Perceptions are fuzzy? Go with your prior.

April 5, 2013


Last week I was fortunate in having the opportunity to give some talks at the Riken Brain Institute outside Tokyo, Japan. I learned about fantastic ongoing work including during my visit: Tomomi Shimogori describe insights her lab has made about the driving force behind topographic organization, Hokto Kazama explained how his lab will use imaging to decode information in the fly brain about incoming olfactory signals and Keiji Tanaka described how the brain changes as learners transition from amateur to expert status

I also spent a lot of time with Justin Gardner discussing recent insights from his lab about perceptual processing humans. Recently, they have been delving into the neural basis of an established behavioral phenomenon: when subjects estimate the speed of low contrast gratings, they tend to mis-judge them a bit, rating them to be slower than they truly are. This has been interpreted by Eero Simoncelli’s lab as evidence for a “slow speed prior”: the idea is that we interpret sensory information by combining sensory evidence with prior beliefs. When the contrast is low, our perception is fuzzy, so we tend to go with the prior, rather than the sensory evidence. The Gardner lab is in a strong position to understand how this works for two reasons: first, they regularly image the brains of well-trained humans using fMRI; second, they have developed methods for decoding the signals they record, allowing them to understand how the brain changes with changes in the stimulus, such as contrast and speed. Using this approach, they find a clear signature of the slow speed prior, most noteably in the same early visual areas that represent the sensory evidence for speed such as V1 and MT. My lab is likewise interested in how priors are combined with sensory information. In the picture, you can see Justin and me arguing about whether insights from speed estimation priors apply to multisensory integration priors.

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