Real-time summarization systems that monitor document streams to identify relevant content have a few options for delivering system updates to users. In a mobile context, systems could send push notifications to users' mobile devices, hoping to grab their attention immediately. Alternatively, systems could silently deposit updates into "inboxes" that users can access at their leisure. We refer to these mechanisms as push-based vs. pull-based, and present a two-year contrastive study that attempts to understand the effects of the delivery mechanism on mobile user behavior, in the context of the TREC Real-Time Summarization Tracks. Through a cluster analysis, we are able to identify three distinct and coherent patterns of behavior. As expected, we find that users are likely to ignore push notifications, but for those updates that users do pay attention to, content is consumed within a short amount of time. Interestingly, users bombarded with push notifications are less likely to consume updates on their own initiative and less likely to engage in long reading sessions---which is a common pattern for users who pull content from their inboxes. We characterize users as exhibiting "eager" or "apathetic" information consumption behavior as an explanation of these observations, and attempt to operationalize our findings into design recommendations.

We present a system for identifying interesting social media posts on Twitter and delivering them to users' mobile devices in real time as push notifications. In our problem formulation, users are interested in broad topics such as politics, sports, and entertainment: our system processes tweets in real time to identify relevant, novel, and salient content. There are three interesting aspects to our work: First, instead of attempting to tame the cacophony of unfiltered tweets, we exploit a smaller, but still sizeable, collection of curated tweet streams corresponding to the Twitter accounts of different media outlets. Second, we apply distant supervision to extract topic labels from curated streams that have a specific focus, which can then be leveraged to build high-quality topic classifiers essentially "for free". Finally, our system delivers content via Twitter direct messages, supporting in situ interactions modeled after conversations with intelligent agents. These ideas are demonstrated in an end-to-end working prototype.