In 2015 psychologists at Binghamton University, led by Celia Klin, showed 126 undergraduates short exchanges. One message read: “Dave gave me his extra tickets. Wanna come?” The replies were words like “Okay,” “Sure,” “Yeah” or “Yup.” Text messages that ended with a period were rated as less sincere than the same replies without one. The study appeared in the journal Computers in Human Behavior.
A 2006 study looked at 200 exclamation points in two online discussion groups for library professionals. It found that they “may function as markers of friendly interaction.”