240 likes | 427 Views
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.
E N D
PAC-meeting, September 17th 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 • 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
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
Spatial orientation Subjective body tilt (SBT) Subjective visual vertical (SVV)
SBT and SVV performance SVV SBT Tilt angle [deg] Response error [deg] Tilt angle [deg]
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
Set-up Vestibular chair
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”
Results single subject Tilt angle Tilt angle
Results of all subjects SBT SVV
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°
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’