They didn’t test learning at all; they tested writing a word or typing a word based on a Pictionary prompt.
I’m not a research scientist, but it seems like you could look at this evidence and just as easily conclude that writing by hand increases the extraneous load for learners, i.e. that the task of writing itself requires more attention or “mental bandwidth” which would be diverted away from whatever you’re hoping they will learn.
I’d like to know if there’s evidence against this alternative explanation.
In this study they observed specific patterns that previously were attributed to learning and remembering.
> "The present findings suggest that the intricate and precisely controlled handwriting movements have a beneficial impact on the brain’s connectivity patterns related to learning and remembering."
But you are right, they do not directly _prove_ that handwriting yields a greater learning effect.
(baseless speculation below)
One thing I've noticed is how drastically my handwriting (and maybe hand dexterity in general) varies wildly from hour to hour, mostly depending on how tired I am or how much caffeine I've had.
If I'm feeling tired and sluggish, my handwriting is a disaster. It doesn't look good. It doesn't feel good. But after some caffeine, or otherwise becoming more alert, suddenly it looks better, and it feels much better as I do it.
Is this just me? I guess it's not surprising that caffeine would have an impact like this. But the part that's surprising to me is how pronounced and reliable it is.
As a seemingly overly visual thinker the aspect of making several small decisions about how to layout what I'm writing down by hand also seems to play a huge role in that. I have to make positioning and thereby spacing and sizing decisions, choose the color, as well as making decisions on in what style (caps, cursive, script) I write each letter. I can easily use graphical elements like lines, arrows, boxes, etc.
Anything created digitally by primarily typing will always have a more dynamic and flowing nature, while following the linearity of the typed sequence of characters. It takes away a lot of the decisions that I have to make when laying out a handwritten note.
Anecdotally, I seem to remember mindmaps created with digital tools that rearrange elements automatically based on available space much less than hand-drawn ones. Yet, those come with their own downsides.