Q-sound proves stereo speakers can fool our brain. It can image objects behind or well beside you over two channels only.
Now that doesn't mean all imaging is an illusion. Our normal hearing in the real world is capable of letting us pinpoint where something is with pretty good precision. The main factors in this ability are used by normal stereo to help us hear what is an audio illusion. We hear sound coming from a position where there is no sound source.
Imaging is an illusion but, if it can be elicited by a determined set of stimuli, they are the measurable element(s).
Good example.
No, I never imply you are ignorant, I know where you are coming from. You believe that since this is something we can hear, can feel, there must be something causing it and we can measure that something...
Yes, you can indirectly measure spatial effects. Since you can edit EQ and create it, you can alter it. You can increase or reduce these effects. You can measure what you have changed in order to create an increase/decrease in these effects.
The problem lies in quantifying this effect. There is no way to quantify this effect objectively. You cannot measure it (like measuring loudness or frequency). You can only assign a subjective number, eg. level 1 - 10. This is essentially same as blind testing. Having said that, it is still possible to at least somehow quantify it. One method I can think of is to use an approach similar to Scoville Heat Units (SHU).
Those EQ settings, we can break it down into minute steps and quantify it (eg. 1 spatial unit or perhaps SPU). We can do a blind test to determine how many times we need to increase before the sample group can detect a change in the spatial effect. I believe we can see a pattern emerging.
Lastly, perhaps you could suggest some answers instead of just questioning. To date, no one has tried to measure spatial qualities and quantify it. Perhaps you could start.
To address the very last response first, if nothing else, this thread proves I am not competent to suggest any answers!
As @escksu pointed out, my experience in other areas of signal processing is apparently inappropriate to how we process audio signals. @Blumlein 88's response is a perfect example of where my previous experience is fouling me up. With a radar system, I can create a signal where there is none there by adjusting the parameters of the source, such as amplitude and phase information over frequency. Or I can move around a real source so it is coming from a different place and at a different rate. What I do, and what comes out the radar dish and into the receiver, is all deterministic and measurable. EW (electronic warfare) systems do this all the time, and even without intentional misdirection other things like multipath and ground or sea bounce can create false images.
My apparent mistake was in thinking the same process was applied to audio signals, such that the position of an image could be determined from the signal sent from the speakers (or rather, reaching the ears, which is more difficult to measure). I can (and have) certainly adjust the signals to the speakers to move a source around, including moving it outside the boundaries of the speakers themselves, using an acoustic rather than radar processor. I did that long ago using bucket-brigade devices for a true time delay plus the usual analog circuitry to manipulate amplitude, phase, frequency response, and so forth. It was a fun project, presented for younger kids who were wowed by how we could move the sound around, but apparently inapplicable to this discussion. If the brain (processor) is making decisions based on (unknown to me) data then my basic premise (hypothesis) is wrong. Thus at this point I think my fundamental premise about what this thread is about and how we perceive spatial sound fields is wrong, and I do not want to waste more time (yours or mine). In this I am indeed ignorant, and following to learn.