> b) type the presented word using the right index finger on the keyboard

The intro states they type one-fingered to avoid hard-to-interpret brain activity and then they draw conclusions as broad as "handwriting promotes learning" because using a pen activates more of the brain that hunt-and-pecking with one finger?

Sure - start with the doable and learn a little. But the breadth of conclusion here is seriously questionable vs. the method of the experiment.