I consider sub-vocalization to be what goes on when you read something out loud (as in, reading a story to a child), but without full movement and making noise. But still producing the signals for your mouth and throat. This would be suppressed by counting out loud regardless of how automatic is the counting. Counting is good precisely because it is automatic, something more difficult could interfere on the conscious thought level rather than on subvocalization level. edit: instead of counting you can try singing a song while reading something unrelated...

I think I have a good test of subvocalization. For those of you who subvocalize, is there a difference between reading and saying the words out loud in your mind?

Ulcbgurfvf: Vs lbh fhoibpnyvmr, gurer vf ab qvssrerapr (gur dhrfgvba qbrfa'g znxr frafr). Vs lbh qba'g fhoibpnyvmr, gura gurer vf n irel pyrne qvssrerapr.

But I can also count out loud while reading with not much effort.

This is interesting. Can you speak pseudorandom numbers as well, or only count in sequence?

(hypothesis: Bayl va frdhrapr. V rkcrpg pbhagvat va frdhrapr gb or zragnyyl nhgbzngvp, yvxr jnyxvat. V qbhog guvaxvat hc "enaqbz" ahzoref vf bcgvzvmrq gung jnl, fb V rkcrpg vg gb erdhver pbafpvbhf nggragvba naq qvfehcg ernqvat.)