verticality perception during body rotation in roll rens vingerhoets pieter medendorp jan van...
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Verticality perception during body rotation in roll
Rens Vingerhoets
Pieter Medendorp
Jan van Gisbergen
NICI & Department of Biophysics
Nici-Juniorendag, 3 mei 2007
Introduction
Introduction
Perceptual updating
The brain has to combine retinal information and information on body orientation to maintain a stable
percept of the world
Introduction
Perceptual updating
Information on body orientation from:
•Visual panoramic cues
•Somatosensory cues
•Vestibular system:-Semicircular Canals
-Otoliths
Introduction
Vestibular System
Introduction
Semicircular canals-Detect angular acceleration
-Response to constant velocity decays
Introduction
Otoliths-Respond to gravito-inertial force (GIF)
-Cannot discriminate between tilt and translation (ambiguity problem)
g
fa
F=G-A
a
Introduction
OtolithsAmbiguity problem:
Neural strategy for otolith disambiguation:
Canal-otolith interaction
Introduction
Canal-otolith interaction model
Head tilt leads to canal signal, acceleration does not
GIFSubjective
vertical
Linear
acceleration
Angularvelocity
Angular
velocity
OtolithsInternal
Model
g
a
ω
w
g~
Canals
+
b
Introduction
Canal-otolith interaction model
Bias mechanism based on static verticality estimates
Now test this model for dynamic verticality perception during roll rotation
GIFSubjective
vertical
Linear
acceleration
Angularvelocity
Angular
velocity
OtolithsInternal
Model
g
a
ω
w
g~
Canals
+
b
bw
g~
g
Bias mechanism
Introduction
Roll-rotation
Sideward rotation about
an axis through the nose
Introduction
Model predictions
0 90 180 270 360
SV
V E
rror
,
(deg
)
Tilt angle (deg)
-180
-90
0
90
18090L18090R0 0
Static
Preceding rotation (deg)0 180 360 540 720 900 1080-180-360-540-720-900-1080
90L 90R 90L90R 90R90L90R90L90R 90L 90R 90L
Dynamic
Error in verticality percept
g~g
Introduction
Questions
-Are systematic errors under dynamic conditions similar to static errors?
-Evidence for phase delay in the verticality percept as predicted by the internal model?
Methods
Methods
Vestibular Chair
Methods
ExperimentsSubjective visual vertical (SVV)-Roll rotation at 30 deg/s, alternating CW and CCW
-Measurements at 15 deg intervals
-Scaling method using flashed lines
-Static:
•0 – 360 deg
•10 measurements 30 s after rotation stop, every 2 s
-Dynamic:
•0 – 1080 deg = 3 complete cycles
•measurements during rotation, every 2 s
Subjective body tilt (SBT)
-Verbal estimation of body tilt at random times during rotation
Methods
Scaling method
Flash!
1 minute past the hour!
Error in SVV = real orientation (30o) – estimated orientation (6o) = 24o
Response error equals error in verticality percept ()
Results
Results
Static CW
0 90 180 270 360-180
-90
0
90
180
Err
or
in S
VV
(d
eg)
Tilt angle (deg)
•Systematic errors
•0 –150o & 240 – 360o
verticality percept biased towards the head
•Bias toward feet near 180o
90R 90L180 00
Results
All subjects
Err
or
in S
VV
,
(de
g)
Preceding rotation, (deg)
Comparison Static & Dynamic
Results
Static vs Dynamic
Preceding rotation, (deg)
Err
or
in S
VV
,
(de
g)
Results
Static vs Dynamic
Err
or
in S
VV
,
(de
g)
Preceding rotation, (deg)
Results
Static vs Dynamic
Dynamic data qualitatively similar but:
-Larger errors in red zone
-More inter-subject variability
-Green zone is broader
-Bistability
Dynamic: complete rotation
Results
Dynamic: complete rotation
Err
or
in S
VV
,
(de
g)
Preceding rotation, (deg)
Results
Dynamic: complete rotation
Preceding rotation, (deg)
Err
or
in S
VV
,
(de
g)
Results
Dynamic: complete rotation
-Error pattern repeats in successive cycles
-No phase delay
Dynamic Subjective Body Tilt
Results
Dynamic SBT
Err
or
in S
BT
,
(de
g)
Preceding rotation, (deg)
Results
Dynamic SBT
Err
or
in S
BT
,
(de
g)
Preceding rotation, (deg)
Results
Dynamic SBT
-Smaller errors than in SVV
-No bistability
-Errors in SVV are not caused by errors in SBT
Errors based on SBTSVV real subject
Results
Dissociation between SVV & SBT
Errors in verticality estimates not caused by misjudgment of body tilt
SVV ideal subject
Model Fits
Results
Model Fits
-SVV in red zone biased toward head w>0
-SVV in green zone biased toward feet w<0
-Dynamic errors larger than static wdyn > wstat
InternalModel
Otoliths
Canals
GIF
AngularVelocity
g
a
ω
LeakyIntegrator
g~
v
AngularVelocity
LinearVelocity
Subjective vertical
+
W
h
hw
g~
g
Results
Static Fits
Err
or
in S
VV
,
(de
g)
Preceding rotation, (deg)
Results
Dynamic Fits
Err
or
in S
VV
,
(de
g)
Preceding rotation, (deg)
Results
Model Fits
-Model can describe SVV responses if:
•W-values differ for static and dynamic
•W-values differ in red and green zone
Results
Analysis of phase shiftsInstead of focusing on the error , we can also look at the amount of compensation for tilt. We refer to this angle as .
compensation for rotation (tilt)
Perfect task execution: = body tilt angle
hw
g~
g
Introduction
Analysis of phase shift
Dynamic CW
Model prediction for
04590
135180225270315360
Tilt
Ang
le (
deg)
0 180 360 540 720 900 1080
Preceding rotation, (deg)
Phase shift:
= 0 when ≈ 370 & ≈735
Actual tilt
Preceding rotation, (deg)
Results
Analysis of phase shifts
-720o
50o
-360o 0o 360o 720o
50oModel
(d
eg)
50o
50oAll subjects
Preceding rotation, (deg)
1 Subject
(d
eg)
50o
50o
Results
Analysis of phase shifts
-No clear evidence for phase lag
-If anything, it is a lead rather than lag
Conclusions
Conclusions
ConclusionsWe have shown that:
-Errors in verticality perception are not caused by misjudgments of body tilt
-The egocentric bias is larger under dynamic conditions than under static conditions
-Verticality judgments are biased toward the feet around 180o tilt. Both statically and dynamically
-There is no evidence for a phase delay