Data protection officials are set to examine Facebook, after it was discovered the social media website conducted a psychology experiment on 689,000 users without their knowledge.

The Information Commissioner's Office (ICO) in Britain has said it will be questioning Facebook about privacy issues.

An ICO spokesperson said "We're aware of this issue, and will be speaking to Facebook, as well as liaising with the Irish data protection authority, to learn more about the circumstances".

The research was conducted on users over a period of one week in 2012.

The experiment involved manipulating users feeds to show either mostly positive or mostly negative posts to see what emotional effect this had on the user.

Two US universities - Cornell University and the University of California at San Francisco - collaborated with the study to gauge if "exposure to emotions led people to change their own posting behaviours".

The study found that users who had fewer negative stories in their news feed were less likely to write a negative post and vice-versa.

The Irish interest comes from the fact that Facebook has its international headquarters based in Dublin.