  Processes of individual attitude formation and their macroscopic consequences
have become an intriguing research topic, and agent-based models of opinion
formation have been proposed to understand this phenomenon. This study
conducted an agent-based simulation and examined the role of mass media in a
noisy opinion formation process, where opinion heterogeneity is preserved by a
weak intensity of assimilation and errors accompanying opinion modifications.
In a computational model, agents conformed to their neighbours' opinions in
social networks. In addition, each agent tended to be influenced by one of a
two external agents with fixed opinions, that is, mass media that take opposite
positions on an opinion spectrum. The simulation results demonstrated that a
small probability of interactions with mass media reduces opinion heterogeneity
even with extreme mass media position values. However, a large frequency of
interactions with mass media increases opinion heterogeneity. Accordingly,
intermediate assimilation strength achieves the least heterogeneous opinion
distribution. The influence of mass media dampens the effects of network
topology. Our simulation implies that mass media can play qualitatively
different roles depending on their positions and intensity of influence.
