I am writing this post from the Sensory Coding and Natural Environment conference in Vienna. It’s a very interesting conference about a topic that I like very much, but it strikes me that many approaches I have seen seem to miss the point of what is natural about natural sensory signals.
So what is natural about natural sensory signals? It seems that a large part of the field, from I have heard, answers that these are signals that have natural statistics. For example, they have particular second and higher order statistics, both spatially and temporally. While this is certainly true to some extent, I don’t find it a very satisfying answer.
Suppose I throw a rock in the air, and I can see its movement until it reaches the ground. The visual signals that I capture can be considered “natural”. What is natural about the motion of the rock, is it that the visual signals have particular statistics? Probably they do, but to me a more satisfying answer is that it follows the law of gravitation. Efficient coding approaches often tend to focus on statistics, because “the world is noisy” (or, “the brain is noisy”). However, even though there are turbulences in the air, describing the motion of the rock as obeying to the law of gravitation (possibly with some noise) is still more satisfying than describing its higher order statistics – and possibly more helpful for an animal too.
In other words, I propose that what is natural about sensory signals is that they follow the laws of nature.
By the way, this view is completely in agreement with Barlow’s efficient coding principle, which postulates that neurons encode sensory information in an efficient way, i.e., they convey a maximum amount of information with a minimum number of spikes. Indeed representing the laws that govern sensory signals leads to a parsimonious description of these signals.