There is indeed. This is a good example of what can happen with task switching when you process it this way since both lines have “line”.
I first used the parallel method for verbal memory. I then afterwards used the parallel method for visual memory. However, to be clear, you do not have to use it for memory only, it’s possible to calculate in parallel although this is significantly exhausting. I tested this with some simple additions (visual parallel) and have had positive results.
The visual parallel is indeed easier than the verbal one(not easier for calculating). In order for me to do the verbal one without interference I use different voices for each line which helps, distinguish it more. I don’t think this is required, but it made it easier for me. I found it easiest to train by first using a second language since I am bilingual, this prevented me from task switching.
Double handed as in, being able to write with both hands at the same time or being able to write with either hand? I personally trained my left hand since I am originally right-handed so now I am ambidextrous, I also practiced writing with both hands recently at the same time and found decent although not as quick results (particularly since I can’t write with 3 hands to speed up 2 hands). I find that there is some transfer (benefits in general), for example if you can parallel verbal, you noticeably become better able to comprehend multiple audio sources at a time compared to prior. Though it’s not quite as broad that you get the full scale benefit.
Parallel with 1 verbal and 1 visual together rather than either exclusively, is much easier and doesn’t take too much training. From Ramon’s books I believe what he did was something like:
Read verbally ‘35477213’
Visualize images of ‘8567’
Glance with visual working memory at ‘6316441’
So he did not even much of any parallel, other than the visual one of visualizing and keeping working memory active. It’s generally much easier to do different tasks in parallel even if they use similar components. For example it takes very little training to do 1 verbal and 1 visual in parallel.
In some cases, to my experience, it’s easier although harder to train, to do parallel as a combination of visual and verbal. For example you can visualize text to process the text verbally in parallel.
The reason for the chunks, is because it’s easier to visually recall a chunk in working memory in this form, for the latter and you make less errors in chunks (particularly if you visualize images).
Parallel doesn’t actually make much of a difference in chunks. At best keeping the chunks different so you clearly know where to start in parallel.
It’s indeed something that you do have to train. If it is difficult that usually means you get the training benefits quicker, if it’s too easy you should increase the amount of digits rather than attempt to increase speed would be my advice. I tend to test a lot of things so I tend to make a lot of discoveries, so I personally think it’s good to try a range of things to see what works best for you.