Monica was just promoted to high school and received a new locker. When Monica went to her old locker, she could not remember the combination of her old locker because she kept confusing it with her new locker. Monica is experiencing:

The answer is retroactive interference.

Explanation:

Retroactive inteference occurs when new information inteferes when remembering old information. It is a common error while recalling numbers, names and dates.

In contrast, proactive inteference takes place when old information interferes when processing new information. An easy way to remember the difference is to say:

Retroactive = cannot remember Proactive = cannot process