My personal experience is that yes, executive function has increased
after training these modalities. After experiencing a plateau at N=5
for dual N back, (steadily improving n-level, but not noticing many
substantial cognitive changes) I switched to pentuple n-back.
Subjectively I can say that first, I can remember images more vividly.
That is, colors are more vivid in my memory, and also in dreams. This
is likely do to the color/image component of pentuple/quad/tri
nbacking. I also notice a decrease in the load that learning a new
topic places on my WM. That is, I feel that my WM capacity is
increased such that I can manipulate more data with ease, making
learning mathematics and abstract concepts quite simple. Dual N
backing increased this by a set amount, and then when the results
seemed to plateau, anecdotally I can say that it appears Pentuple/Quad
N back appear to have kickstarted results again.
Also, since beginning N back training in general, I have astronomical
recall, to the point that if I forget something I have read, a formula
for instance, I can visualize the image of it, then re-read it from
memory. Also, if i consciously forget where I placed something,
subconscious streams of the place I last saw it take place. In other
words, I intuitively recall the location of the item I lost with
stunning accuracy, generally with an exact mental photograph of the
item where I left it. Finding the item, I notice that it is situated
exactly as it was in my memory.
Also increased ability to create humor, and express ideas verbally.
On top of this training, I study a musical instrument, play chess for
2 hours per day, exercise 3-5 days per week, take fish oil, flax, and
other brain supplements and study language.
I can surely say that I feel myself getting smarter week by week; it
is a rather surreal experience.
Currently at between P2B and P3B.