You see a shopper trip over in a busy street. Someone else can help. That's what you tell yourself. This is the bystander effect（旁观者效应） in action—the dilution（淡化） of responsibility in the presence of others — and it has been demonstrated in many past studies.

But life is complicated and psychologists have seen exceptional situations. Recently two experiments were conducted by Marco van Bommel and his team using an online chat room for people with extreme emotional problems. Eighty-six students were logged into the forum （论坛） and shown five messages from troubled users. They were told to write a reply if they wanted, but it was entirely up to the students themselves. 

Basically, participants could see their names on the screen alongside others' names. A counter also told them if the forum was quiet with just one other person logged in, or busy with 30 others online. This arrangement reproduced the classic Bystander Effect—participants were less likely to post replies with more people logged in. However, when the researchers cued （提示） self-awareness by highlighting participants' names in red on the screen, they posted more replies on a busy forum.

A second study was built on these findings, but this time self-awareness was raised by the presence, or not, of a computer web-camera. Over 100 participants took part. Then researchers found that the Bystander Effect was reproduced when web-cameras were absent —on busy forums participants posted fewer replies to needy users. On the contrary, those cued to be self-aware by the web-camera actually wrote more replies.

Nearly any online community can benefit from the research. The ability to turn hesitant bystanders into eager helpers is a recipe for engagement and collective benefit. As in the research, simple design cues could be integrated to help online users remember they are visible to the community.