I became interested in the affirmation particle ja when I noticed that the people I interviewed in Sanpete County, Utah, used it as an everyday affirmation marker. It also seems to work as a marker of local identity. It seems that this particular linguistic feature, which I choose to spell in the Scandinavian and German spelling (cf American yah), is a carry-over from Nordic settlers to the area.
At the moment, I don’t have any publications on ja, but there are a couple in the works. I am co-authoring an article on the history of ja with Jan Heegård Petersen from the University of Copenhagen.
In addition, thanks to Kathryn Remlinger from Grand Valley State University, we have some seed funding for a collaborative project comparing her research site, Michigan’s Upper Peninsula, to my Sanpete County research site.
I have done a couple of presentations on ja in Sanpete County; see links here.