Mirages, as commonly described, are visual experiences where there seems to be something at a particular location in space which is not at that particular location in space. In the most obvious examples, the variation of appearance and reality is typically described as being visually inverted: that what visually seems to be facing one way is actually facing another.
So, in an otherwise empty desert, I see in a small region of the sky, hanging above the horizon in front of me, a street scene — one inverted so that the street occupants’ heads lie below their feet. This is clearly not how they are: they are not walking upside down in the sky. This is an inaccurate visual appearance.
That is a fairly straightforward way of describing the mirage. I imagine it would be risible for many to suggest otherwise. I’m going to suggest otherwise.
The reason I’m going to do that is the account of mirages is more complicated than that it ‘appears upside down and is not upside down’. Once the complications are included, I’m not sure that it’s right to say that things are not how they seem visually. I think that it’s better to say: things are how they visually seem but they do not match expectations of how I might interact with them beyond seeing them. Yet these latter expectations are based on my ignorance of how what I see and what I can touch may interact. This is a multi-sensory error, or an error of multisensory integration, but not of my visual experience itself.
Some examples of mirages: