"Why do we feel so unified? We have discovered something in the left brain,another module that takes all the input into the brain and builds the narrative. We call this the interpreter module…. When we set out to explain our actions, they are all post hoc explanations using post hoc observations with no access to nonconscious processing. Not only that, our left brain fudges things a bit to fit into a makes-sense story. It is only when the stories stray too far from the facts that the right brain pulls the reins in. These explanations are all based on what makes it into our consciousness, but the reality is the actions and the feelings happen before we are consciously aware of them—and most of them are the results of nonconscious processes, which will never make it into the explanations. The reality is, listening to people’s explanations of their actions is interesting—and in the case of politicians, entertaining—but often a waste of time.
"We showed a split-brain patient two pictures: A chicken claw was shown to his right visual field, so the left hemisphere only saw the claw picture, and a snow scene was shown to the left visual field, so the right hemisphere only saw that. He was then asked to choose a picture from an array of pictures placed in full view in front of him, which both hemispheres could see. The left hand pointed to a shovel (which was the most appropriate answer for the snow scene) and the right hand pointed to a chicken (the most appropriate answer for the chicken claw). Then we asked why he chose those items. His left-hemisphere speech center replied, “Oh, that’s simple. The chicken claw goes with the chicken,” easily explaining what it knew. It had seen the chicken claw. Then, looking down at his left hand pointing to the shovel, without missing a beat, he said, “And you need a shovel to clean out the chicken shed.” Immediately, the left brain, observing the left hand’s response without the knowledge of why it had picked that item, put it into a context that would explain it. It interpreted the response in a context consistent with what it knew, and all it knew was: chicken claw. It knew nothing about the snow scene, but it had to explain the shovel.
"Once we understand that the left-brain interpreter process is driven to seek explanations or causes for events, we can see it at work in all sorts of situations. In fact, it can explain the observations of many past experiments…. The left-brain interpreter creates order out of the chaos presented to it by all the other processes spewing out information. We tried again with another emotion and another patient. We flashed a picture of a pinup girl to her right hemisphere, and she snickered. Once again she said that she saw nothing, but when we asked her why she was laughing, she told us we had a funny machine. This is what our brain does all day long. It takes input from other areas of our brain and from the environment and synthesizes it into a story….
"This post hoc interpreting process has implications for and an impact on the big questions of free will and determinism, personal responsibility and our moral compass, which we will look at in the next chapter. When thinking about these big questions, one must always remember, remember, REMEMBER that all these modules are mental systems selected for over the course of evolution. The individuals who possessed them made choices that resulted in survival and reproduction. They became our ancestors…"
--Michael S. Gazzaniga, Who's in Charge?: Free Will and the Science of the Brain