You're not supposed to notice any perceptual differences while the experience is happening. The whole point of microdosing is to experience the positive benefits and changes, over time, without any of the overt psychoactive effects commonly associated with larger doses of psychedelics.

And if someone tries microdosing for a few days and decides that, in retrospect, they were a little less effective and focused in their work, like the great-grandparent suggests? I don't think the immediate criticism of (paraphrased) "It's not microdosing if you notice a fall in work efficacy, because you noticed it" is fair.

Sounds like you agree the threshold of microdosing is defined by the first question, rather than the subsequent ones.

That is, one wants a dose that doesn't make a difference moment to moment and doesn't cause overt psychoactive effects, but does cause some degree of effect noticeable in retrospect.

That's certainly entirely possible. Everyone's neurochemistry is different. I'm not sure that "a few days" is enough to truly assess the situation, but it's a good start. Perhaps a slightly different dosing regimen may still benefit such a person. As well, it's entirely possible that abstinence is best for that person. No way to know that going in, though.

And yes, I do. I also believe that approximate threshold doses (enough to feel a mild "elevated" state, but not to the level of warping one's perception of reality) have benefit as well. The big trips do too, but a threshold dose or less can allow one to still be able to function in a normal way, just with an increased sharpness of mind and an ability to focus easier.

I'm speaking from personal experience here, of course. The thing about psychedelics is that YMMV, which is why being mindful of what we do know about psychedelics is so important.