When considering recognition of the shapes of words, remember this "oldie but a goodie".

Did you konw taht the hmuan biran can raed wrods no mtater waht odrer the lteters are in as lnog as the fisrt and lsat lteters are croerct?

Yes, it is pattern recognition. Single and double spacing after a full stop is just a variation on this. What you are "used" to will always "the right way for me".

Habit can be your friend, and with only a little effort you can change any habit. I used to be a "two spacer", but converted. Actually it can also speed up one's typing as well. Think of all those extra space bar hits your poor thumb doesn't have to perform.

I have to admit though, the dual examples did seem to come across clearer with the two spaces. Hmmm, maybe I need to re-think my habits.