I'm afraid I don't remember. I read somewhere that when asked to count in their minds, people count in one of two ways. It's my understanding that the majority do so verbally, sounding out the words in their minds. But some people count visually, by visualising the numbers, picturing them scroll past on a tape, for example.

Those that verbalise couldn't simultaneously do another verbal task, while the visualisers couldn't do another visual task, suggesting that separate parts of the brain were involved, and occupied by counting.

Now that I knew visual counting was an option (I was a verbaliser) I trained myself to do it. Unfortunately I'm yet to find an situation were the ability to choose between visual and verbal counting has been useful.