Retroactive Interference: This is when newly learned information disrupts the recall of older memories. For example, if you learn French after studying Spanish, the French vocabulary might interfere with your ability to retrieve Spanish words.
Proactive Interference: This occurs when previously learned information interferes with the learning or recall of new information. For instance, if you learn how to ride a bicycle and then try to learn how to ride a motorbike, some of the habits from riding a bicycle may interfere with learning how to operate a motorbike.
Decay Theory: Decay theory suggests that forgetting happens due to natural decay over time. Memories fade away if they are not reinforced or used frequently enough.