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Optimal sensory integration in spatial orientation

PAC-meeting, September 17 th 2009. Optimal sensory integration in spatial orientation. Maaike de Vrijer. Eyes. Sources of information. Tactile system. Vestibular system. Blood pressure. Neck proprioceptors. A priori knowledge. Optimal (Bayesian) observer theory. Sensor 1. Sensor 2.

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Optimal sensory integration in spatial orientation

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  1. PAC-meeting, September 17th 2009 Optimal sensory integration in spatial orientation Maaike de Vrijer

  2. Eyes Sources of information Tactile system Vestibular system Blood pressure Neck proprioceptors A priori knowledge

  3. Optimal (Bayesian) observer theory Sensor 1 Sensor 2 • Combination of two noisy signals leads to lower noise in final estimate • A priori knowledge reduces noise in final estimate but may introduce bias Combined

  4. An example Perception of target location Auditory Vision Problem: sensory systems in spatial orientation cannot be easily isolated Solution: use two spatial orientation tasks that rely on different combinations of the same signals

  5. Spatial orientation Subjective body tilt (SBT) Subjective visual vertical (SVV)

  6. SBT and SVV performance SVV SBT Tilt angle [deg] Response error [deg] Tilt angle [deg]

  7. Objectives: To test whether optimal Bayesian observer theory applies to performance in the two tasks (SBT and SVV) Can the theory explain why performance in body tilt perception (SBT) and visual verticality perception (SVV) differs? Approach: • Psychophysical SBT and SVV experiments • Sensory integration model

  8. Model

  9. Sensory integration model

  10. Experiments

  11. Set-up Vestibular chair

  12. Experiments SVV task: At 9 tilt angles between -120 and 120° Measure of bias (systematic errors) and variability (uncertainty of subject) SBT task: • Reference angles: 0 and 90° tilt, • Measure of bias (systematic errors) • and variability (uncertainty of subject) “Judge orientation of body with respect to 0 or 90°” “Judge orientation of line with respect to gravity”

  13. Results

  14. Results single subject

  15. Results single subject Tilt angle Tilt angle

  16. Results of all subjects SBT SVV

  17. Results of all subjects

  18. Fit results Optimal parameter values : (averaged across subjects) Body sensors: σ=11° • Neck sensors: • σ=5° • Head sensors: • σ=1.9°+0.13∙|tilt| • Prior head-in-space: • σ=11°

  19. Summary • Using a psychometric approach, we measured spatial orientation in two different tasks: body tilt perception (SBT) and subjective visual vertical (SVV) task • Results showed that subjects made systematic SVV errors at tilt angles beyond ~60°. SBT performance was quite accurate but more variable than SVV performance • These findings can be well explained within a Bayesian framework, based on the processing of noisy signals in a statistically optimal fashion. This suggests that the neural computations underlying human spatial orientation are ‘Bayes’ optimal’

  20. Questions?

  21. Combined results

  22. SVV results (single subject) at all tilts

  23. Best-fit parameters

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