Answer:
They were the participants in group 1 who were made to believe that they will be talking to one only person on the other end of the intercom. The experiment was designed to show the bystander effect in the case of an emergency.
These participants were quick to report the emergency to the researcher and they were the only group that recorded a 100% in reporting the emergency under the 4 minutes emergency response time set by the researchers.
Explanation: