Where have you looked so far? Research on the Internet and its affects on society is still hard to come by, although there are a lot of people involved now. I’d expect to see a lot coming soon. Anyway, what is your hypothesis about the psychological impacts of asynchronous communication?
You might look for research about psychological impacts of letters and correspondence. That was the original asynchronous communication. The internet just sped it up a bit. However, I think that the difference between asynchronous and synchronous communication is immediacy, or lack thereof. The lack of immediacy, I think, generates a kind of anticipation. You don’t know when, or if you will be replied to. I remember getting really freaked out when people never got back to me. This happened particularly when I would leave a phone message, and was waiting for folks to get back to me.
You might look into the literature about telephones and messages and answering machines, too. There is many a story about a girl or a guy waiting by the phone, wondering when or if their crush will call them.
Other than the uncertain nature of asynchronous communication, perhaps there is an element of loquation. In synchronous conversation, you take turns, but it is done fairly rapidly. We tend to dislike windbags, and think they are rude. In asynchronous communication, you take turns, but it is at leisure. There’s no pressure to answer now. You can take your time, and even research if you want. You don’t have to say what’s on top of your head. You can reconsider things.
Psychologically, I’d say that would have a calming effect and there would be less anger expressed in asynchronous communication. Although, there are stories of people posting a letter, having second thoughts, and trying to retrieve the letter from the post box. With emails, you might run to another person’s computer, and try to delete the email before they got back from lunch.
So, yeah. Anticipation and greater calmness—those are the two things that come immediately to mind that distinguish asynchronous from synchronous.
What are you doing this research for? High school? College? A paper? For what class?