Please note that this information comes from the book I mentioned previously, Submilinal, by Leonard Mlodinow.

If it’s true that ‘two heads are better than one’ then two brains must be better than one. That’s good because that is what we have – two brains. Much like the brains in all vertebrates, our unconscious developed first and is focused on basic bodily functions, handling large amounts of data, and helping us survive. Our conscious brain is superimposed on it and is oriented towards our ability to communicate with other humans in order to form the community organizations so necessary to our cooperative survival. Our behavior is the result of activities in both of these brains.

Since our conscious brain cannot handle all the sensory data presented to it, our unconscious handles it by quickly sorting through it, deciding what is important to us and discarding the rest. It then stores the important data, but not before stripping out details and summarizing what it wants to save. Note, our minds do not capture data as a camera or audio recording device would in a detailed manner. Later, when we want to access what is stored, our unconscious presents the summarized data and fills in the blank spaces with data it judges is relevant to the request based on our past experiences.

To study this function, an experiment was performed where people listened to recorded statements that included a human cough that blocked out part of a word. For example, ” The (cough followed by the second half of a word ending in ‘eel’) was on the table.” Listeners assumed the eel-word was meal. When the last word was changed to ‘shoe’, listeners claimed the other word was ‘heel’. The brain supplied the most likely missing word based on the last word in the sentence. Other experiments demonstrate the brain does this for visual data as well.

While this function serves us well at social gatherings, it also points to other aspects of our minds. Our unconscious influences how we stereotype people, judge groups of people, and how we form our self image. We like to believe we make decisions based solely on facts, however research suggests we are more complex and biased.