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


1
Simulator Adaptation Syndrome Discussion
  • Dr. Michael A. Mollenhauer
  • Realtime Technologies
  • 6/12/2003

2
Agenda
  • What is Simulator Adaptation Syndrome?
  • Measurement of Symptoms
  • Visual and Vestibular Systems
  • Simulator Design Issues
  • Simulator Application Issues
  • Potential Countermeasures

3
Whats the Problem?
  • Rates of Occurrence
  • 20 40 Fighter Pilots Drop Out of First
    Training Simulator Flights
  • 30 50 Moderate Symptoms in Ground Vehicle
    Simulators
  • 40 60 Older/Experienced Drivers in Ground
    Vehicle Sims
  • Implications for Validity of the Results,
    Participant Motivation, and Product Appeal
  • Do No Harm!

4
What is Simulator Adaptation Syndrome (SAS)?
  • Ill Feelings Associated With The Use Of
    Simulation Devices
  • Syndrome Because Both Polygenic And
    Polysymptomatic
  • Causes Discussion To Follow
  • Symptoms Eye Strain, Headache, Postural
    Instability, Sweating, Disorientation, Vertigo,
    Pallor, Nausea, And Vomiting

5
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
    Simulators
  • 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

6
Who Is Affected?
  • Older More Than Younger
  • Female More Than Male
  • Asian More Than Caucasian
  • Experienced More Than Novice

7
Theories of Simulator Sickness
  • Cue Conflict Theory
  • Poison Theory
  • Theory of Postural Instability

8
Cue Conflict Theory
  • Symptoms Caused by Mismatches Between Sensory
    Expectation and What Actually Occurs
  • Eyes Indicate Movement, Vestibular System Does
    Not
  • Problems
  • Doesnt Identify Why Mismatch is Bad
  • Cannot Explain Adaptation
  • Why Doesnt It Occur With Every New
    Activity/Movement

9
Poison Theory
  • Evolutionary Point of View
  • Blurred Vision, Sensory Conflict, Uncoordinated
    Movement Indicate Recent Poisoning or
    Intoxication
  • Natural Response is to Remove Poison Through
    Emesis
  • Problems
  • No Predictive Capability
  • Does Not Explain Many Aspects of SAS Including
    Adaptation, Age, and Experience Effects
  • No Accounting for Individual Differences

10
Theory of Postural Instability
  • Sensory Systems Are Constantly Trying To Maintain
    Stability
  • Sickness Comes Attempting To Stabilize Under
    Conditions Where Strategies Have Not Yet Been
    Developed
  • 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

11
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

12
Questionnaire Format Example
13
Pertinent Human Sensory Systems
  • Visual System
  • Vestibular System

14
Important Aspects of Visual System
  • Central vs. Peripheral Vision
  • Optic Flow
  • Perception of Depth
  • Movements of the Eye

15
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

16
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
    Images

17
Locomotor Path Determination
18
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

19
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

20
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

21
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

22
Pictoral Depth Cues
  • Relative Size
  • Smaller Objects of Same Shape Appear Further Away
  • Interposition
  • Obscured Objects Seem Further Away

23
Pictoral Depth Cues
  • Texture Gradient
  • Detailed Texture Appears Closer to Observer

24
Pictoral Depth Cues
  • Linear Perspective
  • Parallel Lines Converge at Greater Distances from
    Observer

25
Pictoral Depth Cues
  • Shades and Shadows
  • Orientation and Intensity of Shadows Convey Depth
    Information
  • Relative Height
  • The Higher the Object in a Viewing Plane, The
    Further Away it Appears

26
Pictoral Depth Cues
  • Atmospheric
  • The Washing Out of Objects and Object Detail
    Due to Haze Makes them Appear Further Away

27
Motion Depth Cues
  • Objects That Are Further Away Appear To Move
    Slowly In The Direction Of The Observers
    Movement
  • 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

28
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
    Movement
  • VOR Has a Similar Goal But is Triggered By
    Information from the Vestibular System
  • More Discussion of These Provided Later

29
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
    Information

30
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

31
Utricle and Saccule
  • Functions Similar to Semi-Circular Canals -
    Otolith
  • Utricle Oriented to Detect Acceleration in
    Lateral Direction
  • Saccule Oriented to Detect Acceleration in
    Longitudinal and Vertical Directions
  • Responsible for Orientation With Respect to
    Gravity

32
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

33
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

34
VOR and OKR
  • Work Together Synergistically To Stabilize
    Retinal Image
  • VOR Acts Fast And Corrects Well For 1-7 Hz
    Movement
  • OKR Responds Slower And Corrects Well For lt 0.1
    Hz Movements
  • Tight Feedback Loop Where OKR Helps VOR Adjust
    Gain And Therefore Adapt

35
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
    Adaptation

36
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

37
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

38
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
    Interactions
  • Application Is All About Vection, Vection Is A
    Precursor To Sickness

39
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

40
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

41
CFF Depends On
  • Display Luminance
  • Brighter Displays Decrease CFF
  • Environment Illumination
  • Brighter Environment Decreases CFF,
    Interharmonics
  • 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

42
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

43
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

44
Geometric Display Parameters
  • Inaccurate Cueing
  • Driver Not Oriented Appropriately May Feel
    Skidding
  • Eye Height Too High Results In Inaccurate Speed
    Perception
  • 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
    15
  • Performance Trade-Offs Due to Distance
  • Suggested Minimum Is 40

45
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

46
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

47
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

48
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

49
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

50
Motion Configurations
  • Electric vs. Hydraulic
  • Degrees Of Freedom
  • Operating Envelope
  • Frequency Response
  • Visuals On And Off Motion

51
Impact on Braking Behavior
  • Real World Drivers Adopt Constant Decel
    Profiles For Stopping At Distant Target
  • In Simulators Drivers Adopt A Multi-modal
    Approach
  • Initially Decel Too Much
  • Next They Reduce Decel Or Even Accel To Hit
    Target
  • 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

52
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

53
Impact on Steering Behavior
  • Lack Of Lateral Acceleration Cues Can Lead To
    Over-steering Self Induced Oscillations
  • Nearly Impossible To Look Away And Drive
    Straight
  • 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

54
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.

55
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
    Sensitive
  • 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

56
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
    Expectation
  • Humans Are Adaptable The Longer And More
    Inconsistent The Delay, The Longer The Adaptation

57
Calibration
  • 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

58
Head Mounted Displays
  • With HMDs Full Scene Lag Is Disconcerting
    Proprioceptive Feedback Does Not Match Visual
    Presentation
  • 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

59
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

60
Simulator Adaptation
  • With Increased Exposure We Adapt To Simulator
    Conditions
  • 3 To 5 Exposures Of 10 - 15 Minutes
  • Limit Early Scenario Intensity
  • Consistent Cueing And Motion May Speed Adaptation

61
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,
    Etc.

62
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

63
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
    Rest
  • 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
    Reduction

64
Comfort The Sympathetic Nervous System
  • Last Resort Can Ease Perception of Symptoms
  • Carbonated Beverages (non-alcoholic)
  • Ginger
  • Mints
  • Cool Moving Air
  • Saltines

65
Simulator Design Discussion
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