element-interactivity

Element interactivity is how many things you must hold in mind at once because they depend on each other — a lock with three tumblers turns together or not at all.

Cognitive load theory names it as the source of intrinsic load: a concept with high element interactivity (a chess tactic where three pieces interact) demands more working memory than one with low interactivity (a single-rule fact). The number is a property of the concept, not the learner, so it can be measured before anyone tries to learn it — which makes it a candidate predictor of where a learning threshold sits. When element interactivity exceeds working-memory capacity, the difficulty stops being desirable and restudy wins: "why difficulty helps" is the wrong sentence to teach exactly there.