Recommender systems provide personalized suggestions about items that users will nd interesting. Typically, recommender systems require a user interface that can \intelli-gently" determine the interest of a user and use this information to make suggestions. The common solution, \ex-plicit ratings", where users tell the system what they think about a piece of information, is well-understood and fairly precise. However, having to stop to enter explicit ratings can alter normal patterns of browsing and reading. A more \intelligent" method is to use implicit ratings, where a rating is obtained by a method other than obtaining it directly from the user. These implicit interest indicators have o bvious advantages, including removing the cost of the user rating, and that every user interaction with the system can contribute to an implicit rating.Current recommender systems mostly do not use implicit ratings, nor is the ability of implicit ratings to predict actual user interest well-understood. This research studies the correlation between various implicit ratings and the explicit rating for a single Web page. A Web browser was developed to record the user's actions (implicit ratings) and the explicit rating of a page. Actions included mouse clicks, mouse movement, scrolling and elapsed time. This browser was used by o ver 80 people that browsed more than 2500 Web pages.Using the data collected by the browser, the individual implicit ratings and some combinations of implicit ratings were analyzed and compared with the explicit rating. We found that the time spent on a page, the amount of scrolling on a page and the combination of time and scrolling had a strong correlation with explicit interest, while individual scrolling methods and mouse-clicks were ine ective in predicting explicit interest.

Latency determines not only how players experience online gameplay but also how to design the games to mitigate its effects and meet player expectations.

The growth in the popularity of interactive network games has increased the importance of a better understanding of the effects of packet loss and latency on user performance. While previous work on network games has studied user tolerance for high latencies and has studied the effects of latency on user performance in real-time strategy games, to the best of our knowledge, there has been no systematic study of the effects of loss and latency on user performance. In this paper we study user performance for Unreal Tournament 2003 (UT2003), a popular first person shooter game, under varying amounts of packet loss and latency. First, we deduced typical real world values of packet loss and latency experienced on the Internet by monitoring numerous operational UT2003 game servers. We then used these deduced values of loss and latency in a controlled networked environment that emulated various conditions of loss and latency, allowing us to monitor UT2003 at the network, application and user levels. We designed maps that isolated the fundamental first person shooter interaction components of movement and shooting, and conducted numerous user studies under controlled network conditions. We find that typical ranges of packet loss have no impact on user performance or on the quality of game play. The levels of latency typical for most UT2003 Internet servers, while sometimes unpleasant, do not significantly affect the outcome of the game. Since most first person shooter games typically consist of generic player actions similar to those that we tested, we believe that these results have broader implications.

Today's powerful computers and networks present the opportunity for video across the Internet right to the desktop. However, Internet video often suffers from packet loss and jitter, degrading the user's perceived quality of the video. Understanding the effects of delay, loss and jitter on media quality is critical for choosing delay buffer sizes and packet repair techniques. While the effects of packet loss on perceptual quality are well-understood, to date there have not been careful user studies measuring the impact of jitter on perceptual quality.The major contributions of this work are carefully designed experiments that measure and compare the impact of both jitter and packet loss on perceptual quality of packet video. We find that jitter degrades perceptual quality nearly as much as does packet loss, and that perceptual quality degrades sharply even with low 1eveIs of jitter or packet loss as compared to perceptual quality for perfect video.

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