White noise: https://en.wikipedia.org/wiki/White_noise

https://news.ycombinator.com/item?id=28402424 :

> https://en.wikipedia.org/wiki/Neural_oscillation#Overview says brainwaves are 1-150 Hz? IIRC compassion is acheivable on a bass guitar.

Doodling improves memory retention / learning, too. IDK how much difference the content of a doodle makes? Hypothesis: Additional "cognitive landmarky" content in the doodle or received waveforms would increase retention up to a limit.

Regarding doodling, it seems that any active productive study method is at least somewhat beneficial. I've found this in my own personal experiments. For example, testing myself with cloze deletions, creating Anki cards, generating mind maps, Cornell notes, inline annotation/marginalia, doodling, generating questions, generating mnemonics, mind palaces, etc.

An interesting one is reading and reciting out loud: https://www.tandfonline.com/doi/full/10.1080/09658211.2017.1...

Another non-intuitive method that is helping me a lot is pacing around my house slowly while I read. It goes to show that cognition is an embodied phenomenon. It's unintuitive when intelligence is viewed from the traditional split mind/body paradigm but just take a look at an image of our nervous systems. Those wires to and from our brain and guts wrap around every part of us.

Mnemosyne/Anki, (FreeMind, yEd, Gephi, AtomSpace as-moses, RDF bnodes, ONNX,) mind maps, RestructuredRext, MyST-Markdown, todo.txt (TaskWarrior,), StructuredProcrastination, ActivityWatch, Dogsheep, *-to-sqlite, awesome-quantified-self, https://github.com/woop/awesome-quantified-self

But metrics for actual memory retention? I've heard of TinCan xAPI w/ a LRS. nbgrader, Khan Academy exercises, OpenBadges to demonstrate proficiency,