)
  • Bodys Sole Source of Immediate Acceleration

Semi-Circular Canals
  • 3 Each Oriented To Detect Motion In Each Of The
    Three Planes In Which Motion Can Occur
  • Fluid In Canal Flows During Motion Which
    Stimulates Tiny Hairs On Internal Walls
  • Sensitive To 0.1 Deg/S2
  • Good For Sensing Change Rather Than Sustained

Utricle and Saccule
  • Functions Similar to Semi-Circular Canals -
  • Utricle Oriented to Detect Acceleration in
    Lateral Direction
  • Saccule Oriented to Detect Acceleration in
    Longitudinal and Vertical Directions
  • Responsible for Orientation With Respect to

Otolith Illusions
  • Somatogravic Illusion
  • Lon Accel/Decel Causes Pitch Up/Down Sensation
  • Vertical Accel/Decel Causes Backward/Forward Tilt
  • Oculogravic Effects
  • Somatogravic Illusion Causes Altered Visual
    Perception we actual see pitch down / up
  • Vestibular System is Trying to Lead Vision

Vestibulo-Ocular Reflex
  • Information About Head Movement Is Supplied To
    Visual System
  • Visual System Interprets And Makes Corresponding
    Eye Movement To Stabilize Image
  • Shaking Paper Vs. Shaking Head
  • Very Fast Acting
  • Adaptable VOR Will Adjust Its Gain To Support
    Different Sensory Arrangements

  • Work Together Synergistically To Stabilize
    Retinal Image
  • VOR Acts Fast And Corrects Well For 1-7 Hz
  • OKR Responds Slower And Corrects Well For lt 0.1
    Hz Movements
  • Tight Feedback Loop Where OKR Helps VOR Adjust
    Gain And Therefore Adapt

VOR Adaptation
  • VOR Found To Adapt To Changing Visual
    Magnifications And Correlated To Sickness
  • Individuals Who Adapt Faster Are Less Likely To
    Experience Sickness Symptoms
  • The Greater The Change From Normal, The Longer
    the VOR Adaptation Process
  • Inconsistent Sensory Mapping Prolongs VOR

VOR Adaptation
  • Visual Anomalies Can Alter OKR Feedback Which
    Also Hinders Adaptation
  • Large Individual Differences
  • Plasticity Of VOR or Its Ability to Adapt
    Decreases With Age

Visual Perception of Self-Motion
  • Vection Compelling Feeling Of Self-motion
    While Static With The Environment
  • Generated From Movement Detected In Optic Flow
  • Normally Accompanied By Some Vestibular Sensation
    If Not Then Sensory Conflict
  • Strength Of Vection Increased By
  • Larger Movement Stimulus Larger FOVs
  • Faster Optic Flow - Higher Relative Speed

Challenges of Driving Simulation
  • High Flow Rates Relatively Low Altitude
  • More Flow Due To Proximity Of Buildings, Signs,
    Other Traffic,
  • Often Require More FOV
  • Higher Sensitivity To Environment/Vehicle
  • Application Is All About Vection, Vection Is A
    Precursor To Sickness

Simulator Design Issues
  • Display Flicker
  • Field of View
  • Geometric Display Design
  • Binocular / Monocular Viewing
  • Resolution / Aliasing
  • Display Refresh / Update Rate
  • Motion Cueing
  • Controls / Feedback
  • Transport Delay
  • Calibration
  • Head Mounted/Slaved Displays
  • Environmental Conditions

Display Flicker
  • Why 60 Hz or Better?
  • Perception of flicker interferers with saccadic
    eye movements, causes ocular muscle fatigue and
    eye strain
  • Linked to simulator sickness
  • Critical Fusion Frequency (CFF) is around 40 60
    Hz in dark, foveal viewing conditions

CFF Depends On
  • Display Luminance
  • Brighter Displays Decrease CFF
  • Environment Illumination
  • Brighter Environment Decreases CFF,
  • Refresh Rate
  • Slower Refresh Decreases CFF
  • Eccentricity
  • Periphery More Sensitive, Larger Displays
    Decrease CFF
  • Age
  • Young People More Sensitive To Flicker
  • Gender
  • Women More Sensitive To Flicker

Field of View (FOV)
  • Long Implicated As An Exacerbating Factor
  • More Peripheral Stimulation Results In More
    Vection, Vection Linked To SAS
  • Performance Implications
  • Narrow FOV Results In Poorer Lane Keeping, Less
    Accurate Perception Of Speed, Less Eye/Head
    Movement, And Less Immersion
  • Effects Level Out At Around 140 160 Degrees
  • Implications for Validity
  • Depends On The Task

