My question is: are we really capable of perceptually
segregating multiple sources concurrently, or are we just focusing our
attention on one source, and then shifting it very quickly to another
source?
I think another factor to consider in the concurrent segregation of
sounds is that much of the segregation may be accomplished
pre-attentively. Low-level (in the brain, and even cochlea) feature
detectors may segregate aspects of sounds, if not the sounds
themselves, well before they percolate up to what we call
"consciousness." This would depend on the type of segregating cue
under consideration, whether it is pitch, spatial location, onset
time, etc.