The aim of this study was to measure the perceptual attenuation, measured in decibels, resulting from
the focusing of attention on one stream within a multi-stream auditory sequence. The intensity of a non-focused stream was increased until the accuracy of detecting a temporal irregularity in this stream was the same as
in a focused stream. Eight subjects were required to detect a temporal irregularity created by delaying or advancing one tone which could be situated in one of three temporally regular streams played simultaneously to create a multi-stream sequence. The three streams differed in tempo and frequency. Subjects' attention was focused on one of the streams by preceding the multi-stream sequence with one of the single streams (a cue). We first established the size of temporal irregularity detected at a 90% level in cued streams, confirming that subjects were able to focus on one particular stream. Second, an irregularity of this size was not detected above
chance level in non-cued streams, demonstrating that listeners only focus on the cued stream. Third, for five
subjects, a 15 dB increase in the level of one of the non-cued streams was necessary to bring detection up to
that found in the cued streams. This gain provides an equivalent measure of the perceptual attenuation of non-
focused streams. For three other subjects, detection in the non-cued stream remained at chance performance whatever the level. For all subjects, detection in the cued stream decreased slightly as the level of the non-cued stream increased. We conclude that the attenuation of non-focused auditory streams can attain as much as 15
dB, at least for some subjects.