Proactive interference
Old learning gets in the way of remembering something new.
What it means
Proactive interference is forgetting in which previously learned information disrupts the encoding or retrieval of newer, similar information. It is one of the two directions of interference theory — the forward-acting one, where the past intrudes on the present, as opposed to retroactive interference, where new learning impairs old. The disruption grows with similarity between the competing materials, because overlapping cues come to point to several memories at once, so the older, well-established response competes with the newer target. A signature phenomenon is its build-up and release: recall of successive items from the same category steadily worsens, but switching to a new category produces a sudden rebound in performance, revealing that the deficit was interference rather than simple decay. It matters for understanding everyday memory failures, the difficulty of updating outdated knowledge, eyewitness errors, and the design of effective study and training that minimizes confusable overlap.
Examples
After years of using one password, you keep typing it by mistake when you set a new one — the well-learned old password proactively interferes with recalling the new.
After a year of Spanish, your brain hands you 'gracias' every time you try to thank someone in Italian; the older, better-drilled word simply gets there first.
Swap to a car with the indicator on the other side and you set the wipers going at every junction — years of the old layout keep answering a question you stopped asking.
First described in Interference tradition; Underwood (1957); release effect via Wickens.