The answer is: stimuli are processed with little, if any, conscious effort
The only way for an automatic processing to occurs is if we had repeated a certain action or behavior over and over again for a prolonged period of time.
example of this situation is when you're learning to play a piano. In the beginning , most people would have to constantly changing their attention between the sheet music and the piano keys in order to play the song.
After playing it over a long period of time, people could play a certain song on a piano automatically with their eyes closed.