One of the reasons that certain advertisements are successful is because viewers want to behave like those they observe. What is the general term that psychologists use to describe this type of behavior?

Answer 1

It's one of these.

http://library.thinkquest.org/C0111500/proptech.htm

Answer 2

The behavior of those observed is called modeling. The viewers identify with the model, identification, and therefore imitate the model, imitation.