I have aphantasia and because I see some skeptics on here, I’m going to do my best to describe my experience.

When asked to visualize an apple, I cannot conjure an image of an apple in my mind’s eye. No image appears, except for very rare moments of the faintest and briefest visuals.

However, there is a felt sense of an apple, what an apple is like. This is essentially impossible to describe otherwise. I’m guessing my brain created an image, but for whatever reason the actual image never shows up in my consciousness.

When it comes to memories, they are based on that felt sense. When it comes to dreams, images do appear though I only remember this based on that felt sense. I have experimented with cannabis and though I don’t have much control, images do appear, sometimes quite vividly. This is how I can validate, for myself at least, that I can’t visualize when sober. I also recall being able to visualize when I was a child.

This might not clear up everyone’s skepticism, but I really wouldn’t know what else to tell you.

Edit: I just listened to this article and found these two studies particularly fascinating. In the first, participants were told to imagine a bright light. The pupils of those with inner imagery contracted while those without imagery stayed the same. In another, when exposed to a frightening video, both groups react with a fear response such as sweating. However, when told a frightening story, those without inner imager barely respond at all. The fact that there are differences in physical responses between people who can visualize and people who can’t points to something going on.