  We present a three-week within-subject field study comparing three mobile
language learning (MLL) applications with varying levels of integration into
everyday smartphone interactions: We designed a novel (1) UnlockApp that
presents a vocabulary task with each authentication event, nudging users
towards short frequent learning sessions. We compare it with a (2)
NotificationApp that displays vocabulary tasks in a push notification in the
status bar, which is always visible but learning needs to be user-initiated,
and a (3) StandardApp that requires users to start in-app learning actively.
Our study is the first to directly compare these embedding concepts for MLL,
showing that integrating vocabulary learning into everyday smartphone
interactions via UnlockApp and NotificationApp increases the number of answers.
However, users show individual subjective preferences. Based on our results, we
discuss the trade-off between higher content exposure and disturbance, and the
related challenges and opportunities of embedding learning seamlessly into
everyday mobile interactions.
