Onset asynchrony has been put forward as one of the relevant factors i
n auditory scene analysis (for references, see A.S. Bregman, MIT Press
, Cambridge, 1990). In the present study this issue was further invest
igated using a new paradigm: musically trained subjects were presented
with two successive pairs of simultaneous complex tones and they had
to decide whether the two pairs contained tones with the same pitch. I
f this was the case they had to indicate which tones had been equal in
pitch (the lower in each pair, the higher in each pair, the higher in
the first pair and the lower in the second pair, or vice versa). In E
xperiment 1, the frequency interval between the lower and the higher t
ones of each pair varied between 150 and 750 cents, and in the asynchr
onous conditions the onset of the higher tone was delayed by 20 ms. In
Experiment 2 various musical intervals were used which were either pu
re or slightly mistuned, and in the asynchronous conditions the onset
of the higher tone preceded that of the lower tone by 25 ms. The resul
ts showed that for the degree of onset asynchrony investigated, a faci
litative effect of onset asynchrony on perceptual separation was only
found in a small subset of conditions.