Unlike other approaches, this book assumes there are no weakness' on the part of the students. The student's eyes and brain work well enough.
The issue is what they are seeing is so unlike what they have been taught, they can't figure out what they are looking at.
Dr. Jim Van Manen studied this and discovered some important clues to the code that native ASL alphabet users produce without knowing they use it. The field has taught that native users are not only faster, but their speed is possible because of specific changes that Dr. Jim has found and captured in The Fingerspelling Code.
Dr. Jim Van Manen, author, (2018), 303 pages, soft cover