EDISON - Facebook is drawing a storm of criticism over an apparent experiment it conducted on the news feeds of thousands of its users.

For one week in 2012, the social media giant intentionally altered the number of negative and positive posts in the news feeds of randomly selected users. Researchers were studying the effect the changes had on the posts the subjects then wrote.

The results of the experiment, conducted by researchers from Cornell, the University of California, San Francisco and Facebook, were published this month in the academic journal Proceedings of the National Academy of Science.

There is no indication that the 690,000 subjects were asked if they would like to take part in the study.