Mostly coding numerical simulations, digital signal processing, audio and image analysis/synthesis. Some natural-language processing as well.
Some 'Demoscene' related coding. All of the above in low-level (asm, C++) , high-level, or both (like Julia and some lisp-dialects) programming languages.
Also a linguist, and experimenting with some computer aided language-acquisition tooling and automatic (spaced-repetition audio playlists, etc).