In other words, the ear tunes its response to acoustic stimulus in order to optimize its sensitivity. Magnasco and colleagues propose that some of these so-called strange properties of our hearing apparatus are due to the fact that it operates at a delicate threshold, like a balance poised to tip one way or the other. The threshold has a mathematical representation, the Hopf bifurcation. Sigman's and Cecchi's research on the structure of visual perception in the eye likewise shows that something that a priori was complex like the common structure to all scenes can be explained using the very simple geometric rule of cocircularity. If one assumes the prevailing analogy that the eye functions like a camera, it is relatively easy to discern the basic work of the organ.
Light passes through the cornea and is reflected on the receptor cells of the retina.
It involves recognizing faces and trees, and knowing that a face is always the same when seen from different views or with other objects occluding it. Neuroscientists invest much labor in understanding precisely how the human visual system analyzes images. Sigman, Cecchi and their colleagues at Rockefeller have asked whether or not natural images display consistent statistical properties that the eye recognizes that set them apart from random light and shadow displays. What they found is that there are correlations among objects in the whole visual field, and that their arrangement can be predicted through the simple geometric rule of cocircularity. They are made of contours that are smooth and that are, most of the time, very close to being an arc of a circle.