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 might not be the most representative example (I seem to use visual and spatial more than most people for abstract reasoning), but here goes an attempt to convey one data point...

If I imagine a particular model of car, for example, I can instantly visualize much of what the entire car looks like. I can also move my attention around parts of the visualization, to see more detail. It's more than facts, and more than feelings.

This visualization is different than seeing with eyes, and is not confused with that, but seems to be using some of the same machinery.

I could sketch a detailed drawing from what I'm visualizing, a bit like the car was physically there, and I could keep looking back to it for references. But when it's in my head, I don't have to take my eyes off the drawing, and I can kinda merge my drawing and the reference in my head.

In contrast, if I try to imagine the scent of tire rubber, or of cooking, or any other scent, I cannot. Not even the tiniest bit. There's just nothing there.

As a point of reference for comparison, that's pretty dramatic and binary.

Of course, when I smell a familiar scent, I often identify it instantly. And while I am physically perceiving it, I can experience it, and move my attention around it, and introspect on its character, and have other reactions to it (e.g., good, bad, etc.), etc. But immediately after I stop physically perceiving it, I again can't imagine it. I can only recall previously registered facts about it: that vanilla smells good, kinda sweet(?), and maybe creamy(?). I could know more facts if I was a baker or cook, and I guess reason about how to use vanilla, but I still doubt I could imagine perceiving the scent of vanilla in my head.

And some scents will quickly surface related memories of previous times I perceived the scent, even decades ago. And those non-scent memories will remain activated and linger after the physical scent is removed. (Any rare accompanying wow deja vu sense is brief.)

I can picture the visual appearance of various glass and plastic bottles of vanilla flavoring I've seen over the decades, and how some vanilla flavoring looks in a particular stainless steel teaspoon with ambient light reflecting through it, etc. I can also visualize in detail the visual appearance of things that come to mind when I try to think about things I've seen that have vanilla flavoring. I just can't imagine what they smell or taste like.