People who learn about aphantasia tend to be shocked that there are people out there with a vastly different imagination than theirs; and, moreso, they are shocked that they didn’t know. Everyone understands the general meaning of the phrase “imagine a beach,” and it’s jarring to find out that some literally can’t!

Aphantasia has been actually studied by Serious People, so it definitely counts – it’s a secret segmentation of the population.

I posit that there are many others.

Some others have been studied – “psychogenic” or “emotional” shivers apparently occur while listening to music to about half of people. Are you one? I’m having trouble tracking down prevalence of emotional shivers overall, so I’m not sure which side here is more common.

Some people sometimes mess up their left and their right. I think this is because some people learn a cobweb of tricks for quickly determining left vs right, and others feel that left-ness and right-ness are physical properties of their bodies. According to studies the first thing I found online, maybe about 1/3 of people at least sometimes mix up left vs right.

Here’s one that I’m not finding any studies on, serious or otherwise: general cool twitter person QiaochuYuan posted an interesting twitter poll about experiencing tactile sensations in dreams. It appears to be pretty even! Searching the internet for this mostly brings up froufrou dream analysis nonsense and a smattering of forum posts that are mostly connected to lucid dreaming. And yet – I don’t think I’ve ever felt physical sensation in dreams; apparently about half of my fellow humans do?!

I intend to edit this post as I come across more such segmentations. If we can find about 30 more, we can get pretty close to uniquely identifying a human based only on hidden, unobservable differences!