An amusing commercial shows someone having a bad day, and how that person's mood affects each person down the line, with more bad moods. This emotional "contagion" may be a real-world phenomenon, and it appears that what we experience online can have a similar effect. Examining over 2000 video blogs, or vlogs on YouTube, researchers from Tilburg University, Netherlands, found we mirror the emotions of those we see online and we seek out people who share our emotions.

The research appears in Social Psychological and Personality Science.

"Our research is a reminder that the people we encounter online influence our everyday emotions - being exposed to happy (or angry) people can make us more happy (or angry) ourselves." says Hannes Rosenbusch (Tilburg University). Rosenbusch is the lead author of the study.

Being affected by others' emotions is known as "contagion." People also seek out others like themselves, or in this case, people with similar outlooks and moods. In psychology, this is known as "homophily."

With almost 5 billion videos watched on YouTube daily, the researchers focused on vlogs and vloggers. Vloggers share emotions and experiences in their videos, providing a reliable source of data.

The researchers focused on studying more popular vlogs, with a minimum of 10,000 subscribers. Some of their sample vlogs had millions of subscribers.

To measure if people watching vlogs experienced emotional contagion or homophily, the team studied words and emotions expressed by the vloggers and analyzed the emotional language of online comments. They modeled the effect of both immediate (contagion) and sustained (homophily) emotional reactions (See Figure 1).

The team found evidence that there is both a sustained and an immediate effect that leads to YouTuber emotion correlating with audience emotion. When a YouTuber posts a video with a generally positive tone, the audience reacts with heightened positive emotions. The same is true for other emotional states.

They also note that this research looks at a complicated system: humans. The effects of video emotions on audience emotions probably comprises of a collection of mechanisms like contagion, empathy, and sympathy.

This study is the first to use a video-focused social media source like YouTube to explore contagion and homophily. Other researchers have found similar results looking at text-based social media sites like Twitter and Facebook.

"Our social life might move more and more to the online sphere, but our emotions and the way we behave towards one another will always be steered by basic psychological processes," summarizes Rosenbusch.

Anthony Evans and Marcel Zeelenberg are co-authors of this study.

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