baysian approaches kun guo, phd reader in cognitive neuroscience school of psychology university of...
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Baysian Approaches
Kun Guo, PhD
Reader in Cognitive Neuroscience
School of Psychology
University of Lincoln
Quantitative Methods 2011
Example
Visual system interprets incoming retinal signals in the context of existing knowledge of the world.
Some issues within this process: (1) signals are corrupted by variability of noise; (2) uncertainity in computation.
Brain represents sensory information probabilistically, in the form of probability distribution.
Ideal Bayesian Inference Observer: assigning probabilities to any degree of belief abouth the state of the world.
Posterior ≈ Prior × Likelihood : Visual perception (Bayesian posterior probability of a scene) ≈ Prior probability of the state × Current input from the eye
Vision is an act of interpretationVision is an act of interpretation
Thomas Bayes (1701 – 1761): English mathematician
“An essay towards solving a problem in the doctrine of chances” was read to Royal Society in 1763 (doctrine of chance ~ theory of probability).
Posterior ≈ Prior × Likelihood: a method of statistical inference to calculate the impact of evidence on beliefs. The probability is interpreted as a degree of belief (conditional probability distribution) rather than frequency. In application, the initial degree of belief is called prior and the updated degree of belief is called posterior.
Widely applied in Science, Engineering, Medicine and Law, especially after 1950s.
Bayes’ TheoremBayes’ Theorem
P(A|B): posterior, the degree of belief in A after B is observed.
P(A): prior, the degree of belief in A before B is observed.
P(B|A)/P(B): likelihood, impact of B on the degree of belief in A.
Bayesian InferenceBayesian Inference
Landing light
Time
Predictor 1
Predictor 2
Predictor 3
Target
200 ms
Predictor 4
FP
Stimulus sequence comprised four collinear bars (predictors) which appeared successively towards the foveal region, followed by a target bar with same or different orientation.
Guo et al. (2004) Effects on orientation perception of manipulating the spatiotemporal prior probability of stimuli. Vision Research 44: 2349-2358
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
Stimulus demonstration – non-collinear trial
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
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Normal sequenceRandom order sequenceRandom duration sequence
Spatiotemporal structure of the priors
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
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Subjects
Dis
crim
inat
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resh
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Normal sequenceRandom order sequenceRandom duration sequence
Spatiotemporal structure of the priors
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
0
2
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6
Subjects
Dis
crim
inat
ion
Th
resh
old
(°)
Normal sequenceRandom order sequenceRandom duration sequence
Spatiotemporal structure of the priors
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
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Real orientation
difference
p
Distribution of perceived
orientation difference
Clpt
Psychophysical
function
Grl
Noisy brain
Representation
(Likelihood)
r
Gp Prior distribution
Guo et al., (2004) Vision Res. 44: 2349-2358
normal sequence — higher expectation of co-linearity — sharper prior distribution
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision researchFree parameters: width of prior, width of likelihood, co-linearity threshold, fitting error
Different spatiotemporal structure Different experimental frequency
Applying Bayesian Inference in Vision researchApplying Bayesian Inference in Vision research
Learning and reasoning
Language processing and acquisition
Memory
Vision
Sensorimotor control
Bayesian Applications in Bayesian Applications in Psychology & NeurosciencePsychology & Neuroscience
Reference: Trends in Cognitive Sciences, 2006, Vol 10(7), “Special issue: Probabilistic models of cognition”.