It's frustrating when people suggest I can visualize and just don't know it. The way one thinks is the most first-personally obvious thing in the world, and I've been sore about the way I do it since I was in elementary school wanting to imagine strawberries to count with.
Despite the literature I never accuse visualizers of the reverse (ie that you only think you have mental images), but when I do challenge incredulous friends about their phenomenology some discover it's actually much less pictoral than they'd believed: eg, "imagine a tiger, how many stripes?" or "imagine an ant crawling across a checkered picnic table toward a jar of grape jelly, what color square is it on now? what about now?" or "imagine a 3x3 word matrix whose rows read 'too', 'aid', 'ole' -- read the column words straight off without sounding out or going letter by letter". Granted, others can do these with an ease that amazes me.
"Can you draw a stick human figure? Did it pop into your head when I mentioned stick human figure? There you go, you just visualized it."
Yes I can draw a stick figure. I'm not an idiot, and nothing pops into my head other than the sound of the word and some xkcd affect.
Meanwhile, it astounds me that a single picture can pop into your head: how do you know what position to put the stick figure in -- akimbo, Thinker? Imagine a flower -- ok, which, a rose or a marigold? Do you decide or does it just happen? How many different flowers can you visualize, and how quickly? Do they appear embedded in soil or just floating free? How many different varieties can you see at once? What prevents you from seeing more?
Re: dyslexia -- I drew this link too, as I have very mild dyslexia. My father is profoundly dyslexic but claims vivid imagery.