Both retroactive and proactive interference involve human memory. Put simply, interference is when a specific memory is disrupted because of 'competition' from other memories. Disrupted recollection involves both working memory and long-term memory. Scientists theorize that once something has been stored in long-term memory, it is there permanently, but the ability to recall it may be lost.
Retroactive interference occurs when newly learned information inhibits the retrieval of previously learned material. When new information is learned, new associations are made with existing long-term memories. This weakens existing associations with similarly learned material already stored in long-term memory. In this situation, previously learned and understood information is unable to be remembered. For example, after you switch a long-used password for a website, the old password may be forgotten within a matter of days or weeks.
Proactive interference occurs when information learned previously inhibits the retrieval of newly learned information. In this case, the remnants of the original learning interfere with remembering newly learned information. For example, when a lifelong baseball player suddenly begins to take up golf, she may have difficulty learning the correct golf swing, as the previously learned way of swinging a baseball bat may be getting in the way. This causes some people to swing a golf club in a manner similar to the way one swings a baseball bat.