Kristina Lerman University of Southern California (USC) As the rate of online content production continues to grow, people make a staggering number of daily decisions about what information to consume, rate or share with others. In turn, these decisions affect emerging trends, the spread of information online and how communities discover interesting content. Due to the constraints of available time and cognitive resources, the ease of discovery, as well as signals conveying the opinions of others, strongly affect how people allocate their attention to content. Through empirical analysis and online experiments, we separate factors due to human cognitive biases and the site’s user interface in the decisions people make about what to attend to. We find that position of information in the user interface strongly affects whether it will be seen, while explicit signal about how many others have previously recommended it increases the likelihood of response. Accounting for these factors dramatically simplifies social behavior and allows us to more accurately predict the outcomes of social contagion, social voting and peer recommendation.