an image from the US government EPA "Sunwise" program. I converted it from PDF format. the source link is here - http://www.epa.gov/sunwise/doc/poster.pdf
After going nuts looking for some icons to represent these group activities, I decided to make some. These are using a stylised petal shape but the principle can be adapted into another shape. One of the 'debate' versions initially looked like two people having a punch up being egged on by the crowd. Filled in shapes indicate full participation, hollow ones are passive, half-half are contributing to the activity.