Although it may be hard for most of us to imagine, there are people who don't experience mental imagery, or seeing pictures in your head. Most of us can conjure up images from memory, imagination, or an external description without much effort. About 4% of people cannot do that, although they think and navigate the world just fine. This condition is called aphantasia. It's not really a disability, and many folks who have it are completely unaware. How can you know that the way you think is any different from the way other people think? I can't imagine what it would be like to think without visualizing what I'm thinking, so why would people with aphantasia be able to imagine what those images in the "mind's eye" are like?
Scientists have been studying people with aphantasia, and have found some interesting things about people who have it. This TED-Ed lesson from Adam Zeman tries to explain what aphantasia is like. -via Laughing Squid