Geometric Display Parameters
  • Issue How Well Display System Represents Real
    Viewing Conditions
  • Parameters Eye Height, Angular Ratios, Viewer
    Orientation To Displays
  • Impacts Optic Flow Perception, VOR Adaptation,
    Task Performance
  • The Less Congruent With Reality, The Longer The
    Adaptation -gt Potential SAS

Geometric Display Parameters
  • Inaccurate Cueing
  • Driver Not Oriented Appropriately May Feel
  • Eye Height Too High Results In Inaccurate Speed
  • Display Demagnification Can Result In Inaccurate
    Steering Behavior
  • Flat Displays Viewer Reports Initial
    Translational Movement During Turn Rather Than
    Yaw Rotation
  • Display Distance
  • Vergence And Accommodation
  • No Absolute Threshold But More Is Better Up To
  • Performance Trade-Offs Due to Distance
  • Suggested Minimum Is 40

Binocular/Monocular Viewing
  • Stereo Displays Provide Depth Cues Through
    Binocular Disparity And Vergence
  • Active Stereo
  • Two Images Rendered In Each Frame Representing
    The Perspective View Of Each Eye
  • Shutter Glasses Are Used To Alternate Between The
    Corresponding Views
  • 96 Hz / 48 Hz Per Eye
  • Passive Stereo
  • Uses Polarizing Filters To Accomplish Same Task

Binocular/Monocular Viewing
  • Stereo Provides Positive Impact On Task
    Performance Provided Some Element Of Task
    Requires Viewing Within 15 Feet Or So
  • Appears To Elevate Risk Of SAS By Increasing
    Vection And Reducing Vection Onset Times
  • May Potentially Cause Eye Strain If Not Adjusted
    Appropriately Interpupillary Distance, Focal
    Distance, Etc.
  • Costs Equipment, Performance, Brightness

Resolution / Aliasing
  • Resolution
  • As Resolution Degrades The Eye Attempts To
    Accommodate The Image Causing Eye Strain
  • FAA Requires 3 Arcmin/Pixel Or Better For Flight
    Training Simulators
  • PD5000(?) - 2.3 Arcmin/Pixel, Around 20/40
    20/50 Vision
  • Likely Impact On Task Performance (Sign
    Legibility, Far Target Detection, Etc.)
  • Likely Impact In Oculomotor Discomfort Portion Of
    SAS If Resolution Too Low, May Slow VOR
    Adaptation, May False-Trigger OKR
  • Aliasing
  • Causes Apparent Motion In Scene, Can Be
    Interpreted As Flicker
  • Changes Eye Scanning Strategy

Display Refresh / Update
  • Display Refresh
  • Potential For Perception Of Flicker Or Detection
    Of Smearing Or Ghosting
  • Most CRTs Fast Enough
  • LCDs Phosphor Decay Issues, Smearing, Ticking
    Can Trigger OKR
  • Graphics Update
  • Function Of How Fast Simulator Subsystems Process
  • Variable Rates May Slow VOR Adaptation Processes
  • VOR and visual processing approx 10 20 ms.
  • Slow Rates Appear Jerky And Could Be Perceived
    As Flickering

Motion Theory
  • Scaled Representation Of Dynamic Forces Normally
    10-50 Of Normal
  • In 6 DOF Systems, Onset Provided By Translation,
    Sustained Provided By Tilt
  • Washout Algorithm Always Returning Motion Base
    To Center Below Levels Of Perception
  • Always Some Amount Of Error And Some Amount Of
    Transport Delay
  • Affects Skills Based Driving Behavior More Than
    Knowledge Based Behavior

Motion Configurations
  • Electric vs. Hydraulic
  • Degrees Of Freedom
  • Operating Envelope
  • Frequency Response
  • Visuals On And Off Motion

Impact on Braking Behavior
  • Real World Drivers Adopt Constant Decel
    Profiles For Stopping At Distant Target
  • In Simulators Drivers Adopt A Multi-modal
  • Initially Decel Too Much
  • Next They Reduce Decel Or Even Accel To Hit
  • Drivers Use Vestibular Sense Initially To Set
    Decel Rate Then Maintain That Rate Tight
    Coupling, Fast Acting
  • Without Vestibular Cues, Must Guess At Control
    Input / Response Mapping Until Deduced Visually

Impact on Braking Behavior (contd)
  • Drivers Must Learn To Re-map Their Response To
    What They Perceive Cannot Immediately Perceive
    Deceleration Visually
  • Drivers Eventually Either Reduce Magnitude Of
    Initial Deceleration Or (Experienced) Initiate
    Braking Later And Keep High Deceleration Rates
  • In Motion Simulators Drivers Tend To Adapt Faster
    Than Fixed Base With Vision We Deduce
    Acceleration, With Motion We Perceive
    Acceleration Even If Scaling Inaccurate

