Some people can't see mental images

I have no real basis for this, but I always suspected that the majority of differences in ability to picture things is actually just a difference in semantics about terms like "visualizing", "picturing", etc. I don't think anybody is "literally" envisioning things, as in hallucination. On the other end, I don't think anybody is actually unable to "think of" what a thing looks like. But it's really difficult to objectively describe what it's like to picture something in your head - so difficult, in fact, that I can see some people calling it "literally summoning an image" and others calling it "not seeing anything at all", while both talking about the exact same thing.

Not that there isn't a difference in ability, just that it might not be as dramatic/binary as we seem to think.

I agree with this. I thought I had aphantasia the last time I read about it here.

Then I started interrogating all of the people who claimed to “visualise” things and it turned out we were all doing the same thing - conceptualising in our “mind’s eye”.

For example, anyone I’ve asked to visualise something with their eyes closed can also “visualise” the same thing with their eyes open. It’s happening “somewhere else” and not in your vision.

So I think the term “visualise” leads to a lot of the confusion.