Final answer:
Julie's difficulty with Spanish words creeping into her French speech is an example of proactive interference, where prior knowledge affects the recall of new information.
Step-by-step explanation:
Julie is experiencing proactive interference, which is a phenomenon where old information hinders the recall of newly learned information. In her case, her knowledge of French is interfering with her ability to speak Spanish because the previously learned language (French) is making it difficult to recall the new language (Spanish) she has learned. This type of interference is common in language learning and can occur when someone is multilingual or learning multiple languages in succession.