Tilt perception during rotation about a tilted axis

Rens Vingerhoets1,2

Jan Van Gisbergen1

Pieter Medendorp2,3

1. Department of Biophysics2. Nijmegen Institute for Cognition and information3. FC Donders Centre for Cognitive Neuroimaging

Spatial orientation

• Visual Cues

• Vestibular System

• Somatosensory Cues

Introduction - Sensors

{Semi-circular canals

Otoliths

Introduction - Sensors

The semi-circular canals

• Sensitive to rotation (angular acceleration)

Introduction - Sensors

The otoliths

• Sensitive to acceleration caused by:– Gravity (Tilt)– Inertial acceleration (Translation)

Signal is ambiguous}

Tilt Translation

Introduction - Sensors

How is the otolith ambiguity resolved?

Hypothesis: canal-otolith interaction

Tilt

Angularvelocity

Tilt + Translation

Rotation

Otoliths

Canals

g

a

^

^

ω̂

Internal Model Translation

Rotation about a tilted axisRotation about a vertical axis

Introduction

What is rotation about a tilted axis (OVAR)?

What causes this illusory translation percept?

Introduction

What happens during OVAR?

Otolith signal from tilt misinterpreted as translation?

Left Ear Down(LED)

Right Ear Down(RED)

Nose Up(NU)

Nose Down(ND)

Veridical motion percept

0 30 60 90 120

Time (s)

Ro

tatio

n p

erc

ep

t

Time (s)

LEDRED

NU

R

Illusory motion percept

LED

ND

NU

RED

ND

0 30 60 90 120

Tra

nsl

atio

n p

erc

ep

t

Introduction – Otolith Disambiguation

The model predicts a gradually increasing underestimation of tilt during OVAR

0 30 60 90 120

0

10

20

3030o/s & 45o

Tilt

und

eres

timat

ion

(deg

)

0 30 60 90 120

50o/s & 45o

Time (s)

0 30 60 90 120

50o/s & 15o

Introduction – research question

• Is there evidence for the underestimation of tilt predicted by the canal-otolith interaction model?

• If so, is the time course compatible with canal-signal delay?

Methods

Experimental setup

- Vestibular chair -

Introduction – Subjective Visual Vertical

Tilt perception tested with Subjective Visual Vertical (SVV)

Gravity

Flash!Clockwise

Methods

Experimental setup • 6 subjects • 3 dynamic conditions

- Large tilt & Low speed (45o tilt and 30o/s)- Large tilt & High speed (45o tilt and 50o/s)- Small tilt & High speed (15o tilt and 50o/s)

• Each dynamic condition consisted of 20 runs of 120 s each

• In each LED and RED phase flashed presentation of oriented line

• Subjects used a toggle switch to indicate whether the line had to be more clockwise/counterclockwise to be perceived as earth-vertical

• Time course of SVV determined using an adaptive staircase over runs.

• 2 static conditions: 45o tilt and 15o tilt

Results

Results – Dynamic paradigm

Dynamic results of 1 subjectE

rror

in S

VV

, γ (

deg)

0 30 60 90 120

-30

-20

-10

0

10

20

30

30o/s & 45o

0 30 60 90 120

Time (s)

0 30 60 90 120

50o/s & 45o 50o/s & 15o

Results – Dynamic paradigm

Dynamic results

- Time course of SVV shows gradually increasing underestimation of tilt, just as canal-otolith interaction model predicts

- Initial responses are already biased.

Results – Static paradigm

Results of static tilt

-10

0

10

45o

tilt

Err

or

in S

VV

se

ttin

g (

γ),

(de

g)

-10

0

1015

o tilt

JG NK MV RV SP TG

LED

RED

Tilt underestimation

Tilt overestimation

Tilt underestimation

Tilt overestimation

Results – Dynamic paradigm

Dynamic results

Is the dynamic response pattern simply a linear combination of static effects and canal-otolith interaction?

SVV = A • Dynamic + B • Static

Results – Dynamic paradigm

Fit to dynamic results of 1 subjectE

rror

in S

VV

, γ (

deg)

0 30 60 90 120

-30

-20

-10

0

10

20

30

30o/s & 45o

0 30 60 90 120

Time (s)

0 30 60 90 120

50o/s & 45o 50o/s & 15o

A=1.3 B=0.8

Results – Dynamic paradigm

Coefficients of all subjects

SVV = A • Dynamic + B • Static

-0.5

0

0.5

1

1.5

2

2.5

JG NK MV RV SP TG JG NK MV RV SP TG

A B

Results – Dynamic paradigm

Model predicts dynamic SVV

0 30 60 90 120

-15

0

15

30

Dyn

amic

res

pons

e E

rror

, γ (

deg)

0 30 60 90 120Time (s)

0 30 60 90 120-30

Model Prediction

Pooled dynamic response

30o/s & 45o 50o/s & 45o 50o/s & 15o

Conclusions

Conclusion

• Static effects also play a role in dynamic conditions

• Canal-otolith interaction can account for dynamics of tilt percept

Otoliths

Canals

Internal Model

Tilt

Angularvelocity

Tilt

Translation

Rotation

The End