Immersive videos allow users to freely explore 4 π steradian scenes within head-mounted displays (HMD), leading to a strong feeling of immersion. However users may miss important elements of the narrative if not facing them. Hence, we propose four visual effects to guide the user's attention. After an informal pilot study, two of the most efficient effects were evaluated through a user study. Results show that our approach has potential but it remains challenging to implicitly drive the user's attention outside of the field of view.