Now that I have read all the comments on the linked blog post I have some thoughts to share that I want to have judged seperately.
From user "seez"
Some people can differentiate between orders of magnitude more colors than other people. You can test yourself here: http://www.apartmenttherapy.com/how-well-do-you-see-color-173018
I once had a long argument with a group of friends about why vision was more interesting than sound. Turns out all the ones who sided with vision could differentiate between far more colors.
This seems like it would be easy to test. What is the relevant literature to design a suitable experiment for this?
You can also test if you’re tonedeaf: http://jakemandell.com/tonedeaf/
Similar to the other case, I would like to test for a correlation between enjoyment of music and this. I am not sure what the practical use of this data is but I am interested in it anyway.
From user "St. Rev"
I can’t smell jasmine. I didn’t discover this until I was in my thirties and someone handed me a twig of jasmine flowers. My sense of smell is otherwise better than normal.
From user "Alicorn"
I’m a little bit faceblind (but not as bad as some people, like Leah).
From user "lmm"
This makes me wonder whether there are people who actually get emotionally affected by art, in the same way as I do with music. I enjoy art on an intellectual level, but I’ve never looked at a painting and had it make me feel sad or transcendent or any of the reactions people tend to talk about.
Reading these I wonder about how these discrepancies arise. Are they usually genetic in nature as in that some genetic factor determines certain neurological structures or are they the result of some environmental factor too? The jasmin example sounds more like a defective connection between the brain and receptors in the nose. Then again, only some part of the population is able to smell some metabolic product of asparagus in urine and we know this is a single gene mutation. The faceblind example sounds like some environmental factor being absent such as plenty of faces. The art experience thing I don't know.
Do high IQ people have more of these unusual structures? In my experience more intelligent people report such strange stuff more often and/or are able to empathise with me more. Then again, it could be that intelligent people in general are just more aware of these things and such more considerate.
Anyway I am very happy to see that other people have plenty of these little stuffs and I am not alone in this. I am very happy to be able to participate in this community.
Jasmine, especially the bulbs have a strange, sickly unpleasant smell for me (similar to some of the smells in old toilet rooms, maybe - not the urine part, more like a mushy, fungus smell). I could never find any mention of other people having the same perception.
In his recent excellent blog post, Yvain discusses a few "universal" (commonplace) human experiences that many people never notice they don't have, such as the ability to smell, see some colors, see mental pictures, and feel emotions. I was reminded of a longstanding argument I had with a friend. She always insisted that she would rather be blind than deaf. I could not understand how that was possible, since the visual world is so much richer and more interesting. We later found out that I can see an order of magnitude more colors than she can, but have subpar ability to distinguish tones. And I thought she was just being a contrarian for its own sake. I thought the experience of that many colors was universal, and had rarely seen evidence that challenged that belief.
More seriously, a good friend of mine did not realize he suffered from a serious genetic disorder that caused him extreme body pain and terrible headaches whenever he became tired or dehydrated for the first three decades of his life. He thought everyone felt that way, but considered it whiny to talk about it. He almost never mentioned it, and never realized what it was, until <bragging> I noticed how tense his expressions became when he got tired, asked him about it, then put it together with some other unusual physical experiences I knew he had </bragging>
This got me thinking about when it is likely we might be having unusual sensory experiences and not realize for long periods of time. I am calling these "secretly secret experiences." Here are the factors that might increase the likelihood of having a secretly secret experience.
1) When they are rarely consciously mentally examined: experiences such as the ability to distinguish subtle differences in shades of color are tested occasionally (when choosing paint or ripe fruit), but few people besides interior decorators think about how good their shade-distinguishing skills are. Others include that feeling of being in different moods or mental states, breathing, sensing commonly-sensed things (the look of roads or the sound of voices, etc.) Most of the examples from the blog post fall under this category. People might not notice that they over- or under-experience or differently experience such feelings, relative to others.
2) When they are rarely discussed in everyday life: If my experience of pooping feels very different from other peoples' I may never know, because I don't discuss the experience in detail with anyone. If people talked about their experiences, I would probably notice if mine didn't match up, but that's unlikely to happen. The same might apply for other experiences that are taboo to discuss, such as masturbation, sex (in some cultures), anything considered gross or unhygienic, or socially awkward experiences (in some cultures).
3) When there is social pressure to experience something a certain way: it may be socially dangerous to admit you don't find members of the opposite sex attractive, or you didn't enjoy The Godfather or whatever. Depending on your sensitivity to social pressure (see 4) and the strength of the pressure, this could lead to unawareness about true rare preferences.
4) Sensitivity to external influences: Some people pick up on social cues more easily than others. Some notice social norms more readily, and some seem more or less willing to violate some norms (partly because of how well they perceive them, plus some other factors). I can imagine that a deeply autistic person might be influenced far less by mainstream descriptions of different experiences. Exceptionally socially attuned people might (perhaps) take social influences to heart and be less able to distinguish their own from those they know about.
5) When skills are redundant or you have good substitutes: For example, if we live in a world with only fish and mammals, and all mammals are brown and warm and all fish are cold and silver, you might never notice that you can't feel temperature because you are still a perfectly good mammal and fish distinguisher. In the real world, it's harder to find clear examples, but I can think of substitutes for color-sightedness such as shade and textural cues that increase the likelihood of a color-blind person not realizing zir blindness. Similarly, empathy and social adeptness may increase someone's ability both to mask that ze is having a different experience than others, and the likelihood that ze will believe all others are good at hiding a different experience than the one they portray openly.
What else can people think of?
Special thanks to JT for his feedback and for letting me share his story.