Learning is through associating new information with old information. We establish our knowledge about our world integrating every input factor. I think sometime it is unreasonable.
Nowadays cell phones have this function that people can make a stream of music as the sound of alert or ring tone. I am interested in this function and set one of my favorite songs as alarming sound. But it is a failure and I will never do it again. Because every time I listen to this song I am in a sleepy state and hoping to sleep more, I feel frustrate when I listen to this music. Then after several trails, whenever I listen to this music, I am elicited a noxious emotional response. That is to say, I begin to dislike this song. My brain adds a noxious tag to the innocent song. This is an example of emotional conditioning.
This memory is also flexible and can be extinguished. After I recognize that I don’t like the song, I intentionally listen to this song when I am happy. Then the noxious tag is slower replaced by an amiable tag, I like this song again. This is an old memory covered by new memory, in other words, recognition.