The dissertation is about the dynamics of public attention in the contemporary media system. What shapes the dynamics of public attention to a social issue across media over time is the primary empirical question that guides the following chapters. Nearly 50 years ago, Downs proposed the now-classic issue attention cycle, which explains the evolution of public attention. His issue attention cycle, along with traditional communication theories, such as agenda setting theory, agenda building theory, and gatekeeping theory, have suggested that a small group of elite organizational actors create and shape public attentiveness to social issues. However, more scholars question whether these traditional media theories can explain the evolution of public attention in today's media system. These scholars challenge the present applicability or appropriateness of these theories. To move forward current theories about public attention, this dissertation examines the conceptualization and causes of public attention by synthesizing literature from agenda setting, agenda building, and gatekeeping and information diffusion studies. Setting climate change as an analysis background, this dissertation unfolds with three empirical studies and realizes three research goals: (1) to clarify what public attention is and propose a robust way to measure it, (2) to disaggregate and typologize the attention from different types of actors on Twitter, and (3) to examine the patterns of public attention across different climate-related events. Findings suggest that: (1) Public attention is conceptually and empirically different from news attention, public opinion, and Twitter attention. Public attention is less volatile, intensive and responsive to the real-life events in contrasting to the news attention and Twitter attention. (2) In terms of the relationship between attention from news, Twitter, and strategic organizations across mass media and digital media over time, Twitter attention is the most volatile and intensive comparing to news, public attention, and public opinion. The impact of strategic organizational attention (measured by press releases) exists at the daily level but does not sustain at the monthly level. (3) In terms of the transmedia diffusion of climate change attention, organizational actors in general are the source and individual actors are the spreaders of attention. Dynamic networks analysis show that individual actors sometimes become the top sources. (4) The event contexts play a role in determining who leads public attention.
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