That really depends on the study. The basic assertion above holds very well through casual testing, numbers above six do not. So take that for what it is I guess.
Die reading is generally considered symbol recognition, not sight counting, anyway. Unicode has pipped dice ⚀⚁⚂⚃⚄⚅. The same patterns also appear on cards...
When reading 2d or 3d, I know some who can hit the total in under a second accurately, generally not long enough for the addition... but that's the same skill as sight-reading words. Just alternate spellings for one, two, three, four, five, six, seven, eight, nine, and so on to 18. ⚃⚃⚄, ⚃⚄⚃, or ⚄⚃⚃ is 13. If you're dyslexic, you might not even notice the 3 spellings in the die-face symbols.
Oh, they're also used on dominos... but dominos differ from cards for 7-15 patterns. (I had a set of double 15's. Makes for LONG games) Unicode only has to double-6. 🁬🁼🂌 Those three dominos showcase all 6 symbols.
That tracks. I know a few (older) people who add heart/spade/clove/diamond symbols rather than their numerals when adding cards in cribbage.
Also usually symbol recognition. There are standard patterns for A-10.
When it comes to cards, however, I use the indicies, not the patterns... because 99% of bridge/poker card use I've had has arabic indicies and held cards hide the face of the card. I've seen one in a museum without indicies.