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Our Quest

What is your brain doing when your eyes are open? The human brain creates vivid perceptions of the world by analyzing the light that enters through two clear little windows in your head. How does it do that?

This question can be asked from many different angles. Right now we are focusing on psychophysical experiments and modeling, in order to determine what the brain does during perception, rather than direct measurement of brain activity to find out how it does it. We are busy exploiting our recent discovery of cue recruitment: that the brain can learn to utilize a new visual signal for purposes of constructing visual percepts. Cue recruitment experiments offer a very powerful new tool for understanding how the visual system uses visual information during perception.

News

VSS 2006 (Sarasota, May 5-10): Backus Lab Abstracts

Human Frontier Science Project. The HFSP has awarded a three year grant to Prof. Backus and his collaborators Marc Ernst, Guy Wallis, and Mike Kearns to study cue recruitment within a Bayesian theoretical/machine learning framework. --30 Mar 2006

ECVP 2006 (St. Petersburg, August 20-25). A symposium on Associative Learning in Perception will take place at this year's European Conference on Visual Perception. --1 Feb 2006

Recent papers

1. Cue recruitment. Fifty years later, it now looks like Hebb and Brunswik were right: the visual system can indeed learn to utilize new visual cues by means of classical (Pavlovian) conditioning, which is the simplest form of associative learning. In other words, the appearances of physical stimuli can be made to depend on new signals that did not at first have any effect. We now hope to extend this discovery. Some of the important questions are: Is this form of learning as important for normal vision as philosophers and scientists used to think? How should it be modeled mathematically? How closely related is it to other adaptations by the visual system? Is it different for young and old people?   Get article from PNAS (institutional subscription required)   Get PDF from this site

2. Explanation of illusory motion in repeated asymmetric patterns. We've shown how static patterns (such as the "Rotating Snakes" illusion by Akiyoshi Kitaoka) can give rise to compelling illusions of perceived motion.    Get article from Journal of Vision 

3. Recalibration in the use of eye position to interpret horizontal disparity after exposure to vertical disparity stimuli. This is a somewhat technical paper. It was already known that perceived depth from stereoscopic vision depends on more than just horizontal disparities (differences between what the left and right eyes see): it also depends on veritical disparities, and on a signal that tells the brain how the eyes are physically rotated within the head. Here we show that a systematic discrepancy between vertical disparity and eye position can cause the system to recalibrate how it uses eye position during the construction of perceived depth from horizontal disparities.    Get article from Vision Research (inst. subscr. required)    Get PDF from this site

Hebb, D.O. (1949). Organization of Behavior. (New York: Wiley). Hebb is known today mostly for the "neurophysiological postulate" (neurons that fire together wire together). But he also proposed mechanisms by which patterns of activity in cell assemblies, corresponding to perceptual experiences, might be learned in an analogous fashion.   More on Hebb

Brunswik, E. (1956). Perception and the representative design of psychological experiments. (Berkeley, CA: University of California Press). Brunswik was the last major psychologist to defend the claim that appearance could be made contingent on a new signal through Pavlovian conditioning. His book was published posthumously.  More on Brunswik