Researchers at Sheffield University and the University of St. Andrews, United Kingdom revealed that the key is the way in which the learned information is forgotten.
When one learns a language and then doesn't use it, one may find that relearning a few words will trigger many others to come back and be relearned. The same happens with other skills that involve mental associations. The authors term this phenomenon "free-lunch learning."
Researchers Jim Stone and Peter Jupp created a mathematical model to show the opposite effect, called "negative free-lunch learning."
These are cases in which relearning parts of forgotten associations decreases the recall of the remaining parts.
They found that if forgetting is induced by random fluctuations in the strength of synaptic connections, then free-lunch learning would be observed.
However, if forgetting is induced by directional decay in synaptic connectivity, then negative free-lunch learning occurs.
The study is published in the open-access journal PLoS Computational Biology.