Adaptive control of exposure. A proportional exposure cap is a maximum fraction applicable to a recipient's total viewable attention in a time window. The total viewable attention represents all viewable advertising content which will be provided to the recipient. A notification of availability of an opportunity to expose a specified recipient to advertising content is received during the time window. The specified recipient's consumed viewable attention is detected. The specified recipient's total viewable attention for the time window is predicted. Responsive to the maximum fraction of the specified recipient's predicted total viewable attention for the time window being greater than the consumed viewable attention of the specified recipient, content is sent to the specified recipient and the consumed viewable attention is updated.