Why do we find some things surprising while others are tedious? What are the qualities that draw our attention? What is novelty and is novelty the sole factor that leads to surprise?
From neurology it is known that surprise is a decisive factor intervening in many aspects of our life. For example, our memory is guided by this: we remember especially what we have found to be surprising. Moreover, two parts of our nervous system, the sympathetic and the para-sympathetic systems, have distinct functions based on what is and what isn't surprising: the sympathetic system deals with unexpected events and it sets us into the alert-mode, while
the para-sympathetic system deals with the monotonous aspects of life.
However, on what makes something surprising and alerts us?
Two Californian computer scientists, Laurent Itti and Pierre Baldi, tacked this question and managed to create the first bayesian theory of surprise. The previous attempts were non-bayesian and didn't lead to any revelatory results. The distinction between bayesian and non-bayesian is that the non-bayesian methods have tried to describe surprise as if it is an objective feature of something, as if something is surprising in itself, while the bayesian method Itti and Baldi have devised acknowledges that surprise is a relational property. I.e. something that is surprising for you might not be surprising for me.
The key of the entire approach is Bayes' formula
, a formula that describes how the probability of something changes when some new information appears. In this case, one wants to see how surprising the new information is.
Itti and Baldi's idea is simple: if the prior probability (before the new information has arrived) is very different from the posterior probability (after the new information has arrived) than the information has been highly surprising.
So, what makes something surprising and alerts us? It is the potential of changing our beliefs and life to a large extent. It is not the mere novelty, but the potentially useful novelty. Thus, it may not come as a surprise that our brain functions in such a way that we tend to remember the unexpected events and ignore the everyday redundant stuff.