Retroactive interference
New learning crowds out and disrupts memory for older material.
What it means
Retroactive interference is forgetting in which newly acquired information impairs the retrieval of previously learned, similar information. It is the backward-acting counterpart to proactive interference within interference theory: here the present reaches back and degrades the past. The effect intensifies when the new and old material overlap, because the fresher memory competes for the same retrieval cues and can overwrite or block access to the earlier trace. Classic demonstrations show that people who learn a second, similar list recall the first list worse than people who merely rest during the interval, implicating active interference rather than the passive decay of time alone. It matters for understanding why cramming similar subjects back-to-back is counterproductive, why updated information can erase the original, and why sleep — which limits new interfering input — protects memory consolidation.
Examples
Learning the layout of a new office makes it harder to recall the layout of your previous one, as the newer spatial memory interferes with the older.
After changing your password, the new one keeps surfacing when you try to recall the old one for an archived account, the fresher memory blocking access to the earlier trace.
A Spanish speaker who takes up Italian starts reaching for Italian words mid-sentence, as the newer overlapping vocabulary competes for the same cues and the older language suffers.
First described in Interference tradition; Müller & Pilzecker (1900); McGeoch (1932).