48 vs 160 Kbps does not fully describe the difference of what went into their ears, it depends on the music as well. How about the actual frequency range/distribution of each of the samples for example? Other questions to ask: did the participants fly or experience any other drastic change in altitude (ear-popping) shortly before the test? Did they have their coffee yet?

they already have http://news.bbc.co.uk/2/hi/science/nature/4318888.stm