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Gasper Tkacik

 

Wednesday 25th March 2015

Time: 4pm

 

Basement Seminar Room

Alexandra House, 17 Queen Square, London, WC1N 3AR

 

“Beyond sensory bottleneck: Efficient coding of elements of visual form”

 

It has long been appreciated that the statistical properties of natural 
stimuli shape neural processing mechanisms in the sensory periphery, but 
the extent to which such a principle can be formulated for and applied to 
central processing is unclear. The periphery faces a transmission 
bottleneck, so efficiency implies compression of signal components with a 
predictably wider range. Cortex faces a different challenge – it must use 
limited samples to make inferences to guide decisions. In this regime, 
efficient coding predicts the opposite from the periphery: that greater 
resources are allocated to the signal components with a wider range. To 
test this hypothesis, we carry out two parallel studies. In one, we 
measure the joint distribution of local two-, three-, and four-point 
spatial correlations in an ensemble of natural images. In the other, we 
measure human perceptual sensitivity to these correlations and their 
combinations via psychophysical experiments that use synthetic visual 
textures. We show that psychophysical performance, described by dozens of 
independent parameters, can be predicted with surprising accuracy from the 
distribution of spatial correlations found in the natural images. Thus, 
the efficient coding principle extends beyond the sensory periphery to the 
central nervous system, where it applies in a very different guise and 
accounts for the sensitivity to higher-order elements of visual form.