When I was in high school I learned about retroactive inhibition. Retroactive inhibition occurs when learning something new causes you to forget something you used to know. For example, if you know how to play a clarinet and then learn how to play a saxophone, you might find that you get confused when you try to play clarinet again.
When I went to college my Psychology class studied both retroactive inhibition and proactive inhibition. Proactive inhibition occurs when something you learned in the past prevents your learning something new.
Or is it the other way around? Ever since learning about proactive inhibition, I've never been able to keep retroactive and proactive inhibition straight.