Turner, B., Fuchs, C., & Todman, A. (2015). Static vs. Dynamic Tutorials: Applying Usability Principles to Evaluate Online Point-of-Need Instruction. Information Technology & Libraries, 34(4), 30-54. doi:10.6017/ital.v34i4.5831
This article finds "that web usability testing was a useful tutorial-testing tool while discovering that participants learned most effectively from text-and-image tutorials, since both rounds of participants completed tasks more accurately and more quickly than those who received audio/video instruction or no instruction." Helpfully, there are links to the tutorials used in the appendices of the paper, so you can unscientifically see if you agree with the findings too!