Impact on Steering Behavior
  • Lack Of Lateral Acceleration Cues Can Lead To
    Over-steering Self Induced Oscillations
  • Nearly Impossible To Look Away And Drive
  • Drivers Tend To Take Corners At Higher Speeds -
    Generally More Aggressive
  • Drivers Adopt A Slightly Different Visual
    Scanning Behavior Looking Away From The Forward
    Roadway Less
  • Lateral Acceleration Cues Are Linked To
    Perception Of Risk When Cornering Drivers Have
    Been Shown To Select Speeds Closer To Reality In
    Motion Base Sims

Impact of Motion on SAS
  • Direct Motion Vs. No Motion Studies Inconclusive
  • Not A Silver Bullet for SAS
  • Bad Calibration, Additional Transport Delay, Less
    Capable Motion Systems May Exacerbate SAS
  • Good Motion May Speed VOR Adaptation And Slow
    SAS Onset
  • There Is Hope For Better Motion To Be Part Of
    The Solution Reduced Transport Delay Through
    Prediction, Accurate Cueing, Etc.

Controls / Feedback
  • Impact On Driver Connectedness To Road
  • May Affect SAS By Altering Control And Response
    Expectations, No Proven Link
  • Drivers Often Report Loose Steering Or Really
  • Again Impacted By Tight Coupling Vestibular
    Senses And Motor Inputs Reflex Level Processing
  • Impact On Motor Skill Development Mapping of
    Ratio of Input to Resulting Response

Transport Delay
  • Time From Control Input To Presentation Of
    Resulting Changes Back To The Operator
  • Can Come From Any Sim Subsystem May Be Additive
  • Detectable Visually Down To Approx 50 Ms,
    Vestibular Down To Approx 20 Ms
  • Leads To Cue Conflict Because Various Stimuli Are
    Not Aligned With Each Other And With Human
  • Humans Are Adaptable The Longer And More
    Inconsistent The Delay, The Longer The Adaptation

  • Good Engineering Doesnt Eliminate SAS But Poor
    Engineering Will Certainly Bring It On
  • Delays And Errors Can Contribute To Cue Mismatch
  • Inconsistent Error Delays VOR Adaptation

Head Mounted Displays
  • With HMDs Full Scene Lag Is Disconcerting
    Proprioceptive Feedback Does Not Match Visual
  • Lack Of Rest Frame Identification
  • New Head Tracking Prediction Methods Reduce Lag
    But Introduce Some Error (Overshoot)
  • Weight Issues Changes Mapping Between Neck And
    Shoulder Muscle Feedback And Expected Visual
    Response, Alters VOR Adaptation

Environmental Conditions
  • High Ambient Temperature
  • Speeds Perception Of Symptoms
  • No Proven Link To SAS Causation Likely That
    Heat Pre-sensitizes Body By Elevation Of
    Respiration, Heart Rate, Blood Pressure, Etc.
  • Ambient Lighting
  • Fluorescent Lights Can Introduce Display
    Interharmonics Perceived As Flicker

Simulator Adaptation
  • With Increased Exposure We Adapt To Simulator
  • 3 To 5 Exposures Of 10 - 15 Minutes
  • Limit Early Scenario Intensity
  • Consistent Cueing And Motion May Speed Adaptation

Potential Countermeasures
  • Appropriate Mapping Of Visual Presentation
  • Transport Delay Reduction
  • Consistency In Cueing No Variable Lags Or
    Update Rates
  • Elimination Of Visual Artifacts Aliasing, Poor
    Resolution, Ticking, Flicker
  • Elimination Of Visuals Overcueing Pitch, Roll,

Potential Countermeasures (contd)
  • Presentation Of Vehicle References
  • Addition Of Tightly Coupled Motion
  • Realistic Controls Mapping (More Important For
    Experienced Drivers)
  • Adaptation Routine
  • Several Short, Benign Driving Segments With
    Adequate Time Between Drives
  • Reduce FOV If Possible

Potential Countermeasures (contd)
  • Independent Visual Background (IVB) And Impact On
    Rest Frame Hypothesis
  • IVB Stable Inertial Rest Frame Presented In
    Visual Scene (Central Better Than Periphery)
  • IVB Acts As A Stabilizer Allowing The Nervous
    System To Consistently Select Which Frame Is At
  • Study Found Significant Reduction In Sickness
    When Presenting IVB In Virtual Environments
  • Follow On Study Found That Use Of A Naturalistic
    IVB (Clouds) Decreased Sickness In Driving
    Simulator More Clouds, More Sim Sickness

Comfort The Sympathetic Nervous System
  • Last Resort Can Ease Perception of Symptoms
  • Carbonated Beverages (non-alcoholic)
  • Ginger
  • Mints
  • Cool Moving Air
  • Saltines

Simulator Design Discussion