I&#x27;m curious, since perception is an interesting thing when you can no longer trust your sense: are you <i>certain</i> that you actually heard a fully functioning, never before heard, tunable symphony, or did you simply believe that you were? That is, did the symphony itself exist in your mind, or just your perception of it?<p>I ask because I often have the experience in dreams, that I experience something which I perceive to make sense until I actually try to make sense of it, whereupon it falls apart. My  brain only generates my response to the input, not the input itself, and when queried for the input fails to produce it.