Almost everyone has seen pictures that deceive our eyes in some way. Some of them have two possible interpretations, others make us evaluate wrongly the size or the alignment of geometric figures. More complex figures can induce the illusion of movement when no actual movement is happening. And yet, illusion is a concept that is actually hard to define from a philosophical point of view, since it requires comparison with the true nature of the object, something we would tend to define as perceived by our senses. The number of different illusions and the way they work is actually so large that systematizing them into a few types or a theoretical framework has proved to be a surprisingly hard task.
The way our brain interprets the information it receives from our eyes can be considered similar to the way we reason. The task is indeed similar. Given what we know, the brain tries to arrive at the best possible conclusion. It uses heuristics and rules we still are starting to understand. These heuristics are usually good for solving some set of problems, either problems our ancestors had to deal with (get food, find a mate, etc.) or problems we learned to solve during our life time. The same way our brains have to deal with images. Given the visual information our eyes receive, our brain tries its best to interpret what exists in the world around us. It extrapolates and reaches conclusions that are not conscious, simply providing us with its best guess. And, most of the time, that guess is remarkably good.
Just as we discussed before, the fact we sometimes make mistakes of interpretation of visual information is not necessarily a bad thing for our survival. Recognition of patterns, whether those patterns emerge in the financial market or are the behaviour of the game one is hunting, is a very useful skill. And if one is the first to identify it, there is more to gain. This can be enough to compensate for the cost of false detections. And, indeed, in general reasoning as well as in interpreting visual information, we are able to identify patterns very fast, which leads to falsely identifying random meaningless noise with something important. This general phenomenon is called apophenia.
One interesting and helpful example of how this applies to our visual perception is our tendency to identify faces everywhere, from simple typographical juxtaposition of characters like :) or ;-( to seeing faces on rocks or on toasts or on shadowy, blurred images from Mars. This is called pareidolia. Quickly identifying other people as well as inferring their emotional state is certainly an useful trait for a social animal like humans are (see Demon-Haunted World: Science as a Candle in the Dark
). While this can be interesting and allows us to create new ways to communicate and to give extra meaning to some forms of art, the reality is that much of what we see as faces is a probably hard-wired conclusion of our brains. Indeed, evidence from MRI scanning of our brains show that the specific areas of the cortex that become more active when we see faces also show the same type of activity when we just perceive something as a face . The timing of the activity is also consistent with an early interpretation of the image as an actual face and not a later re-interpretation of the image by our brains. Amazingly, it is already possible to do neural reconstruction of the face someone is seeing from the detected pattern of the activity of the brain.
