Proactive vs Retroactive Interference: The One Rule for AP Psych

You learned your new locker combination in September. It's almost November and your hand still spins last year's numbers. Is that proactive or retroactive interference?

If you had to stop and think, you're not alone. These two terms sound alike, and the AP Psychology exam can test whether you know which is which. This guide gives you one rule that settles it every time, plus examples, the research behind it, and practice questions.

What interference is

Interference theory says we often forget because memories compete with each other, not just because time passes. When two pieces of information are similar, one can block or blur the other when you try to recall it.

There are two directions this can go. Old memories can push forward and mess with new ones. Or new memories can reach back and mess with old ones. That's the whole difference between proactive and retroactive.

In the AP Psychology course, this sits in Unit 2 under Topic 2.7, Forgetting and Other Memory Challenges. If you want the full unit, start with our AP Psychology Unit 2 review.

Proactive interference: old blocks new

With proactive interference, something you learned earlier makes it harder to learn or recall something newer. The old memory acts forward in time.

Examples:

• You keep entering last year's locker combination instead of this year's.
• It's January and you still write last year on your homework.
• You took French before, and now Spanish is harder because French words keep popping into your head.
• You moved to a new country and keep thinking in your old currency.

In every case, the memory you can't get to is the newer one.

Retroactive interference: new blocks old

With retroactive interference, something you learned more recently makes it harder to recall something older. The new memory acts backward in time. Think "retro," like looking back.

Examples:

• You memorized your new phone number, and now you can't remember your old one.
• You started Italian this year, and your French from middle school is slipping.
• A teacher with a new class of students starts forgetting names from last year's class.

Here the memory you can't get to is the older one.

The one rule that never fails

Most mistakes happen because students try to label the memory that's causing the problem. Flip it. Find the memory that's failing.

Try it on the locker. You can't get the new combination out. So it's proactive.

The same forward and backward logic shows up with amnesia, which is also in Unit 2. Anterograde amnesia means you can't form new memories after a brain injury. Retrograde amnesia means you can't remember events from before the injury.

The research behind it

Two classic findings are worth knowing, as summarized by Simply Psychology:

• Similarity matters (McGeoch & McDonald, 1931). People learned a word list, then either rested or learned other material before recalling it. The more similar the second set of material was to the first list, the worse their recall. Synonyms of the original words caused the most forgetting.
• Old lists pile up (Underwood, 1957). Looking across many studies, people who had learned one earlier list recalled about 70-80% of a new list a day later. People who had learned twenty earlier lists recalled only about 20%. Underwood argued that a lot of what looked like forgetting over time was really proactive interference.

The takeaway for you: interference is strongest when the information is similar.

How to use this when you study

• Don't stack similar material back to back. Since similarity drives interference, studying Spanish vocab right after French vocab is asking for trouble. Put something different in between.
• Space your review. Coming back to material over several days beats one long cram session.
• Quiz yourself. Retrieval practice, actually pulling the answer out of your head, makes memories stronger than rereading.
• Make your own examples. Think of a time each type happened to you. Personal examples are easier to recall on test day.

Practice questions

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Keep going with Unit 2

Interference is one piece of Unit 2. The full review covers perception, heuristics, encoding, storage, retrieval, forgetting and intelligence, with flashcard and quiz prompts for each topic. The 2027 AP Psychology exam is on Friday, May 14, 2027.

• AP Psychology Unit 2: Cognition review
• AP Psychology Unit 1: Biological Bases of Behavior
• Full AP Psychology study guide

For official AP Psychology resources, visit apcentral.collegeboard.org.

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