Of course, my bet would be that as a working hypothesis the distinction b/t cognitive and perceptual illusions simplifies messier processes in the brain, and that we’ll come to a better understanding soon enough. But I guess that’s often true.

I suspect the distinction between perceptual illusions and cognitive illusions might answer your question. If the the sound is properly mixed, then the plane’s roar through the theater would constitute a perceptual illusion, much in the same way the portrayal of depth on a flat screen would constitute a perceptual illusion. A cognitive illusion, however, would occur if filmgoers were to believe that the plane is really flying over their heads. Depending on the sound — think cell phones or distant thunder –, it is quite possible that filmgoers experience momentary cognitive illusions when listening to the cinema, though obviously I am not suggesting that people need to believe there is a plane in the theater in order for the mix to provide filmgoers with an illusory experience.

So, I would agree that it is problematic to simply parrot a discourse that conflates these two definitions, but I am not doing that in my post. As for finding a better word, I think “illusion” is fine.

You may have used the concept of illusionism only for convenience (“creating the illusion that the plane is also traveling through the theater”) but I do wonder if there’s a better way we might explain what’s happening in these instances of panning. There’s definitively some kind of added value to the panning effect in terms of our sensory/emotional engagement with a film. Practitioners (sound designers, directors) typically explain such innovations in terms of illusionism/immersion (e.g. Cameron and Jackson’s justifications for HFR). But recreating this discourse within film studies (as in so many film theories relying on an illusion/awareness binary) seems like a mistake. Most audience members do not actually think a plane is flying overhead. How have scholars of film sound tried to explain this sort of thing without resorting to the concept of “illusion”?