Most of the time it feels like we can know why we make the decisions we make and do the things we do. It feels like we have our reasons and we know them. But what we are actually doing is probably making very good guesses of why we do what we do. This may seem different but it is very similar to our perception of the outside world. The brain puts in the pieces that fit the best very good guesses.
The interpreter, or perhaps interpreters, was postulated by Michael Gassaniga to explain the way the left hemisphere reacted to the actions of the right hemisphere in split-brain individuals. Here are a couple of paragraphs from his book, The Ethical Brain.
Over the past thirty years I have been studying a phenomenon that was first revealed during work with split-brain patients, whod had the connections between the two brain hemispheres severed to relieve severe epilepsy. My colleagues and I werent looking for the answer to the question of what makes us seem unified, but we think we found it. It follows from the idea that if the brain is modular, a part of the brain must be monitoring all the networks behaviors and trying to interpret their individual actions in order to create a unified idea of the self. Our best candidate for this brain area is the left-hemisphere interpreter. Beyond the finding, described in the last chapter, that the left hemisphere makes strange input logical, it includes a special region that interprets the inputs we receive every moment and weaves them into stories to form the ongoing narrative of our self-image and our beliefs. I have called this area of the left hemisphere the interpreter because it seeks explanations for internal and external events and expands on the actual facts we experience to make sense of, or interpret, the events of our life.
Experiments on split-brain patients reveal how readily the left brain interpreter can make up stories and beliefs. In one experiment, for example, when the word walk was presented only to the right side of a patients brain, he got up and started walking. When he was asked why he did this, the left brain (where language is stored and where the word walk was not presented) quickly created a reason for the action: I wanted to go get a Coke.
Of course, this guessing is only obvious under unusual situations. Ordinarily our brain has most of the information it needs to make a good estimate of the reasons for our actions and to create a reasonable narrative of our life for our conscious model. Unfortunately, we dont know which bits are pure fictions.