Retroactive interference is the disruptive effect of new learning on the recall of older information. Recently acquired material makes earlier material harder to retrieve.

A student who learns one list of vocabulary and then a second list often finds that items from the second list intrude when trying to recall the first. The more similar the two sets of material, the greater the interference. Sleep and other forms of reduced mental activity after learning can protect against retroactive interference by limiting the acquisition of new competing traces.

Retroactive interference is the counterpart of proactive interference, in which older learning disrupts newer learning. Both demonstrate that memories compete with one another rather than existing in isolation. Strategies such as distinctive encoding, spaced practice, and avoiding similar material in close succession can reduce the problem.

What you learn later can crowd out what you learned before.