As a cognitive psychologist, I spend a lot of time thinking about how the brain works. It was shocking, then, when I recently learned that there is something in my brain that doesn't work. Specifically, that I am extremely lacking in my ability to generate mental imagery, a condition called aphantasia.
The most incredible part is that I made it this far in my life without realizing that the way that people describe mentally imagining (e.g., scenery, colors, memories, etc.) is a literal visual experience. I'm not sure how it hadn't occurred to me previously that the way that I mentally list things such as the colors of objects or events that happened is not the "normal" way of accomplishing these tasks. Apparently, because the experience of these mental states (moving pictures or lists of events for memories, for example) is a very subjective thing (perhaps even classifiable as a type of qualia), discovering that the way that you do it is different from other people takes some seriously frustrating discussion.
For me, it happened during a graduate course. We were discussing mental rotation, mental "zooming in", and other cognitive tasks such as imagining colors. I became increasingly uncomfortable. Eventually, I interrupted the discussion to ask some questions along the lines of "But you can't really imagine colors, can you?" and "Surely this is all metaphorical, like, imagining traits of colors?" and "You actually see where something is in space when you imagine it?". But no, it turns out, as indicated by my lifelong navigation troubles, that when people claim to be imagining mental maps of spaces that they were accomplishing something that I had never quite learned to do.
This discovery led to me feeling really weird for a couple of days, and several discussions with friends as we tried to piece together how it is that I accomplish tasks that the average person uses mental imagery for. I also found out, now that I was paying attention, that my ability to use mental imagery isn't completely absent, just very impoverished. For example, when I am tired (e.g., just waking up) or asleep, I can do some basic visual imagining like other people apparently always can. I also believe that my abilities are improving, slightly, through exercising them -- whenever I walk through a building these days, I do my best to imagine what the map looks like. It takes a serious level of focus.
If you are interested in reading more about this, there are some recent articles such as this one: https://www.livescience.com/61183-what-is-aphantasia.html
Or check out this video from SciShow that explains how recent the naming of this condition was: https://www.youtube.com/watch?v=lpK6ZJea9fk